A Bouzzit
email: aziz.bouzzit@cyu.fr

A Arciniegas

L Martinez

S Serfaty

N Wilkie-Chancellier

ULTRASONIC SURFACE WAVE PARAMETERS MONITORING USING 3D VIBROMETRY AND ELLIPSOMETRY FOR LOCAL MATERIAL CHARACTERIZATION

Keywords: Ellipsometry, 3D vibrometer, Rayleigh waves, Material characterization. ---------

Rayleigh wave is widely used in non-destructive testing and evaluation, the three-dimensional vibrations inspection highlights the bivariate nature of these waves and their elliptic motion. The links between this motion and the material properties are well established, however, theoretical expressions are very sensitive to the measurement errors and the purity of the surface wave. If the classical processing often uses independently the two components of the wave, it seems more complete to process the two components together using the adequate bivariant filters. This work presents the monitoring of the 3D propagation of ultrasonic Rayleigh waves and the signal processing dedicated to the identification of their characteristic parameters. It is particularly focused on the wave ellipticity, i.e. the horizontal to vertical component ratio (H/V-ratio). This phenomenon is studied analytically, numerically and experimentally. Over a scanned area, the local mechanical parameters are estimated using time signals extracted from each single point. The obtained results for Aluminum show a good agreement between the analytical, numerical and experimental studies of Rayleigh wave ellipticity. Moreover, these H/V ratios are consistent with the theoretical values found in literature. This method is also applied on simulation data to study orthotropic materials (wood/bone), obtaining promising results.

INTRODUCTION

Nondestructive testing of cultural heritage can be challenging due to the delicate nature of the objects and materials. Surface acoustic waves (SAW) like Rayleigh waves [START_REF] Rayleigh | Lord Rayleigh_On Waves Propagated along the Plane Surface of an Elastic Solid_1885[END_REF] are useful in material investigation as they propagate on the material's surface, making them accessible. Rayleigh waves have low attenuation and can cover a relatively large distance before being attenuated, making them ideal for acoustic contactless nondestructive testing. A 3D laser vibrometer can be used to extract the three components of deformation generated by the SAW, highlighting the elliptic nature of the motion of the Rayleigh wave [START_REF] Bayón | Estimation of dynamic elastic constants from the amplitude and velocity of Rayleigh waves[END_REF]. This motion can be characterized by the ellipticity (χ=H/V) and orientation of the ellipse (θ), both are related to the mechanical properties of the material. Geophysicists used directional geophones to measure the three components of the vibration of surface waves These measurements allowed them to be the first to use the ellipticity of Rayleigh waves to characterize soil. The H/V spectral ratio was introduced by Nogoshi and Igarashi in 1971 [START_REF] Nogoshi | On the amplitude characteristics of microtremor, Part II[END_REF], and later popularized by Nakamura [START_REF] Nakamura | Clear identification of fundamental idea of Nakamura's technique and its applications[END_REF], [START_REF] Nakamura | A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface[END_REF], who highlighted a correlation between the H/V spectral ratio and the fundamental resonance frequency of the observed geological site. The simplicity and efficiency of this method made it popular in geophysical studies, and Molnar et al. have listed its applications and advancements [START_REF] Molnar | A review of the microtremor horizontal-to-vertical spectral ratio (MHVSR) method[END_REF]. Malischewsky developed models for H/V ratio as a function of mechanical properties [START_REF] Malischewsky | Love's formula and H/V-ratio (ellipticity) of Rayleigh waves[END_REF]. Meanwhile, laser vibrometry and material characterization advanced with the technique of Aussel and Monchalin for elastic constant determination [START_REF] Aussel | Precision laserultrasonic velocity measurement and elastic constant determination[END_REF] and method of Orta et al for identifying orthotropic elastic stiffness [START_REF] Orta | On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data[END_REF]. Staszewski et al. provided an overview of laser doppler vibrometry for structural health monitoring [START_REF] Staszewski | A Review of Laser Doppler Vibrometry for Structural Health Monitoring Applications[END_REF].

In 2006, Bayon proposed a contactless method for estimating the dynamic elastic constant of isotropic materials using a 2D laser vibrometer and the H/V ratio model by Malischewsky. The Young's modulus (E) and Poisson's ratio (ν) can be estimated from the H/V ratio and Rayleigh wave velocity with an accuracy of 0.82% for E and 4.4% for ν [START_REF] Bayón | Estimation of dynamic elastic constants from the amplitude and velocity of Rayleigh waves[END_REF]. However, accurate results require extracting a pure Rayleigh wave to avoid errors introduced by the presence of other wave types. In practical cases, extracted signals may contain different types of waves and noises that interfere with the spectra of the Rayleigh wave, leading to errors in the H/V estimation. The bivariate signal processing frame provides a solution to this issue by estimating the eigenpolarization of a bivariate signal, considering both components of the signal at the same time [START_REF] Flamant | A complete framework for linear filtering of bivariate signals[END_REF]. This method is more effective than the traditional H/V spectral ratio method, which is sensitive to noise and added undesired waves in the signal. The Hermitian linear time invariant filters used in bivariate signal processing can accurately estimate the dominant polarization of the Rayleigh wave, despite the presence of other waves and noises in the extracted signal. This paper presents the theoretical background of the H/V value for an isotropic half-space and its sensitivity to measurement errors. It also introduces the Hermitian filters method for estimating the eigenpolarization of a bivariate signal and validates it using theoretical and finite element simulation signals. The experimental setup used for signal extraction and the results obtained through the Hermitian filters method are presented and discussed.

THEORATICAL BACKGROUND

The theoretical expression of H/V

Rayleigh waves are a kind of surface wave that propagate along the free surface of a body. The disturbance caused by these waves is confined to a thin surface layer whose depth is proportional to its wavelength. When the medium is homogeneous and isotropic, the particle motion of Rayleigh waves near the surface is retrograde and elliptical. The major normal axis of the ellipse is perpendicular to the free surface, which means that the vibration plane contains the direction of propagation and is perpendicular to the surface [START_REF] Viktorov | Rayleigh and Lamb Waves: Physical Theory and Applications[END_REF]. The velocity of Rayleigh waves, as well as the phase velocities of bulk waves longitudinal and shear, are related by this mathematical equation [START_REF] Bayón | Estimation of dynamic elastic constants from the amplitude and velocity of Rayleigh waves[END_REF], [START_REF] Nkemzi | A new formula for the velocity of Rayleigh waves[END_REF], [14]

R 3 -8(R-1)(R-2-2κ 2 )=0 (1)
where R = VR 2 /VT 2 and κ = VT/VL , if VL, VT and VR are respectively the longitudinal, transverval and Rayleigh wave velocities.

The theoretical expression of the ratio between the in-plane and the out-of-plane deformations, is expressed as function of R by the formula [START_REF] Malischewsky | Love's formula and H/V-ratio (ellipticity) of Rayleigh waves[END_REF]:

(2)

In the case of an isotropic half-space, the mechanical properties of the material, Young modulus (E), Poisson ratio (ν) and the density (ρ) are related to the phase velocities of Rayleigh longitudinal and shear waves and the theoretical expression are well defined. Based on this relation the inverse problem relating the mechanical properties with the H/V ratio and VR is established [START_REF] Bayón | Estimation of dynamic elastic constants from the amplitude and velocity of Rayleigh waves[END_REF], [15]. Measurement errors made on H/V will affect the estimated values for the mechanical properties. The study of the relative error committed on the estimation of H/V as function of the relative error on R showed that, for a 10% relative error on R the relative deviation on the estimation of H/V is around 20% and can reach up to 87% depending on the material. These results highlight the importance of measuring H/V with minimum errors. Unlike the H/V spectral ratio method, the advantage of this framework is that the two components are treated simultaneously rather than separately. Hermitian filters are linear time invariant filters that operate on the frequency domain by performing a Hermitian transform on each frequency of the input bivariant signal, modifying both the power and polarization properties. The diattenuation axis of the filter represents the polarization at which the gain is maximum, known as the eigenpolarization [START_REF] Flamant | A complete framework for linear filtering of bivariate signals[END_REF]. By adjusting the polarization parameter, the filter can detect if the input signal matches the Hermitian filter's polarization. A bank of these filters is needed to detect the range of polarization values in the input signal. This approach allows for better estimation of polarization parameters in the presence of Rayleigh wave propagation and different types of noise. The method is tested on theoretical, finite elements simulation, and experimental signals.

Hermitian filtering for the estimation of the ellipse parameters

VALIDATION

This section evaluates the ability of Hermitian filters to estimate polarization parameters of a bivariant signal from a propagating Rayleigh wave on the sagittal plane, using different signal types. The signals include a synthetic monochromatic signal with fixed polarization parameters, a signal extracted from a finite element simulation of a Rayleigh wave on the surface of an aluminum block, and a signal monitored using a 3D vibrometer measuring a Rayleigh wave on the surface of an aluminum block.

Synthetic signal

For aluminum the values of longitudinal and shear waves velocity are respectively VT=6374m/s and VL=3111 m/s. By using equations ( 1) and ( 2 These results reflect the performance of the proposed method in the case of a perfect monochromatic harmonic bivariant signal. In the next subsection the performance is tested on a more realistic signal from numerical simulations.

Figure 3:

The gain as function of χ and θ for the synthetic signal.

Simulation signal

The numerical simulation allow us to generate more realistic signals, extracted from Rayleigh waves propagating on material with different properties and shapes.

The propagation of SAW on an aluminum block is simulated with the same properties used in the synthetic case (VL=6374m/s, VT=3111 m/s. and a density of ρ =2730 kg/m 3 ) by a finite element method allowing time and space discretization of the propagation. The excitation is a 5 cycles tone burst with central frequency f0=0.75MHz.

The simulation is carried out using a 3D model, the position of extraction is chosen on the sagittal plane of the propagation, as in this plane only two components of the deformation change, the normal and the tangent in direction of propagation of the wave.

A time dependent solver is used to study the propagation of the SAW, the time step between two iterations is fixed to dt=1/(10 f0). The geometry of the material is discretized using a triangular mesh where the maximum element size is fixed to LMax=VT/(10 f0). For the simulated signal the maximum gain is found for the parameters χsimul= 0.625 and θsimul =1.602 rad. Based on the VT and VL the theoretical values of χ and θ are the same as the synthetic case.

The relative error on the estimation of the parameter are Errχ=0.16% and Errθ=1.9%. For the ellipticity, the error is the same as in the synthetic case, meaning that the performance of the benchmark of filters is the same for a monochromatic and tone burst excitation. But the error on θ is rather high compared to synthetic case. Despite that, the method is able to estimate with good accuracy (<2%) the polarization parameters of the wave.

Experimental signal

In order to complete the validation process, it is necessary to test the proposed method on actual experimental signals obtained from a propagating Rayleigh wave. To achieve this, a block of aluminum measuring 20×12.5×10 cm³ is utilized to support the wave propagation. The velocities of the Rayleigh and shear waves on the block are respectively measured to be VR=2888m/s, VT=3092 m/s. The surface wave is generated using a fc=1 MHz shear wave transducer mounted on the side of the block. This last applied a force tangent to surface, this will generate a Rayleigh wave on the adjacent face [START_REF] Adler | Measurements of acoustic surface waves on fluid-filled porous rocks[END_REF] and the signal is extracted on the sagittal plane of the wave using the experimental set up shown in Figure [START_REF] Malischewsky | Love's formula and H/V-ratio (ellipticity) of Rayleigh waves[END_REF]. Despite the presence of noise in the signal obtained from the experimental setup, the Hermitian filter benchmark successfully estimates the polarization parameters of the propagating of Rayleigh wave with very small relative error. The same experimental signal is analyzed using the H/V spectral ratio method, the results are illustrated on Figure [START_REF] Staszewski | A Review of Laser Doppler Vibrometry for Structural Health Monitoring Applications[END_REF]. Two mean intervals are to be noticed, in the bandwidth, the values of H/V vary with σ=0.17 standard deviation around the theoretical one, and out of the bandwidth, where the values show big deviations. As a result, one will only be interested in the values within the bandwidth. The relative error between the estimated H/V spectral value and the theoretical value is plotted in Figure (10-c) : the error is once more relatively low for the frequencies within the bandwidth. The mean value of the relative error over this interval is 20% with 18% standard deviation. This value is bigger than the one estimated by the benchmark of Hermitian filters (Errχ=1.4%). This result shows the capacity of the proposed method to estimate the parameters of polarization of bivariant Rayleigh wave, as the estimation is based on the eigenpolarization of the signal rather than the simple ratio between the spectra of the two components.

APPLICATION ON DIFFERENT MATERIALS

The following section employs the benchmark of filters to estimate the polarization of simulated Rayleigh waves that travel through various materials (such as wood and bones).

The purpose is to examine how the ellipticity of the wave changes based on different factors such as the type of wood or the postmortem interval of the bone. The propagation of waves in the sagittal plane of different materials is simulated using a 2D finite element method with a timedependent solver, the parameters of the simulation are the same as those used in subsection 3.2.

Wood: two different species.

Wood is commonly found in cultural heritage objects, and it's essential to identify the species of wood used for restoration purposes. In this section, simulations of Rayleigh waves were conducted on two classes of wood (softwood: DOUGLAS FIR and hardwood: SWEETGUM) with different rigidities to observe if the χ=H/V parameter varies. The material properties of the two species of wood used in the simulation, the stiffness tensor and the density of orthotropic wood with 12% humidity (dry state), are extracted from the Wood handbook [START_REF] Ross | Wood handbook : wood as an engineering material[END_REF], and simulations were limited to the RL plane (direction of wood fibers) to save time. Figure [START_REF] Flamant | A complete framework for linear filtering of bivariate signals[END_REF] illustrates the bivariant signal extracted from the simulation of Rayleigh wave propagation on the two species of wood. The results obtained show that the ellipticity values for DOUGLAS FIR (χDOUGLAS-FIR=0.024) and SWEETGUM (χSWEETGUM =0.103) are lower compared to aluminum (χAl =0.625). This can be attributed to the orthotropic nature of wood, which makes it more resistant to deformation in certain directions than others [START_REF] Bucur | Surface wave propagation in wood: prospective method for the determination of wood off-diagonal terms of stiffness matrix[END_REF]. In the case of the simulated woods, the deformation is easier in the normal direction than in the tangent direction, as seen in the a b c significant difference in amplitude between the uz and ux components of deformation. The χ values also differ between the two types of wood, with hardwood having a higher value by a factor of 5 compared to softwood. Therefore, χ could be a useful parameter in distinguishing between the two species of wood. The mean values of χ for different bones range from 0.74 to 0.84 (0.74< χbone<0.84), and it can be observed that mean value of χ increases as a function of postmortem interval. The increasing trend of χ suggests that the rigidity of bones may increase with PMI, which is supported by the observation of χ increasing from softwood to hardwood. For a given material, the ellipticity of Rayleigh waves also increases with rigidity.

We have demonstrated that the ellipticity of Rayleigh waves can serve as a characterization parameter to distinguish between hardwood and softwood, and provide an indication of bone rigidity (related to PMI). However, these results are preliminary and based only on simulated signals, and experimental validation is necessary. Furthermore, a theoretical model comparison would the extraction of additional useful information, beyond simply comparing values.

CONCLUSION

This work presents a nondestructive evaluation method for cultural heritage material using surface acoustic waves such as

  As a Rayleigh wave travels in the sagittal plane, only the normal and tangent components in the direction of propagation change. This unique characteristic makes the extracted signals in the sagittal plane being classified as bivariant signals. The bivariant signals framework offers valuable tools for processing signals with two components.

Figure 1 :

 1 Figure 1: The information flow followed to estimate the ellipticity parameters. The process of determining the polarization value is depicted in Figure (1) : ellipticity χ and orientation θ. Initially, the bivariant signal undergoes filtering with various eigenpolarization values. Then, the gain at the output of each filter is determined, and the polarization parameters of the filter with the highest gain are retrieved. These parameters correspond to the dominant polarization of the input signal. Ellipticity values range from χ∈[-1;1] and orientation values range from θ∈[-π/2; π/2]. Discretizing the value ranges with small steps yields precise polarization estimation, but at the cost of longer computation time. In Figure (1), the subscripts i,j represent the indices of discretized values for χ and θ , and M and N are the total number of values for χ and θ , respectively. Plotting gain values as a function of χ and θ allows for better visualization of gain variation and the maximum position. This approach allows for better estimation of polarization parameters in the presence of Rayleigh wave propagation and different types of noise. The method is tested on theoretical, finite elements simulation, and experimental signals.

  ), the values of the ellipticity and orientation are estimated to be χ=0.626 and θ=π/2 rad. A bivariant signal is synthesized based on this values (Figure[START_REF] Bayón | Estimation of dynamic elastic constants from the amplitude and velocity of Rayleigh waves[END_REF]) and injected to the bank of Hermitian filters.

Figure 2 :

 2 Figure 2: Synthetic bivariant signal of a monochromatic Rayleigh wave.In Figure[START_REF] Bayón | Estimation of dynamic elastic constants from the amplitude and velocity of Rayleigh waves[END_REF] the two components of a Rayleigh wave in the sagittal plane (ux,uz) are plotted on the left. The variation of uz as function of ux is plotted on the right, highlighting the elliptic shape. The variation of the gain at the output of each filter is then presented as function of χ and θ (Figure(3)). For this synthetic signal, the maximum gain corresponds to χsynth= 0.625 and θsynth = 1.571 rad, the relative error on the estimation of the parameters are Errχ=0.16% and Errθ=0%. These results reflect the performance of the proposed method in the case of a perfect monochromatic harmonic bivariant signal. In the next subsection the performance is tested on a more realistic signal from numerical simulations.

Figure ( 4 )

 4 illustrates the calculated deformation of the Rayleigh wave at the instant ti=3.7µs , also the position of the excitation and the extraction are indicated along with the sagittal plane of the wave. The extracted bivariant signal is shown in Figure[START_REF] Nakamura | A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface[END_REF] in a time signal of the two components and in a plot of uz as function of ux. As the excitation, the recovered signal is a tone burst with central frequency of f0, compared to the synthetic case this signal is a more realistic and will also us to test the proposed method. The simulation signal is passed though the benchmark of filters and the results are shown in Figure[START_REF] Molnar | A review of the microtremor horizontal-to-vertical spectral ratio (MHVSR) method[END_REF].

Figure 4 :

 4 Figure 4: Simulation results : displacement at instant ti=3.7µs .

Figure 5 :

 5 Figure 5: The bivariant signal extracted from the simulation.

Figure 6 :

 6 Figure 6: The gain as function of χ and θ for the simulated signal.

Figure 7 :

 7 Figure 7 : Experimental set-up. The vibrometer is positioned to face the side on which the wave is propagating. The pulse generator JSR Ultrasonics DPR300 generates the excitation and synchronization signals. The Laser Vibrometer Polytec ® PSV 500-3D-V extracts the time signals, and can measure the three components of displacement (ux,uy,uz) with frequencies up to 25MHz. The extraction can be performed on a single point or a grid of predefined points, this will allow us to estimate the mechanical properties. of the material located

Figure 8 :

 8 Figure 8: Bivariant signal measured using the experimental setup.

Figure ( 8 )

 8 Figure[START_REF] Aussel | Precision laserultrasonic velocity measurement and elastic constant determination[END_REF] depicts the experimental case signal, which exhibits noise that was not present in the previous two types of signals. This signal was subjected to the Hermitian filter benchmark, and the resulting gain variation with respect to χ and θ is shown in the figure.

Figure 9 :

 9 Figure 9: The gain as function of χ and θ for the experimental signal.From the VT and VR for values for the aluminum block, and by means of equation (2), the theoretical value of the elliptic parameters are χtheo = 0.639 and θtheo=π/2 rad. Our method estimates these two parameters for the experimental case to be χexp = 0.629 and θtheo= 1.546 rad. The relative error

Figure 10 :

 10 Figure 10: a-Fourier transform of the two components of signal, b-H/V spectral ratio, c-the error relative to the theoretical value.The Fourier transform of the two components of the experimental bivariant signal are presented in Figure(10-a) for frequencies ranging from 0 to 2.5 MHz. The two components have relatively the same content in terms of frequency, the bandwidth is ranging roughly from 0.3 to 1.3 MHz. In this interval, oscillations can also be seen, resulting from the noise present in the signal and its interference within the bandwidth of propagating wave. The H/V spectral ratio method consists on calculating the ratio between the FFT of the two components of the bivariant signal (Uz/Ux). The results of this operation is plotted on Figure(10-b), a line representing the theoretical value of χ is also plotted. Two mean intervals are to be noticed, in the bandwidth, the values of H/V vary with σ=0.17 standard deviation around the theoretical one, and out of the bandwidth, where the values show big deviations. As a result, one will only be

Figure 11 :

 11 Figure 11 : Extracted bivariant signal from simulation: a-DOUGLAS FIR, b-SWEETGUM.

4. 2

 2 Bones: different post mortem intervals (PMI)Accurately estimating the postmortem interval (PMI) of bones is crucial in the fields of archaeology and criminology. In this study, simulations were conducted to analyze the propagation of Rayleigh waves on bones with varying PMIs, and their polarization properties were extracted using the Hermitian filter benchmark. The simulations were carried out using the rigidity tensor of bones with different PMIs, and the average values of these tensors can be found in A. Angermuller's thesis (2021)[START_REF] Angermuller | Etudes de signatures ultrasonores de l'os en vue d'une datation post mortem[END_REF]. For the same PMI the values on the tensor varies from an individual to another due to the variation in the growth conditions. For this, only the mean values of the tensors are used and the variation is represented with the error bars in the results. Four simulations were performed for PMIs of 3 years, 13 years, 50 years, and archaeological remains older than 500 years. The results of the simulations are summarized in Figure[START_REF] Viktorov | Rayleigh and Lamb Waves: Physical Theory and Applications[END_REF].

Figure 12 :

 12 Figure 12 : χ=H/V variation as function of the PMI of the bone.

  Rayleigh waves. A 3D laser vibrometer measures the three components of the deformation generated by the propagating wave, and the ellipticity and orientation of the elliptical motion characterize the motion. A method based a b on Hermitian filters extracts the eigenpolarization of a bivariant signal to estimate the polarization properties of Rayleigh waves. Results from simulations and experiments show the capacity of χ to distinguish between different types of wood and characterize bones with different PMI. Future work will focus on the theoretical model for the orthotropic case to extract more useful information about the mechanical constants of the wood or bones, followed by experimental validation.

ACKNOWLEDGMENTS

This work is supported and funded by CY Cergy Paris University.


Loïc Leclercq
email: loïcleclercq-loic.leclercq@univ-lille1.fr

Keywords: cellular interactions, cyclodextrins, endogenous substances, extraction, greener active ingredients, host-guest chemistry, lipids

In the field of host-guest chemistry, some of the most widely used hosts are probably cyclodextrins (CDs). As CDs are able to increase the water solubility of numerous drugs by inclusion into their hydrophobic cavity, they have been widespread used to develop numerous pharmaceutical formulations. Nevertheless, CDs are also able to interact with endogenous substances that originate from an organism, tissue or cell. These interactions can be useful for a vast array of topics including cholesterol manipulation, treatment of Alzheimer's disease, control of pathogens, etc. In addition, the use of natural CDs offers the great advantage of avoiding or reducing the use of common petroleum-sourced drugs. In this paper, the general features and applications of CDs have been reviewed as well as their interactions with isolated biomolecules leading to the formation of inclusion or exclusion complexes. Finally, some potential medical applications are highlighted throughout several examples.

Introduction

Cyclodextrins (CDs) were discovered and identified over a century ago [1][2][3]. Between 1911 and 1935, Pringsheim and co-workers demonstrated the ability of CDs to form complexes with many organic molecules [4,5]. Since the 1970s, the structural elucidation of the three natural CDs, α-, β-, and γ-CDs composed of 6-, 7-, and 8-membered α-D-glucopyranoses linked by α-1,4 glycosidic bonds, allowed the development and the rational study of their encapsulation properties [6,7]. As their water solubility differs significantly, a great variety of modified CDs has been developed to improve the stability and the solubility of inclusion complexes [8][9][10]. Nowadays, CDs are widely applied in many fields [11][12][13][START_REF] Frömming | Cyclodextrins in pharmacy[END_REF][START_REF] Campos | [END_REF][16][17][18][19][20][21][22][23][24][25][26][27][28] due to their host-guest properties, their origins (produced from starch by enzymatic conversion), their relatively low prices, their easy modifications, their biodegradability and their low toxicity. Moreover, CDs are able to interact with a wide range of biomol- ecules opening the way for many biological applications. The majority of these researches are based on the ability of CDs to extract lipids from the cell membrane. The objective of this contribution is to focus on the potential use of natural and chemically modified CDs in the vast array of medical and biological applications.

Review

Cyclodextrins: synthesis, structure and physicochemical properties.

i) Native cyclodextrins

As mentioned earlier, the ordinary starch hydrolysis (e.g., corn starch) by an enzyme (i.e., cyclodextrin glycosyl transferase, CGTase) allows the production of the native CDs [13]. To reduce the separation and the purification costs, selective α-, βand γ-CGTases have been developed in the last two decades [29]. Nevertheless, the cheapest remains the β-CD whereas the most expensive is the γ-CD. The molecular shape of the native CDs can be represented as a truncated cone with "hydrophobic" cavity which can accommodate hydrophobic compounds (Scheme 1). In aqueous solution, the complexation is enthalpically and entropically driven. In addition, complementary interactions (e.g., van der Waals forces, H-bonds, etc.) appear between the CD and the guest. The non-polar suitably-sized guest may be bound in numerous molar ratios (e.g., 1:1, 2:1, 1:2, etc.). In all cases, the knowledge of the binding constants (K ass ) is crucial because these values provide an index of host-guest binding forces. CDs can also form exclusion complexes where the CDs are bound to the guest through a H-bond network. For instance, the complexation of [PMo 12 O 40 ] anion by β-and γ-CD results in a one-dimensional columnar structure through a combination of intermolecular [C-H•••O=Mo] and [O-H•••O] interactions [30]. Unfortunately, the natural CDs as well as their inclusion complexes are of limited aqueous solubility leading to their precipitation. Fortunately, native CDs are effective templates for the generation of a wide range of molecular hosts through chemical modifications.

ii) Modified cyclodextrins

In order to meet specific requirements in the host-guest complex, chemical modifications make it possible to tailor CDs to a particular guest. The hydroxy groups serve as scaffolds on which substituents can easily be introduced. From a chemical synthesis point of view, the reactivity difference between the primary and secondary hydroxy groups allows selective functionalization on the narrow or the wider edge of the truncated cone (Table 1). Access to the gamut of functional groups greatly expands the utility of native and modified CDs in their numerous applications.

iii) Applications of cyclodextrins

As natural CDs and their derivatives are able to encapsulate a wide range of guest molecules into their cavity, they can be used in a wide range of applications including analytical chemistry [21,22,31], agriculture [START_REF] Campos | [END_REF], food technology [16], catalysis [23][24][25]32], cosmetics [26], textile processing [28,[START_REF] Leclercq | Smart medical textiles based on cyclodextrins for curative or preventive patient care[END_REF], and environmental protection technologies [27,[START_REF] Boyle | [END_REF]. Nevertheless, the first global consumer of CDs is clearly the pharmaceutical industry [35,36]. Indeed, CDs are very useful to form inclusion complexes with a wide range of drugs and become a very valuable tool for the formulator in order to overcome delivery limitations [37,38]. As a result, numerous formulations that use CDs are now on the market worldwide (Table 2).

iv) Toxicity and biological effects of native and modified cyclodextrins

As safety and toxicity are important criteria for consideration before using CDs in pharmaceutical products, this section deals with toxicological issues. The native α-and β-CD, unlike γ-CD, cannot be hydrolyzed by pancreatic amylases and human salivary but can be fermented by the intestinal microflora. When administered orally, native CDs and hydrophilic derivatives are not absorbed from the human gastrointestinal tract and thus making them practically nontoxic due to their high molecular mass ranging from almost 1 000 to over 2 000 g/mol and their a Note that the list is not exhaustive and that only one trade name is given (IV: intravenous, IM: intramuscular, ED: eye drop). Adapted from [37].

hydrophilic nature with a significant number of H-bond donors and acceptors [39]. Indeed, CDs violate three criteria of the Lipinski's rule: i) no more than 5 H-bond donors, ii) no more than 10 H-bond acceptors, iii) a molecular mass less than 500 g/mol, and iv) an octanol-water partition coefficient (log P) not greater than 5 [40]. As these criteria apply only to absorption by passive diffusion of compounds through cell membranes, the absorption of the native CDs and their hydrophilic derivatives are not allowed in their intact form and any cellular absorption, if it occurs, is by passive transport through cytoplasmic membranes (i.e., by transporter proteins) [41]. In contrast, lipophilic derivatives (e.g., ME-β-CD) interact more readily with membranes than the hydrophilic derivatives, they cannot readily permeate cell membranes (see below) [42]. Moreover, oral administration of alkylated CD derivatives, such as ME-β-CD, is limited by its potential toxicity [43]. Indeed, ME-β-CD is partially absorbed from the gastrointestinal tract into the systemic circulation. Moreover, they have been shown to be toxic after parenteral administration. The opposite holds for hydrophilic CD derivatives, such as HP-β-CD and SBE-β-CD, which are considered safe for parenteral administration. In a general way, the γ-CD, HP-β-CD and SBE-β-CD, S-β-CD and G2-β-CD appear to be globally safer than α-, β-and alkylated CDs which are less suitable for parental administration [44,45]. Table 3 presents the pharmacokinetics and safety overview of some natural and modified CDs. When administered, natural and hydrophilic CD derivatives disappear rapidly from systemic circulation and are distributed to various tissues of the body such as kidney, liver, urinary bladder, etc. Nevertheless, they are mainly renally excreted intact. At high concentrations, α-, β-

-β-CD ≈90% ≤3% >2 10 G 2 -β-CD - - >5 - ME-β-CD >95% 0.5-12% >8 1.5-2.1 SBE-β-CD - - >10 >15
a Taken from [44,[47][48][49][50][51][52][53]. b Randomly methylated β-CD.

and alkylated CDs present renal damage and dysfunction [46]. In 2008, Stella and He discussed the detailed studies of toxicology, mutagenicity, teratogenicity and carcinogenicity of various CDs [45]. Overt signs of acute toxicity are not apparent for CDs (i.e., no inflammatory response and no cell degeneration). They are also not genotoxic, not teratogenic or mutagenic. However, CDs affect the human organism only at extremely high concentrations. Nevertheless, the principal side effect of natural and modified CDs is probably the cell toxicity. This effect is directly correlated to their hemolytic activities. Indeed, several in vitro studies reported erythrocyte lysis although the toxicological implication in vivo is negligible. The lysis mechanism is related to their capacity to draw phospholipids and cholesterol out of the biological membrane (see below). Based on this, the complexation of endogenous substances are of potential interest for many applications.

Biomolecule/cyclodextrin inclusions complexes

Native and modified CDs can be used to complex certain chemicals produced naturally present in cells and tissues (i.e., endogenous substances). Indeed, CDs are able to form complexes with various biomolecules including lipids, carbohydrates, proteins and nucleic acids. In this section, some biomolecule/CD inclusion complexes are presented.

i) Complexation of lipids and consequences

Lipids are hydrophobic or amphiphilic molecules very diverse, including, among other fats, waxes, sterols, fat-soluble vitamins, phospholipids, mono-, di-and triglycerides, etc. Their amphiphilic nature causes the molecules of certain lipids to organize into liposomes when they are in aqueous medium. This property allows the formation of biological membranes. Indeed, cells and organelles membranes are composed of lipids. Lipids also provide various other biological functions, including cell signaling and storage of metabolic energy by lipogenesis. Bio-logical lipids are basically due to two types of compounds acting as "building blocks": ketoacyl groups and isoprene units.

From this point of view, they can be divided into eight categories: fatty acids (and their derivatives: mono-, di-and triglycerides and phospholipids), acylglycerols, phosphoglycerides, sphingolipids, glycolipids and polyketides, which result from the condensation of ketoacyl groups, sterols (e.g., cholesterol) and prenols, which are produced from condensation of isoprene units [START_REF] Voet | Biochemistry[END_REF]. These compounds can be easily included inside the CDs because they are hydrophobic or amphiphilic molecules.

As mentioned earlier, and as it will become exceeding clear throughout the following sections, the majority of research involving CDs has revolved around their ability to manipulate lipid (phospholipids and cholesterol) composition in different cells [START_REF] Zidovetzki | [END_REF][56][57][58]. Although numerous studies deal of this topic, the mechanism of this process is poorly investigated (i.e., only the consequences of this phenomenon are reported). For sake of clarity, only some typical examples are reported in this section.

The first well-documented effect of CDs is probably hemolysis which corresponds to the lysis of red blood cells (erythrocytes) and the release of their contents into surrounding fluid (blood plasma). In 1982, Irie and co-workers reported that native CDs are able to cause hemolysis of human erythrocytes [59]. This behavior occurs at relatively high concentrations (>1 mM) and that the degree of cholesterol extraction is a function of the CD used, its concentration, incubation time, temperature. For instance, in given conditions (isotonic solution with similar incubation time and temperature), the observed hemolysis is in the order γ-CD < α-CD < β-CD.

This different effect, observed for native CDs, has been explained by Ohtani et al. in 1989 [58]. As the membrane of erythrocytes is composed of proteins (43%) associated with lipids (49%) and carbohydrates (8%) and as the fraction of cholesterol is 25% of total membrane lipids [START_REF] Voet | Biochemistry[END_REF], the proposed explanation is based on the specific interaction of natural CDs with the erythrocyte membrane components. Indeed, α-and β-CD are excellently suited to solubilize phospholipids and cholesterol, respectively, whereas γ-CD is generally less lipidselective. In more detail, the CD affinity for solubilizing various lipid components of the erythrocyte membranes are in the order γ-CD << β-CD < α-CD for phospholipids and α-CD < γ-CD << β-CD for cholesterol [58]. These findings are corroborated by the work of Leventis and Silvius which have reported that β-and γ-CD accelerate the rate of cholesterol transfer by a larger factor than they accelerate the transfer of phospholipid, whereas the opposite is true for α-CD [60]. The hemolytic properties of CDs are a general behavior not limited to human erythrocytes: All mammalian red blood cells are affected by the parent CDs. For instance, dog erythrocytes are also affected by native CDs in the order γ-CD < α-CD < β-CD [61]. Thus, the magnitude of the hemolytic activity observed for dog erythrocytes is consistent with the order of magnitude of human erythrocytes (see discussion above). However, the hemolytic activity is largely influenced by the substituents attached to the CDs. The presence of hydrophilic substituents (e.g., glucosyl, 2-hydroxypropyl, 3-hydroxypropyl, maltosyl, sulfate, sulfobutyl ether, etc.) reduces the hemolytic activity in comparison with the parent CDs while the lipophilic ones (e.g., methylated CDs) demonstrate the strongest hemolytic activities [START_REF] Arima | Recent findings on safety profiles of cyclodextrins, cyclodextrin conjugates, and polypseudorotaxanes[END_REF]. As for parent CDs, these differences are ascribed to the different solubilization effects of lipid components and their sequestration in the external aqueous phase.

As the hemolysis is attributed to the removal of erythrocyte membrane components, particularly phospholipids and cholesterol, the value of the binding constants between CDs and lipids can be very relevant. To the author's knowledge there is only one paper in the literature that describes the binding constants between CDs (α-or γ-CD) and short phospholipids (i.e., diheptanoylphosphatidylcholine, DHPC) [START_REF] Ishikawa | [END_REF]. In this study, the association constants were estimated from 1 H NMR measurements. The results proved that the K 1 values are in the order α-CD < γ-CD while the K 2 values are in the order γ-CD < α-CD. This behavior was attributed to the large cavity of γ-CD which is able to incorporate both alkyl chains of DHPC simultaneously. In contrast, the formation of a 1:2 inclusion complex with α-CD is easier than with γ-CD. These findings are corroborated by Fauvelle and co-workers who reported that α-CD has the strongest affinity to phospholipids (e.g., phosphatidylinositol) [64,65]. In 2000, Nishijo et al. studied the interactions of various CDs with dipalmitoyl, distearoyl, and dimyristoylphosphatidylcholine liposomes. This study highlights that the liposome-CD interaction depends on the length of the fatty acid chain of the phospholipid, the cavity size, and the nature of the substituents at the CD [66]. In the literature, the binding constant between cholesterol and β-CD was estimated around 1.7 × 10 4 M -1 from a solubility method [67,68]. This value proves the good stability of the inclusion complex because of the driving force of complexation: hydrophobic interaction. Despite there is no information on the binding constant observed for the inclusion of cholesterol in γ-CD, the cavity internal diameter of the β-CD and its derivatives perfectly matches the size of the sterol molecules contrary to γ-CD (too large) [START_REF] Ravichandran | Inclusion Phenom[END_REF]70]. Moreover, the positive correlation observed between the hemolytic activities of various modified CDs and their ability to solubilize cholesterol reveal that HP-β-CD was shown to be a more efficient cholesterol-acceptor molecule than HP-γ-CD. This is apparently due to the diameter of its internal cavity that matches the size of this molecule. Finally, it is noteworthy that all CDs lose their abilities to induce hemolysis, when their cavities are occupied with guest molecules due to a reduced interaction with the erythrocyte membranes [71]. All these observations support the aforementioned affinities of α-CD for phospholipids and of β-CD for cholesterol.

In addition, sub-hemolytic concentrations of native CDs are also demonstrated to cause shape changes in human erythrocytes. The hemolytic effect is concomitant with shape changes (from biconcave discocyte to stomatocyte or echinocyte) depending on the cavity size of the CDs. For instance, α-and γ-CD induce progressive shape changes from discocytes into stomatocytes and from stomatocytes into spherocytes [58]. In contrast, β-CD leads only to swelling of erythrocytes. Similar effects are found for chemically modified CDs. For instance, Motoyama et al. have reported morphological changes in erythrocytes induced by methylated CDs such as 2,6-di-Omethyl-α-CD and 2,6-di-O-methyl-β-CD (DM-α-CD and DM-β-CD) [72,73]. The authors reported that DM-α-CD induces morphological changes in rabbit erythrocytes leading to stomatocytes, while DM-β-CD leads to echinocytes. This difference is ascribed to the cavity size of the CDs and their ability to extract either sphingomyelin and/or cholesterol of lipid rafts. Lipid rafts are constituted of cholesterol, glycolipids, and sphingomyelin. Nevertheless, their structures have heterogeneity with the presence of cholesterol-rich and sphingomyelin-rich domains. Consequently, DM-α-CD extract sphingomyelin form sphingomyelin-rich domains while DM-β-CD extract cholesterol from cholesterol-rich lipid rafts (Scheme 2). This assertion is supported by the work of Nishijo et al. which reported the binding constants of the 1:1 and 1:2 (cholesterol:DM-β-CD) complexes (1.09 × 10 2 M -1 and 5.68 × 10 4 M -1 , respectively, at 25 °C) [74]. Finally, it is noteworthy that the presence of DM-α-CD and DM-β-CD also leads to hemolysis. As cholesterol interacts with markedly higher affinity with sphingolipids (e.g., sphingomyelin) than with common membrane phospholipids, the extraction of cholesterol by DM-β-CD or sphingomyelin by DM-α-CD leads to strong modification of the cholesterol-rich or sphingomyelin-rich lipid rafts, respectively [60]. Therefore, even if the target is significantly different, the final effect is the same (i.e., hemolysis).

It should be noted that this cholesterol and/or phospholipids extraction is not limited to erythrocytes. Indeed, all eukaryotic or prokaryotic cells are affected by the presence of CDs. For instance, the cytotoxicity of native, methylated, and hydroxypropylated α-, β-, and γ-CDs have been studied on an in vitro model of blood-brain barrier by Monnaert and co-workers [75].

The results prove that the native CDs are the most toxic (γ-CD < β-CD < α-CD). As expected, lipid effluxes on the brain capillary endothelial cells in the presence of native CDs reveal that α-CD extracts only phospholipids whereas β-CD is able to remove phospholipids and cholesterol. In contrast, γ-CD is less lipid-selective than the other native CDs. This differential effect compared to the order of magnitude of hemolytic activity (γ-CD < α-CD < β-CD) could be ascribed to the lower cholesterol content in blood-brain barrier cells compared to erythrocytes. Indeed, the cholesterol fraction is markedly higher in erythrocytes than in other cells. As for hemolysis, the presence of hydrophilic substituents (e.g., 2-hydroxypropyl and sulfobutyl ether) annihilates the cytotoxicity while the presence of methyl residues induces cell death of various cells (Caco-2, TR146, PC-12, etc.) [76][77][78]. For instance, cell death induced by DM-β-CD is caused by a marked apoptosis mechanism (i.e., a process by which cells trigger their self-destruction in response to a signal which leads to cell changes prior to death) for NR8383, A549 and Jurkat cells [79]. This apoptosis process results from cholesterol extraction leading to inhibition of the activation of PI3K-Akt-Bad pathway. The presence of DM-α-CD had repercussions that were totally opposite to the DM-β-CD. Indeed, the cell death results from a non-apoptotic mechanism (i.e., necrosis). This differential effect could be attributed to a dissimilarity of interaction between the methylated CDs with the cholesterol-rich lipid rafts and with the sphingomyelin-rich domains for DM-β-CD and DM-α-CD, respectively. These results suggest that lipid rafts of cell membranes would be involved in cell death and cellular function.

However, the mechanism of cholesterol extraction mediated by

CDs is still open to discussion. For instance, Yancey et al. proposed that CDs diffuse into the proximity of the erythrocyte membrane leading to lipid complexation without complete desorption in the aqueous phase [80]. In contrast, Besenicar et al.

proposed that CDs complex lipids during their naturally exchange from the membrane to the aqueous phase [81]. Stella and He supposed that the CDs interact directly with the membrane of the cells prior to lipid efflux [45]. In the same idea, Mascetti et al. proposed that CDs interact directly with cholesterol [82]. Based on molecular simulations, López et al. proposed the following mechanism: i) association of CDs in aqueous solution to form dimers, ii) binding of dimers at the membrane surface, iii) extraction and complexation of cholesterol, and iv) desorption of CD/cholesterol in the aqueous solution [83]. However, whatever the molecular mechanism, the lipid efflux mediated by CDs is clearly different from those of surfactants. Indeed, at low concentrations, the mechanism involves the penetration of the detergent molecules into the lipid membrane leading to increase its fluidity. In contrast, at higher concentrations, the extraction of membrane constituents is ensured by micellar solubilization [84,85].

ii) Complexation of peptides and proteins and some applications

Proteins are polymers of amino acids covalently linked through peptide bonds. The nature of the proteins is determined primarily by their amino acid sequence, which constitutes their primary structure. Amino acids have very different chemical properties; their arrangement along the polypeptide chain determines their spatial arrangement. This is described locally by their secondary and tertiary structures. The secondary structure describes the arrangement of amino acid residues observed at the atomic scale stabilized mainly by H-bonds (e.g., α-helix, β-sheet and turns). The tertiary structure corresponds to the general shape of the observable protein across the whole molecule. It describes the interactions between the different elements of the secondary structure. Finally, the assembly of several protein subunits to form a functional complex is described by the quaternary structure [START_REF] Voet | Biochemistry[END_REF]. As some amino acids have hydrophobic side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, tryptophan, cysteine and methionine), they can be easily included inside the CDs. This complexation leads to modification of the protein. For sake of clarity, only some typical examples are reported in this section.

In their paper on the differential effects of natives CDs, Ohtani and co-workers highlighted that, in addition to the extraction of lipids, these CDs are also able to solubilize proteins in the order α-CD < γ-CD << β-CD [58]. In 1991, Sharma and Janis studied the interaction of CDs with hydrophobic proteins leading to the formation of soluble and insoluble complexes [86]. CDs caused the precipitation of lipoproteins in the order γ-CD < α-CD < β-CD. This behavior could be ascribed to the formation of inclusion complexes. However, the presented data did not exclude the formation of exclusion complexes.

Several years later, Horský and Pitha reported a study on the interaction of CDs with peptides containing aromatic amino acids [START_REF] Horský | Inclusion Phenom[END_REF]. From competitive spectrophotometry measurements, with p-nitrophenol as a competing reagent at pH 7.4, the authors determined the stability constants of aromatic amino acids and their oligopeptides with α-, β-, HP-β-, and ME-β-CD. The estimated constants of free L-phenylalanine (Phe) increased in the order ME-β-CD ≈ HP-β-CD < α-CD < β-CD. Moreover, the results proved that the stability of oligopeptides containing Phe is higher than that of Phe itself. For instance, the binding constant of free Phe with β-CD was estimated at 17 M -1 whereas with the Gly-Gly-Phe tripeptide, the binding constant was 89 M -1 . Nevertheless, the complexation occurs when the native functional form of the proteins is unfolded.

In 1996, Bekos et al. investigated the role of the L-tyrosine (Tyr) residue in the binding of pentapeptides to α-and β-CD [START_REF] Bekos | Inclusion Phenom[END_REF]. The two peptides used in this study were: Tyr-Ile-Gly-Ser-Arg (YIGSR) and Tyr-Gly-Gly-Phe-Leu (YGGFL). The former interacts specifically with the integrin receptors on specific neuronal cells whereas the latter is known to bind to brain receptor sites. From steady-state fluorescence spectroscopy, the estimated constants of free Tyr increased in the order α-CD < β-CD. As in the previous study, the stability constants of pentapeptides containing Tyr with β-CD were higher than that of Tyr itself (48,224, and 123 M -1 for free Try, YIGSR, and YGGFL, respectively). Therefore, the pentapeptide conformation affects the stability of the pentapeptide/β-CD inclusion complex. In contrast, the pentapeptide/α-CD inclusion complex was not affected by the oligopeptide conformation (27,20, and 20 M -1 for free Try, YIGSR, and YGGFL, respectively).

The same year, Lovatt and co-workers investigated the dissociation of bovine insulin oligomers induced by aqueous solution of α-, HP-β-, and ME-β-CD [START_REF] Lovatt | Inclusion Phenom[END_REF]. The energetics of the dissociation of insulin oligomers have been investigated by microcalorimetry. As expected, the dissociation of insulin oligomers is increased upon the addition of CDs. This dissociation is clearly related to the interaction of these CDs with the protein side chains. Indeed, the dissociation of insulin oligomers is endothermic without CDs whereas in the presence of α-CD, the dissociation is less endothermic due to the exothermic binding of α-CD to exposed groups on insulin monomers after dissociation. Therefore, the α-CD facilitates the oligomer dissociation.

In contrast, the dissociation is observed to be more endothermic in the presence of HP-β-and ME-β-CD although oligomer dissociation is induced. The authors suggest that the binding of HP-β-and ME-β-CD is endothermic and entropy driven.

As native and modified CDs are able to complex some amino acids which constitute peptides and proteins, these molecules can be useful for their separation by capillary zone electrophoresis. In this context, Rathore and Horváth reported that carboxymethyl-β-CD (CM-β-CD) in the electrophoretic medium (aqueous buffer solution, pH 2.5) enhanced the separation in capillary zone electrophoresis (raw fused-silica) of standard proteins such as α-chymotrypsinogen A, cytochrome c, lysozyme and ribonuclease A [90]. The obtained results proved that the separation of peptides and proteins can be enhanced by adding CDs to the electrophoretic medium. Unfortunately, only certain CDs can be used as selectivity enhancers. Indeed, in contrast to CM-β-CD, the addition of DM-β-CD had no effect on the separation of the mentioned proteins and peptides.

In 2006, the group of Yamamoto studied the effect of β-, γ-, G1-β-, and Me-α-CD on the thermal stability of an aqueous buffered solution of chicken egg white lysozyme by circular dichroism and fluorescence spectroscopy [91]. The thermal stability is significantly lowered in the presence of β-, γ-, and G1-β-CD whereas the opposite is true for the Me-α-CD. It should be noted that the thermal stability reduction is very important for G1-β-CD. Based on fluorescence spectroscopy, the authors suggested that CDs include the side chains of tryptophan (Trp) residues of lysozyme within their internal cavities to diminish the hydrophobicity of the hydrophobic core of lysozyme and consequently to lower the thermal stability (Scheme 3). In addition, some CD molecules persist in binding to the side chains of Trp residues to retard the renaturation of lysozyme.

Scheme 3: Proposed mechanism for the conformational change of egg white lysozyme with temperature elevating in the presence of modified CDs.

From the findings described above, it can be presumed that the effect of CD is directly linked to its ability to complex Trp and the behavior of Me-α-CD can be related to its cavity size. The binding constants are always weaker with modified α-CD than with functionalized β-CD (see discussion above). In 2009, a 1 H NMR spectroscopic study revealed that the 1 H NMR signals corresponding to Trp residues were shifted upon the addition of G1-β-CD due to encapsulation of the tryptophan residues in the G1-β-CD cavity [92]. In addition, the 1 H NMR signals for cysteine 64 and isoleucine 98 were also influenced to a considerable extent with the addition of G1-β-CD. This allows the conclusion that these hydrophobic amino acid residues are also included by this CD. These results are highly compatible with the very important thermal stability reduction observed in the presence of G1-β-CD. Therefore, the interaction of CDs with proteins is very complicated due to the presence of many binding sites.

Thaumatins refer to a family of proteins present in the sweetness of the katemfe fruit (Thaumatococcus daniellii Bennett) endemic in West Africa. It is used worldwide in human nutrition and pharmacology as a sweetener, flavor enhancer or to mask bitterness and it is 100,000 times sweeter than sucrose. Thaumatin has been shown to bind to G-protein-coupled receptors (GPCRs) which are transmembrane proteins, responsible for signal transduction. Therefore, the interaction of CDs with thaumatin could be used to modify the interaction of thaumatin with GPCRs and to modify its sweet-taste profile. In this context, Thordarson et al. studied the interaction of α-CD with thaumatin [93]. The 1D and 2D NMR experiments revealed that α-CD binds to aromatic residues of thaumatin with a binding constant of 8.5 M -1 . As the active binding site of the thaumatin protein is known, the authors have synthesized a heptapeptide (Lys-Thr-Gly-Asp-Arg-Gly-Phe) that mimics this binding site of thaumatin. The results show that α-CD binds to the C-terminal solvent accessible phenylalanine residue with a binding constant of 8.8 M -1 . As the α-CD may interact with the active binding site on thaumatin, the regulation of the interaction of thaumatin with GPCRs is probably possible.

Varca et al. published on the possible applications in the formulations of protein-like structures, such as enzymes, peptides and amino acids, for pharmaceutical applications [94]. The authors highlight that the formation of cyclodextrin/protein supramolecular complexes can be used to improve their stabilizations. However, the intrinsic characteristics of guest proteins can be also modified. In addition, it is exceedingly clear throughout this paragraph that peptides and proteins have moderate binding constants with CDs compared to lipids.

iii) Complexation of carbohydrates

The International Union of Pure and Applied Chemistry (IUPAC) defines carbohydrates as a class of organic compounds containing a carbonyl group (aldehyde or ketone) and at least two hydroxy residues (OH). It is noteworthy that substances derived from monosaccharides by reduction of the carbonyl group, by oxidation of at least one functional group at the end of the chain in carboxylic acid, by replacement of one or more hydroxy groups by a hydrogen atom, an amine, a thiol or any similar group are also called carbohydrates. Carbohydrates are, with proteins and lipids, essential constituents of living organisms because they are key biological intermediates for energy storage. In autotrophs, such as plants, sugars are converted into starch whereas for heterotrophic organisms, such as animals, they are stored as glycogen. However, polysaccharides serve also as structural components: cellulose for plants and chitin for arthropods. Moreover, saccharides and their derivatives play key roles in the immune system, fertilization, blood clotting, information transfer, etc. For instance, the 5-carbon monosaccharide ribose forms the backbone of the genetic molecule RNA (see below) and is also an important component of coenzymes (ATP, FAD and NAD).

In 1992, Aoyama et al. reported on the selective complexation of pentoses and hexoses by β-CD [95]. Based on competitive inhibition of the 8-anilinonaphthalene-1-sulfonate binding followed by fluorescence measurements, the binding constants can be estimated. The obtained results reveal that D-ribose, D-and L-arabinose, D-xylose, D-lyxose, D-2-deoxyribose, and methyl β-D-ribopyranoside were complexed by β-CD (binding constants ≤14 M -1 ). In contrast, aldohexoses and their derivatives (D-glucose, D-galactose, D-mannose, D-and L-fucose, and methyl α-D-fucopyranoside) were not complexed (binding constants ≈ "0" M -1 ). These binding constants can be directly correlated to the hydrophobicity of the sugar. Nevertheless, the H-bonds between the hydroxy groups of bound sugar and the OH groups of β-CD are also extremely important for determining the structure and for the selectivity of the complex.

It is noteworthy that several other publications have studied the interaction of D-glucose with native CDs. For instance, Hirsh and co-workers estimated the binding constants of D-glucose to α-CD and β-CD at 450 and 420 M -1 , respectively, from blood glucose meter [96]. In contrast, Hacket et al. determined the binding constant of D-glucose to β-CD at 0.6 M -1 by fluorimetric competition titrations [97]. The results obtained by Hacket et al. are closer to the values published by Aoyama and co-workers. In addition, it is quite logical that D-glucose interacts weakly with native CDs due to its size and its hydrophilic property. However, from these conflicting results, Turner proposed to use kinetic measurements to determine the association constants of several sugars with β-CD [START_REF] Turner | The study of b-cyclodextrin interactions with sugars using "inhibition kinetics" and the bromination of pyrimidine derivatives[END_REF]. This new method has been published in 2000 [START_REF] Tee | [END_REF] and the binding constants obtained by these three groups are reported in Table 4.

iv) Complexation of nucleic acids

Current and potential medical and biological applications

As mentioned earlier, CDs are able to complex biomolecules. Unfortunately, the strength of this behavior depends of the molecular structure. For instance, the binding constants increased in the order carbohydrates << nucleic acids << proteins < lipids. Consequently, the majority of biological investigations about CDs involved their ability to extract lipids (cholesterol or phospholipids) from the plasma membrane. As expected, this capacity can be very useful for numerous applications. For sake of clarity, only some typical applications of CD/cellular interactions are reported.

i) Cell membrane cholesterol efflux

As previously mentioned, CDs are able to interact and to complex cholesterol and others lipids [114]. A great number of publications deals with this topic and with the consequences of this phenomenon (e.g., hemolysis or cytotoxicity, see section above). Since the nineties, β-CDs are known to have a high affinity, in vitro, for sterols as compared to other lipids [58,115]. Consequently, these molecules can be used to manipulate the cellular cholesterol content, to modify cholesterol metabolism [115,116] and to stimulate the removal of cholesterol from a variety of cells in culture [80,[117][118][119]. It should be noted that the cholesterol extraction by CDs is both time and dose dependent. In addition, the exposure of cells to modified β-CD in the 10-100 mM concentration range results in high rates of cell cholesterol efflux. Some typical examples are presented in this section.

CDs have been used to demonstrate the presence of different kinetic pools of cholesterol within cell models. Indeed, CDs have been used recently to monitor the movement of cholesterol from monolayers [57] or liposome bilayers [60]. For instance, a typical paper has been published in 2001 by Leventis and Silvius [60]. In order to characterize the CDs capacity to bind cholesterol, the authors examined the catalytic transfer of cholesterol between liposomes composed of 1-stearoyl-2-oleoyl phosphatidylcholine (SOPC) or SOPC/cholesterol. In the steady state under such conditions where a negligible fraction of the sterol is bound to CD (i.e., in the presence of submillimolar concentrations), β-and γ-CDs accelerate considerably the rate of cholesterol transfer between lipid vesicles (63-and 64-fold, respectively). This improvement is clearly greater than the transfer of phospholipid. The opposite is true for α-and methylβ-CD. The kinetics of CD-mediated cholesterol transfer indicates that the transbilayer flip-flop of cholesterol is very rapid (halftime < 1-2 min at 37 °C). In the case of β-CD, the author reported on the relative affinities of cholesterol for different phospholipids. As expected, strong variations in cholesterol affinity were observed depending on the degree of chain unsaturation and the headgroup structure. The transfer revealed that cholesterol interacts with markedly higher affinity with sphingolipids than with other membrane phospholipids. As extension of this work, Huang and London highlighted the possibility of preparing asymmetric vesicles during the exchange of membrane lipids between different vesicles by selective inclusion of phospholipids and/or cholesterol into the CD cavity The results show that the rate of efflux is approximately three orders of magnitude higher than the cholesterol transfer from cells to synthetic vesicles. Therefore, Me-β-CDs are very efficient to extract large amounts of membrane cholesterol at a very high rate. CDs can also catalyze the exchange of cholesterol between serum lipoproteins and cells [56].

ii) Cardiovascular diseases

The atherosclerosis vascular disease (ASVD) is caused by an inflammation of the arterial wall that is caused by increased cholesterol blood levels and an accumulation of cholesterol crystals in the subendothelial spaces leading to arteriosclerotic plaque formation [127]. It is noteworthy that the cholesterol represents a maximum of 10% of the total mass of plaque. Consequently, the elasticity of the artery walls is reduced, pulse pressure can be modified and blood clot can be formed (Scheme 6). Cardiovascular disease is currently the leading cause of death worldwide. As plasma levels of cholesterol are associated with cardiovascular morbidity and mortality, the use of CDs to solubilize and to remove cholesterol (and plaque) is very promising to combat this deadly condition.

It is noteworthy that high concentrations of modified β-CDs result in rates of cell cholesterol efflux far in excess of those achieved with physiological cholesterol acceptors such as highdensity lipoproteins (HDL). Indeed, plasma levels of HDL are inversely associated with cardiovascular morbidity and mortality because this lipoprotein is responsible for transporting cholesterol to the liver where it can be eliminated [128].

The opposite holds for low-density lipoproteins (LDL). Their function is to transport cholesterol, free or esterified, in the As the critical step in the formation of atherosclerosis plaque is the recruitment of monocytes (a type of white blood cells), which can differentiate into macrophages and ingest LDL, Murphy et al. proposed to prevent the activation/expression of monocyte adhesion [130]. For this cell adhesion, molecules such as CD11b are required. Therefore, the authors reported that β-CD, but not its cholesterol complex, inhibits CD11b activation. As the cholesterol content of lipid rafts diminished after treatment with the cholesterol acceptors, the authors proposed that the cholesterol efflux from serum monocytes is the main mechanism and is probably an effective means of inhibiting the development of atherosclerotic plaques.

In 2015, Montecucco et al. reported the anti-atherosclerotic action of KLEPTOSE ® CRYSMEB (a mixture of methylated β-CD where 2-O-methylations are dominant) in atherosclerotic mouse models [131]. As expected, their interfering action with cholesterol metabolism has a positive impact on atherogenesis, lipid profile and atherosclerotic plaque inflammation. In addition to reduce triglyceride serum levels, this CD reduces cholesterol accumulation in atherosclerotic plaques by the modification of HDL-cholesterol levels. It is noteworthy that HDL and apolipoprotein A-I (ApoA-I) cause a dose-dependent reduction in the activation of CD11b (i.e., anti-inflammatory effect on monocytes) through interactions with several receptors and ABCA1 for HDL and ApoA-I, respectively. However, the process, which leads to an aberrant accumulation of cholesterol in artery walls forming atherosclerotic plaques, is complex. Thus the alteration of RCT as well as the expression and the functionality of transporters (ABCA1, ABCG1, and SR-BI) involved in this process could be very useful in the fight against atherosclerosis pathogenesis. As pointed out by Coisne and co-workers, "RCT alterations have been poorly studied at the arterial endothelial cell and smooth muscle cells levels" [132]. Consequently, the authors investigated the effect of different methylated β-CDs on the RCT of arterial endothelial and smooth muscle cells. It should be noted that these two cell types express basal levels of ABCA1 and SR-BI whereas ABCG1 was solely found in arterial endothelial cells. The authors highlighted the correlation between the percentages of cholesterol extraction and the methylation degree of the CDs. This effect was clearly independent of the membrane composition. The expression levels of ABCA1 and ABCG1, as well as the cholesterol efflux to ApoA-I and HDL, were reduced due to cholesterol-methylated β-CD interaction. Consequently, the cellular cholesterol involved in atherosclerotic lesions is lowered and the expression of ABCA1 and ABCG1 transporters involved in RCT is clearly modulated.

In 2016, Zimmer et al. published on the effect of HP-β-CD in order to reduce atherosclerotic plaques [133]. The HP-β-CD can be used to dissolve cholesterol crystal (responsible for the complex inflammatory response) which can be excreted from the body in urine. Mice were fed with a cholesterol-rich diet for 12 weeks in order to promote fatty plaques in their blood vessels (i.e., to obtain atherosclerotic mice). After 8 weeks, they started the injection of HP-β-CD (2 injections by week). Over the remaining four weeks, the authors observed a plaque reduction in atherosclerotic mice that had consumed HP-β-CD compared with plaques in the blood vessels of untreated animals (≈46% reduction). From a mechanistic point of view, the researchers suspect that the CD boosts the activity of macro-phages, enabling them to attack excess cholesterol without causing inflammation. Indeed, CD increases liver X receptor (LXR) involved in the antiatherosclerotic and anti-inflammatory effects as well as in the RCT improvement.

Moreover, α-CD can also be used to reduce LDL cholesterol and alters plasma fatty acid profile [134,135]. In 2016, a double blind, placebo-controlled clinical trial has been published on the effect of oral α-CD [136]. After 12 to 14 weeks, a daily 6 gram dose of α-CD allowed to reduce fasting plasma glucose levels (1.6%, p < 0.05) and insulin index (11%, p < 0.04) in 75 healthy men and women. In addition, the LDL cholesterol levels were reduced by 10% (p < 0.045) compared with placebo. This CD was well tolerated and no serious adverse events were reported. Only about 8% of patients treated with α-CD reported side effect such as minor gastrointestinal symptoms (3% for the placebo). Consequently, the use of α-CD, safe and well tolerated, showed a reduction in LDL cholesterol, and an improvement of fasting plasma glucose.

The ability of CDs to change the contractibility of arterial smooth muscles indicates that the cellular cholesterol level is an extremely important factor for the cardiovascular system. Continued research on this front could potentially lead to major advancement in the fight against heart disease.

iii) Neurologic diseases

Like in other body systems, the cells of the nervous system are also susceptible to cholesterol extraction mediated by CDs. In the present section, for sake of clarity, only the potential applications of CDs to fight the Alzheimer's and Niemann-Pick type C diseases (AD and NPC, respectively) are reported.

AD is a chronic neurodegenerative disease which represents 60% to 70% of cases of dementia. This disease is characterized by the formation of amyloid plaques in the brain and is often associated to the cerebral accumulation of amyloidogenic peptides (Aβ42). This production is mediated by two neuronal enzymes (β-and γ-secretase) which can be inhibited by methylated under similar conditions, β-CD reduced both the cell-free and cell-associated virus more effectively than acyclovir (i.e., antiherpetic drug). Indeed, the results reveal an almost complete protection of Vero cells against acyclovir-sensitive and acyclovir-resistant strains of HSV. The ability of β-CD to impede virus replication is proposed as antiviral mechanism.

The potential occurrence of synergistic effects presents a special case, and may occur when one substance increases the activity of another. Currently, gaps in our knowledge of the circumstances under which such effects may occur (e.g., mixture composition, contact time, species, and exposure concentrations) often hamper predictive approaches. However, since the CDs are able to extract cholesterol and other lipids from the viral membrane, it is likely that their combination with virucides or antiviral drugs which act on the same target results in a synergistic effect. Based on this assumption, our group studied the combination of di-n-decyldimethylammonium chloride,

Conclusion

This review proposes an overview of the current and potential applications of CDs throughout their interactions with endogenous substances that originate from within an organism, tissue or cell. The majority of these applications are based on the capacity of CDs to withdraw cholesterol of the plasma membrane. This behavior presents several applications such as cholesterol manipulation, control of viral and bacterial infections, treatment of Alzheimer's and heart diseases, etc. Moreover, CDs present a viable basis in the context of "green pharmacy and medicine". In the last decade, the concept of "ecofriendly pharmacy" emerged in response to the Kreisberg's question: "what clinicians can do to reduce the environmental impacts of medications" [165]? Of course, the answers are based on similar principles than green chemistry initially developed by Anastas and Warner [166]. The principles cover various concepts such as: i) the use of bio-sourced ingredients, ii) the use of "green concepts" during the production (chemicals, synthesis processes, life cycle engineering, packaging, waste management), iii) the reduction of the negative impact of medication transportations, iv) the reduction of healthcare environmental footprint, v) the reduction of the use of pharmaceuticals and, vi) the improvement of the ultimate drug disposal with the use of take-back programs [167]. As CDs are bio-sourced compounds with very low toxicity dangers and easily biodegradable, they can be used to obtain more sustainable drug formulations in which CDs act as an active green ingredient and not only as an excipient. It is noteworthy that these CDs can be used alone or in combination with common petro-sourced medications. If a synergistic effect between the two molecules is obtained, a significant amount of the drug can be replaced by eco-and biocompatible CDs whilst maintaining the same biological activity. This is particularly interesting as it solves at least partially the negative impact of pharmaceutical formulations to the environment. Consequently, in this context of "greener pharmacy", CDs will contribute without doubt to preserve our planet in the coming years.

Scheme 1 :

 1 Scheme 1: Structure and conventional representation of native CDs.

Scheme 2 :

 2 Scheme 2: Proposed mechanism for morphological changes in erythrocytes induced by methylated CDs.

Scheme 4 :

 4 Scheme 4: Sugar hydrophobicity scale according to Janado and Yano and correlation with the binding constant values observed with β-CD.

5 :

 5 Scheme 5: Principle of chemically switched DNA intercalators based on anthryl(alkylamino)-β-CD/1-adamantanol (Left: unchanged DNA strand. Right: DNA strand intercalated at four locations).

  [120]. Moreover, CDs can also be used to monitor the intracellular movement of cholesterol in tissue culture cells[121].As the cholesterol extraction by CDs occurs usually at very high rates, CDs have been used to demonstrate the presence of dif-ferent kinetic pools of cholesterol within cells. Unfortunately, only few papers have studied the dynamics of this process on cells. For instance, the kinetics of cholesterol efflux have been examined in different cell lines such as fibroblasts [117], human erythrocytes [122], rat cerebellar neurons [123], differentiated human neurons and astrocytes [124], etc. All these results indicated that CDs induce cholesterol, sphingolipids, and phospholipids extraction from the cytoplasmic membrane typically in a range of 50-90% of the original amount. Castagne and co-workers studied the cholesterol extraction of native and modified β-CDs on endothelial cells (HUVEC) [125]. The measurement of the residual cholesterol content of cells reveals that cholesterol was extracted in a dose dependent relationship. As expected, a correlation was obtained between the cytotoxicity and the affinity for cholesterol. The affinity of CDs for cholesterol was classified in the order β-CD < HP-β-CD < Me-β-CD. Similar results are obtained with other biological membranes [117-126]. Another typical example has been published by Steck et al. The authors investigated the cholesterol movement created by the treatment of human erythrocytes with Me-β-CD [122].

Scheme 6 :

 6 Scheme 6: Normal (left) and diseased artery (right).

  blood and through the body to bring them to the cells. HDL particles also reduce macrophage accumulation, and thus help prevent or even regress atherosclerosis. The alteration of cellular cholesterol regulation, named the reverse cholesterol transport, RCT, could be used to block atheroprogression associated with different severity degrees of atherosclerosis pathogenesis. From the pioneering works of Irie et al., it became clear that CDs can be useful to prevent atherosclerosis [115,129].

Scheme 7 :

 7 Scheme 7: Kinetics of [DiC 10 ] insertion into the viral envelope without (left) or with γ-CD (right). Note that, after this step, the presence of [DiC 10 ] cations induces morphological changes that enhance the envelope fluidity and lead to the virus inactivation after envelope disruption (1. phospholipid, 2. cholesterol, 3. envelope, and 4. nucleocapsid).

[

  DiC 10 ][Cl] (the most widely used cationic surfactant with intrinsic virucidal activity), and native CDs (α-, β-and γ-CD) [159]. A marked synergism was observed with γ-CD against lipid-containing deoxyribonucleic and ribonucleic acid viruses (HSV-1, respiratory syncytial virus, RSV), and vaccinia viruses, VACV). Indeed, noticeable reductions of the [DiC 10 ][Cl] concentration (i.e., active virucide) were obtained: 72, 40 and 85% against HSV-1, RSV and VACV, respectively. In all cases, submillimolar [DiC 10 ][Cl] and γ-CD concentrations were re-quired to obtain a "6-log reduction" (equivalent to 99.9999% reduction) of the viral titer. Therefore, for these diluted solutions, free CD and [DiC 10 ] species prevail due to the Le Châtelier's principle. Moreover, the micellization equilibrium is not relevant as the virucidal activity was clearly obtained in the premicellar region. Thus, the proposed mechanism of the synergy is based on the ability of CD to extract rapidly cholesterol from the viral envelope. Indeed, γ-CD catalyzes the rapid exchange of cholesterol between the viral envelope and the aqueous solution. The sequestration of cholesterol in the bulk phase facilitates the [DiC 10 ] insertion within the lipid envelope which leads to the virus inactivation (Scheme 7). This means that γ-CD accelerates the rate of cholesterol extraction by a larger factor than α-or β-CD. The proposed mechanism is highly compatible with the results of Leventis and Silvius (see above)[60]. These results demonstrate a clear effect of CDs on the "viability" of enveloped viruses and provide evidences of their potential use in order to improve the efficiency of common antiviral medications. As cholesterol extraction is general and not limited to viral infections, a whole range of studies have shown that the presence of CDs impedes the entry of bacteria, fungi and parasites into host cells. This effect has been demonstrated for Plasmodium species [160], Campylobacter jejuni [161], Leishmania donovani [162], etc. and this behavior can be explained by the vital role of the lipid rafts in the binding and the entry of pathogens into host cells. Therefore, synergistic effects can also be obtained for bacteria, fungi and parasites. For instance, the combination of [DiC 10 ][Cl] and β-CD allows a clear reduction of the minimum inhibitory concentration, MIC, against Candida albicans compared to [DiC 10 ][Cl] alone. This effect was only observed for the β-CD/[DiC 10 ] mixture: the MIC values for αand γ-CD/[DiC 10 ] mixtures were similar to that of [DiC 10 ][Cl] alone. This behavior was attributed to the interaction of β-CD with the lipid membrane components [163]. Other relevant examples can be found in the review of Macaev et al. [164].

Table 1 :

 1 Structures, acronyms and characteristics of some modified cyclodextrins. a

	Abbreviation	Substituents (R)	Characteristics
	ME	-H or -CH 3	soluble in cold water and organic solvents, hemolytic
	HP	-H or -CH 2 CH(OH)CH 3	highly water-soluble, low toxicity
	S	-H or -SO 3 Na	pK a > 1, water soluble
	SBE	-H or -(CH 2 ) 4 SO 3 H	water soluble
	G1	-H or -glucosyl	highly water soluble
	G2	-H or -maltosyl	low toxicity

a ME: methyl; HP: 2-hydroxypropyl; S: sulfate; SBE: sulfobutyl ether; G1 glucosyl; G2: maltosyl.

Table 2 :

 2 Some marketed pharmaceutical formulations with CD. a

	CD	Drug	Formulation	Trade name	Market
	α-CD	Alprostadil	IV solution	Rigidur	Europe, USA
	α-CD	Cefotiam hexetil	Oral tablet	Pansporin T	Japan
	β-CD	Iodine	Topical solution	Mena-Gargle	Japan
	β-CD	Nicotine	Sublingual tablet	Nicorette	Europe
	β-CD	Piroxicam	Oral tablet	Flogene	Brazil, Europe
	HP-β-CD	Hydrocortisone	Topical cream	Dexocort	Europe
	HP-β-CD	Itraconazole	IV solution	Sporanox	Europe, USA
	HP-β-CD	Mitomycin	IV solution	Mitozytrex	USA
	ME-β-CD	Chloramphenicol	ED solution	Clorocil	Europe
	SBE-β-CD	Voriconazole	IV solution	Vfend	Europe, USA
	SBE-β-CD	Ziprasidone	IM solution	Zeldox	Canada, USA
	γ-CD	Minoxidil	Topical solution	Alopexy	Europe
	HP-γ-CD	Diclofenac	ED solution	Voltarenopthta	Europe

Table 3 :

 3 Pharmacokinetics and safety overview of some native and modified CDs for rats. a

	CD	Fraction excreted	Oral adsorption	LD 50 oral (g/kg)	LD 50 IV (g/kg)
		unchanged in urine
	α-CD	≈90%	2-3%	>10	0.5-0.75
	β-CD	≈90%	1-2%	>5	0.45-0.79
	γ-CD	≈90%	<0.02%	>>8	4
	HP

Table 4 :

 4 Association constants for the sugar/β-CD complexes (K).

		Guest		K (M -1 )
		D-arabinose	0.7 a	1.5 b	0.9 c
	Pentoses	D-ribose	5.3 a	6.3 b	4.8 c
		D-xylose	1.0 a	1.6 b	1.6 c
		D-galactose	"0" a	0.5 b	0.3 c
	Hexoses	D-glucose	"0" a	0.6 b	0.4 c
		D-mannose	"0" a	1.0 b	0.7 c

a Taken from

[95]

.

b

Taken from

[97]

.

c

Taken from

[START_REF] Turner | The study of b-cyclodextrin interactions with sugars using "inhibition kinetics" and the bromination of pyrimidine derivatives[END_REF]

.

These values are relatively close to each other and the sugar/β-CD binding constants increase in the order of D-galactose ≈ D-glucose < D-mannose < D-arabinose < D-xylose < D-ribose. This magnitude is consistent with the order of magnitude of the sugar hydrophobicity scale determined by Janado and Yano in 1985 (Scheme 4) [100]. This hydrophobicity scale is corroborated by Wei and Pohorille for the hexose series

[101]

. Therefore, even if all the literature values for the binding constants obtained by the different methods are not especially self-consistent, it is clear that β-CD can selectively recognize pentoses in contrast to hexoses

[102]

. However, the binding constants remain very small (see Table

4

). Based on all these results, the interaction of CDs with carbohydrates in aqueous solution can be completely neglected. Similar conclusions were made by

Paal and Szeijtli [103]

.

  Since anthrylamines have potent DNA-intercalating properties, Ikeda et al. have attached an anthrylamine to a β-CD[113]. The obtained anthryl(alkylamino)-β-CD was used as chemically switched DNA intercalator. However, as the anthryl residue is locked in the CD cavity, its intercalation into DNA is not possible in aqueous solution. Upon addition of a ligand that is tightly bound in the CD cavity (e.g., 1-adamantanol), the host molecule releases the anthryl unit, which then leads to strong intercalation with the double-stranded DNA molecule leading to structural distortions (Scheme 5). This behavior was clearly established from 1 H NMR spectroscopy (shifts and broadening of anthryl signals) in the presence of the 1-adamantanol guest. This concept could be very useful in nucleic acid reactions of medicinal and biotechnological importance for new drug delivery systems. Unfortunately, the binding constants between CDs and nucleic acids remain relatively modest and close to those observed for peptides and proteins (see above).

  Cholesterol levels in the plasma membrane are extremely important in many parts of the viral infection process such as the entry and release of virions from the host cell as well as for the transport of various viral proteins. CDs have a clear antiviral ac-In these cases, the ability of CDs to decrease membrane cholesterol was proposed as antiviral mechanism. Nevertheless, the biological effects of the CDs can be classified according to their role: i) to impede the viral entry in the host cell, ii) to decrease the relative infectivity of the virions, iii) to decrease the observed viral titer, and iv) to disrupt the surface transport of influenza virus hemagglutinin. Few typical examples of the CD effect on the pathogenicity of several viruses are reported.

		is characterized by an abnormal endosomal/lysosomal storage
		disease associated with genetic mutations in NPC1 and NPC2
		genes coding for proteins involved in the intracellular choles-
		terol transport. Consequently, functions of the impaired pro-
		teins cause a progressive neurodegeneration as well as liver and
		lung diseases. As these two proteins act in tandem and promote
		the export of cholesterol from endosomes/lysosomes, CDs can
		bypass the functions of NPC1 and NPC2 and can trap and trans-
		port membrane-stored cholesterol from endosomes/lysosomes
		[139]. This ability of CDs to sequester and to transport choles-
		terol could potentially lead to major advancements in our ability
		to fight neurodegenerative diseases.
		iv) Antipathogen activities
		The HIV is a widely studied virus in terms of the effects of
		CDs. For instance, sulfated CDs are able to inhibit HIV infec-
		tion [151,152]. In 1998, Leydet et al. demonstrated anti-HIV
		and anticytomegalovirus activity of several charged CD deriva-
		tives [153]. In 2008, Liao et al. reported that HP-β-CD exhibits
		also an anti-HIV activity based on cholesterol depletion [154].
		However, the mechanism had not yet been determined. Since
	β-CDs via cholesterol depletion [137]. Additionally, Yao and	the membrane cholesterol [155] and lipid raft-based receptors
	co-workers demonstrated that HP-β-CD reduces cell membrane	[156] are strictly required for infectivity and HIV entry, CDs
	cholesterol accumulation in N2a cells overexpressing Swedish	are excellent candidates for its use as a chemical barrier for
	mutant APP (SwN2a) [138]. Moreover, this CD dramatically	AIDS prophylaxis.
	lowered the levels of Aβ42 in cells as well as the amyloid
	plaque deposition by reduction of APP protein β cleavage and	Another common viral disease is caused by herpes simplex
	by up-regulation of the gene expression involved in cholesterol	virus (HSV) leading to several distinct medical disorders in-
	transport. In cell models, this CD also improved clearance
	mechanisms.
	CDs also exert significant beneficial effects in NPC disease,
	which shares neuropathological features with AD. This disorder

tivity against influenza virus [140], human immunodeficiency virus (HIV-1) [141], murine corona virus [142], poliovirus [143], human T cell leukemia virus (HTLV-1) [144], Newcastle virus [145,146], varicella-zoster [147], duck and human hepatitis B virus [148,149], bluetongue virus [150], etc. cluding orofacial and genital herpes or encephalitis [157]. In this context, the anti-HSV properties of native CDs (α-and β-CD) have been estimated against HSV-1 and HSV-2 [158].

The antiviral properties were clearly dependent on the cavity size: α-CD exhibited no significant antiherpetic activity, while,

Acknowledgments

This review is dedicated to the memory of Michel Teeten who taught me experimental biology.

Interactions between cyclodextrins and cellular components:

Towards greener medical applications?


Senior Elodie Bordat-Chauvin

Christopher Mathieu

Professor at Goldsmiths Victoria D Christopher Alexander

Mathieu

Accomplishing Cultural policy in Europe

While both editors are sociologists (one is a member of the Executive Board of the European Sociological Association), the contributors come from very different backgrounds: a gerontologist, a theatre director, several researchers who have held positions in business schools or management departments, and others who have worked in anthropology or ethnomusicology departments and finally in cultural institution studies. The contributors come from all over Europe (Malta, Spain, Norway, Sweden, Austria, Germany or France), but also from the Americas (Argentina and the USA), which allows the book's perspective to be decentralised. The diversity of the authors' careers, disciplines and backgrounds undoubtedly provides a variety of views on how to implement cultural policies in Europe. The choice of the word 'accomplishing' in the title is interesting. In the abstract we can read that this concept means: "from policy formulation and administration, artistic and cultural production activities to institutional governance". In the introductory chapter, the authors propose to "unpack" the title in order to "explain the rationale" of the book: "at one level, to illustrate the expanse of activities undertaken by different types of actors in producing the cultural and artistic outcomes influenced by cultural policies" (p. 1). And "the second aim is to show the intricacies and contextual specificities of how these processes play out across countries, policy levels and artistic fields" (p. 1). They point out: "how cultural policy is accomplished in European settings, in its breadth as well as its depth" and that "accomplishing cultural policy involves more than just formulating policy, which is part of the equation, but more or less begins and ends with the political and administrative processes around policy formulation and implementation, including evaluation" (pp. 1-2). "Accomplishing as a movement is a way of conceiving of processes that take place simultaneously across the arts and cultural landscape, at multiple levels, producing very real and significant goals and

outcomes, some of which are directly or indirectly influenced by cultural policy" (p.3) and part of it is " incompletion, failure and unintended results" (p. 3). For a French sociologist, as I am, it is interesting to note that instead of the traditional definitions of cultural policy proposed by Guy Saez (in particular the fact that cultural policy is more than the sum of cultural activities) or Philippe Urfalino (a moment of coherence and convergence between the definition of the role that the State can make culture play for society and the organization of public action), we find Alain Touraine, in his writings on social movements. This concept allows the authors to develop their theoretical framework of "primary tendencies and countercurrents". The recognition of the "hyper-instrumentalisation" of arts and culture, as well as marketdriven objectives, is interesting; and the conclusion, taken from Hadley and Gray (2017), is very provocative: "cultural policy is seen as having become non-cultural policy, that is, cultural objectives are sublimated to other priorities". I agree with the authors that cultural policies are increasingly conceived with an instrumental vision, in particular to solve urgent social problems such as the inclusion of marginalised populations or the reception of migrants, or as instruments of well-being and happiness, "using the arts as therapeutic tools to improve their lives" (p. 9). Mathieu and Visanich state that "arts and culture are an essential component of individual and collective quality of life". This assumption is widely shared by public authorities, in particular the European Commission, which regularly quotes this Eurobarometer survey to underline that 70% of Europeans feel happier living near a cultural heritage site. The author of these lines cannot help but think of "Happycracy" by E. Illouz and E. Cabanas, which highlights the problem of defining happiness using supposedly objective criteria. It is true, however, that public actors at all levels "recognise this intrinsic importance [...] of art and culture", which, according to the authors, makes possible "physical and mental health" (p. 5).

The debate on cultural policy and neoliberalism and public funding of arts and culture presented in this book is still very much alive. The first section of the book focuses on the issue of 'commercialisation of culture and the backlash', while the second section also explores responses to the 'market-centred paradigm' by focusing on the role of cultural policies in social inclusion and, by the same process, in promoting the exercise of cultural rights. Among the populations often marginalised by cultural policies, this book includes case studies on the inclusion of migrants, older people, but also the effects of the state's financial withdrawal from culture, with the example of Greece. The third part, "Procedures in arts funding", seems less clear-cut, as the case studies are so diverse (non-public funding in museums in Europe, project funding in Malta and visual arts in Flanders). Finally, the fourth part deals with the process of evaluation and good governance.

The introduction to the book is so rich and interesting that it could be the subject of a whole review. Space does not permit me to discuss all the chapters, or even the four sections. However, I would like to highlight two very exciting contributions.

Mariano Martin Zamorano's article analyses the cultural policies of Barcelona's left-wing governments, which sought to present an alternative to the Creative City paradigm through the 'commons' approach. Described as pro-commons, these cultural policies aim to enable the construction of collaborative spaces in which social movements would have more power in cultural institutions (on this point, see also Barbieri, 2017).

Zamorano identifies two characteristics of these cultural policies in the Spanish case. The first is a re-territorialisation, with neighbourhoods considered as 'new centralities' in the city (in line with Bookchin's municipal/communist approach), because 'culture is understood as an open space of community convergence' (p.22), rather than something elaborated in the centre and transferred to the peripheries. The second characteristic involves new forms of cultural participation with the extension of the possibility of using "common cultural property by both producers and consumers of culture" (p.23). One of the main questions of this paper is whether these new approaches succeed in overcoming inequalities in access to and participation in culture. The answer seems to be no. Aleysia Whitmore's contribution on the politics of cultural diversity in the South of France is very stimulating indeed she dares to use many words that are taboo in France. "A music project whose purpose is to celebrate a culture or community, as opposed to promoting artistic education or access for all (and democracy), is viewed as promoting difference and division and is considered communautariste. Communautarisme, literally communalism, is the prioritisation of group identity over national identity" (p. 88). As Whitmore points out, the fear of communautarisme (a term that appeared in the speeches of the alt-right and was then picked up by the media) hinders the realisation and funding of many cultural projects. All the more so since the adoption of the law "against separatism" and the "republican commitment contract" [START_REF] Talpin | Loi séparatisme : la critique associative face au contrat d'engagement républicain[END_REF]. To counter this perceived risk of communitarianism, cultural administrators are called upon to strengthen intercultural dialogue and social cohesion (p. 90). She demonstrates very well the discrepancies between the totally apolitical and 'neutral' description of musicians and arts administrators when they talk about their projects with participants from immigrant backgrounds (such as the Work Songs community choir) and what she observes as a 'North American ethnographer' (p. 91); and their strategies to counter possible critiques of communautarisme with the proper communication tools such as 'intercultural dialogue ' (p. 94), 'ouverture' and 'cultural exchange' (p. 100). Although her investigation focuses on the south of France in 2018, her findings are quite relevant for other French regions in 2023.

In conclusion, I would like to emphasise that this is a very interesting book for students of cultural management, but also for cultural policy researchers.