Vadim M Kovrugin

Diana O Nekrasova

Oleg I Siidra

Olivier Mentre

Christian Masquelier

Sergey Yu Stefanovich

Marie Colmont

Mineral-Inspired Crystal Growth and Physical Properties of Na 2 Cu(SO 4 ) 2 and Review of Na 2 M (SO 4 ) 2 (H 2 O) x ( x = 0-6) Compounds

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

■ INTRODUCTION

Mineralogy has always provided an inspiration for finding new materials with useful properties. [START_REF] Krivovichev | Minerals as Advanced Materials II[END_REF][2][3] Nowadays, the experimental mineralogy of sulfates is experiencing a renaissance due to their geochemical abundance in nature on Earth and recent discoveries of significant amount of sulfates on the surface of Mars. 4,[START_REF] Karunatillake | The Association of Hydrogen with Sulfur on Mars across Latitudes, Longitudes, and Compositional Extremes[END_REF] Synthetic sulfate compounds are also of special interest from the viewpoint of exhibiting promising physical properties. For example, novel polyanionic materials with high voltage potential of electrodes can be fabricated by substituting a phosphate anion by a sulfate anion, [START_REF] Barpanda | Sulfate Chemistry for High-Voltage Insertion Materials: Synthetic, Structural and Electrochemical Insights[END_REF][START_REF] Rousse | Sulfate-Based Polyanionic Compounds for Li-Ion Batteries: Synthesis, Crystal Chemistry, and Electrochemistry Aspects[END_REF][START_REF] Lu | Polyanionic Solid-Solution Cathodes for Rechargeable Batteries[END_REF][START_REF] Shiva | NaFe 2 PO 4 (SO 4 ) 2 : A Potential Cathode for a Na-Ion Battery[END_REF][START_REF] Masquelier | Phosphates, Silicates, Sulfates) Frameworks as Electrode Materials for Rechargeable Li (or Na) Batteries[END_REF][START_REF] Lander | Sulfate-Based Cathode Materials for Li-and Na-Ion Batteries[END_REF] thus taking advantage of the higher electronegativity of SO 4 groups. [START_REF] Padhi | Mapping of Transition Metal Redox Energies in Phosphates with NASICON Structure by Lithium Intercalation[END_REF] Indeed, the mineral-inspired eldfellite-type NaFe(SO 4 ) 2 phase has been recently considered as a low-cost cathode in a rechargeable Na ion battery, demonstrating about 80 mAh/g of reversible capacity with a discharge voltage of 3.0 V vs Na + /Na for a relatively long life. [START_REF] Singh | NaFe(SO 4 ) 2 : An Intercalation Cathode Host for Low-Cost Na-Ion Batteries[END_REF][START_REF] Yu | Ionic Diffusion and Electronic Transport in Eldfellite Na x Fe-(SO 4 ) 2[END_REF][START_REF] Ri | First-Principles Study of Mixed Eldfellite Compounds Na x (Fe 1/2 M 1/2 )(SO 4 ) 2 (x = 0-2, M = Mn, Co, Ni): A New Family of High Electrode Potential Cathodes for the Sodium-Ion Battery[END_REF][START_REF] Banerjee | Unveiling the Thermodynamic and Kinetic Properties of Na x Fe(SO 4 ) 2 (x = 0-2): Toward a High-Capacity and Low-Cost Cathode Material[END_REF] However, we should note that most anhydrous sulfates are unstable under ambient conditions and are easily hydrated. This fact as well as complicated synthesis methods make them difficult for investigation. In contrast, the hydrated sulfates have been shown to be earth-abundant mineral species and can be relatively easily prepared in a laboratory. Though several works devoted to the investigation of electrochemical behavior of the kroḧnkite type, Na 2 Fe-(SO 4 ) 2 (H 2 O) 2 , [START_REF] Barpanda | Kroḧnkite-Type Na 2 Fe(SO 4 ) 2 •2H 2 O as a Novel 3.25 V Insertion Compound for Na-Ion Batteries[END_REF][START_REF] Meng | Superior Sodium-lithium Intercalation and Depressed Moisture Sensitivity of a Hierarchical Sandwich-Type Nanostructure for a Graphene-sulfate Composite: A Case Study on Na 2 Fe(SO 4 ) 2 •2H 2[END_REF][START_REF] Meng | Architectureproperty Relationships of Zero-, One-and Two-Dimensional Carbon Matrix Incorporated Na 2 Fe(SO 4 )[END_REF][START_REF] Watcharatharapong | Mechanistic Study of Na-Ion Diffusion and Small Polaron Formation in Kroḧnkite Na 2 Fe(SO 4 ) 2 •2H 2 O Based Cathode Materials[END_REF] and blodite type, Na 2 M(SO 4 ) 2 (H 2 O) 4 (M = Mg, Fe, Co, Ni, Zn), [START_REF] Reynaud | Design of New Electrode Materials for Li-Ion and Na-Ion Batteries from the Bloedite Mineral Na 2 Mg(SO 4 )[END_REF] compositions have been reported so far, the electrochemical performance (reversible discharge capacities less than ∼80 mAh/g) is worse than that of anhydrous sulfates. Taking into account structural linkages between hydrated and anhydrous sulfates, [START_REF] Marinova | Mixed Sodium Nickel-Manganese Sulfates: Crystal Structure Relationships between Hydrates and Anhydrous Salts[END_REF] the hydrates can be used as precursors for syntheses of anhydrous compositions. [START_REF] Saha | Manipulation of the Hydration Levels in Minerals of Sodium Cadmium Bisulfate toward the Design of Functional Materials[END_REF][START_REF] Marinova | From Kroḧnkite-to Alluaudite-Type of Structure: Novel Method of Synthesis of Sodium Manganese Sulfates with Electrochemical Properties in Alkali-Metal Ion Batteries[END_REF] Herein, we further explore this avenue and turn our mind to investigation of crystal growth and crystal chemistry of anhydrous and hydrated mineral-inspired transition-metal sulfates. Recent studies have demonstrated that the design of synthetic analogues of mineral-inspired phases may offer new, uncommon information and deep insight into aspects of crystal structure and crystal growth. [START_REF] Gavryushkin | Hydrothermal Synthesis and Structure Solution of Na 2 Ca(CO 3 ) 2 : "Synthetic Analogue" of Mineral Nyerereite[END_REF][START_REF] Kovrugin | Emulating Exhalative Chemistry: Synthesis and Structural Characterization of Ilinskite, Na[Cu 5 O 2 ](SeO 3 ) 2 Cl 3 , and Its K-Analogue[END_REF][START_REF] Skofteland | Potassium Merlinoite: Crystallization, Structural and Thermal Properties[END_REF] On the basis of all these considerations, we report on the synthesis of the synthetic analogue of the recently reported exhalative mineral saranchinaite, [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF] Na 2 Cu(SO 4 ) 2 , discuss its structural, optical, thermal, electrochemical, and magnetic properties for the first time, and review various structure types in a series of Na 2 M(SO 4 ) 2 (M = Mn, Co, Ni, Cu, Zn, Cd) compositions.

■ EXPERIMENTAL SECTION

Single-Crystal Growth. By analogy with a formation of saranchinaite as a result of high-temperature exhalative processes occurring in the fumarole fields of Tolbachik volcano, [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF] single crystals of Na 2 Cu(SO 4 ) 2 were grown by slow cooling of a melt containing equimolar quantities of anhydrous CuSO 4 (Prolabo, 98%) and Na 2 SO 4 (Alfa Aesar, 99%). As reported in our previous works, this method has appeared to resemble crystal growth processes from volcanic gases. [START_REF] Kovrugin | Emulating Exhalative Chemistry: Synthesis and Structural Characterization of Ilinskite, Na[Cu 5 O 2 ](SeO 3 ) 2 Cl 3 , and Its K-Analogue[END_REF][START_REF] Kovrugin | Oxocentered Cu(ii) Lead Selenite Honeycomb Lattices Hosting Cu(i)Cl 2 Groups Obtained by Chemical Vapor Transport Reactions[END_REF][START_REF] Kovrugin | Pathways for Synthesis of New Selenium-Containing Oxo-Compounds: Chemical Vapor Transport Reactions, Hydrothermal Techniques and Evaporation Method[END_REF] Precursors were predried at 100 °C for 2 h and further rapidly mixed and ground in an agate mortar in air for 5 min. The reaction mixture of precursors was loaded into a quartz ampule (ca. 15 × 0.9 cm), which was evacuated (10 -2 mbar) and further sealed. The ampule was placed horizontally in a tubular furnace and heated to 950 °C at a rate of 230 °C/h and further held at this temperature for 72 h to produce a blue homogeneous melt. Then it was slowly cooled at a rate of 12.5 °C/h to 650 °C and further held for 24 h more. Finally, the furnace was slowly cooled to room temperature at a rate of 13.0 °C/h. The resulting solid products in the evacuated ampule are shown in Figure 1a.

The as-prepared Na 2 Cu(SO 4 ) 2 is sensitive to air moisture and starts to transform to the hydrated kroḧnkite-type Na 2 Cu-(SO 4 ) 2 (H 2 O) 2 composition after 12 h of exposure to air, which is accompanied by a color change to a pale blue material. Single crystals of Na 2 Cu(SO 4 ) 2 in a crystalline matrix of Na 2 Cu(SO 4 ) 2 (H 2 O) 2 are shown in Figure 1b. Note that the observed hydration process is reversible, and the solids may be easily dehydrated by heating of the crystalline sample to 300 °C for 2 h.

Polycrystalline Sample Preparation. Powder samples of Na 2 Cu(SO 4 ) 2 were prepared by a coprecipitation-type synthesis process. CuSO 4 •5H 2 O (Sigma-Aldrich, ≥99.0%) and Na 2 SO 4 (Alfa Aesar, 99%) were used as starting materials, while distilled water was used as solvent. The starting precursors taken in a 1.2:1.0 (=CuSO 4 • 5H 2 O:Na 2 SO 4 ) ratio were completely dissolved in water with vigorous magnetic stirring at room temperature in two steps. The speed of rotation was maintained at 300 rpm during the reaction. First, sodium sulfate was dissolved in water for 15 min. Then copper sulfate pentahydrate was added, and it was dissolved for the same time period until the solution became a homogeneous bright blue color (Figure 1c). Afterward, the solution of the reactants was heated to 110 °C for 5 h until evaporation. The resulting powder with a light blue color contains both saranchiniate-type Na 2 Cu(SO 4 ) 2 and kroḧnkitetype Na 2 Cu(SO 4 ) 2 (H 2 O) 2 phases, as identified by powder X-ray diffraction analysis. Finally, the obtained mixture was heated to 300 °C for 2 h to produce a polycrystalline sample of anhydrous Na 2 Cu(SO 4 ) 2 (Figure 1d). A high-purity (99%) sample was confirmed by X-ray powder diffraction analysis. Note, however, that there were several small peaks of an unidentified impurity, as illustrated in Figure 2 (inset).

The equimolar amounts of starting precursors resulted in a preparation of Na 2 Cu(SO 4 ) 2 with a small amount of Na 2 SO 4 as an admixture. The probable hydration of starting precursors may serve as an explanation for the observed impurity of sodium sulfate.

The as-prepared powder sample of Na 2 Cu(SO 4 ) 2 is less sensitive to air moisture in comparison to the crystals grown in an evacuated ampule. Hence, the powder is stable in air for about 2 days. To prevent further hydration, the sample should be kept in an oven at 100 °C or in a glovebox.

Single-Crystal X-ray Diffraction. Single crystals of Na 2 Cu(SO 4 ) 2 selected for X-ray diffraction (XRD) data collection were mounted on thin glass fibers and tested on a Bruker APEX II DUO X-ray diffractometer with a Mo IμS microfocus X-ray tube (λ = 0.71073 Å) operated at 50 kV and 0.6 mA. More than a hemisphere of threedimensional XRD data was collected with a frame width of 0.5°in ω and a 35 s count time for each frame. Then the collected data were integrated and corrected for absorption using a multiscan type model using Bruker software. Initial atomic coordinates for the crystal structure of synthetic Na 2 Cu(SO 4 ) 2 were taken from the structure of the previously reported mineral phase. [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF] The crystal structure was further refined in the noncentrosymmetric P2 1 space group to R 1 = 0.020 (wR 2 = 0.044) for 6263 reflections with |F o | ≥ 4σF by using the SHELXL program implemented in the WinGX program package. [START_REF] Sheldrick | Crystal Structure Refinement with SHELXL[END_REF] The main crystallographic information for the synthetic and mineral phases is summarized in Table 1. Selected interatomic distances and results of bond valence calculations for Cu 2+ are given in Table 2. Fractional atomic coordinates, atomic displacement parameters, and a comparison of Na-O bonds in the structures of synthetic and mineral phases are given in Tables S1-S3 in the Supporting Information. CCDC-1866049 (CSD, Cambridge) contains the supplementary crystallographic information for synthetic Na 2 Cu(SO 4 ) 2 .

Powder X-ray Diffraction. Routine powder XRD analyses of the samples were performed at room temperature using a D8 Advance Bruker diffractometer (Cu Kα radiation, λ = 1.5405 Å), with a step width of 0.02°. A high-quality XRD pattern used for profile matching analysis was recorded in the 2θ range of 5-100°with a step size of 0.01°using a Rigaku Smartlab diffractometer equipped with a 9 kW rotating anode. The profile matching analysis was carried out in the JANA2006 crystallographic system. [START_REF] Petrícěk | Crystallographic Computing System JANA2006: General Features[END_REF] The background was fitted using a Chebyshev polynomial function, and the peak shapes were described by a pseudo-Voigt function. The refined unit-cell parameters in the space group P2 Infrared Spectroscopy (FTIR). The infrared (IR) spectrum (Figure 3a) of polycrystalline Na 2 Cu(SO 4 ) 2 was measured using a PerkinElmer Spectrum Two FTIR spectrometer equipped with a diamond attenuated total reflectance (ATR) accessory with a resolution of 4 cm -1 and 16 scans. Absorption bands in the IR spectrum of Na 2 Cu(SO 4 ) 2 and their assignments are as follows (cm -1 ): 1248-955 (ν 4 S-O stretching vibrations), 684-605 (ν 1 and ν 3 S-O bending vibrations), 520 (ν Cu-O stretching vibrations). The splitting of all bands in the range 900-1250 cm -1 is due to the presence of eight symmetrically independent (SO 4 ) 2-anions with a distorted-tetrahedral geometry. The band assignments were done according to refs 33-39. Note that after several hours of exposure to open air, Na 2 Cu(SO 4 ) 2 starts to hydrate with the appearance of an intense band at 860 cm -1 (Cu•••O-H bending vibrations).

Thermal Analysis (DTA). Differential thermal analysis was done on a TGA 92 SETARAM instrument in an air atmosphere with a heating rate of 5 °C min -1 from room temperature up to 630 °C and the reverse (Figure 3b). Thermal evolution of synthetic Na 2 Cu(SO 4 ) 2 occurs in three steps upon heating. The observed thermal phenomena are consistent with the temperature values of the phase transformations for the natural phase (mineral) determined recently by our high-temperature powder XRD (HTPXRD) study. [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF] Thus, the powder XRD patterns collected for the mineral (Na,K) 2 Cu(SO 4 ) 2 phase (Figure S1) were used for further comparative thermal analysis. The first small endothermic peak centered at 410 °C is related to the formation of an unidentified phase, which disappears at around 500 °C. The second endothermic peak observed at 506 °C indicates the total disappearance of synthetic Na 2 Cu(SO 4 ) 2 with a formation of Na 2 Cu 3 O(SO 4 ) 3 composition (synthetic analogue of puninite [START_REF] Siidra | Copper Oxosulphates from Fumaroles of Tolbachik Volcano: Puninite, Na 2 Cu 3 O(SO 4 ) 3a New Mineral Species and Structure Refinements of Kamchatkite and Alumoklyuchevskite[END_REF] ), which remains stable until ∼530 °C. The third endothermic intense peak centered at 535 °C can be associated with the final decomposition of polyanionic Na 2 Cu 3 O(SO 4 ) 3 into Na 2 SO 4 , CuO, and unidentified phase(s). Exothermic peaks at 523 and 401 °C found on the reverse DTA curve are related to recrystallization processes. Optical Properties. The green color of Na 2 Cu(SO 4 ) 2 corresponds well to the optical reflection spectrum with an intense maximum in the region of 500-550 nm (Figure 4). The optical band gap E g can be estimated as ca. 580 nm. The most powerful peak in the spectrum is precisely the second harmonic radiation at λ 2ω = 0.532 μm, which may be excited in a noncentrosymmetric substance under neodymium laser radiation with λ ω = 1.064 μm. Such an adverse match complicates to some degree a neodymium laser application for determination of the nonlinear optical activity of Na 2 Cu(SO 4 ) 2 in the usual transmitted light scheme. [START_REF] Kurtz | A Powder Technique for the Evaluation of Nonlinear Optical Materials[END_REF] An intense impulse YAG:Nd laser was used as a source of radiation at wavelength λ ω = 1.064 μm, while second harmonics (SHs) were registered in the reflection mode. The green light of SH generated in the powder sample (λ 2ω = 0.532 μm) was selected in the backward scan using colored glass filters. Then the SH signal was registered with a photomultiplier and its intensity I 2ω measured by a lock-in integrator. The measured signal from the sample under investigation was calibrated in relation to a quartz standard. The Na 2 Cu(SO 4 ) 2 powder had nearly the same dispersion as an α-quartz powder used as a reference. The value Q = I 2ω /I 2ω (SiO 2 ) = 0.2 was found to present the SHG activity of Na 2 Cu(SO 4 ) 2 on both heating and cooling between room temperature and 400 °C. In order to correct this value for the SH emission in the colored substance, it is necessary to multiply it by a factor of 10 corresponding to the 1/10 share of light at λ 2ω = 0.532 μm penetrating through Na 2 Cu(SO 4 ) 2 particles. Because nonlinear coefficients of two materials are related to the square roots of Q, we estimate the averaged nonlinear coefficient for Na 2 Cu(SO 4 ) 2 to be ⟨d⟩ = 1. Magnetic Measurements. The magnetic characterization of synthetic Na 2 Cu(SO 4 ) 2 was performed on a polycrystalline sample using a MPMS SQUID-VSM (Quantum Design) magnetometer in temperature and field ranges of 1.8-400 K and 0-7 T, respectively. The temperature dependence of the magnetization was determined under various magnetic fields after cooling the sample in a field (FC, field cooling) or in a zero field (ZFC, zero-field cooling).

■ RESULTS AND DISCUSSION Structure Analysis. Na 2 Cu(SO 4 ) 2 crystallizes in the noncentrosymmetric monoclinic space group P2 1 . The structural data for the synthetic phase are in good agreement with the data reported for natural saranchinaite containing in addition a small amount of potassium. [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF] Nevertheless, one interesting point is worth a special discussion.

The unusual structural feature of its crystal structure is an atypical coordination environment of O around Cu 2+ sites. In the structure, there are four crystallographically independent Cu positions. Each Cu site forms four short Cu-O eq bonds in its equatorial plane that define regular CuO 4 squares (average ⟨Cu-O eq ⟩ = 1.978, 1.952, 1.945, and 1.970 Å for Cu1, Cu2, Cu3, and Cu4, respectively). Each square is complemented by one longer apical Cu-O ap bond, thus forming rather regular CuO 5 tetragonal pyramids (⟨Cu-O ap ⟩ = 2.287, 2.264, 2.352, and 2.260 Å for Cu1, Cu2, Cu3, and Cu4, respectively) typical for copper oxide compounds.

All Cu 2+ cations also have additional weaker and longer (2.8-3.1 Å) contacts with two O add atoms each. Bond valence calculations for Cu-O add bonds dictate that they should be taken into consideration and included in the coordination sphere of Cu 2+ cations. A Cu-O distance of ∼3.03 Å provides 0.03 vu and contributes about 1.5% to the overall bond valence sum (BVS). Therefore, Cu-O distances with bond valence ≥0.03 vu were considered (see Table 2). Accordingly, the coordination spheres of the Cu1 and Cu4 sites can be described as distorted octahedra with one additional sixth O ligand each (Cu-O sixth = 2.839 Å (0.04 vu) and 2.942 Å (0.03 vu) for Cu1 and Cu4, respectively), which is common for minerals and synthetic compounds. [START_REF] Burns | Coordination-Geometry Structural Pathways in Cu 2+ Oxysalt Minerals[END_REF] The most remarkable observation concerns the coordination of the Cu2 and Cu3 sites adopting scarce heptahedral CuO 7 coordination (Figure 5) with two additional oxygen atoms O located at distances of 2.882 Å (0.04 vu), 2.954 Å (0.03 vu) and 2.938 Å (0.03 vu), 3.012 Å (0.03 vu) from Cu2 and Cu3 centers, respectively. Each pair of these additional O anions is located geometrically strictly below two O corners of one the diagonals of square bases of the CuO 5 pyramids with O eq •••O add distances of 2.39-2.42 Å for the Cu1-Cu4 sites. The O add -Cu-O add angles are in the range between 64 and 74°. This unusual relatively regular 7-fold coordination of Cu 2+ is very rare for inorganic compounds under ambient conditions. [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF][START_REF] Yoshiasa | Crystal Structure of the High Pressure Phase(II) in CuGeO 3[END_REF][START_REF] Nadeem | Three Isolated Structural Motifs in One Crystal: Penetration of Two 1D Chains through Large Cavities within 2D Polymeric Sheets[END_REF] The coordination of Cu 2+ sites in the crystal structure of Na 2 Cu(SO 4 ) 2 is shown in Figure S2.

The atomic environment of eight Na + cations in the structure of synthetic Na 2 Cu(SO 4 ) 2 does not change significantly from those reported for saranchinaite (Table S3). Note that the only differences in the coordination of the Na5 site in both structures (Figure 6) are caused by the partial substitution of Na + by K + in the structure of the mineral phase. The terminal oxygen atoms of every copper polyhedron are bridged by sulfate SO 4 anions to form a complex 3D framework with a large system of pores and cavities filled by Na + cations (Figure 8c). Crystal Growth of Anhydrous Na-Containing Sulfates. The synthesis of anhydrous sulfates is quite a challenging task. In most cases, the sulfates demonstrate a relatively low thermal stability accompanied by decomposition of sulfate groups to SO 3 and SO 2 + O 2 . [START_REF] Schmidt | In Chemical Vapor Transport Reactions-Methods, Materials, Modeling[END_REF] As a consequence, an inert atmosphere or lower than atmospheric pressure (vacuum) is used to maintain the stability of sulfate anions during the chemical reaction. For example, alluaudite-type Na 2.32 Co 1.84 (SO 4 ) 3 [START_REF] Dwibedi | Na 2.32 Co 1.84 (SO 4 ) 3 as a New Member of the Alluaudite Family of High-Voltage Sodium Battery Cathodes[END_REF] and Na 2.5 Fe 1.75 (SO 4 ) 3 [START_REF] Gonĩ | Na 2.5 Fe 1.75 (SO 4 ) 3 /Ketjen/RGO: An Advanced Cathode Composite for Sodium Ion Batteries[END_REF] compounds were synthesized in Ar/N 2 -regulated furnaces by low-temperature solid-state reactions at 350 °C. Crystal growth from a melt in the temperature range of 460-500 °C in an artificial inert-flow reactor was used for the preparation of V-containing sodium sulfates NaV(SO 4 ) 2 , 49 Na 3 V(SO 4 ) 3 , 50 Na 8 (VO) 2 (SO 4 ) 6 , [START_REF] Nielsen | Crystal Structure and Spectroscopic Characterization of a Green V(IV) Compound, Na 8 (VO) 2 (SO 4 ) 6[END_REF] and Na 2 VO(SO 4 ) 2 . [START_REF] Fehrmann | Crystal Structure and Vibrational Spectra of Na 2 VO(SO 4 ) 2[END_REF] Similar experiments carried out in sealed Ag containers or quartz ampules led to crystallization of Na 5 (CuO 2 )(SO 4 ) 53 and Na 11 (CuO 4 )(SO 4 ) 3 [START_REF] Amann | Synthesis and Characterization of Na 11[END_REF] or of Na 8 (CoO 3 )(SO 4 ) 2 [START_REF] Moller | Ein Natrium-Oxocobaltat(II)-Sulfat: Na 8[END_REF] and Na 4 (MoO 2 )(SO 4 ) 3 , 56 respectively. The experimental details of synthesis methods of the compounds in the Na 2 M(SO 4 ) 2 (M = Mn, Co, Ni, Cu, Zn, Cd) family are summarized in Table 3 for the reader's convenience.

Among the others, it is noteworthy that anhydrous Na 2.74 Mn 1.86 (SO 4 ) 3 , 24 Na 2.76 Mn 1.78 (SO 4 ) 3 , [START_REF] Marinova | From Kroḧnkite-to Alluaudite-Type of Structure: Novel Method of Synthesis of Sodium Manganese Sulfates with Electrochemical Properties in Alkali-Metal Ion Batteries[END_REF] and Na 3 Fe-(SO 4 ) 3 [START_REF] Scordari | Crystal Structure of Na 3 Fe(SO 4 ) 3 : A High-Temperature Product (400 C) of Sideronatrite [Na 2 Fe(SO 4 ) 2 OH•3H 2 O[END_REF] were prepared by a dehydration of mineral-type hydrated phases: from the kroḧnkite-type Na 2 Mn-(SO 4 ) 2 (H 2 O) 2 and sideronatrite-type Na 2 Fe(SO 4 ) 2 (OH)-(H 2 O) 3 compounds, respectively. Moreover, the synthetic Na 2 Cu(SO 4 ) 2 compound reported in this work can be also produced from the kroḧnkite mineral itself by a dehydration process, as described in the Experimental Section. Remarkably, dehydration processes of the hydrated phases with similar chemical formulas may lead to different structural architectures, as will be discussed below. These observations in agreement with similar ideas already reported [START_REF] Saha | Manipulation of the Hydration Levels in Minerals of Sodium Cadmium Bisulfate toward the Design of Functional Materials[END_REF][START_REF] Marinova | From Kroḧnkite-to Alluaudite-Type of Structure: Novel Method of Synthesis of Sodium Manganese Sulfates with Electrochemical Properties in Alkali-Metal Ion Batteries[END_REF] suggest that abundant hydrated sulfate minerals may be considered as lowcost prospective precursors for the design of novel anhydrous compounds with various structure types.

Dehydration of the Na 2 M(SO 4 ) 2 (H 2 O) x Compositions. In the present work we focus on several families of mineral-like A key structural difference between the monoclinic kroḧnkite-type and triclinic fairfieldite-type structures is the different hydrogen-bonding network that links the chains of M(SO 4 ) 4 (H 2 O) 2 composition. [START_REF] Driscoll | Investigation into the Effect on Structure of Oxoanion Doping in Na 2 M(SO 4 ) 2 •2H 2[END_REF] All of the phases belonging to these groups are summarized in Table 4. It is of interest to note that the analysis of the reported phase transitions of these phases upon dehydrating reveals intriguing peculiarities. In most cases, the loss of water molecules led to the formation of Na 2 M(SO 4 ) 2 anhydrous compositions. However, note that the phase transitions for the isostructural kroḧnkite-type (x = 2) compounds resulted in a formation of the anhydrous sulfates of different structure types (Table 4). The observed variations of the structural transformations cannot be explained by ionic (high spin) mismatch between the size of transition metals (Cd > Mn > Fe > Co > Zn > Cu > Ni) [START_REF] Shannon | Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides[END_REF] only but implies a subtle interplay between several factors simultaneously. From a structural point of view, the H 2 O molecules in the structures of these hydrates can be regarded as a "glue" 60 binding the other structural units. Thus, the release of water upon dehydration may lead to a structural transformation in accordance with the different preferred stereochemical coordination of metal cations as well. That is, for example, the Na 2 Cu(SO 4 ) 2 (H 2 O) 2 phase transforms to anhydrous Na 2 Cu(SO 4 ) 2 [START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF] with a well-pronounced Jahn-Teller distortion for Cu 2+ in its structure, whereas the structure of Na 2 Mn(SO 4 ) 2 (H 2 O) 2 transforms to the alluaudite-type Na 2+δ Mn 2-δ/2 (SO 4 ) 3 phase. [START_REF] Marinova | From Kroḧnkite-to Alluaudite-Type of Structure: Novel Method of Synthesis of Sodium Manganese Sulfates with Electrochemical Properties in Alkali-Metal Ion Batteries[END_REF] In the latter case, we suggest that the difference in transition-metal ionic radii (Mn 2+ (0.83 Å) > Cu 2+ (0.73 Å)) is a crucial factor for the structural transformation. Indeed, a similar kroḧnkite → alluaudite transformation has been observed for the dehydration of Na 2 Fe(SO 4 ) 2 (H 2 O) 2 with a relatively large Fe 2+ cationic radius (0.78 Å). [START_REF] Barpanda | Kroḧnkite-Type Na 2 Fe(SO 4 ) 2 •2H 2 O as a Novel 3.25 V Insertion Compound for Na-Ion Batteries[END_REF][START_REF] Marinova | From Kroḧnkite-to Alluaudite-Type of Structure: Novel Method of Synthesis of Sodium Manganese Sulfates with Electrochemical Properties in Alkali-Metal Ion Batteries[END_REF] In contrast, the Co-and Ni-containing Na 2 M(SO 4 ) 2 (H 2 O) 2 compositions with a smaller size of cations (0.75 and 0.69 Å, respectively) transform to another structural type of anhydrous Na 2 M(SO 4 ) 2 exhibiting no pronounced distortion effects for transition-metal cations. [START_REF] Driscoll | Investigation into the Dehydration of Selenate Doped Na 2 M(SO 4 ) 2 •2H 2 O (M = Mn, Fe, Co and Ni): Stabilisation of the High Na Content Alluaudite Phases Na 3 M 1.5 (SO 4 ) 3-1.5x (SeO 4 ) 1.5x (M = Mn, Co and Ni) through Selenate Incorporation[END_REF] In order to get a deeper insight into the dehydration effects on the crystal structures, the coordinations of M 2+ cations in the structures of the compounds under consideration have been analyzed. In most of the structures, transition-metal cations exhibit octahedral environments of different degrees of distortions except for the Na 2 Cu(SO 4 ) 2 phase discussed in the present work. To quantify the degree of distortions of MO 6 polyhedra, the Δ d parameter defined previously for perovskites, [START_REF] Alonso | Evolution of the Jahn-Teller Distortion of MnO 6 Octahedra in RMnO 3 Perovskites (R = Pr[END_REF] mixed MO 6 (M = Cu, Zn) octahedra in Cu, Zn oxysalt minerals [START_REF] Siidra | CuZn(SO 4 ) 2 , a New Mineral with Chalcocyanite Derivative Structure from the Naboko Scoria Cone of the 2012-2013 Fissure Eruption at Tolbachik Volcano, Kamchatka, Russia[END_REF] and recently the mixed MnO n Cl m octahedral coordination environments [START_REF] Kovrugin | Synthesis and Structural Variety of First Mn and Bi Selenites and Selenite Chlorides[END_REF] was used. This parameter concerns the deviation of M-O distances with respect to its average value for each polyhedron and can be calculated as follows: 2 , where ⟨d⟩ is the average M-O distance in a given octahedron (Table 4).

Δ d = (1/6)∑ n=1,6 [(d n -⟨d⟩)/⟨d⟩]
Several observations for the reported phase transformations upon dehydration can be made. The average octahedral M-O distances are increasing upon Na 2 M(SO 4 ) 2 (H 2 O) x → Na 2 M(SO 4 ) 2 dehydration in most of the structures with the greatest distance difference revealed for the Na 2 Mn-(SO 4 ) 2 (H 2 O) 2 → Na 2+δ Mn 2-δ/2 (SO 4 ) 3 transformation: from 2.152 to 2.221 Å. The only exception is the Na 2 Co-(SO 4 ) 2 (H 2 O) 2 → Na 2 Co(SO 4 ) 2 transformation, which results in a shortening of the ⟨Co-O⟩ distance from 2.141 to 2.109 Å. Although these variations of average bond lengths cannot be explained by a simple ionic mismatch, the calculated Δ d parameter of octahedral distortions can provide more useful i n f o r m a t i o n . F o r t h e h y d r a t e d c o m p o s i t i o n s Na 2 M(SO 4 ) 2 (H 2 O) 2 (M = Cd 2+ , Mn 2+ , Fe 2+ ) with octahedra centered by transition metals with larger ionic radii, the octahedral coordination environments are quite regular before (10 4 Δ d = 2, 3, 11, respectively) as well as after (10 4 Δ d = 7, 3, 10, respectively) dehydration. In contrast, the degree of octahedral distortions is increasing after transformations for the phases containing the smaller Co 2+ , Cu 2+ , and Ni 2+ cations: from 10 4 Δ d = 4, 11, 6, respectively, for hydrated Na 2 M(SO 4 ) 2 (H 2 O) 2 (M = Co 2+ , Cu 2+ , Ni 2+ ) compounds up to 10 4 Δ d = 37, 257, 14, respectively, for anhydrous Na 2 M(SO 4 ) 2 (M = Co 2+ , Cu 2+ , Ni 2+ ) phases. Note that this strong deviation of the geometrical shape of copper polyhedra from the ideal octahedron in the structure of Na 2 Cu(SO 4 ) 2 results from a well-pronounced Jahn-Teller distortion and also suggests considering the coordination of Cu 2+ in the structure to be distinct from an octahedron.

Structure Types and Structural Complexity of the Na 2 M(SO 4 ) 2 Compounds. Since the structural relationships between the crystal structures of hydrates and anhydrous salts have been very recently discussed, [START_REF] Marinova | Mixed Sodium Nickel-Manganese Sulfates: Crystal Structure Relationships between Hydrates and Anhydrous Salts[END_REF] it is also of interest to compare different structure types corresponding to various chemical Na 2 M(SO 4 ) 2 (M = Mn, Co, Ni, Cu, Zn, Cd) compositions (Table 3). There are five different structure types. Four of them are presented in Figure 8 (the structure type V has been reported for metastable β-Na 2 Cd(SO 4 ) 2 which was reported without any structural data except for its unit cell parameters [START_REF] Saha | Manipulation of the Hydration Levels in Minerals of Sodium Cadmium Bisulfate toward the Design of Functional Materials[END_REF] ).

Two compounds with the largest metal ionic radii (Cd 2+ = 0.95 Å; Mn 2+ = 0.83 Å) crystallize in the same structure type denoted herein as I (Figure 8a). Here, the transition-metal cations form rather regular octahedra with an average ⟨Cd-O⟩ and ⟨Mn-O⟩ bond lengths of 2.317 and 2.301 Å, respectively.

Despite differences in size (Co (0.75 Å) > Ni (0.69 Å)), the phases containing chemically similar Co 2+ and Ni 2+ metals belong to the same structure type II (Figure 8b) with quite regular octahedra of transition metals (⟨M-O⟩ = 2.094 and 2.077 Å for M = Co 2+ , Ni 2+ , respectively).

We did not find reported structural data for the Fecontaining (Fe 2+ = 0.78 Å) compound in the literature. Note, however, that Reynaud et al. though succeeded in preparing the iron-based polycrystalline sample with impurities, which also suggests the structure type II for Na 2 Fe(SO 4 ) 2 . [START_REF] Reynaud | Design of New Electrode Materials for Li-Ion and Na-Ion Batteries from the Bloedite Mineral Na 2 Mg(SO 4 )[END_REF] Interestingly, in spite of the observed similarities in unit cell dimensions of the crystal structures of Na 2 Cu(SO 4 ) 2 and Na 2 Zn(SO 4 ) 2 containing nearly isometric Cu 2+ (0.73 Å) and Zn 2+ (0.74 Å) cations, respectively, these structures differ significantly from each other (Figure 8c,d). Again, this may be explained by different preferred coordinations of transitionmetal cations. Copper cations have pronounced Jahn-Teller distorted coordination in synthetic Na 2 Cu(SO 4 ) 2 , which is not typical for Zn 2+ usually exhibiting [START_REF] Siidra | CuZn(SO 4 ) 2 , a New Mineral with Chalcocyanite Derivative Structure from the Naboko Scoria Cone of the 2012-2013 Fissure Eruption at Tolbachik Volcano, Kamchatka, Russia[END_REF] a more regular surrounding of ligands in comparison to Cu 2+ . Indeed, the only two Zn sites in the structure of Na 2 Zn(SO 4 ) 2 form relatively regular 5-fold trigonal bipyramids (⟨Zn-O⟩ = 2.043 Å).

It is of interest also to compare polymorphic variations in the Na 2 M(SO 4 ) 2 group from the viewpoint of structural complexity, which can be estimated as a Shannon information content per unit cell (I G,total , bits/unit cell (uc)) according to a recently developed approach. [START_REF] Krivovichev | Structural Complexity of Minerals: Information Storage and Processing in the Mineral World[END_REF][START_REF] Krivovichev | Topological Complexity of Crystal Structures: Quantitative Approach[END_REF][START_REF] Krivovichev | Ladders of Information: What Contributes to the Structural Complexity of Inorganic Crystals[END_REF] The I G,total values calculated by using the ToposPro 68 software are given in Table 3. The obtained results show a correlation among the unit-cell volumes, revealing that the structures with large cells of isotypic Na 2 Co(SO 4 ) 2 and Na 2 Ni(SO 4 ) 2 are the most complex in comparison with the others.

Our results also revealed that the structure of Na 2 Cu(SO 4 ) 2 (I G,total = 592.846 bits/uc) is more complex than that of Na 2 Zn(SO 4 ) 2 (I G,total = 496.846 bits/uc) with close unit cell dimensions and both crystallizing in the monoclinic crystal system. This observation is consistent with the general expectation that the absence of an inversion center and a pronounced Jahn-Teller distortion in the structure of Na 2 Cu(SO 4 ) 2 may lead to an increase in structural complexity. The estimated I G,total values allow classification of the structure types I and II-IV as simple and complex, respectively. Simple and complex structures are 34% and 0.03% of all reported inorganic compounds. [START_REF] Krivovichev | Which Inorganic Structures Are the Most Complex?[END_REF] Electrochemistry. The Cu 2+/ Cu 3+ redox potential has been predicted to provide a high operating voltage in rechargeable battery systems. [START_REF] Sun | 2 Cu 2 O(SO 4 ) 2 : A Possible Electrode for Sustainable Li-Based Batteries Showing a 4.7 V Redox Activity vs Li + /Li 0[END_REF] However, this phenomenon still lacks further studies and an overall understanding. For example, a recent report revealed a very limited electrochemical performance for K 2 Cu 2 (SO 4 ) 3 and K 2 Cu 3 O(SO 4 ) 3 . [START_REF] Lander | Structure, and Electrochemical Properties of K-Based Sulfates K 2 M 2 (SO 4 ) 3 with M = Fe and Cu[END_REF] Nevertheless, it has been also demonstrated that Li 2 Cu 2 O-(SO 4 ) 2 is able to offer a reversible electrochemical activity at 4.7 V vs Li + /Li corresponding to the Cu 2+/3+ redox transition associated with the reversible change of 0.3 Li. [START_REF] Sun | 2 Cu 2 O(SO 4 ) 2 : A Possible Electrode for Sustainable Li-Based Batteries Showing a 4.7 V Redox Activity vs Li + /Li 0[END_REF] Hence, as a further attempt to explore the oxidation of Cu 2+ to Cu 3+ in the course of an electrochemical reaction, several tests were performed using Na 2 Cu(SO 4 ) 2 as a cathode material, providing a theoretical capacity of ∼89 mAh/g (for 1 e -transfer per Cu cation).

The electrochemical behavior of Na 2 Cu(SO 4 ) 2 either vs Na or vs Li was examined using Swagelok-type cells assembled in argon-filled glovebox and cycled at room temperature. Unfortunately, difficulties in Na + extraction have been encountered during the electrochemical cycling in Na-and Li-based types of the cells, and the removal of a significant amount of Na + from the structure of Na 2 Cu(SO 4 ) 2 failed. As seen from Figure S3a, the irreversible extraction is limited to a value of only 0.04 Na + per formula unit at ∼4.0 V vs Li + /Li. The cycling of the Na 2 Cu(SO 4 ) 2 -based cathode vs Na reveals the occurrence of a probable redox process at a higher voltage of around 4.7 vs Na + /Na (Figure S3b), which is beyond the voltage stability window of the electrolytes available up to now. Thus, Na 2 Cu(SO 4 ) 2 is not suitable as a cathode material.

The bond valence energy landscape (BVEL) defined using the BondStr software (FullProf suite [START_REF] Rodríguez-Carvajal | Recent Advances in Magnetic Structure Determination by Neutron Powder Diffraction[END_REF] ) also demonstrates that there are no interconnected pathways for sodium migration in the structure of Na 2 Cu(SO 4 ) 2 (Figure 9) considering a percolation energy of 1.6 eV reported for the movement of Na + in polyanionic compounds. [START_REF] Boivin | Vanadyl-Type Defects in Tavorite-like NaVPO 4 F: From the Average Long Range Structure to Local Environments[END_REF][START_REF] Kovrugin | A High Voltage Cathode Material for Sodium Batteries: Na 3 V(PO 4 ) 2[END_REF] Magnetism. The magnetic properties of Na 2 Cu(SO 4 ) 2 reflect well its crystal structure in the sense that, according to the orientation of the d x 2 -y 2 magnetic orbitals (Cu 2+ , d [START_REF] Shiva | NaFe 2 PO 4 (SO 4 ) 2 : A Potential Cathode for a Na-Ion Battery[END_REF] , S = 1/2) roughly assigned to the CuO 4 square planes, no magnetic overlap is achieved apart from the dimers formed by Cu2 and Cu3. Here, the Cu2-O3-Cu3 angle is 118.3°, which suggests significant superexchange contribution. Accordingly, we considered half of copper atoms as mainly paramagnetic and the other half as strongly engaged in antiferromagnetic dimer interactions. The Curie-Weiss fit shown in Figure 10a gives μ eff = 1.85 μ B /Cu and Θ CW = -17.2 K, which validate predominant antiferromagnetic exchanges. The accident observed below ca. 50 K mainly occurred due to the intradimer interactions, as detailed below. It was fitted using an χ T (T) plot (Figure 10b) through the susceptibility equation

χ ρ β ρ β χ = + + - -Θ + - Ng kT Ng k T (3 e ) (1 ) 4 ( ) J kT Cu 2 2 / 2 2 dia
where the first term represents the intradimer susceptibility of the Cu fraction ρ following the Bleaney-Bowers equation, [START_REF] Bleaney | Anomalous Paramagnetism of Copper Acetate[END_REF] while the second term is the complementary Cu 2+ paramagnetism with interaction quantified by Θ, N, g, β, k, and χ dia having their usual meanings.

The fit was first constrained to ρ = 50% but then greatly improved on relaxing g = 2.237(3), J/k = 138.7(7) K (96.4 cm -1 ), Θ = -0.95(1) K, χ dia = -21 × 10 -6 emu/mol, and ρ = 45.8(2)%. The g value is in good agreement with the effective moment greater than the "spin-only" value (μ eff = 1.74 μ B ), while Θ and J/k confirm a strong AFM dimer in a nearly paramagnetic matrix. The ratio ρ suggests a few percent of extra intrinsic and/or extrinsic paramagnetic impurities, not revealed by XRD.

■ CONCLUSION

The novel anhydrous sulfate Na 2 Cu(SO 4 ) 2 has been synthesized by two different methods for the first time and structurally characterized. A unusual structural feature of the new synthetic Na 2 Cu(SO 4 ) 2 phase is the presence of heptahedral CuO 7 polyhedra with two additional long and weak Cu-O distances, which are interconnected through common O corners in polar chains.

Electrochemical, magnetic, thermal, and optical behaviors of Na 2 Cu(SO 4 ) 2 have been also determined. The title compound demonstrates a very limited electrochemical activity and highly stable Na sublattice (that is, low mobility of Na ions) in its crystal structure. The magnetic behavior of Na 2 Cu(SO 4 ) 2 reflects its crystal structure with half of the copper cations as mainly paramagnetic and the other half as strongly engaged in antiferromagnetic dimer interactions.

Analysis of the synthesis methods reported for the preparation of other Na-containing anhydrous sulfates and our studies of the structural polymorphism in the group of Na 2 M(SO 4 ) 2 (M = Mn, Co, Ni, Cu, Zn, Cd) compositions suggest that abundant hydrated sulfate minerals may be considered as low-cost prospective precursors for the design of novel compounds of various structure types.

We believe that the preparation of synthetic analogues of known minerals is able to serve fundamental science well. [START_REF] Krivovichev | Minerals as Advanced Materials I[END_REF] It can help to solve complex crystal structures (e.g., synthetic nyerereite [START_REF] Gavryushkin | Hydrothermal Synthesis and Structure Solution of Na 2 Ca(CO 3 ) 2 : "Synthetic Analogue" of Mineral Nyerereite[END_REF] ) or to make a model system for an investigation of various physical properties in the laboratory, when it is difficult to obtain samples with a good crystallinity and sufficient amount in nature (e.g., zeolites [START_REF] Cundy | The Hydrothermal Synthesis of Zeolites: Precursors, Intermediates and Reaction Mechanism[END_REF] ). Hence, minerals and mineral-like synthetic compounds can serve as sources of inspiration for elaboration of new materials in many research areas the solid-state chemistry.

■ ASSOCIATED CONTENT

* S Supporting Information

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.8b01658.

Fractional

  1 are a = 8.9655(1) Å, b = 15.5366(1) Å, c = 10.1384(1) Å, β = 107.07(1)°, and V = 1350(1) Å 3 . The final observed, calculated, and difference powder XRD patterns resulting from the profile-matching procedure are plotted in Figure 2.

Figure 1 .

 1 Figure 1. Evacuated ampule with Na 2 Cu(SO 4 ) 2 (a), single crystal of Na 2 Cu(SO 4 ) 2 in kroḧnkite-based matrix (b), homogeneous aqueous precursor for Na 2 Cu(SO 4 ) 2 (c), and pure powder sample of Na 2 Cu(SO 4 ) 2 (d).

Figure 2 .

 2 Figure 2. Results of the profile-matching analysis of Na 2 Cu(SO 4 ) 2 from the powder XRD data. Impurities are shown by black triangles.

Figure 3 .

 3 Figure 3. Infrared (FTIR) spectrum (a) and DTA curves (b) for Na 2 Cu(SO 4 ) 2 .

  4[d 14 (SiO 2 )] ≈ 0.5 pm/V. This is very close to the nonlinearities of earlier investigated sulfates such as LiKSO 4 and Li 2 SO 4 •H 2 O with nonlinear coefficients d 33 = 0.71 pm/V and d 22 = 0.4 pm/V, respectively. 42 Electrochemical Measurements. Electrochemical tests were performed in Swagelok-type cells assembled in an argon-filled glovebox. Electrodes were prepared by ball milling (15 min) in air of a polycrystalline sample of Na 2 Cu(SO 4 ) 2 with carbon C sp as a conductive additive (83.3:16.7 wt %). About 8 mg of the as-prepared composite was studied as a cathode separated from either Na or Li metal as a negative electrode by two sheets of Whatman GF/D borosilicate glass fiber soaked in a liquid electrolyte. Solutions of NaPF 6 or LiPF 6 (1 M) in EC:DMC (1:1 weight ratio) were used as the electrolytes. Fluoroethylene carbonate (FEC; 3% mass) was added to the Na-based electrolyte. Galvanostatic tests were conducted with an Apple Mac Pile II potentiostat.

Figure 4 .

 4 Figure 4. Light reflectivity from Na 2 Cu(SO 4 ) 2 powder measured with a PerkinElmer Lambda 1050 spectrophotometer at room temperature.

Figure 5 .

 5 Figure 5. Heptahedral coordination of Cu 2+ in the structure of Na 2 Cu(SO 4 ) 2 .

  In the crystal structure of Na 2 Cu(SO 4 ) 2 , all copper polyhedra are connected to each other via medium/long Cu--O add ---Cu bridges and polymerized into polar chains running along the c direction as shown in Figure7. Thus, the noncentrosymmetric symmetry of the structure is justified by the "up" only orientation of CuO 5 pyramids along [001]. Note that Cu2 and Cu3 metal centers are located relatively close to each other (Cu2•••Cu3 = 3.36 Å; cf. Cu3•••Cu4 = 4.90 Å) and share a common O corner of their square O bases, forming a dimer. Such a close arrangement of the two neighboring Cu2 and Cu3 polyhedra may be responsible for overall slight shortening of the Cu-O contacts, thus favoring unusual heptahedral Cu2O 7 and Cu3O 7 coordination polyhedra. Indeed, the average Cu-O distances to the seven closest O ligands for Cu2 (2.273 Å) and Cu3 (2.297 Å) are slightly smaller than those for Cu1 (2.300 Å) and Cu4 (2.312 Å).

Figure 6 .

 6 Figure 6. Geometrical environment of the Na5 site in the structure of synthetic Na 2 Cu(SO 4 ) 2 . Projections of the O positions in the structure of saranchinaite are shown in green for comparison. Distances are given in Å.

Figure 7 .

 7 Figure 7. Interconnection of CuO 5 pyramids and comparison of bond lengths and valence values for long Cu-O distances in the structures of synthetic (blue) and mineral (orange) phases. Cu-O contacts <0.03 vu are given in italics. Displacement ellipsoids are drawn at the 80% probability level.

Figure 8 .

 8 Figure 8. Projections of the crystal structures of Na 2 M(SO 4 ) 2 : M = Mn (a), structure type I; Co (b), structure type II; Cu (c), structure type III; Zn (d), structure type IV. Sulfate, manganese, cobalt, copper, and zinc polyhedra are shown in yellow, plum, blue, cyan, and green, respectively; sodium is denoted by purple balls.

Figure 9 .

 9 Figure 9. Two cross sections at 1/2 translation along the a axis demonstrating sodium diffusion pathways shown in pink inside the structure of Na 2 Cu(SO 4 ) 2 defined from BVEL with a percolation energy of 1.6 eV. Displacement ellipsoids are drawn at the 80% probability level.

Figure 10 .

 10 Figure 10. Thermal evolution of the magnetic susceptibility (a) and temperature dependence of χ T (b) for Na 2 Cu(SO 4 ) 2 .

Table

  . Single-Crystal and Structure Refinement Data for Synthetic Na 2 Cu(SO 4 ) 2 and Its "Natural" Analogue Saranchinaite[START_REF] Siidra | Na 2 Cu(SO 4 ) 2 , a New Exhalative Mineral from Tolbachik Volcano, Kamchatka, Russia, and a Product of the Reversible Dehydration of Kroḧnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2[END_REF]

			Na 2 Cu(SO 4 ) 2	(Na,K) 2 Cu(SO 4 ) 2 28
			Crystal Data
	space group		P2 1	P2 1
	a (Å)		8.9711(3)	9.0109(5)
	b (Å)		15.5482(5)	15.5355(8)
	c (Å)		10.1421(3)	10.1507(5)
	β (deg)		107.155(1)	107.079(2)
	V (Å 3 )		1351.73(7)	1367.06(12)
	Z		2	2
	ρ calc (g cm -3 )		2.964	2.970
	μ (mm -1 )		3.987	3.982
		Data Collection
	F(000)		1176	1181
	θ range (deg)		2.1-31.6	2.1-22.7
	hkl limits		-13 → +13	-9 → +9
			-15 → +22	-16 → +16
			-14 → +14	-11 → +11
	total no. of rflns		16018	10024
	no. of unique rflns (R int )		6585 (0.0238)	3642 (0.0394)
	no. of unique rflns, F > 4σF	6263	3236
			Refinement
	R 1 (F > 4σF), wR 2 (F > 4σF)	0.0204, 0.0436	0.0295, 0.0580
	R 1 (all), wR 2 (all)		0.0224, 0.0443	0.0381, 0.0610
	GOF		1.009	0.965
	Δρ atoms	Na 2 Cu(SO 4 ) 2	saranchinaite	atoms	Na 2 Cu(SO 4 ) 2	saranchinaite
	Cu1-O14	1.929(2) [0.51]	1.947(7) [0.49]	Cu3-O1	1.928(2) [0.51]	1.936(7) [0.50]
	Cu1-O19	1.938(2) [0.50]	1.945(7) [0.49]	Cu3-O4	1.938(2) [0.50]	1.946(7) [0.49]
	Cu1-O5	2.020(2) [0.40]	2.027(8) [0.39]	Cu3-O7	1.946(2) [0.49]	1.952(7) [0.48]
	Cu1-O15	2.025(2) [0.39]	2.041(7) [0.38]	Cu3-O3	1.968(2) [0.46]	1.970(7) [0.46]
	Cu1-O23	2.287(2) [0.19]	2.283(8) [0.20]	Cu3-O31	2.352(2) [0.16]	2.352(7) [0.16]
	Cu1-O29	2.839(3) [0.04]	2.777(9) [0.05]	Cu3-O9	2.938(2) [0.03]	2.968(7) [0.03]
	Cu1-O32	3.065(3) [0.02]	3.100(9) [0.02]	Cu3-O24	3.012(3) [0.03]	3.030(7) [0.03]
	av [BVS]	2.173 [2.03]	2.170 [1.98]	av [BVS]	2.297 [2.17]	2.308 [2.14]
	Cu2-O13	1.947(2) [0.48]	1.943(7) [0.49]	Cu4-O30	1.960(2) [0.47]	1.975(7) [0.45]
	Cu2-O26	1.950(2) [0.48]	1.954(7) [0.48]	Cu4-O16	1.962(2) [0.47]	1.971(7) [0.46]
	Cu2-O3	1.951(2) [0.48]	1.959(7) [0.47]	Cu4-O18	1.979(2) [0.45]	1.985(7) [0.44]
	Cu2-O6	1.961(2) [0.47]	1.963(7) [0.47]	Cu4-O12	1.980(2) [0.44]	1.980(7) [0.44]
	Cu2-O2	2.264(2) [0.21]	2.264(7) [0.21]	Cu4-O9	2.260(2) [0.21]	2.261(7) [0.21]
	Cu2-O23	2.882(2) [0.04]	2.921(8) [0.04]	Cu4-O31	2.942(2) [0.03]	2.950(7) [0.03]
	Cu2-O17	2.954(2) [0.03]	2.747(7) [0.04]	Cu4-O10	3.101(2) [0.02]	3.089(7) [0.02]
	av [BVS]	2.273 [2.19]	2.250 [2.18]	av [BVS]	2.181 [2.06]	2.187 [2.03]

max , Δρ min (e Å -3 ) 0.549, -0.437 0.459, -0.465 Table 2. Cu-O Bond Lengths (in Å) and Bond Valence Sums in Brackets (in Valence Units, vu) in the Structures of Synthetic Na 2 Cu(SO 4 ) 2 and Its "Natural" Analogue Saranchinaite 28 a a Interatomic distances with bond valence values <0.03 vu are given in italics.

Table 3 .

 3 Crystallographic Data and Preparation Methods of Anhydrous Na 2 M(SO 4 ) 2 Phases (M 2+ = Transition Metal)

		struct type	a, b, c (Å); β (deg); (V (Å 3 ));
	formula	(I G,total )	space group	preparation method		ref
	Na 2 Mn(SO 4 ) 2	I (72.211)	10.101, 8.240, 8.730; 114.6 (660.5); C2/c	in situ XRD at 227 °C from Na 2 Mn 1.17 (SO 4 ) 2 S 0.33 O 1.17 (H 2 O) 2		78
	Na 2 Co(SO 4 ) 2	II (828.523) 23.346, 10.300, 17.412; 98.9 (4137.0); C2/c	solid-state synthesis via an equimolar reaction of CoSO 4 •7H 2 O and Na 2 SO 4 at 550 °C in Ar	21, 79
	Na 2 Ni(SO 4 ) 2	II (828.523) 23.225, 10.262, 17.335; 99.0 (4080.2); C2/c	in Ar solid-state synthesis via an equimolar reaction of Na 2 SO 4 and NiSO 4 •6H 2 O at 550	°C	22, 79
	Na 2 Cu(SO 4 ) 2	III (592.846)	8.971, 15.548, 10.142; 107.2 (1351.7); P2 1	(a) evaporation from an aqueous solution containing nearly equimolar quantities of Na 2 SO 4 and CuSO 4 •5H 2 O	a
				(b) slow cooling of the melt containing equimolar quantities of CuSO 4 and Na 2 SO 4 in an evacuated ampule from 950 °C
	Na 2 Zn(SO 4 ) 2	IV (496.846)	8.648, 10.323, 15.103; 90.9 (1348.1); P2/n	slow cooling of the melt containing equimolar quantities of ZnO and Na 2 S 2 O 7 in an evacuated ampule from 500 °C	80
	α-Na 2 Cd(SO 4 ) 2 I (72.211)	10.059, 8.225, 8.656; 114.6 (651.0); C2/c	evaporation from an aqueous solution containing equimolar quantities of CdSO 4 and Na 2 SO 4	23, 81, 82
	β-Na 2 Cd(SO 4 ) 2 V (no str. data)	15.114, 9.051, 12.779; 126.5 (1405.7); P2 1 /c	fast quenching of the α-Na 2 Cd(SO 4 ) 2 -based melt from 570 °C		23

a This work.

Table 4 .

 4 Hydrated Na 2 M(SO 4 ) 2 (H 2 O) x (M = Transition Metal; x = 2, 4, 6) Compounds: Reported Results of Phase Transformations upon Heating, Average M-O Bond Lengths, and Distortion Δ d 2+ sites in the given structure. groups of hydrated Na 2 M(SO 4 ) 2 (H 2 O) x transition-metal sulfates: namely, the picromerite (x = 6, M = Co, Ni, Cu) group, the blodite (x = 4, M = Fe, Co, Ni, Zn, Cd) group, the kroḧnkite (x = 2, M = Mn, Fe, Co, Cu, Cd) group, and the only known phase isostructural with fairfieldite (x = 2, M = Ni).

	formula/⟨M-O⟩ (Å); 10 4 Δ d	ref	r ion (M 2+ ) (Å)	formula (struct type)/⟨M-O⟩ (Å); 10 4 Δ d	transition temp (°C)	ref
				Kroḧnkite Type
	Na 2 Mn(SO 4 ) 2 (H 2 O) 2 /2.152; 3	24, 58, 61, 83, 84	0.83	→Na 2+δ Mn 2-δ/2 (SO 4 ) 3 /2.221; 3	200	24
	Na 2 Fe(SO 4 ) 2 (H 2 O) 2 /2.125; 11	17-20	0.78	→Na 2+δ Mn 2-δ/2 (SO 4 ) 3 /2.148; 10 + Na 6 Fe(SO 4 ) 4	300	17, 24
	Na 2 Co(SO 4 ) 2 (H 2 O) 2 /2.141; 4	58, 61	0.75	→Na 2 Co(SO 4 ) 2 (II)/2.109; 37 a	190	61
	Na 2 Cu(SO 4 ) 2 (H 2 O) 2 /2.138; 11	28, 58, 85-87	0.73	→Na 2 Cu(SO 4 ) 2 (III)/2.173; 257 a	200	28
	Na 2 Cd(SO 4 ) 2 (H 2 O) 2 /2.287; 2	23, 83, 84	0.95	→α-Na 2 Cd(SO 4 ) 2 (I)/2.317; 7	550	23
				Fairfieldite Type
	Na 2 Ni(SO 4 ) 2 (H 2 O) 2 /2.037; 6	58, 61	0.69	→Na 2 Ni(SO 4 ) 2 (II)/2.077; 14 a	240	61
				Blodite Type
	Na 2 Fe(SO 4 ) 2 (H 2 O) 4 /2.129; 2	17, 21, 88	0.78	→Na 2 Fe(SO 4 ) 2 (II)/no struct data	120	21
	Na 2 Co(SO 4 ) 2 (H 2 O) 4 /2.101; 2	21, 89, 90	0.75	→Na 2 Co(SO 4 ) 2 (II)/2.109; 37 a	180	21
	Na 2 Ni(SO 4 ) 2 (H 2 O) 4 /2.065; 1	22, 89, 91	0.69	→Na 2 Ni(SO 4 ) 2 (II)/2.077; 14 a	140	22
	Na 2 Zn(SO 4 ) 2 (H 2 O) 4 /2.101; 2	89, 92-94	0.74	→loss of water/no struct data	138	94
	Na 2 Cd(SO 4 ) 2 (H 2 O) 4 /2.276; 2	23	0.95	no information
			Picromerite Type
	Na 2 Co(SO 4 ) 2 (H 2 O) 6 /2.092; 2	95	0.75	→loss of water/no struct data	101	95
	Na 2 Ni(SO 4 ) 2 (H 2 O) 6 /2.056; 1	96	0.69	→loss of water/no struct data	110	96
	Na 2 Cu(SO 4 ) 2 (H 2 O) 6 /2.090; 20	97	0.73	no information

a Average values for several M

  atomic coordinates, atomic displacement parameters, Na-O bond lengths in the structures of new Na 2 Cu(SO 4 ) 2 and saranchinaite, selected HTPXRD patterns revealing phase transformations of saranchinaite with increasing temperature, coordination of Cu 2+ in the structure of synthetic Na 2 Cu(SO 4 ) 2 , and electrochemical curves (PDF)Accession Codes CCDC 1866049 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033. E-mail for V.M.K.: kovrugin_vm@hotmail.com. *E-mail for O.I.S.: o.siidra@spbu.ru.

	■ AUTHOR INFORMATION Corresponding Authors
	ORCID
	Vadim M. Kovrugin: 0000-0002-9010-625X
	Oleg I. Siidra: 0000-0003-1908-3152
	Olivier Mentre: 0000-0002-1822-6003
	Christian Masquelier: 0000-0001-7289-1015
	Notes

*

The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS

This work was financially supported by the Russian Science Foundation through grant 16-17-10085. V.M.K. was supported by the NAIADES project of the Regional Council of Picardie and the University of Picardie Jules Verne. The Ph.D. thesis of D.O.N. was carried out within the framework of the international French-Russian cotutorial Ph.D. program (CampusFrance). The Fonds Europeén de Developpement Reǵional (FEDER), the CNRS, the Reǵion Nord Pas-de-Calais, and the Ministere de l'Education Nationale de l'Enseignement Supeŕieur et de la Recherche are acknowledged for funding the X-ray diffractometers. D.O.N. also acknowledges support of the Saint-Petersburg State University through its internal travel grant 3.42.713.2017 for a visit to the LRCS. The authors also acknowledge Nora Djelal and Jean-Luc Paugam for their technical assistance with the DTA and IR analyses. We also thank an anonymous reviewer for constructive comments and useful suggestions.


Kalani Kariyawasam

Wadih Ghattas

Yossef López

Los Santos

Nicolas Doucet

Sylvain Gaillard

Jean-Luc Renaud

Frédéric Avenier

Prof Jean-Pierre Mahy

Rémy Ricoux

Kalani Kariyawa

Yossef L Ópez D

Jean-Luc Renau

Fr Éd Éric Avenier

Jean-Pierre Ma

R Émy Ricoux

Artificial iron

Keywords: artificial metalloenzymes, catalysis, hydrogenation, Kn ölker's complex identification number, DIBALH, diisobutylaluminium hydride, DTNB, 5, trifluoroacetophenone, TMS, tetramethylsilane, TpCPP, tetra-4-carboxyphenyporphyrin, TpSPP, tetra-4-sulfonatophenlyporphyrin

Introduction

The reduction of polarized multiple bonds (ketones, imines, etc.) plays a major role in modern organic synthesis. This reaction can be carried out using metal hydrides such as LiAlH 4 [1], DIBALH [2], BH 3 [3], or NaBH 4 [4]. However, these reducing agents are used in stoichiometric amounts and, as a result, generate numerous by-products. In addition, the control of chemo-and stereoselectivity can be difficult in the presence of these hydrides. Nonetheless, obtaining enantiomerically pure products resulting from such transformations (chiral alcohols or chiral amines) is a key step in the synthesis of pharmaceutical DOI: 10.1002/bab.1906 Published online in Wiley Online Library (wileyonlinelibrary.com) or agrochemical products. To this end, alternative synthesis routes are now commonly used, involving the metallo-catalyzed version of reduction reactions such as hydrogenation under high pressure of molecular hydrogen and hydrogen transfer reactions in the presence of a hydrogen atom donor [5]. Depending on the nature of the metal and its ligands, the main advantage of this approach is the possibility to control regio-, chemo-, and/or stereoselectivity of the reaction. Unfortunately, the most commonly used catalysts for this type of reaction are based on weakly available, expensive, and toxic noble metals such as ruthenium [5], iridium [6], or rhodium [7]. The development of cheaper, more efficient, and eco-compatible catalysts has become a challenge of modern chemistry. In this context, iron-catalyzed hydrogenation has recently emerged as the most economical and environmentally preferred route of synthesis. It was recently demonstrated that Kn ölker-type iron complexes could be efficient catalysts for the hydrogenation of aromatic ketones in water [8]. However, this prior report has revealed that the reaction temperature was also decisive since no conversion was observed at 40 • C, and only 13% conversion was observed at 60 • C.

In addition to the enantioselective transformations catalyzed by metal complexes, catalysis by artificial metalloenzymes has become an interesting tool for the synthesis of enantiopure compounds in water [START_REF] Letondor | Proc. Natl. Acad. Sci[END_REF]. This technology combines the attractive features of enzymatic catalysis with those of chemical catalysis [START_REF] Schwizer | [END_REF]. Given the great potential of these biohybrid catalysts in asymmetric synthesis and, knowing that Kn ölker's iron complexes are efficient catalysts in water, a recent report illustrated the synthesis of biotinylated Kn ölker's complexes incorporated into streptavidin using the so-called "Trojan horse" strategy [11]. The artificial iron hydrogenases thus prepared catalyzed the reduction of ketones in aqueous medium, with the best conversion rates (26%) and enantiomeric excess (34%) obtained with para-methoxy-acetophenone as substrate [11].

Xylanases hydrolyze β-1,4 glycosidic bonds in the main chain of xylan, the major component of plant cell wall hemicellulose. In the pulp-bleaching process, the enzymatic hydrolysis of xylan at high temperature has gained importance from an environmental standpoint. Consequently, growing interest in temperature-tolerant xylanases working under extreme pH and ionic strength conditions has led to the discovery, cloning, and characterization of numerous enzymes. This includes xylanase A (Xln A) from Streptomyces lividans, an enzyme exhibiting optimal activity at 60 • C and pH 6 [12]. This robust biocatalyst can also be easily purified, and its sequence and three-dimensional structure are known [13], making it a good scaffold for the production of artificial metalloenzymes. It has been shown that noncovalently inserted Fe(III) and Mn(III) complexes of anionic porphyrins into Xln A leads to artificial metalloenzymes, exhibiting good peroxidase activity [12]. In addition, the Fe(III)-porphyrin-based hybrid biocatalysts Fe(III)(TpCPP)-and Fe(III)(TpSPP)-Xln A were found to catalyze the stereoselective oxidation of thioanisole in the presence of imidazole with roughly 40% enantiomeric excess r This artificial metalloenzyme was found to be able to cat- alyze efficiently the transfer hydrogenation of aromatic ketones by sodium formate in water, yielding the corresponding secondary alcohol as a racemic.

r The data were rationalized with a computational strategy and suggested that the Kn ölker's complex was most likely flexible and could experience free rotational reorientation within the active-site pocket of xylanase, allowing it to access the subsite pocket populated by substrata. [14,15]. The most efficient biohybrid was undoubtedly observed for the stereoselective oxidation of styrene derivatives by oxone, catalyzed by the Mn(III)(TpCPP)-Xln A hemozyme, which led to an 80% ee in favor of the R isomer in the particular case of p-methoxystyrene [16].

In this paper, we report the preparation and characterization of a new artificial metalloenzyme that was obtained by the covalent attachment of a Kn ölker-type iron complex into xylanase A. This artificial metalloenzyme can efficiently catalyze the transfer hydrogenation of the benchmark substrate trifluoroacetophenone (TFAC) by sodium formate in water, yielding the corresponding secondary alcohol as a racemic. The reaction proceeded more than threefold faster with the XlnS212CK biohybrid than with the Kn ölker's complex alone. In addition, efficient conversion of TFAC to its corresponding alcohol was reached within 60 H with XlnS212CK, whereas a 2.5-fold lower conversion was observed with Kn ölker's complex alone as catalyst.

Experimental

Physical measurements

UV-visible spectroscopy studies were performed on double beam UVIKON 860XL and Cary 300BIO Varian spectrophotometers.

1 H NMR and 13 C NMR spectra were recorded on Bruker AM 250, 300, and 360 spectrometers. Chemical shifts δ are given in ppm using the solvent as internal reference with respect to tetramethylsilane (TMS). Electrospray ionization mass spectrometry experiments were carried on a MicrOTOF-Q Bruker spectrometer. [11] In a two-necked round bottom flask under argon atmosphere, a 2.5 M solution of nBuLi in hexane (34.5 mL, 86.3 mmol) was added dropwise to a solution of propargylic alcohol (2.1 g, 37.5 mmol) in 100 mL dry THF at -78 • C. The solution was slowly warmed up to room temperature and stirred for an additional 1 H. The reaction mixture was cooled down to -78 • C, and trimethylsilyl chloride (11 mL, 86.3 mmol) was slowly added. The resulting mixture was stirred at room temperature overnight. The reaction was then cooled down to 0 • C, and an aqueous solution of 2.6 mL of 95% sulfuric acid in 15 mL of water was added slowly. The resulting solution was stirred for an additional 3 H at room temperature. Water (20 mL) was added until dissolution of the inorganic salts. The aqueous layer was extracted with diethyl ether (3 × 50 mL). Organic layers were dried over Na 2 SO 4 and filtered, and the solvent was removed under reduced pressure. The crude product was purified by distillation (3.5 g, 73 %).

Preparation of the Kn ölker's complex 2.2.1. 3-(Trimethylsilyl)prop-2-yn-1-ol (S1)

1 H NMR (CDCl 3 , 300 MHz), δ(ppm/TMS): 4.27 (d, J = 4.9 Hz, 2H), 0.18 (s, 9H). [11,17] In a three-necked round bottom flask under argon atmosphere, a 1 M solution of bromine in dry dichloromethane (38. [11,17] In a two-necked round bottom flask under argon atmosphere, a solution of Boc 2 O (1 g, 4.6 mmol) in 25 mL dry dichloromethane was added dropwise to a solution of ethylenediamine (10 mL, 150 mmol) in 40 mL dry dichloromethane at 0 • C. The reaction mixture was stirred 1 H at 0 • C and then overnight at room temperature. Water (40 mL) was added, and the organic layer was recovered, washed twice with 40 mL water, and dried over Na 2 SO 4 . After filtration, the solvent was removed under reduced pressure and the residue was purified by chromatography on a neutral alumina column eluted with ethyl acetate/methanol (95/5) to afford S3 as a colorless oil (0.42 g, 57%).

3-(Trimethylsilyl)prop-2-ynyl bromide (S2)

1 H NMR (CDCl 3 , 300 MHz), δ (ppm/TMS): 4.86 (br s, 1H), 3.17 (q, J = 5.9 Hz, 2H), 2.80 (t, J = 5.9 Hz, 2H), 1.44 (s, 9H), 1.42 (br s, 2H).

ESI-MS m/z [M + H] + : Calc. 161.1285, Found 161.1284.

N-tert-Butoxycarbonyl,N -maleimidoethylenediamine (S4) [17]

In a round bottom flask, N-methoxy-carbonyl maleimide (119 mg, 0.77 mmol) was dissolved in 10 mL of a saturated aqueous NaHCO 3 solution on ice. The reaction mixture was stirred 40

Min on ice and then 1 H 30 Min at room temperature. The pH of the solution was adjusted to 3 with concentrated H 2 SO 4 on ice. The aqueous layer was then extracted with ethyl acetate (3 × 150 mL). Organic layers were dried over Na 2 SO 4 , filtered and the solvent was removed under reduced pressure. The crude product was then purified by chromatography on a silica gel column eluted with heptane/ethyl acetate (1/1) to afford S4 as a white solid (131 mg, 71%). 1 H NMR (CDCl 3 , 300 MHz), δ (ppm/TMS) : 4.86 (br s, 1H), 3.17 (q, J = 5.9 Hz, 2H), 2.80 (t, J = 5.9 Hz, 2H), 1.44 (s, 9H), 1.42 (br s, 2H).

N-(2-Aminoethyl

)maleimide (S5) [17,18] In a round bottom flask, compound S4 (130 mg, 0.54 mmol) was dissolved in 2 mL dichloromethane at 0 • C. TFA (760 µL, 9.9 mmol) was added and the resulting solution was stirred for 2 H at room temperature. The mixture was concentrated to 1 mL, and ice-cold diethyl ether (2 mL) was added. The obtained precipitate was filtered off and washed with ice-cold diethyl ether (3 × 10 mL).

1-(2-(Bis(3-(trimethylsilyl)prop-2-yn-1yl)amino)ethyl)-1H-pyrrole-2,5-dione (S6) [11]

In a round bottom flask under argon atmosphere, S5 (90.5 mg, 0.36 mmol) and S3 (136 mg, 0.71 mmol) were added in 20 mL of dry acetonitrile. N,N-Diisopropylethylamine (63 µL, 0.36 mmol) was added, and the resulting mixture was stirred for 2 H at room temperature, and then for an additional 16 H at 70 • C. After cooling down, the solvent was removed under reduced pressure and 50 mL of water was added. The aqueous layer was then extracted with ethyl acetate (3 × 30 mL). Organic layers were dried over Na 2 SO 4 and filtered, and the solvent was removed under reduced pressure. The crude product was then purified with by chromatography on a silica gel column using a pentane/ ethyl acetate (95/5 to 90/10) gradient to obtain a white solid (70 mg, 54%) 1 H NMR (CDCl 3 , 300 MHz), δ (ppm/TMS): 7 (s, 2H), 3.4 (s, 4H), 2.8 (t, 2H), 2.6 (t, 2H), 0.16 (s, 18H) ppm. 13 C NMR (CDCl 3 , 300 MHz), δ (ppm/TMS): 170.6 (C q ), 134 (CH), 100.8 (C q ), 89.8 (C q ), 49.4 (CH 2 ), 43.4 (CH 2 ), 35.36 (CH 2 ), -0.07 (CH 3 ).

ESI-MS m/z [M + H] + : calcd. 361.1762, Found 361.1763.

Kn ölker's complex (S7) [11]

In a round bottom flask under argon atmosphere, S6 (122 mg, 0.34 mmol) and Fe 2 (CO) 9 (123 mg, 0.34 mmol) were introduced in 5 mL degassed and dry toluene. The reaction mixture was heated at 110 • C for 14 H. The resulting brownish solution was cooled down to room temperature and purified by column chromatography on neutral alumina topped with a pad of Celite (eluent: dichloromethane/cyclohexane, 6/4) to afford the desired product S7 as a yellow-brown solid (95 mg, 53%).

FIG. 1

Coupling of the S7 Kn ölker's complex to XlnS212C and XlnK48C enzyme variants : synthesis of the xylanase A-derived biohybrid XlnS212CK.

1 H NMR (CHCl 3 , 300 MHz), δ (ppm/TMS) : 6.68 (s, 2H), 3.88 (d, 2H), 3.72 (t, 2H), 3.35 (d, 2H), 3.04 (t, 2H), 0.24 (s, 18H). 13 C NMR (CHCl 3 , 300 MHz), δ (ppm/TMS) : 170.7 (C q ), 134.1 (CH), 112.9 (C q ), 69.2(C q ), 53.3 (CH 2 ), 52.3 (CH 2 ), 36.5 (CH 2 ), -0.8(CH 3 ) ppm.

ESI-MS m/z [M + H] + : Calcd. 529.0908, Found. 529.0908.

Protein expression and purification

Wild-type and mutant forms of Xln A were expressed and purified from the supernatant of S. lividans using a slightly modified version of a previously reported protocol [12]. Genetic constructs for cysteine mutants at positions K48 and S212 were a generous gift from Prof. Claude Dupont (INRS). Briefly, S. lividans was first precultured in 12 mL TSB medium for 2 days and further expressed for 72 H at 34 • C by inoculation in M14 minimal medium using xylose as the sole carbon source. The culture supernatant was concentrated by ultrafiltration and dialyzed against 20 mM citric buffer (pH 4.5). The dialyzed enzyme solution was then loaded on a HiPrep CM FF 16/10 column (GE Healthcare) preequilibrated with 20 mM citric buffer (pH 4.5). The enzyme was eluted with a linear gradient of the same buffer containing 1 M NaCl. Fractions were collected, and protein elution was monitored at 280 nm. Elution fractions were further analyzed by SDS-PAGE, and fractions containing Xln A were collected, pooled, dialyzed against water, and lyophilized.

Monitoring of thiol accessibility

The accessibility of the C212 thiol group was monitored using Ellman's test [19]. In a standard assay, 5 µL of a 10 mM solution 5,5'-dithio-bis-(2-nitrobenzoic acid) in water was added to 445 µL of reaction buffer (0.1 M sodium phosphate pH 8.0, 1 mM EDTA) in a 1-mL quartz cuvette. The absorbance at 412 nm was then monitored as a function of time, using a Jasco spectrophotometer, after the addition of 50 µL of a 100 µM protein solution until complete reaction. The final absorbance obtained at the plateau was noted A eq , and the initial absorbance measured before protein addition was noted A 0 . The reduced cysteine content was then calculated from the difference in absorbance A eq -A 0 , corrected by the dilution factor, using an ε M value of 14150 M -1 cm -1 at 412 nm.

Molecular modeling 2.5.1. Construction of the Xln A-Kn ölker's biohybrid complex

The crystal structure of Xln A from S. lividans (PDB entry 1E0W) was used as the starting template for construction of the Xln A-Kn ölker biohybrid complex [20]. To predict backbone perturbations caused by introduction of the S212C substitution, a standard RosettaBackub protocol was used [21]. The universal force field and steepest descent protocols available in the Avogadro 1.2.0 suite were applied to properly estimate conformation of the Kn ölker's molecule (including the Fe ion as transition metal). The Xln A-Kn ölker's complex was created using the Build-Structure tools available in UCSF Chimera 1.14. Amino acid residues in the vicinity of the Kn ölker's molecule were then energy minimized using the force field provided by the Molegro Virtual Docker suite 6.0 (MVD). Through this energy minimization step, the thermodynamic barriers between the Xln A receptor protein and Kn ölker's ligand were evaluated to extract the most realistic representations of this hybrid complex. During this particular analysis, both the Kn ölker's complex ligand and Xln A were first considered as separated entities.

Conformational exchange experienced by Xln A

To simulate conformational exchange experienced by Xln A, we applied two coarse-grained methodologies that predict shortand long-range protein dynamics. To simulate local residue dynamics, the stochastic method based on a Monte Carlo analysis was applied using the CABSflex 2.0 server [22]. Default server parameters were used for this analysis, which recently demonstrated results comparable to other all-atoms MD simulations protocols (i.e., similar to 10-ns simulations in aqueous solvent) [23]. Long-range protein dynamics were predicted using a normal mode analysis (NMA) methodology through the ElN émo server [24]. NMA computed two trajectories with 10 models, corresponding to the lowest frequency normal modes. Parameters used a perturbation range of -100 and a cutoff of 8 Å. Collectivity scores were considered to manually select the best two elastic network models. All coarse-grained methodologies were performed using the S212C model obtained from the RosettaBackub server as starting PDB structure [21].

Molecular docking simulations

To simulate coordination of the Xln A-Kn ölker's biohybrid complex with the TFAC substrate molecule, we performed virtual docking simulations using the MolDock scoring function implemented in the MVD suite 6.0 [25]. The virtual docking procedure was performed in two sequential phases. We first performed blind (free) docking of the substrate on the whole biohybrid complex as receptor target, after which we used a reduced searching area acquired from the best docking conformers obtained from the first phase of the docking simulation. Simulations were performed without incorporation of water molecules, and the best conformers arose from a pool of 1,000,000 docking combinations. Results from both sequential phases were compiled from 500 iterations per run and 20 runs per process. The ligand molecule was obtained

Biotechnology and

Synthesis of the Kn ölker's complex S7 [11,17,18].

from the PubChem database under accession CID number 9905.

Coupling of the Kn ölker's complex to the S212C variant of Xln A

The concentration of accessible thiols calculated via Ellman's test was used as the free cysteine concentration available for the coupling of the Kn ölker's complex S7. Five equiv. of S7 diluted in DMSO was mixed with the Xylanase A S212C variant (XlnS212C) in the coupling buffer (HEPES 10 mM, 150 mM NaCl, pH 7.75), for a final DMSO concentration of 2% in the desired volume. The mixture was incubated overnight at 4 • C. The mixture was loaded on a gel filtration column (HiLoad 16/600 Superdex TM 75, GE Healthcare) equilibrated in buffer A (HEPES 10 mM, 150 mM NaCl, pH 8) that was previously incubated with Chelex R 100 resin and filtered. The coupling efficiency was measured by using Ellman's test and MALDI-TOF MS analysis.

The molar extinction coefficient of the Kn ölker's complex was determined in HEPES 10 mM, NaCl 150 mM, pH 7 containing 5 % ethanol and was found to be similar to that measured in ethanol, ε M = 3,100 M -1 cm -1 at 280 nm. The molar extinction coefficient of the biohybrid at 280 nm was calculated by adding the computed molar extinction coefficient of the protein variant to that measured for the Kn ölker's complex moiety and was found to be ε M = 67,500 M -1 cm -1 .

Protein mass spectrometry analysis

Protein solutions were desalted on a Zeba Spin column (Thermo) against 10 mM HEPES buffer pH 8 and then diluted in a sinapinic acid matrix for MALDI-ToF MS analysis in linear mode by using a MALDI-ToF/ToF UltrafleXtreme spectrometer (Bruker Daltonics).

Catalysis of the hydrogen transfer reaction

Results and Discussion

Xln A mutant selection and modeled biohybrid formation

Covalently attaching an artificial complex to the active-site cavity of an enzyme to yield a newly designed, stable, and active biocatalyst remains a challenging task to this day,

SCHEME 2

Postulated mechanism of the catalytic hydrogenation by iron artificial metalloenzyme in water.

FIG. 3

Maldi-ToF spectra of the XlnS212C variant measured before (blue) and after (red) functionalization with the Kn ölker's complex compound.

FIG. 4

Hydrogenation of TFAC S8 by sodium formate catalyzed by Kn ölker's complex S7 or by the XlnS212CK biohybrid.

FIG. 5

Time course of hydrogenation of TFAC by XlnS212CK ( ) in aqueous buffer in comparison with CK alone in EtOH (᭡).

especially in light of issues pertaining to protein and biohybrid stability. To help with proper positioning and orientation of the Kn ölker's complex in the solvent-exposed active site of Xln A, active-site residues K48 and S212 were selected as potential targets for cysteine mutagenesis, in addition to being subjected to molecular modeling investigation. Residues K48 and S212 are located on opposite sides of the active-site cavity, allowing subsequent formation of a covalent adduct between the enzyme and the Kn ölker's complex using the free thiol group of the cysteine side chain. Our experimental results showed that biohybrid formation was unsuccessful at residue 48, most likely due to unfavorable steric clashes between the enzyme and the Kn ölker's complex upon covalent anchoring at this position (Fig. 1). However, coupling of the Kn ölker's complex to Xln A mutant S212C was successfully achieved, yielding the XlnS212CK enzyme variant (Fig. 1).

In accordance with experimental results, molecular modeling confirmed that the Kn ölker's complex can be accommodated in the active-site of Xln A upon covalent anchoring at this position (Fig. 2A).

However, the MolDock scoring function of the MVD force field revealed that this biohybrid remains energetically unfavorable when subjected to side-chain energy stabilization in the vicinity of the active-site cavity. Even after energy minimization, residues delineating the catalytic pocket of Xln A remain highly unstable ( 80 kcal/mol for the biohybrid complex) (Fig. 2A, right panel). These results illustrate that an energy contribution is required to stabilize the Kn ölker's complex and to establish proper thermodynamic conditions essential for enzyme-ligand stabilization. This also strongly suggests that formation of the Xln A-Kn ölker's biohybrid requires conformational rearrangements within the protein scaffold.

To provide a more realistic model representation of the experimentally observed biohybrid complex, we performed Monte Carlo and NMA simulations to estimate short-and longrange conformational exchange experienced by the enzyme in solution. Coarse-grained simulations strongly suggest that the active-site cavity of Xln A experiences short-and longrange conformational rearrangements to allow Kn ölker's complex stabilization within the active-site cavity (Fig. 2B). Upon structural reorganization, energetically favorable protein conformers that stabilize biohybrid complex formation were readily observed, specifically for short-range flexibility models, which displayed favorable biohybrid complex energy values ( G up to -20 kcal/mol).

Synthesis of the Kn ölker's complex (S7)

The Kn ölker's complex (S7) bearing a maleimido group that enables its covalent anchoring into the XlnS212C variant by reaction with the thiol function of C212 was prepared in seven steps, as described in Scheme 1.

Tert-butyl(2-aminoethyl)carbamate S3 was first prepared in an overall 50% yield in two steps starting by the trimethyl silylation of propargylic alcohol by trimethylsilyl chloride, followed by a bromination by Br 2 in the presence of triphenyl phosphine and pyridine in dichloromethane, as described in the literature (Scheme 1) [11,17]. N-(2-Aminoethyl)maleimide S5 was then prepared in an overall 40% yield in three steps involving the monoprotection of one amino group of ethylenediamine by Boc 2 O, followed by the introduction of the maleimido group by peptide coupling with N-methoxy-carbonyl maleimide in the presence of sodium hydrogenocarbonate and, finally, deprotection of the amino group by trifluoroacetic acid (Scheme 1) [17,18]. The 1-(2-(bis (3-(trimethylsilyl)prop-2-yn-1-yl)amino)ethyl)-1H-pyrrole-2,5-dione ligand (S6) was then obtained in a 54% yield by reaction of S3 with S5 in dry acetonitrile in the presence of N,N-diisopropylethylamine, as described in the Experimental section [11]. Final introduction of the iron(III) ion was performed by reaction of S7 with Fe 2 (CO) 9 in dry toluene under inert atmosphere, producing the S7 Kn ölker's complex at 53% yield, which was then fully characterized by 1 H and 13 C NMR and ESI MS.

Synthesis and characterization of the XlnS212CK biohybrid

The reactivity and accessibility of the thiol function of cysteine 212 in the XlnS212C enzyme variant was first assessed by the time-resolved Ellman's assay using sulfhydryl reagent 5,5-dithio-bis-(2-nitrobenzoic acid) (DTNB) that reacts with sulfhydryl groups and releases 2-nitro-5-thiobenzoate (TNB), which displays a maximum absorption at 412 nm [19]. The final labeled cysteine concentration was equal to protein concentration, indicating full accessibility, reactivity, and lack of disulfide bridge formation at cysteine 212, even after several weeks of storage without any reducing agent. The XlnS212C variant was then functionalized by incubation with 5 equiv. of the S7 Kn ölker's complex dissolved in DMSO overnight at 4 • C, in coupling buffer (HEPES 10 mM, 150 mM NaCl, pH 7.75) (Fig. 1). This resulted in the formation of the XlnS212CK biohybrid, bearing Kn ölker's complex S7 covalently linked to cysteine 212, which was further characterized by MALDI-ToF mass spectrometry (Fig. 3). Peaks at 33,158 ± 5 and 33,598 ± 5 Da were, respectively, observed for the XlnS212C variant and for the xylanase A-derived biohybrid XlnS212CK, in agreement with the covalent anchoring of one Kn ölker's complex S7 per protein after loss of three CO ligands (Fig. 3).

Aqueous transfer hydrogenation of TFAC by metal complexes

TFAC S8 was chosen as a benchmark substrate to delineate the catalytic activity of the newly synthesized complexes in aqueous transfer hydrogenation reactions using formate as a hydrogen source (Fig. 4). First, this substrate may be readily reduced into the corresponding α-(trifluoromethyl)benzyl alcohol S9 thanks to the electron-attracting character of the CF 3 substituent [26]. Second, TFAC is well known to be hydrogenated into asymmetric trifluoromethyl benzyl alcohol by naturally occurring hydrogenases like carbonyl reductase [27], which makes it a perfect candidate for studying the enantioselectivity of the catalysis. The hydrogenation of TFAC was carried out in aqueous medium, under the following reaction conditions: a 25 mM solution of the carbonyl substrate in HEPES buffer (pH 8) was allowed to react at 65 • C with 3 M sodium formate in the presence of 90 µM Me3NO and 30 µM catalyst [28].

The same conditions were then chosen to explore the catalytic activity of the XlnS212CK artificial hydrogenase, and the influence of Xln A on the kinetics and selectivity of the hydrogenation reaction catalyzed by Kn ölker's complex cofactor S7 was investigated.

Hydrogenation of TFAC by the XlnS212CK biohybrid

The reaction was followed by gas chromatography using acetophenone as internal standard. Whereas the reaction was negligible in the absence of catalyst (data not shown), it was catalyzed by both the Kn ölker's iron complex S7 and the Xln A-Kn ölker's iron biohybrid complex XlnS212CK. XlnS212CK catalyzed the hydrogenation of TFAC into alcohol S9 with an initial rate of 8.8 µMH -1 , whereas Kn ölker's complex S7 alone was poorly soluble in water thus producing alcohol S9 with an initial rate of only 2 µMH -1 (data not shown). Under these conditions, the reaction thus proceeded about 4.4-fold faster with the XlnS212CK biohybrid than with the Kn ölker's complex S7 alone as catalyst. It is noteworthy that, in ethanol the Kn ökler's complex S7 was soluble and produced alcohol S9 with an initial rate of 2.6 µMH -1 . Over time, the production of alcohol S9 slowed down to reach a plateau after about 60 H. After reaching the plateau, approximately 2.5-fold more alcohol S9 was produced in the presence of the biohybrid XlnS212CK than in the presence of the Kn ölker's complex S7 alone as catalyst (Fig. 5). This confirmed that the XlnS212CK biohybrid was a better catalyst for the hydrogenation of TFAC by sodium formate in water, which could potentially be explained by the fact that the protein scaffold may facilitate solubilization of the hydrophobic Kn ölker's complex and the TFAC substrate in water.

Finally, the enantiomeric excess was measured using a chiral GC column, as described in the Experimental section. Trifluoromethyl benzyl alcohol was formed as a racemic mixture, exhibiting poor control of the substrate orientation and/or stabilization inside the hydrophobic pocket of the XlnS212CK biohybrid.

Virtual docking of TFAC to the XlnS212CK biohybrid

To rationalize these experimental results and to simulate a precoordination complex that could favor hydrogenation of the TFAC molecule, we performed virtual docking of this substrate to XlnS212C and XlnS212CK. Blind virtual docking was first performed on free XlnS212C to uncover pockets and/or preferred hotspots that favor TFAC binding to the enzyme. After testing over 1,000,000 blind docking combinations, we found that the most favorable TFAC ligand conformers are always preferentially positioned within a given subsite of the Xln A binding pocket ( G = -62 kcal/mol, Fig. 6A).

Even upon anchoring of the Kn ölker's complex to the enzyme scaffold, docking simulations illustrate that the most favorable TFAC-binding site remains unchanged, targeting the same active-site pocket within Xln A, even after conformational rearrangements of the active-site cavity ( G values up to -81 kcal/mol, Fig. 6B-6D). Interestingly, none of our docking models show catalytically productive atomic coordination between the Kn ölker's complex and the TFAC substrate molecule, further supporting the lack of enantioselectivity conferred by the XlnS212CK biohybrid scaffold. Indeed, this observation suggests that the Kn ölker's complex is most likely flexible and can experience free rotational reorientation within the activesite pocket of Xln A, allowing it to access the subsite pocket populated by TFAC.

Reaction mechanism

Based on our results and previously reported work [29], a three-step mechanism can be proposed for the reduction of TFAC by sodium formate catalyzed by the XlnS212CK biohybrid (Scheme 2). First, in agreement with the necessity to add Me3NO in the medium for the reaction to occur, it is reasonable to assume that oxidation by Me3NO of one CO ligand stabilized by the iron atom in the starting Kn ölker's complex S7 provides the activated 16-electron iron species S7b. The subsequent hydrogen activation should lead to the hydride iron complex S7c [29].

The C=O bond may then be reduced either through a one-step process (as shown in Scheme 1) or through a stepwise process. Finally, the reduced products are released and the Kn ölker's complex S7 regenerated.

Conclusions

In conclusion, we have demonstrated that a new artificial hydrogenase made by covalent grafting of the iron Kn ölker's complex S7 bearing a maleimido reactive function anchored to a xylanase S212C variant can efficiently catalyze the transfer hydrogenation of the benchmark substrate TFAC by sodium formate in water, yielding the corresponding secondary alcohol as a racemic. The reaction proceeded more than threefold faster with the XlnS212CK biohybrid than with the Kn ölker's complex S7 alone. In addition, efficient conversion of TFAC to its corresponding alcohol was reached within 60 H with XlnS212CK, whereas 2.5-fold lower conversion was observed with Kn ölker complex S7 alone as catalyst. As previously reported for metal complexes such as metalloporphyrins [13,14], this confirmed that incorporation of iron Kn ölker's complex S7 into the hydrophobic pocket of a protein such as Xln A is productive and favorable, most likely due to increased solubility provided by the protein scaffold for such hydrophobic substrate and Kn ölker moiety. In contrast, incorporation of the Kn ölker's complex in the chiral cavity of XlnS212C did not induce the expected reaction enantioselectivity, suggesting poor control of substrate and/or Kn ölker's complex orientation with respect to the iron center within the active-site pocket of Xln A.

On the basis of these results, we aim to build new artificial metalloenzymes based on the same scaffold. To improve activity of the biohybrid catalyst, water-soluble metalloporphyrins incorporating different metal centers such as ruthenium will be synthesized. Improving enantioselectivity may be achieved either by chemical modifications such as using spacers of variable lengths between the xylanase protein and the Kn ölker's complex, or by performing additional mutagenesis within the active-site pocket of Xln A to better accommodate and improve complex stabilization.

Highlightsr

  We report a new artificial hydrogenase made by covalent anchoring of the iron Kn ölker's complex to a xylanase variant.

FIG. 2

 2 FIG.2

  Reactions were carried out in 1 mL sealed vials for a 200-µL reaction volume. In each vial, 86.2 µL of a 69.6 µM XlnS212CK solution in 10 mM HEPES 150 mM NaCl pH 8 (final concentration: 30 µM), 5 µL of a 3.6 mM Me 3 NO solution in water (final concentration: 90 µM), 40.8 mg of sodium formate (final concentration: 3 M), and 10 µL of a 500 mM TFAC solution in ethanol (final concentration: 25 mM) and 10 mM HEPES 150 mM NaCl pH 8 were added for a final volume of 200 µL with 7.5% of EtOH. The vials were tightly closed and set in a dry block (Reacti-therm heating and stirring module) heated at 65 • C with a vigorous stirring. The reaction was stopped after various times, and 20 µL of a 31 mM acetophenone solution in acetonitrile was then added. The organic products were then extracted twice with 500 µL of ethyl acetate, dried with Na 2 SO 4 and filtered. The samples were then analyzed by GC. GC conditions used to determine the conversion: Zebron ZB semivolatiles column (25 m, 0.25 mm, 0.25 µm) and helium vector gaz. Injector temperature: 300 • C, oven temperature : 50 -54 • C, 1 • CMin -1 , then 54-150 • C, 15 • CMin -1 , and 150 -220 • C, 50 • CMin -1 , then hold at 220 • C for 1 Min. Detection by FID at 300 • C GC conditions used to determine the ee of the product: hydrodex y-DiMOM column (25 m, 0.25 mm, 0.25 µm) and helium vector gaz. Injector temperature: 240 • C, oven temperature: 100-118 • C, 5 • CMin -1 hold 15 Min, then 118-150 • C, 10 • CMin -1 and hold for 1 Min Detection by FID at 300 • C.

  FIG. 6

New Artificial iron hydrogenases

Biotechnology and Applied Biochemistry

Acknowledgments

The authors thank Nhung Nguyen-Thi and Roger Dubuc (INRS) for helpful technical assistance with protein expression and purification. This work was supported in part by a Discovery grant from the Natural Sciences and Engineering Research Council of Canada (NSERC) under award number RGPIN-2016-05557 (to N.D.), in addition to a grant from the National Institute of General Medical Sciences (NIGMS) of the National Institutes of Health (NIH) under award R01GM105978 (to N.D.). N.D. is the recipient of a Fonds de Recherche Qu ébec -Sant é (FRQS) Research Scholar Junior 2 Career Award (number 32743). This work was supported in part by an ANR grant Carb2zyme (ANR-17-CE11-0014-02) and the LabEx CHARM3AT (ANR-11-LABEX-0039)