Sergii Snegir

Yannick J Dappe

Oleksiy L Kapitanchuk

Delphine Coursaut

Emmanuelle Lacaze

KINKED ROW-INDUCED CHIRALITY DRIVEN BY MOLECULE-SUBSTRATE INTERACTIONS

Combining STM measurements on three different substrates (HOPG, MoS2, and Au[111]), DFT calculations, and using a previously developed phenomenological model, we analyze the origin of the self-assembly of 4-Cyano-4′-n-decylbiphenyl (10CB), into kinked row structures. This molecule has an alkyl chain with 10 carbons and a cyanobiphenyl group of particularly large dipole moment. 10CB represents a toy model that we use here to unravel the relationship between the induced kinked structure, in particular, the corresponding chirality expression, and the balanced intermolecular/moleculesubstrate interaction. We show that the local ordered structure is driven by the typical alkyl chain/substrate interaction for HOPG and Au [111] and the cyanobiphenyl group/substrate interaction for MoS2. The strongest molecule/substrate interactions are observed for MoS2 and Au [111]. These strong interactions should have led to non-kinked, commensurate adsorbed structures. However, this latter appears impossible due to steric interactions between the neighboring cyanobiphenyl groups that lead to a fan-shape structure of the cyanobiphenyl packing on the three substrates. As a result, the kink-induced chirality is particularly large on MoS2 and Au [111]. A further breaking of symmetry is observed on Au [111] due to an asymmetry of the facing molecules in the rows induced by similar interactions with the substrate of both the alkyl chain and the cyanobiphenyl group. We calculate that the overall 10CB/Au [111] interaction is of the order of 2 eV per molecule. The close 10CB/MoS2 interaction, in contrast, is dominated by the cyanobiphenyl group, being particularly large due to dipole-dipole interaction between the cyanobiphenyl groups and the MoS2 substrate.

Introduction

For more than 30 years, a large variety of adsorbed molecular monolayers has been revealed and their structures studied in detail. Despite the considerable work already performed, the structure of a given self-assembled monolayer (SAM) for a new molecule/substrate combination remains unpredictable yet. A fundamental difficulty resides in mastering the relationship between the molecule/substrate, intermolecular interactions, and the emerged 2D supra-molecular structure. It is difficult because the relevant interactions, responsible for the induced ordered structures, are all of the same order of magnitude, moreover of value often not precisely known. Despite such complexity, the scientific interest towards 2D supra-molecular structures remains very high 1 since the crystalline structures, induced on crystalline substrates, can provide a number of potential applications 2 . To recall only a few, 2D molecular structures could be used as mother-templates for the stabilization of 3D molecular films that can be chiral [START_REF] Ernst | Supramolecular Chirality[END_REF][START_REF] Katsonis | [END_REF][5][6] . This kind of 2D chirality becomes increasingly interesting due to the number of techniques now able to overcome the recurring problem of the formation of mirror-image domains that would finally render the overall system racemic 7-15 . A 2D mothertemplate may also serve as a molecular sieve for the selection of guest-molecules by structural criteria [16][17][18] or by chiral criteria 19-20 . Besides these applications, 2D molecular templates were found recently efficient even for the formation of ordered arrays of nanoparticles 21 .

It is thus essential to establish how the different interactions combine if we want to be able to predict the induced structure associated with a given combination of molecule and crystalline substrate. It becomes now possible to make progress in this direction due to the constant improvement of numerical simulations, namely more accurate potentials in molecular dynamics, 22 or more significant system capability in DFT in particular 17, 23 . Therefore, we have chosen a particularly simple object, lamellar SAM made of elongated molecules, 10-Alkyl-cyanobiphenyl molecules (10CB) to understand how to demarcate all forces responsible for 2D superstructure formation. 10CB molecules have been studied in the past, but here we study them on three different substrates, HOPG, MoS 2

ARTICLE

Journal Name 2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx

and Au [111]. It is known that examining the self-assembly of the same molecule on different substrates is a useful tool if we want to disentangle the respective influence of substrate/molecule interactions and intermolecular interactions on the assembly process [24][25][26] .

10CB belongs to the class of n-Alkyl-cyanobiphenyl molecules (n-CB). Their structure consists of an aliphatic part (-[CH 2 ] n -CH 3 ) and an aromatic part. Two phenyl rings represent the aromatic part with the terminal -C≡N (cyano) group associated with the presence of a large dipole moment

27

. When the number of methylene units n (n = 5, 6, 7, 8, 9, 10, 12) varies, the molecular ordering on crystalline substrates may change. This effect was evidenced on highly oriented pyrolytic graphite (HOPG) [28][29][30][31][32] and molybdenum disulfide (MoS 2 ) [33][34][35][36] substrates. It has been shown that the n-CB molecular rows can be kinked, inducing a specific kind of chirality related to the direction of the kinks 13 . These kinked rows are common structures for a number of adsorbed molecules [37][38][39] and we intend here to work towards a more general understanding of the origin of these kinked rows. We use a phenomenological model of lamellar structures 40 combined with DFT calculations and STM data analysis to unravel the role of the molecule/substrate and intermolecular interactions. We show that whereas the three kinds of structures are globally similar, they present specific differences. We thus explore how the combination of the interactions induces these kinked structures which mostly concerns van der Waals interactions between alkyl chains and cyanobiphenyl groups, steric interactions between cyanobiphenyl groups and molecule/substrate interactions. Not only are we able to confirm the specifically strong interactions between the cyanobiphenyl groups and MoS 2 most probably due to the large cyanobiphenyl dipolar moment, but we evidence a further breaking of symmetry for 10CB/Au [111].

Experimental

An ethanolic solution of 10CB molecules (2.5×10 -7 mol.L -1 ) was deposited on the surface of HOPG, MoS 2 , and Au[111] and let evaporating before the STM measurements. The HOPG and MoS 2 substrates were cleaved just before the solution deposition and the Au[111]/mica substrate was annealed before deposition using a butane/propane torch. The STM measurements of freshly prepared gold surface revealed longrange herringbone patterns associated with periodically white stripes on STM images (Fig. S0

STM measurements.

The SAMs were all studied under ambient atmospheric conditions using a commercial STM equipped with a low current head (Bruker, Nanoscope 3A). The calibration of the STM piezoceramics occurs regularly using the HOPG surface. The STM tip was prepared by mechanical cutting of a Pt/Ir (80:20) wire. For each monolayer, several STM-images were recorded in constant current mode with I t ranging from 1.2 to 3 pA and tip bias U t from 50 to 1500 mV. They were obtained from different samples and tips to check reproducibility and to ensure that the results are free from artefacts. All distances have been measured from five different images with further averaging. This allowed minimizing the errors caused by the thermal drift of the STM tip when working under ambient conditions. All chemicals were purchased from Aldrich and used as received. HOPG, MoS 2, and mica substrates covered with gold were purchased from Bruker (Germany) and Phasis (Switzerland), respectively. DFT calculations. All geometrical configurations and molecular wave functions were obtained for an isolated 10CB molecule in neutral form using the quantum-chemical calculations. The full geometry relaxation, the electron density (HOMO and LUMO levels), and the energies calculations are performed at the density functional theory (DFT) level with the hybrid B3LYP functional and standard 6-31G* basis set using the Gaussian'03 program package.

Adsorption energies of alkyl chains and head groups on gold have been calculated using the localized-orbitals basis set DFT code Fireball

43

. Hence we have considered a 5x5 unit cell of Au(111) composed of 5 atomic layers in the XY plane. This unit cell is reproduced periodically in the XY plane through the DFT calculations and we have used a standard optimized spd basis set 44 . Then the molecular group has been placed on top of the gold slab and the full system has been optimized until the forces went below 0.1 eV/Å. Then from the obtained configuration, we have determined the interaction energy between the molecular group and the surface at different distances along the Z-axis. Van der Waals's interactions have been taken into account through the use of a specific formalism previously used for similar systems 44 . This formalism is a perturbation theory which takes into account two major contributions: the first one is due to the small overlaps between the electronic wavefunctions of the two subsystems, and lead to a repulsive contribution. This contribution is determined through a Taylor expansion with the overlaps of the Löwdin orthogonalization of the atomic wavefunctions. The second contribution, namely the van der Waals interaction, arises from the dipolar interaction between the two subsystems. Hence, we calculate here all the atomic dipole interactions between atoms from the two subsystems and add this energy in perturbation theory to the whole system. The dipole-dipole interaction is evolving in 1/r 3 , within the perturbation theory, we recover a 1/r 6 behavior, characteristic of van der Waals interactions.

Results and discussion

The SAM of 10CB molecules on a HOPG substrate form large mono domains of size exceeding 400 nm domains are slightly dislocated with respect to each other, forming straight domain walls (Fig. 1a). The STM analysis of a higher resolution image (Fig. 1b) reveals the presence of a specific intra-row structure. The rows are formed of periodic groups of 10 molecules, shifted from each other, leading to kinked rows. A scheme on top of the STM image shows in Fig. 1b the simplest unit cell between 2 consecutive kinks made of 10 molecules.

Each unit cell corresponds to an arrangement of 10 elongated bright spots representing the location of the π-conjugated cyanobiphenyl head-groups of the 10CB molecules 29 . The shape of the spots agrees well with the calculated profile of the frontier wave functions of the 10CB molecules (Fig. S1a). The head-groups point inward with their -C≡N groups, facing each other, in agreement with previous results on the same system 29 . In Fig. 1b the contrast is poor on top of the alkyl tails compare to one of the aromatic head-groups. It is due to the low electron density of the alkyl tails. Nevertheless, a finetuning of the STM tunnelling parameters allowed us to visualize the alkyl tails as repetitive bright spots (Fig. 1b). The extremities of two alkyl chains of two neighboring molecules in one unit-cell are separated by 5.3±0.4 Å (Fig. 1). This value is consistent with the value 2×T H =4.9 Å, where T H is the HOPG lattice parameter. The alkyl groups thus fit on the lattice, along the [100] direction, as expected 45, 46 . The period P of the unit cells, measured along the [1-10] direction (Fig. 1b), is equal to 41.7±1.5 Å, which is close to 10×T H ×√3=42.5 Å. This confirms the commensurability of the unit cell and suggests that its orientation is imposed by the HOPG, with the border of the unit cell being oriented along the [100] direction (Fig. S2). The relative shift of the unit cells along the [100] direction at each kink is equal to the value of one T HOPG : 2.5±0.3 Å which again confirms the local epitaxy of the 10CB molecules on the HOPG lattice (see Tab. 1 and Fig. S2).

Remarkably, the mean distance between endpoints of the neighboring cyanobiphenyl head-groups is 6±0.2 Å, larger than between endpoints of the alkyl chains, 5.3±0.4 Å, suggesting that the cyanobiphenyl groups do not fit the HOPG lattice. The larger inter-cyanobiphenyl group distance is consistent with a slightly fan-shaped structure, opposite to the strict alignment of the alkyl chains.

As a result, the STM contrast for the molecules at the edges of a unit cell is higher than for other molecules (Fig. S3). Such difference can be explained by different STM tunnelling conditions through the cyanobiphenyl groups at the edges of a unit cell with respect to the different carbon atoms of the HOPG. This suggests a different location on the HOPG lattice. From this, we can conclude about a non-perfect epitaxy of the molecules on HOPG, especially for the cyanobiphenyl groups at the border of the unit cell.

The SAM of 10CB molecules on MoS 2 contains large mono domains, of width around 200×200nm 2 , also with a lamellar structure. The observations revealed the formation of a faceto-face molecular arrangement of 10 molecules within a unit cell of MoS 2 (Fig. 2). The structure looks very similar to the one on HOPG (Fig. 1), but the STM contrast of 10CB on MoS 2 was obtained only under a high applied bias, above 1.4 V, due to the semiconducting nature of the MoS 2 substrate 47 .

From the images in Fig. 2b, it is easy to identify the two phenyl rings of each 10CB molecule as they appear as two separate bright spots. In contrast, alkyl-chain appears as one elongated bright spot. The mean distances between the endpoints of the cyanobiphenyl groups and between the terminal groups of the alkyl chains in a single unit cell are equal to respectively 6±0.5 Å and 5.5±0.4Å, respectively.

These distances are close to the one on HOPG. On MoS 2 (Tab. 1), the head groups present an epitaxy with the lattice since they are separated by about 6 Å, i.e. 2×T MoS2 with T MoS2 = 3.16 Å, the MoS 2 lattice constant. This confirms an orientation of the biphenyl groups close to being parallel to the [120] direction, as already evidenced for 8CB on MoS 2 [48][49][50] . The fan-shaped orientation is retained (Fig. 2a) with a slightly enlarged distance between the head group extremities with respect to the extremities of the alkyl chains as shown on Fig. 2. The unit cell period P is established from the crosssection along the [120] direction. It is equal to 48.5±0.5 Å which is indeed close to T MoS2 ×9×√3=49.3 Å (see Tab. 1, Fig. S4).

ARTICLE

To summarize, the packing structures of 10CB on HOPG and MoS 2 are locally identical but with different epitaxial properties. On the one hand, they display similar intermolecular distances and a fan-shaped arrangement of the molecules within the unit cell. They also display specific orientations of the molecules with respect to the crystallographic directions of the substrates leading to a unitcell period of 41.7 Å along the longitudinal direction [1-10] on HOPG and of 48.5 Å, a much larger value, along [120] on MoS 2 .

The SAM of the 10CB molecules on Au[111] form domains with various lateral sizes. The grain boundaries between domains correspond to dislocations of rows or disordered regions when the domains are tilted with respect to each other (Fig. 3a). When the substrate has been specifically prepared, the Au[111] reconstruction can be observed, coexisting with the 10CB network and not strongly modified by the adsorbed molecules. The observation of the Au[111] reconstruction suggests an orientation of the cyanobiphenyl groups only slightly disoriented from the direction perpendicular to the [110] (Fig. S6), thus in agreement with alkyl chains oriented along the [110] direction and the cyanobiphenyl groups at 35°-40° from the alkyl chain direction (Fig. S1 andS5). This suggestion is confirmed by a distance between the extremities of the alkyl chains equal to 5.9±0.1 Å, in other words very close to 2×T Au = 5.8 Å. The period P of the unit cells, measured along the [112] direction (Fig. 3b), is equal to 49.8±0.4 Å, which is close to 10×T Au ×√3=49.9 Å. These measurements demonstrate the local epitaxy of 10CB molecules also on Au [111] with the border of the unit-cell parallel to the [110] direction (see Tab. 1, Fig. S5). The comparison between the typical distances of the cells and their relationship with the underlying substrates are summarized in Tab.1 for each substrate, HOPG, MoS 2 and Au [111].

The 10CB kinked structure on Au [111] looks similar to the one on HOPG and MoS 2 but a careful STM analysis of various domains (Fig. 3b) reveals two main differences. First, the number of molecules involved in the cells is different. Hence, even if we still can observe some packing made of 10 molecules in a cell, the majority of the cells are constituted of 8 molecules instead of 10, as revealed by Fig. 3b and Fig. 5b.

In addition, the alternation of cells with different numbers of molecules is not regular. Second, the network on Au [111] systematically displays an additional anisotropy. Indeed, the facing molecules in the cell are clearly not equivalent in terms of STM contrast of the -CH 3 terminal groups of the alkyl chains, as pointed out by the arrows on Fig. 3b (see also Fig. 5b). This observation reveals that within the cells, the alkyl chains present two different positions on the Au lattice. This suggests that the facing molecules have different interactions with the substrate. This evidences a new breaking of symmetry along the direction of the alkyl chains, leading to an additional chiral feature on Au[111], compared to HOPG and MoS 2 only characterized by the presence of the kinks.

Discussion

The three structures on the three substrates are obtained after evaporation of the solvent and are not changed after an annealing at around 50°C. The similarity between the structures obtained on the different substrates, their observed stability over time together with the result of the annealing, does not strictly demonstrate the equilibrium of the different structures but at least demonstrate that they are particularly stable structures. We indeed never observed a change of configuration while running the experiment. We thus analyse them using a phenomenological model based on the minimization of the free energy. Also, due to the large molecule-substrate and intermolecular interactions, the entropy term may be neglected with respect to the energy term.

Epitaxy within the unit-cell

On HOPG the ordering of the 10CB molecules results from the well-known epitaxy of the alkyl chains 46, 51 . According to DFT simulations (Fig. S1a), the lowest energy conformation of a single and free 10CB molecule corresponds to an angle ψ between its alkyl chain and its cyanobiphenyl group at 37° that can fluctuate easily between 25° and 45°, due to the small torsion energy values. (Fig. S1) 40, 49 .

Since the mean distance between the alkyl chains on HOPG is of the order of 5.3 Å, the distance between the head-groupscalculated from simple geometric consideration lies around 5 Å but can easily reach 6 Å. This corroborates with both the observed fan-shape of the cyanobiphenyl groups showing a continuous variation of the angle ψ from one side to the other and the average distance between the endpoints of the cyanobiphenyl groups which is closer to 6 Å than to the expected 5 Å. The minimum distance between the cyanobiphenyl groups is considered as 8 Å in the absence of repulsive interaction

52

. For a distance of 6 Å between the cyanobiphenyl groups, there is an overlapping of the van der Waals radii (Fig. S7). The structure in the unit-cell being imposed by the alkyl chain packing, steric interactions must take place between the cyanobiphenyl groups and lead to the observed fan-shape structure within the unit-cells.

On MoS 2 , the distance between the alkyl chains is similar to the one on HOPG and the same fan-shape is observed, leading to a distance between the cyanobiphenyl groups of the order of 6 Å in average, close to 2×T MoS2 =6.3 Å. The epitaxy is now driven by the cyanobiphenyl groups oriented in average along the [120] direction of MoS 2 , known to be the favorable average orientation of the cyanobiphenyl groups on MoS 2 [48][49][50] . However, the distance between cyanobiphenyl groups remaining small, a fan-shape of the molecular structure is again induced within the unit-cell in relation with steric interactions. On Au [111], like on HOPG, the even larger alkyl chain/substrate interactions 53 favor an orientation of all alkyl chains along the [110] direction. The Au[111] period is larger, but the still observed cyanobiphenyl fan-shaped arrangement suggests that the steric interactions between the cyanobiphenyl groups are still present in relation to a distance between the cyanobiphenyl groups still smaller than 8 Å 52 .

To summarize, the unit cell structure of 10CB may be explained by a local epitaxy imposed by the molecule/substrate interactions favored by the alkyl chains on HOPG and Au [111] and by the cyanobiphenyl groups on MoS 2 , On HOPG and on MoS 2 the small lateral distances between the molecules, in particular, the neighboring alkyl chains, also suggests non-negligible intermolecular attractive van der Waals interactions between neighboring molecules in the unit cell. However, how to explain the presence of the kinks on all substrates independently of the distance between neighboring molecules?

Origin of the kinks and consequences

A former theoretical investigation has shown that the kinks can induce the formation of an incommensurate SAM depending on the average distance between the kinks 40

. The observation of cells on Au [111] of size varying between 8 and 10 molecules with no regular pattern is fully consistent with an incommensurate adsorbed structure. The feature that can be defined similarly for all studied substrates in order to characterize the kinked molecular rows is the angle α between the average row orientation associated with the kinks and the substrate crystallographic direction parallel to the short side of the cell (Fig. 123, Fig. S5). For α =0°, the rows are straight, and there is no kink-induced symmetry breaking. As such, α is one of the features defining the SAM chirality on a given substrate. The theoretical model has shown that α depends on two parameters 40 . The first parameter is the ratio P/L 0 , where P is the longitudinal period of packing along the substrate crystallographic direction (Fig. 123, Tab. 1), and L 0 is the natural longitudinal period of a free-standing 10CB monolayer without substrate. L 0 is expected to be close to two times the molecular length. For rows of period L 0 non-negligible attractive interactions between neighboring rows are expected to be mediated by van der Waals attractions between the terminal groups of alkyl chains of molecules belonging to neighboring rows. It has already been shown that van der Waals attractions between the extremities of alkyl chains can be the driving force at the origin of a SAM structure, for example, for triphenylene molecules adsorbed on Au[111] 6 . However, a period small enough to allow for significant attractive interactions between neighboring rows may be not compatible with a commensurate period, this latter being favorable for molecule/substrate interactions. The second parameter is thus the ratio of the molecule/substrate interaction over the interaction between neighboring rows. As underlined by the ellipses on Fig. S5, in close proximity to the kinks, the distance between the extremities of alkyl chains belonging to neighboring rows is significantly decreased and thus the Van der Waals attractive interactions are increased. The kinks thus favor attractive inter-row interactions.

It has been shown in the theoretical model that the feature α defined by the kink value increases with P/L 0 and thus with P 40 . This is in perfect agreement with the observed increasing P values from HOPG to Au[111] (Tab.1). The larger α values on MoS 2 and Au[111] also suggest, according to the model, a larger molecule/substrate interaction for these two latter substrates with respect to HOPG. Small α values are indeed only possible for small molecule/substrate interactions 40 . The experimental observations thus allow for an interpretation of the two large P values obtained on MoS 2 and on Au[111] (48.5 Å and 49.8 Å Table 1). In both cases, P could have been decreased to 8×a×√3 on MoS 2 instead of 9×a×√3 and 9×a×√3 on Au[111] instead of 10×a×√3, without even reaching a value as small as the observed 41.7Å on HOPG. According to the model, a corresponding small α value would be obtained for small enough molecule/substrate interactions only. For large molecule/substrate interactions either α = 0 or large α values are possible 40 .

To understand why α = 0 is not possible, we have to come back to the observed fan-shaped structure of the cyanobiphenyl groups, which demonstrates the presence of steric interactions between the cyanobiphenyl groups. These steric interactions can be released in the presence kinks and this explains the observed different STM contrast at the unit-cell border: the STM contrast would be associated with slightly different localization of the corresponding cyanobiphenyl groups to the underlying substrate. If steric interactions take place, the formation of infinitely straight rows (α = 0°) is not allowed. We consequently interpret the observed large (and similar) α and P values on MoS 2 and on Au[111] as related to similar large molecule/substrate interactions, larger than the ones of the 10CB molecules on HOPG that prevent only small α values. Steric interactions between the cyanobiphenyl groups in the same time prevent the possibility of α = 0° (no kink).

Molecule/substrate interactions

We can now focus on the molecule/substrate interactions and use the previously obtained information to quantify them. It is well-known that similarly to HOPG and despite a non-real epitaxy of the -CH 2 -groups on Au[111], there is a strong tendency of the alkyl chains to align along the [110] direction on Au[111] 53 . This is in agreement with the measured distance between the alkyl chains, commensurate to Au [111]. Due to the favorable locations for the -CH 2 -groups of the alkyl chains along the [110] direction 54 , we would expect identical locations for all the alkyl chains in a 10CB cell on Au[111] 54 . However, our experiment reveals different STM contrasts at the endpoints of the alkyl chains of the facing molecules (Fig. 3 and Fig. 4b). This result suggests that two different molecule/substrate interactions may impose the observed 10CB/Au[111] packing, namely not only the alkyl chain/Au[111] but also the cyanobiphenyl/Au[111] ones. To support this hypothesis, we have performed DFT calculations of the Au[111] interactions with an alkyl chain and with a cyanobiphenyl group. The results are presented on Fig. 4a where the interaction value is shown as a function of the distance between the functional group and the Au[111] lattice. We have recovered large alkyl chain/Au[111] interactions, at around -1.2 eV for an alkyl chain made of 10 methylene units. This value is close to -1.06 eV that can be extracted from the known value of -0.106 eV/CH 2 group, previously found experimentally 55 . It is about two times larger than on HOPG . So the 10CB/HOPG interaction can be considered as lower than -2×0.65 eV taking into account the cyanobiphenyl/HOPG interactions as lower than 0.65 eV per molecule. The 10CB/Au[111] interaction is thus larger in agreement with the analysis of the kinked structure in the previous section. We expect similar molecule/substrate interactions per unit length on MoS 2 with respect to Au [111], in relation to the close values of α and P for the two substrates. Based on the value obtained on Au[111], we obtain -2.2 eV per molecule on MoS 2 accounting for the different epitaxy between the two substrates that leads to different distances between molecules (Table 1). To evaluate the part of these interactions related to the alkyl chain/MoS 2 interactions, we consider the case of an epitaxy of the alkyl chain on MoS 2 equivalent to the one on HOPG. This gives a limit for the most significant interactions that can be expected. Van der Waals interactions are 1.5 larger on MoS 2 than on HOPG, in relation to the differences between the dielectric permittivity of the two materials 57-61 . So we calculate that the limit value is -1.5×0.65 = -0.97 eV. The interactions are even weaker since alkyl chains are not in epitaxy with MoS 2 . As a result, the interaction between the cyanobiphenyl group and MoS 2 is stronger than between the alkyl chain and MoS 2 , despite a larger number of carbon atoms in the alkyl chains. This result is in contrast with the Au[111] substrate (Fig. 4). This confirms the occurrence of specific interactions between the cyanobiphenyl group and MoS 2 already evidenced by the analysis of the 8CB SAM 62 . This could be related to the dipolar nature of the MoS 2 surface associated with the presence of a plane of molybdenum below the last sulphur plane, thus favoring significant dipole-dipole interactions with the n-CB molecules and their large dipole moment 27 .

Conclusions

In molecule/substrate interactions and intermolecular interactions, where attractive van der Waals interactions between alkyl chains (both laterally and longitudinally) and between cyanobiphenyl groups, steric interactions between cyanobiphenyl groups are involved. The balance of interactions leads to kinked lamellar monolayers with various chiral features. Locally the structure is similar for all substrates and monitored by the epitaxy, either of the alkyl chains (for HOPG and Au [111]) or the cyanobiphenyl groups (for MoS 2 ), which controls the orientation of the unit-cell and its lateral structure. Ideally, this would induce non-kinked straight rows (α = 0), commensurate parallel and perpendicular to the rows. However, two interactions act against straight rows: (1) steric interactions between the cyanobiphenyl groups -they induce fan-shaped structures and are released in presence of kinks-;

(2) attractive interactions between the rows -they mainly occur between the extremities of alkyl chains belonging to neighboring rows and are favored at the proximity of the kinks. For significant molecule/substrate interactions (MoS 2 and Au[111]), the smallest commensurate period perpendicular to the rows would impose straight rows which is forbidden. It is thus replaced by a large commensurate period. As a result, the attractive inter-row interactions also impose large kinks in order to minimize the inter-row distance. On MoS 2 and Au[111], of large and similar molecule/substrate interaction, large and similar average tilts of the rows are induced, corresponding to large chiral features, more significant than for HOPG. We expect this behavior to be generalizable to most of the kinked-row structures. Finally, using DFT calculations, we now understand the nature of the more significant interactions on Au[111] and MoS 2 . On Au [111], the molecule/substrate interactions (around 2 eV per molecule) allow for an additional asymmetric feature, one of the facing molecule is dominated by the alkyl chain/Au [111] interaction, the other one by cyanobiphenyl group/ Au[111] interaction. On MoS 2 , this is not the case. The molecule/substrate interactions (around 2.2 eV per molecule) are only dominated by the cyanobiphenyl group interaction with MoS 2 . It confirms the specificity of the interaction of the n-CB series on MoS 2 , most probably due to their large dipole moment. These large molecule/substrate interactions could also influence MoS 2 monolayers for new attractive electronic properties.

.) 41 . 42 .

 4142 This pattern corresponds to the well-known Au[111]/22×√3 reconstruction, with 23 surface atoms fitting into 22 lattice sites by compressing the topmost layer of the surface with the additional atoms The existence of the reconstruction was considered as evidence of the surface purity.

Figure. 1

 1 Figure.1 STM images of the SAM of 10CB molecules on a HOPG surface. a) -the large scale image (130×48 nm 2 ) represents the border of the domain. b) -the small scale image (10×10 nm 2 ) represents the internal kinked structure of the rows. The molecules superimposed on the STM image are mapping the unit cell. The angle α is the angle between the main crystallographic direction [100] of the HOPG substrate and the average row orientation created by the kinked structure. The corresponding STM parameters are I t = 2 pA, U t = 0.28 V.

Journal Name 4 |

 4 J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx

Figure. 2

 2 Figure.2 STM images of the SAM of 10CB molecules on a MoS 2 surface, a) -the large-scale image (20×7 nm 2 ), b) -the smallscale image (10×10 nm 2 ) represents the 10CB, arranged in the rows with a kinked structure. The molecular structures superimposed on the image are mapping the unit cell. The angle α is the angle between the main crystallographic direction [110]. of the MoS 2 substrate and the average row orientation created by the kinked structure. The corresponding STM parameters are I t =10 pA, U t = 1.4 V.

Figure 3 .

 3 Figure 3. STM images of the SAM of 10CB molecules on an Au[111] surface. (a) -the large-scale image (130×48 nm 2 ) presents domains oriented in equivalent direction, different by 120°. (b) -the small-scale image (10×10 nm 2 ) represents 10CB molecules arranged in a kinked structure. The molecules superimposed on the STM image define the most common cell structure containing eight molecules. The angle α is the angle between the crystallographic direction [110] of the Au substrate and the average row orientation created by the kinked structure. The period P of the cells packing runs along the [112] crystallographic direction. The corresponding STM parameters are I t = 1.4 pA, U t = 180 mV.

  It increases from HOPG to Au[111] : α = 4.7° for 10CB/HOPG, 8.9° for 10CB/MoS 2 , 10.2° for 10CB/Au[111]), evidencing larger chiral features for 10CB/MoS 2 and 10CB/Au[111] with respect to 10CB/HOPG.

56 .Figure 4 . 54 .

 56454 Figure 4. a) Calculated adsorption energy curves for alkyl chain made of 10 methylene units (black) and cyanobiphenyl head groups (red) on Au[111] surface, as a function of the moleculesurface distance -and b) STM image of 10CB molecules on Au[111] in multicolor scale which shows the difference of STM contrasts at the endpoints of facing molecules within a cell.

40

 40

Table 1 . SAMs experimental parameters with respect to the substrate lattice parameters.

 1

	SURFACE	Substrate Lattice param. T, Å	Separation. * alkyl-chains, Å	Shortest dist. † head-groups, Å	Unit cell shift, Å	Period of packing P, Å	Number of mol. in a unit cell
			5.3±0.4	6±0.2	2.5±0.2	41.7±1.5
	HOPG	2.46					10
			2×THOPG	-	THOPG	10×THOPG×√3
			5.7±0.1	7.3 ±0.2	5.8±0.2	49.8±0.4
	Au[111]	2.88					8/10
			2×TAu	-	2×TAu	10×TAu×√3
			5.5±0.4	6±0.5	7.8±0.7	48.5±0.5
	MoS2	3.16					10
			-	2× T MoS2	-	9× T MoS2 ×√3

*-

was measured between the extremities of the alkyl chains. †-was measured between the extremities of the cyanobiphenyl groups ARTICLE Journal Name

6 | J. Name., 2012, 00, 1-3

This journal is © The Royal Society of Chemistry 20xx

  conclusion, combining STM measurements and DFT calculations, we interpret the variations of the 10CB monolayer organization on HOPG, MoS 2 and Au[111] as the

	ARTICLE	Journal Name
		result	of	the	combination	of	all	interactions,

8 | J. Name., 2012, 00, 1-3

This journal is © The Royal Society of Chemistry 20xx

, characterized by a lamellar packing of the molecules. The rows of neighboring

This journal is © The Royal Society of Chemistry 20xxJ. Name., 2013, 00, 1-3 | 3

This journal is © The Royal Society of Chemistry 20xxJ. Name., 2013, 00, 1-3 | 5

This journal is © The Royal Society of Chemistry 20xxJ. Name., 2013, 00, 1-3 | 7

Acknowledgments

The authors acknowledge the partial financial support of this work through the Collaborative Research Center (SFB) 767 of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)

Conflicts of interest

All authors declared no any conflicts of interests. The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes

Supporting Information is available as separated file References


PhD Nadine Hamieh
email: nadine.hamieh@iplesp.upmc.fr

Sofiane Kab

Marie Zins

Jacques Blacher

Ph.D Pierre Meneton

Ph.D Jean-Philippe Empana

Ph.D Nicolas Hoertel

Frederic Limosin

Ph.D Marcel Goldberg

Ph.D Maria Melchior

Ph.D Sofiane Student

PharmD Kab

Ph.D Jacques Blächer

Ph. D Frédéric Limosin

Sc.D Cedric Lemogne

Depressive symptoms and non-adherence to treatable cardiovascular risk factors' medications in the CONSTANCES cohort

Keywords: depressive symptoms, hypertension, diabetes, dyslipidaemia, medication, adherence

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Depression is not only one of leading causes of disability worldwide, but it has been repeatedly associated with cardiovascular disease (CVD) [START_REF] Nicholson | Depression as an aetiologic and prognostic factor in coronary heart disease: a meta-analysis of 6362 events among 146 538 participants in 54 observational studies[END_REF][START_REF] Hamieh | Depression, treatable cardiovascular risk factors and incident cardiac events in the Gazel cohort[END_REF] . In addition, cardiovascular risk factors are highly prevalent in the presence of depression [START_REF] Meng | Depression increases the risk of hypertension incidence: a meta-analysis of prospective cohort studies[END_REF][START_REF] Yu | Depression and Risk for Diabetes: A Meta-Analysis[END_REF][START_REF] Olusi | Serum lipid concentrations in patients with major depressive disorder[END_REF] . The association between depression and CVD could thus be partially explained by poor adherence to medications regarding treatable cardiovascular risk factors, namely hypertension, diabetes mellitus and dyslipidaemia. The prevalence of non-adherence to medications in chronic diseases, including hypertension, diabetes and dyslipidaemia 6 , is estimated to be 50% in developed countries [START_REF]Adherence to long-term therapies: Evidence for action[END_REF] . Moreover, around 20% of newly prescribed medications are never filled, and around 50% of those that are filled are not taken correctly in terms of frequency, dosage, duration and timing [START_REF] Osterberg | Adherence to medication[END_REF] . As hypertension, diabetes, and hypercholesterolemia contribute to 68% of all deaths worldwide 6 , improving adherence to medications treating these conditions is a critical challenge for public health [START_REF] Ting | Quality improvement: science and action[END_REF][START_REF] Dimatteo | Variations in patients' adherence to medical recommendations: a quantitative review of 50 years of research[END_REF] . This challenge might be even more critical in individuals with depression.

Overall, depression has been associated with poor adherence to medications in various settings [START_REF] Grenard | Depression and medication adherence in the treatment of chronic diseases in the United States: a metaanalysis[END_REF] . A recent meta-analysis showed that depressed patients are 1.76 times more likely to be nonadherent to chronic disease medications compared to their non-depressed counterparts. Specifically, the adjusted odds ratios (OR) of being non-adherent among depressed patients are 1.73 (95% confidence interval (CI): 1.24-2.87) and 1.79 (95% CI: 1.28-2.51) compared to non-depressed patients in six studies on diabetes and eight studies on hypertension or dyslipidaemia, respectively [START_REF] Grenard | Depression and medication adherence in the treatment of chronic diseases in the United States: a metaanalysis[END_REF] . However, adjustment variables differ from one study to the other and residual confounding could not be excluded. In addition, most of these studies were conducted in clinical samples and evidence from the general population is sparse. To our knowledge, eight studies assessed these associations using population-based samples, but only three were prospective studies using objective measures of treatment adherence [START_REF] Bauer | Depressive symptoms and adherence to cardiometabolic therapies across phases of treatment among adults with diabetes: the Diabetes Study of Northern California (DISTANCE)[END_REF][START_REF] Sjosten | Effect of depression onset on adherence to medication among hypertensive patients: a longitudinal modelling study[END_REF][START_REF] Gentil | Association between depressive and anxiety disorders and adherence to antihypertensive medication in community-living elderly adults[END_REF] and none of these three studies assessed hypertension, diabetes, and hypercholesterolemia jointly.

Taking advantage of a population-based cohort study linked to administrative claim database, we aimed to examine the prospective association between depressive symptoms and subsequent nonadherence to medications each targeting hypertension, diabetes type 2 and dyslipidaemia in a largescale, diverse adult population living in France.

METHODS

Study Design

The CONSTANCES cohort is a large population-based study of 18-69 years old volunteers randomly selected from 22 health-screening centres (HSCs) in different districts across France since 2012 that reached 200,000 participants by early 2019 [START_REF] Zins | The French CONSTANCES population-based cohort: design, inclusion and follow-up[END_REF] . These volunteers were covered by the French national health insurance fund; hence, this study covered 85% of the adult population in France and excluded self-employers, farmers and undocumented immigrants. Volunteers were asked at inclusion to complete self-administrated questionnaires by mail on lifestyle and socio-demographic characteristics as well as socio-professional and health statuses. Additionally, they underwent health examination such as laboratory tests and physical examination in the HSCs. If a new disease was discovered after the full assessment, including hypertension, diabetes and dyslipidaemia, the participants were informed and offered a medical consultation to review their results with the HSC physicians.

Participants' data were matched to the 'Système National d'Information Interrégimes de l'Assurance Maladie' (SNIIRAM) database through specific identifiers. This database included information on all reimbursed medications [START_REF] Bezin | The national healthcare system claims databases in France, SNIIRAM and EGB: Powerful tools for pharmacoepidemiology[END_REF]

Study populations

We first defined the presence of hypertension, diabetes type 2 and dyslipidaemia by either self-reports in the medical questionnaire administrated by the physician at inclusion, or abnormal blood pressure/ blood tests on the medical examination offered at study inclusion, or both. Abnormal blood pressure was defined as a systolic blood pressure of ≥140 mmHg and/or diastolic blood pressure of ≥90 mmHg.

Abnormal glycaemia, cholesterol, triglycerides levels were defined as fasting glucose ≥7 mmol/l, fasting LDL-cholesterol >4.08 mmol/l and/or fasting triglycerides ≥1.7 mmol/l respectively. Blood pressure and blood tests were collected from laboratory tests at inclusion during the visit to the HSCs based on standardized procedures [START_REF] Ruiz | High quality standards for a large-scale prospective population-based observational cohort: Constances[END_REF] . For instance, blood pressure was measured using oscillometric sphygmomanometer based after 5 minutes of rest. The blood tests were collected and pre-treated within a maximum of 30 minutes period, then transported to the central laboratory on the same day at 4-8 degrees [START_REF] Zins | The French CONSTANCES population-based cohort: design, inclusion and follow-up[END_REF] .

A total of 151,207 participants were enrolled in CONSTANCES between February 2012 and March 1, 2018. Among them, 128,700 had available SNIIRAM data and 45,052 were included before January 1, 2015, thus having 36 months of follow-up (Supplemental Figure 1). Among these 45,052 individuals, we included individuals with the condition under study (i.e. either hypertension, diabetes or dyslipidaemia), who had at least one drug prescriptions filled in the 6 months before inclusion and who completed the Center for Epidemiologic Studies Depression (CES-D) scale at inclusion. Since our primary outcome was medication non-adherence at follow-up, being on medication on the day of inclusion was not required as inclusion criteria. Information on date of drug prescriptions filled was collected from the SNIIRAM database. Pharmacological treatment of the conditions under study was identified according to the World Health Organization's Anatomical Therapeutic Chemical (ATC) classification [START_REF]ATC/DDD Index[END_REF] .

Assessment of depressive symptoms

Depressive symptoms were assessed at baseline using the French version of the CES-D scale [START_REF] Morin | Psychometric properties of the Center for Epidemiologic Studies Depression Scale (CES-D) in French clinical and nonclinical adults[END_REF] . The CES-D scale is composed of 20 items that assess depressive symptoms in the past week such as agitation, guilt, loss of appetite and interest, fatigue, suicidal thoughts and sadness (e.g. I felt sad, I felt lonely) on a scale from 0-3 with 0 being 'rarely' (<1 day) and 3 'most of the time' (5 to 7 days).

Internal consistency of CES-D scale is generally high (α = 0.90 in the CONSTANCES cohort).

Volunteers with a score of ≥19 were considered to be clinically depressed according to the validated threshold for the French version (sensitivity and specificity >85% for the diagnosis of major depression) [START_REF] Morin | Psychometric properties of the Center for Epidemiologic Studies Depression Scale (CES-D) in French clinical and nonclinical adults[END_REF] . However, to incorporate volunteers with more severe depressive symptoms for minimizing type I error, sensitivity analyses were performed with the CES-D score using two thresholds with higher specificity: 21 (sensitivity 82%, specificity 91%) and 22 (sensitivity 79%, specificity 92%) [START_REF] Morin | Psychometric properties of the Center for Epidemiologic Studies Depression Scale (CES-D) in French clinical and nonclinical adults[END_REF] .

Assessment of non-adherence to medications

Non-adherence to cardiovascular risk factors' medications under study was assessed by tracking the reimbursement of ad hoc medications over 18 months after the date of inclusion and 18 months afterwards (19-36 months). To measure medication non-adherence, we divided the sum of trimesters with at least one drug dispensed by the total number of trimesters (i.e. 6 trimesters) [START_REF] Steiner | The assessment of refill compliance using pharmacy records: methods, validity, and applications[END_REF] (Supplemental Equation 1). Participants were considered non-adherent if they purchased the studied drugs less than 80% of time, a commonly used threshold in studies of medication non-adherence [START_REF] Steiner | The assessment of refill compliance using pharmacy records: methods, validity, and applications[END_REF] . In addition, exploratory analyses were performed using medication non-adherence between the first 3-6 months after the date of inclusion (i.e. had at least one trimester without drug dispensed) to test whether nonadherence to medications would be more sensitive to depressive symptoms in this period.

Assessment of covariates

Age (continuous, years), sex, living with a partner (yes; no), country of birth (France; other), educational level (≤ high school diploma: ≤13 years of education; undergraduate degree: between 14 and 16 years of education; postgraduate degree: ≥17 years of education) and employment status (yes; no) were collected at inclusion from volunteers' self-reports. Physical activity (0: not active to 6: very active) and prescribed and followed diet (yes; no) at inclusion were also collected from the same source for descriptive purpose. Personal history of CVD (yes: history of angina pectoris, myocardial infarction, stroke or peripheral arterial diseases; no) was collected from the medical questionnaires administrated by the physician at inclusion. Body mass index, BMI (<25; ≥25 and <30; ≥30 kg/m 2 ) was calculated at inclusion.

Statistical analysis

All analyses were conducted using the SAS system software (version 9.4, SAS Institute, Cary, NC). Independent t-tests, Chi-Square tests and Fisher's exact tests were computed for demographic and clinical characteristics by the presence of depressive symptoms. First, as our primary analyses, the associations between depressive symptoms at inclusion and non-adherence to medications treating hypertension, diabetes or dyslipidaemia either in the first 18 months or between 19 and 36 months of follow-up were studied with unadjusted and fully-adjusted logistic regression models. Based on an anticipated rate of non-adherence of 25% in this sample of individuals presumably more health-conscious than the general population, an anticipated rate of 20% of participants with depressive symptoms (i.e. a CES-D score >19) and an anticipated Odds-Ratio of 1.75 for non-adherence in the presence of depressive symptoms [START_REF] Grenard | Depression and medication adherence in the treatment of chronic diseases in the United States: a metaanalysis[END_REF] , we calculated that a minimum of 706 participants would be needed for a given condition to achieve a statistical power of 80% with an alpha risk set at 5% [START_REF] Demidenko | Sample size determination for logistic regression revisited[END_REF] . This sample size was corresponding to the expected sample size of participants with diabetes, with larger samples being expected for participants with hypertension or dyslipidaemia. Fully-adjusted models were adjusted for all the covariates mentioned above, except for prescribed diet and physical activity. These two variables were excluded since they could be part of the non-pharmacological treatment of the condition, thus capturing a part of medical adherence. In other words, adjusting for these variables may result in an artificial underestimation of the association of depressive symptoms with medication non-adherence. Second, as exploratory analyses, these analyses were repeated between the first 3-6 months to explore whether non-adherence to medications would be more sensitive to depressive symptoms in this period. Since socio-demographics (i.e. age, sex and educational level) may be effect modifiers of the association between depressive symptoms and non-adherence to medications, we tested for statistical interactions between depressive symptoms and these variables. Should these interactions be significant, we planned to further examine the association between depressive symptoms and nonadherence to medications in stratified analyses.

All analyses were computed using multiple imputations to handle missing values in the covariates.

RESULTS

The characteristics of participants with hypertension (N=4,998), diabetes (N=793) and dyslipidaemia (N=3,692) are presented in Table 1. The overlap between the three populations under study is displayed in Supplemental Figure 2. The prevalence of depressive symptoms varied from 16.2% in individuals with dyslipidaemia to 21.8% in those with diabetes. The majority of study participants were men, living with a partner, French by birth, non-employed, physically active, had a high school diploma at best and a BMI between 25 and 30, did not follow a prescribed diet, did not have a personal history of CVD. Over the first 18 months of follow-up, 0.2% of individuals with hypertension, 0.4% with diabetes and 0.1% with dyslipidaemia died and thus were not included in the subsequent analyses as well as 0.9%, 1.4% and 0.4% between 19-36 months.

Among individuals with hypertension, diabetes and dyslipidaemia, respectively 13.1% vs. 11.5%, 10.5% vs. 5.8% and 29.0% vs. 27.1% of those with vs. without depressive symptoms were non-adherent (i.e. had a proportion of trimesters with at least one drug dispensed of <80%) over the first 18 months of follow-up, and15.9% vs. 13.6%, 11.1% vs. 7.4% and 34.8% vs. 36.6% between 19-36 months.

Among participants with diabetes, hypertension or dyslipidaemia, depressive symptoms were neither associated with non-adherence to medications over the first 18 months of follow-up, nor afterwards (Table 2). Similar findings were obtained in the fully adjusted models while using CES-D thresholds of 21 and 22 (Supplemental Tables 1 and2). None of the interactions between depressive symptoms and socio-demographic variables were significant (all P≥0.06); hence, we did not further stratify our analyses according to these variables. However, in the exploratory analyses, depressive symptoms became associated with non-adherence to anti-diabetic medications between the first 3-6 months of follow-up with ORs ranging from 2.40-2.80 whatever the CES-D score threshold (Supplemental Table 3).

DISCUSSION

This study aimed to examine the prospective association between depressive symptoms, and nonadherence to medications for treatable major cardiovascular risk factors, namely hypertension, diabetes type 2, and dyslipidaemia, in a population-based setting. Overall, the results suggest that depressive symptoms were neither associated with non-adherence to medications for hypertension, diabetes, and dyslipidaemia over the first 18 months, nor afterwards. However, depression might be associated with non-adherence to antidiabetic medications for diabetes between the first 3-6 months.

There were certain strengths in this study. First, to our knowledge, this is the first study that examines the association between depressive symptoms and non-adherence to medications targeting the three main treatable cardiovascular risk factors in a single prospective, population-based cohort using administrative claim databases rather self-reported adherence. Second, the systematic linkage between a national population-based cohort and a national healthcare administrative database offered the opportunity to use actual prescriptions filled as dependent variable with no loss to follow-up while considering several potential confounders or effect modifiers. Overall, except for educational level, the significant associations of these potential confounders with non-adherence to medications were somehow consistent with those found in the literature [START_REF] Abegaz | Nonadherence to antihypertensive drugs: A systematic review and meta-analysis[END_REF][START_REF] Gupta | Risk Factors for Nonadherence to Antihypertensive Treatment[END_REF][START_REF] Naderi | Adherence to drugs that prevent cardiovascular disease: meta-analysis on 376,162 patients[END_REF][START_REF] Van Der Laan | Factors associated with antihypertensive medication non-adherence: a systematic review[END_REF] . Third, the clinical and laboratory data were collected according to standardized procedures by specialized teams at health-screening centres [START_REF] Ruiz | High quality standards for a large-scale prospective population-based observational cohort: Constances[END_REF] .

Fourth, because the results of these procedures were disclosed to the participants, non-adherence is unlikely to be explained by a lack of awareness of the disease.

However, this study had also limitations, mainly resulting from the characteristics of the SNIIRAM database. First, this database does not provide detailed information on the conditions warranting the prescription of medications. For instance, some anti-diabetic medications may have been prescribed to lose weight [START_REF] Knowler | Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin[END_REF] . Second, the SNIIRAM database does not contain information about actual medication use. However, it is unlikely that patients with regularly filled prescriptions did not take their medication at all. Third, detailed information about non-pharmacological treatments is not available in this database. For instance, participants who did not take pharmacological treatment were considered to be non-adherent, although some of them were possibly prescribed non-pharmacological treatments (e.g. change in diet, increased physical activity) only [START_REF] Williams | ESC/ESH Guidelines for the management of arterial hypertension[END_REF][START_REF] Mach | ESC/EAS Guidelines for the management of dyslipidaemias: lipid modification to reduce cardiovascular risk[END_REF] . Fourth, although the CONSTANCES cohort is a large community-based population in France, with a broad sociodemographic diversity, the majority had a favourable social context. In addition, the prevalence of the conditions was lower than expected from the general population and this could be explained by the fact that CONSTANCES participants are more interested in their health. However, the low prevalence of diabetes is a very common phenomenon in any cohort [START_REF] Meneton | A Global View of the Relationships between the Main Behavioural and Clinical Cardiovascular Risk Factors in the GAZEL Prospective Cohort[END_REF] where individuals with diabetes are typically less prone to participate than to those with hypertension and dyslipidaemia. Furthermore, we showed that socio-demographics were not significant effect modifiers, thus limiting the risk of our results to be affected by selection biases. Fifth, the CES-D scale measures self-reported depressive symptoms and not major depression. For instance, functional impairment because of depressive symptoms is a diagnostic criterion of major depression that is not assessed by the CES-D. However, the association between depression and increased risk of CVD is not specific to major depression but also observed for subthreshold depressive symptoms. Our hypothesis was therefore that current depressive symptoms could impede medication adherence. However, since these symptoms were assessed only once at baseline, they may reflect a transient state that was not present later during follow-up. Sixth, we did not take into account antidepressant medications because, as stated above, our hypothesis was about current depressive symptoms and antidepressants per se were not supposed to have a direct effect on medication adherence. In addition, data from the French national health insurance system suggest that antidepressant drugs are frequently prescribed for reasons other than depression (i.e. migraine) [START_REF] Mercier | Understanding the prescription of antidepressants: a Qualitative study among French GPs[END_REF] . Finally, although the broader hypothesis we aimed to test was whether medications adherence to treatable cardiovascular risk factors could be a potential mediator of the association between depressive symptoms and cardiovascular disease, the present study only tested a part of this hypothesis.

The lack of association between depressive symptoms and non-adherence to medications for hypertension or dyslipidaemia in the participants concerned was not in line with our hypothesis. This lack of association was indeed consistent with the results of some previous studies [START_REF] Maguire | Exploring the impact of depressive symptoms and medication beliefs on medication adherence in hypertension--a primary care study[END_REF][START_REF] Steiner | Sociodemographic and clinical characteristics are not clinically useful predictors of refill adherence in patients with hypertension[END_REF][START_REF] Wang | Noncompliance with antihypertensive medications: the impact of depressive symptoms and psychosocial factors[END_REF] but not with others [START_REF] Krousel-Wood | Predictors of decline in medication adherence: results from the cohort study of medication adherence among older adults[END_REF][START_REF] Forsyth | Perceived discrimination and medication adherence in black hypertensive patients: the role of stress and depression[END_REF][START_REF] Siegel | Antihypertensive medication adherence in the Department of Veterans Affairs[END_REF][START_REF] Bautista | Symptoms of depression and anxiety and adherence to antihypertensive medication[END_REF][START_REF] Krousel-Wood | Association of depression with antihypertensive medication adherence in older adults: crosssectional and longitudinal findings from CoSMO[END_REF] for hypertension. It was also not in line with the results of one study for dyslipidaemia [START_REF] Stilley | Psychological and cognitive function: predictors of adherence with cholesterol lowering treatment[END_REF] ; however, the authors did not assess depressive symptoms by themselves: they combined it with anxiety. Overall, these studies were either retrospective [START_REF] Steiner | Sociodemographic and clinical characteristics are not clinically useful predictors of refill adherence in patients with hypertension[END_REF][START_REF] Schoenthaler | Self-efficacy mediates the relationship between depressive symptoms and medication adherence among hypertensive African Americans[END_REF] or prospective with a follow-up period of 2 years at best. Furthermore, only three studies [START_REF] Bauer | Depressive symptoms and adherence to cardiometabolic therapies across phases of treatment among adults with diabetes: the Diabetes Study of Northern California (DISTANCE)[END_REF][START_REF] Sjosten | Effect of depression onset on adherence to medication among hypertensive patients: a longitudinal modelling study[END_REF][START_REF] Gentil | Association between depressive and anxiety disorders and adherence to antihypertensive medication in community-living elderly adults[END_REF] used prospective population-based cohorts to assess the medication adherence based on objective measures. These three studies showed a positive association between depressive symptoms and non-adherence to medications over time. However, the first study measured non-persistence rather than non-adherence [START_REF] Sjosten | Effect of depression onset on adherence to medication among hypertensive patients: a longitudinal modelling study[END_REF] . The second study assessed nonadherence to medications targeting various cardio-metabolic conditions among adults with diabetes [START_REF] Bauer | Depressive symptoms and adherence to cardiometabolic therapies across phases of treatment among adults with diabetes: the Diabetes Study of Northern California (DISTANCE)[END_REF] and the third one used either depressive symptoms or anxiety as independent variable among old adults with hypertension [START_REF] Gentil | Association between depressive and anxiety disorders and adherence to antihypertensive medication in community-living elderly adults[END_REF] .

In contrast, the lack of a significant association between depressive symptoms and nonadherence to medications in individuals with diabetes in our primary analyses is more difficult to reconcile with the literature [START_REF] Gonzalez | Depression, self-care, and medication adherence in type 2 diabetes: relationships across the full range of symptom severity[END_REF][START_REF] Dirmaier | Diabetes in primary care: prospective associations between depression, nonadherence and glycemic control[END_REF][START_REF] Raum | Medication non-adherence and poor glycaemic control in patients with type 2 diabetes mellitus[END_REF][START_REF] Gonzalez | Symptoms of depression prospectively predict poorer self-care in patients with Type 2 diabetes[END_REF][START_REF] Katz | Correlates of Medication Adherence in the TODAY Cohort of Youth With Type 2 Diabetes[END_REF][START_REF] Lin | Relationship of depression and diabetes self-care, medication adherence, and preventive care[END_REF][START_REF] Katon | Diabetes and poor disease control: is comorbid depression associated with poor medication adherence or lack of treatment intensification?[END_REF] . Only two studies [START_REF] Gentil | Impact of depression and anxiety disorders on adherence to oral hypoglycemics in older adults with diabetes mellitus in Canada[END_REF][START_REF] Kilbourne | How does depression influence diabetes medication adherence in older patients?[END_REF] showed no association between these two variables and mainly when medication adherence was assessed using electronic caps [START_REF] Kilbourne | How does depression influence diabetes medication adherence in older patients?[END_REF] . However, most studies linking depression with non-adherence to anti-diabetic medication were either retrospective studies [START_REF] Gonzalez | Depression, self-care, and medication adherence in type 2 diabetes: relationships across the full range of symptom severity[END_REF][START_REF] Dirmaier | Diabetes in primary care: prospective associations between depression, nonadherence and glycemic control[END_REF][START_REF] Raum | Medication non-adherence and poor glycaemic control in patients with type 2 diabetes mellitus[END_REF] or prospective with only one timepoint at follow-up. Indeed, depressive symptoms were associated with an almost two-time higher odd of being non-adherent to anti-diabetic medications in the first 18 months, whereas the OR was close to one for antihypertensive or lipid lowering medications. However, compared to hypertension and dyslipidaemia, our study might have lacked statistical power for diabetes because of the lower than expected proportion of those being non-adherent to anti-diabetic medications (i.e. 7% instead of 25%). This proportion would have required a 50% larger sample to achieve a statistical power of 80% [START_REF] Demidenko | Sample size determination for logistic regression revisited[END_REF] . Compared to hypertension and dyslipidaemia, the treatment for controlling diabetes is by far more demanding for patients, as they have not only to implement both pharmacological and non-pharmacological treatments, but also to monitor the condition several times a day, as well as being aware of possible acute complications of both the disease (e.g. ketoacidosis) and treatment (e.g. hypoglycaemia) and to be prepared to manage them in first line; hence depressive symptoms have more room to eventually interfere with medication adherence. Finally, the effect of a potential association between depressive symptoms at inclusion and non-adherence to anti-diabetic medication may have reduced after 18 months of follow-up because depressive symptoms are a potentially transient state rather than a permanent trait. In support to this hypothesis, exploratory analyses showed that depressive symptoms were associated with nonadherence to anti-diabetic medications between the first 3-6 months of follow-up only. Hence, further studies may consider depressive symptoms as time-dependent variables to examine this hypothesis. Specifically, repeated measures of depressive symptoms would allow testing the hypothesis of a detrimental effect of depressive symptoms on adherence to anti-diabetic medications -or other demanding treatment -in the short run only with a within-individual approach. In addition, studies that would rely on data gathered in the general population rather in volunteers only are needed to provide more definitive conclusions regarding the lack of association between depressive symptoms and adherence to medications for hypertension or dyslipidaemia.

In conclusion, in a population-based cohort, depressive symptoms were not associated with nonadherence to medications for hypertension, diabetes and dyslipidaemia in primary analyses. Although we may have lacked power for anti-diabetic medications, our results suggest that non-adherence to medications targeting treatable cardiovascular risk factors is unlikely to explain much of the association between depressive symptoms and CVD incidence. Although this association has been established for years, ruling out the hypothesis of a mediation by medication non-adherence is critical for depressive symptoms to be considered as CVD risk factor on its own 2 . Our finding suggests that other pathways (i.e. pathophysiological pathways) should be further explored to understand this association and identify relevant targets for preventive strategies. For example, depressive symptoms could lead to autonomic dysregulation triggering increased risk of CVD as the cortisol levels are high in depressed individuals and they are associated with CVD outcomes [START_REF] Tawakol | Relation between resting amygdalar activity and cardiovascular events: a longitudinal and cohort study[END_REF] . However, exploratory results suggest that depressive symptoms may be associated with anti-diabetic medications non-adherence in the short run. Although this finding warrant replication, it suggests that searching and treating depression may be especially important in individuals with diabetes as it may contribute to foster medications adherence. Future studies based on repeated measures of depressive symptoms and adherence in larger samples may further test this hypothesis.

  , which served to identify the use and adherence to pharmacological treatments targeting several diseases including cardiovascular risk factors such as hypertension, diabetes and dyslipidaemia from January 1, 2009 to December 31, 2017. The CONSTANCES cohort received authorization from regulatory bodies supervising medical research in France which are the 'Commission de l'Informatique et des Libertés -CNIL' (authorization no. 910486), the Institutional Review Board of the National Institute for Medical Research-INSERM, the 'Conseil National de l'Ordre des Médecins -CNOM' and 'Conseil National de l'Information Statistique -CNIS' 15 .

  no), BMI (<25, ≥25 and <30, ≥30) and personal history of CVD (yes, no).

25 Supplemental Table 3 .*

 253 Association between depressive symptoms and non-adherence to medications in volunteers with hypertension, diabetes and dyslipidaemia in the CONSTANCES cohort study between the first 3-6 months, according to different thresholds of CES-D score, 2012-2018 (odds ratios, ORs and 95% confidence intervals, CI). Adjusted for age, sex, living with a partner (yes, no), country of birth (France, other), educational level (≤ high school diploma, undergraduate degree, postgraduate degree), employment status (yes, no), BMI (<25, ≥25 and <30, ≥30) and personal history of CVD (yes, no).

Table 1 .

 1 Volunteers' characteristics at the inclusion in the CONSTANCES cohort study *Depressive symptoms were defined as having a CES-D score ≥19.

		Hypertension	Diabetes	Dyslipidaemia
		N=4,998	N=793	N=3,692
	Depressive symptoms*, %	17.5	21.8	16.2
	Mean (SD) age, years	60.3 (8.1)	61.0 (7.5)	61.0 (7.5)
	Male sex, %	56.7	69.2	61.4
	Living with a partner, %	70.3	66.0	70.3
	Country of birth (France), %	92.7	86.7	93.6
	Educational level
	≤ High school diploma, %	60.9	67.2	61.1
	Undergraduate degree, %	25.4	19.8	24.5
	Postgraduate degree, %	13.7	13.0	14.4
	Employment status, %	38.1	33.5	34.4
	Prescribed and followed diet, %	7.0	20.8	7.8
	Physical activity
	0 (not active), %	3.3	5.4	3.3
	1, %	7.7	10.0	6.4
	2, %	18.3	22.9	18.4
	3, %	18.4	18.5	18.5
	4, %	23.9	21.1	23.2
	5, %	13.2	10.7	14.5
	6 (very active), %	15.2	11.4	15.7
	BMI
	<25, %	27.6	14.0	30.7
	≥25 and <30, %	41.8	40.5	44.8
	≥30, %	30.6	45.5	24.5
	Personal history of CVD, %	11.1	14.0	16.1
	Medication non-adherence †
	0-18 months, %	11.9	7.1	27.6
	19-36 months, %	14.7	9.2	36.9

Table 2 .

 2 Association between depressive symptoms and non-adherence to medications in volunteers with hypertension, diabetes and dyslipidaemia in the CONSTANCES cohort study, according to the duration of exposure to medications, 2012-2018 (odds ratios, ORs and 95% confidence intervals, CI).

		Hypertension			Diabetes		Dyslipidaemia
		N	OR	P	N	OR	P	N	OR	P
		cases/	(95% CI)		cases/	(95% CI)		cases/	(95% CI)
		N			N			N
		particip			particip			partici
		ants			ants			pants
	18 months	587/4,9						1,010/
		87			54/790			3,681
	Unadjusted		1.16			1.89			1.09
	model		(0.93-1.4			(1.04-3.4	0.0		(0.90-1.3	0.3
			4)	0.18		2)	3		3)	6
	Fully-adjusted		1.08			1.82			1.04
	model*		(0.86-1.3			(0.95-3.4	0.0		(0.85-1.2	0.7
			6)	0.51		8)	7		8)	1
		695/4,9						1,328/
	19-36 months	53			64/782			3,654
			1.19			1.22			0.92
	Unadjusted		(0.97-1.4			(0.68-2.2	0.5		(0.77-1.1	0.4
	model		6)	0.09		0)	1		1)	0
			1.08			1.18			0.86
	Fully-adjusted		(0.87-1.3			(0.64-2.2	0.5		(0.71-1.0	0.1
	model*		4)	0.48		0)	9		5)	4

Table 1 .

 1 Association between depressive symptoms and non-adherence to medications in volunteers with hypertension, diabetes and dyslipidaemia in the CONSTANCES cohort study, according to the duration of exposure to medications, 2012-2018 (odds ratios, ORs and 95% confidence intervals, CI). †Depressive symptoms were defined as having a CES-D score ≥21.

		Hypertension			Diabetes		Dyslipidaemia
		N	OR	P	N	OR	P	N	OR	P
		cases/	(95% CI)		cases/	(95% CI)		cases/	(95% CI)
		N			N			N
		particip			particip			partici
		ants			ants			pants
	18 months	587/4,9						1,010/
		87			54/790			3,681
	Unadjusted		1.25			1.65			1.08
	model		(0.99-1.5	0.05		(0.87-3.1	0.1		(0.87-1.3	0.4
			8)	3		2)	2		3)	8
	Fully-adjusted		1.17			1.59			1.03
	model*		(0.92-0.2			(0.79-3.1	0.1		(0.82-1.2	0.8
			0)	0.20		9)	9		9)	0
		695/4,9						1,328/
	19-36 months	53			64/782			3,654
			1.24			1.28			0.88
	Unadjusted		(0.99-1.5	0.05		(0.69-2.3	0.4		(0.72-1.0	0.2
	model		3)	4		8)	3		8)	1
			1.11			0.93			0.82
	Fully-adjusted		(0.89-1.3			(0.47-1.8	0.8		(0.66-1.0	0.0
	model*		9)	0.36		2)	3		1)	6

* Adjusted for age, sex, living with a partner (yes, no), country of birth (France, other), educational level (≤ high school diploma, undergraduate degree, postgraduate degree), employment status (yes, no), BMI (<25, ≥25 and <30, ≥30) and personal history of CVD (yes, no).

Table 2 .

 2 Association between depressive symptoms and non-adherence to medications in volunteers with hypertension, diabetes and dyslipidaemia in the CONSTANCES cohort study, according to the duration of exposure to medications, 2012-2018 (odds ratios, ORs and 95% confidence intervals, CI). † Depressive symptoms were defined as having a CES-D score ≥22.

* Adjusted for age, sex, living with a partner (yes, no), country of birth (France, other), educational level (≤ high school diploma, undergraduate degree, postgraduate degree), employment status (yes,

ACKNOWLEDGMENTS

The authors thank CNAM and its health screening centres for collecting most of the data. They also thank the National Old-Age Insurance Fund for its contribution to the cohort establishment, and ClinSearch, Asqualab and Eurocell for data quality control.

FUNDING SOURCES

Nadine Hamieh was supported by a grant from Association Philippe Jabre. Cédric Lemogne was supported by a grant from IReSP (LEMOGNE AAP16_PREV-13). The National Health Insurance Fund (Caisse nationale d'assurance maladie des travailleurs salaries, CNAM), MSD, Lundbeck, AstraZeneca, and ANR (ANR-11-INBS-0002) supported the CONSTANCES cohort. None of these funding sources had any role in the design of the study, collection and analysis of data or decision to publish.

DECLARATION OF INTEREST

Frédéric Limosin declares personal fees and non-financial support from Lundbeck, and non-financial support from Janssen-Cilag and Otsuka Pharmaceutical, outside the submitted work. Cédric Lemogne declares personal fees from Boehringer Ingelheim, Janssen-Cilag, Lundbeck and Otsuka Pharmaceutical, outside the submitted work. The remaining authors declare no conflicts of interest. * Adjusted for age, sex, living with a partner (yes, no), country of birth (France, other), educational level (≤ high school diploma, undergraduate degree, postgraduate degree), employment status (yes, no), BMI (<25, ≥25 and <30, ≥30) and personal history of CVD (yes, no).