Highly ordered and vertically oriented mesoporous silica films can be generated by electro-assisted self-assembly (EASA). The method involves the electrogeneration of hydroxide ions at an electrode surface immersed in an hydrolyzed sol solution (containing typically tetraethoxysilane, TEOS, and cetyltrimethylammonium bromide, CTAB) in order to catalyze polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the support. Vertically aligned mesostructures have been demonstrated by TEM imaging and by grazing incidence X-ray diffraction (GIXD), this latter technique enabling characterization of thin films directly on their underlying electrode surface. The influence of the electrosynthesis medium composition (precursor and surfactant concentrations, surfactant chain length) on the mesostructural order and film thickness has been thoroughly examined. It was shown that the highly ordered and oriented mesoporous silica films can be obtained over a wide composition of the starting sol (i.e., 10−200 mM CTAB and 50−350 mM TEOS) and that the lattice parameter can be moderately tuned by changing the chain length of the surfactant template. Thickness of these films can be accurately controlled by applying galvanostatic conditions and by varying the deposition time, which offer the versatility to be applied in the same way to electrodes of different nature without overpotential problems encountered in the potentiostatic mode. Thin mesoporous films are often covered with an additional byproduct made of particulate aggregates arising from bulk gelification at the electrode/solution interface. Getting aggregate-free thin films is possible by working in diluted solutions (i.e., [TEOS] < 125 mM and CTAB/TEOS ratio <0.32) and with a short deposition time (∼10 s). Voltammetric experiments carried out on these films deposited onto planar indium−tin-oxide electrodes, after template extraction, have revealed very sensitive responses to solution-phase redox probes as a result of fast mass transport from the external solution through the film to the electrode surface. Quantitative characterization of these mass transfer processes reveals that apparent diffusion coefficients as high as about 1 × 10−7 cm2 s−1 can be reached but great care should be taken in defining the film synthesis conditions that may lead to some additional limiting effects.

International audienceThe distinction between cocrystals and salts is usually investigated in hydrogen-bonded systems as A?H···B ? [A]?···[H?B]+, where the position of the hydrogen atom actually defines the ionicity of the complex. The same distinction, but in halogen-bonded systems, is addressed here, in complexes formed out of N-iodoimide derivatives as halogen bond donors, and pyridines as halogen-bond acceptors, anticipating that the position of the iodine atom in these A?I···B ? [A]?···[I?B]+ systems will also define their degree of ionicity. We show that the crystalline halogen-bonded complexes of N-iodosuccinimide (NIS) with pyridine, 4-methylpyridine, and 4-dimethylaminopyridine can be described as ?close-to-neutral? cocrystals while the crystalline halogen-bonded complex of N-iodosaccharin (NISac) with 4-dimethylaminopyridine adopts a ?close-to-ionic? structure. Theoretical calculations were performed (i) in gas phase on isolated NIS···Py-NMe2 and NISac···Py-NMe2 complexes, and (ii) on the periodic crystal phases, and combined with the topological analysis of the electron density distribution ?(r). We demonstrate unambiguously that the crystal environment actually plays a crucial role in the stabilization of the ?close-to-ionic? structure of the NISac···Py-NMe2 complex. An external homogeneous electric field ε applied to this complex (all atoms frozen at the crystalline geometry, except iodine) in either gas phase (ε = 3.7 GV m?1) or periodic pseudo-isolated configuration (ε = 2.8 GV m?1) is able to shift the iodine atom at the crystal geometry, miming the polarization effect induced by the local crystal electric field. The strong influence of the crystalline environment on the iodine position is demonstrated by using plane wave DFT periodic calculations on optimized NIS·Py-NMe2 and NISac·Py-NMe2 crystal structures, as well as by applying this plane wave basis set formalism to a hypothetical solid where the halogen-bonded complexes are pushed apart from each other within a periodic syste

Chalcogen bonding has been investigated in terms of the electron density distribution ρ(r) around chalcogen atoms. The evolution of ρ(r) along the series of chalcogen atoms is shown based on ab initio calculations on chalcogenophthalic anhydrides C8O2H4Chal (Chal = O, S, Se, and Te), where the Chal atom is in its sp 3 hybridization. From a detailed analysis of the experimental and theoretical electron density and the L(r) = −∇2ρ(r) function in the crystal phase of C8O2H4Se, we characterize directionality and strength of chalcogen bonding (Se···O and Se···Se) and hydrogen bonding (Se···H) interactions. In addition, several isolated dimers and a trimer of C8O2H4Se have been also studied at the X-ray geometry in order to compare interaction energies with those estimated from the measured electron density. Similarly to halogen atoms in halogen bonding interactions, the anisotropic distribution of ρ(r) around the Chal atoms was found to be at the origin of chalcogen bonding. Therefore, the concepts, developed earlier for halogen bonding, are extended here to chalcogen bonding interactions. From the results of this work, the L(r) function proves to be more precise than the σ-hole concept to identify electrophilic sites of Se-atoms in sp 3 hybridization.

Trimers based on intermolecular halogen-bonding interactions (Hal 3 -synthons) have been studied in hexachlorobenzene, hexabromobenzene, pentachlorophenol, and pentabromophenol. Attention is paid to the comparison of Cl 3 -and Br 3 -synthons and to their competition with hydrogen bonds (HBs), based on the experimental and theoretical charge density analyses in crystal and gas phases. The main differences between Cl 3 -and Br 3 -synthons are established coming from the particular structure of the valence shell charge concentration region in Cl and Br atoms. Electrophilic−nucleophilic interactions take place within the intermolecular regions of Hal 3 -synthons by putting face-to-face charge depletion (CD) and charge concentration (CC) regions belonging to the valence shell of the halogen atoms. The electrostatic interaction follows the electrophilic and nucleophilic power of these regions and is monitored by the negative Laplacian values normalized to charge density unit (L/ρ) at the corresponding topological critical points (CPs) of the L(r) = −∇ 2 ρ(r) function. According to the topological and energetic properties at CPs of ρ(r) and L(r), it is observed that Hal 3 -synthons can successfully compete with intermolecular HBs in the analyzed structures. On the basis of the estimated interaction energy and the electrostatic descriptor Δ(L/ρ) = (L/ρ) CC − (L/ρ) CD , we conclude that a strong dispersion contribution assists Hal3-synthons in this competition.

We compare here the halogen bond characteristics of bimolecular adducts involving either N-bromo- or N-iodosaccharin as strong halogen bond donors, with 4-picoline as a common XB acceptor. In the NBSac·Pic system, the bromine atom of NBSac is displaced toward the picoline, almost at a median position between the two nitrogen atoms, N and N', with NBr and BrN' distances at 2.073(6) and 2.098(6) Å respectively. This extreme situation contrasts with the analogous iodine derivative, NISac·Pic, where the N-I and IN' distances amount to 2.223(4) and 2.301(4) Å respectively. Periodic DFT calculations, and molecular calculations of adducts (PBEPBE-D2 aug-cc-pVTZ) either at the experimental frozen geometry or with optimization of the halogen position, indicate a more important degree of covalency (i.e. shared-shell character) in the adduct formed with the bromine atom. A stronger charge transfer to the picoline is also found for the bromine (+0.27 |e|) than for the iodine (+0.18 |e|) system. This inversion of halogen bond strength between I and Br finds its origin in the strong covalent character of the interaction in these adducts, in line with the strength of covalent N-Br and N-I bonds. Detailed characterization of the critical points (CPs) of the L(r) = -∇ρ(r) function along bonding directions has permitted the adducts to be distinguished and they can be respectively described as "neutral" NISac/Pic and "intermediate" NSac/Br/Pic, the latter with Br being close to formal equivalent NBr and BrN' interactions but still more associated to the XB donor than to the picoline, as indicated by the topological and energetic properties of the ρ(r) function at the bond critical points (BCPs).

Chalcogen bonding results from non‐covalent interactions occurring between electrodeficient chalcogen atoms and Lewis bases. Among the chalcogens, tellurium is the strongest Lewis acid, but Te‐based compounds are scarcely used as organocatalysts. For the first time, telluronium cations demonstrated impressive catalytic properties at low loadings in three benchmark reactions: the Friedel–Crafts bromination of anisole, the bromolactonization of ω‐unsaturated carboxylic acids and the aza‐Diels–Alder between Danishefsky's diene and imines. The ability of telluronium cations to interact with a Lewis base through chalcogen bonding was demonstrated on the basis of multi‐nuclear (17O, 31P, and 125Te) NMR analysis and DFT calculations.

One key challenge in inorganic mesoporous films is the development of oriented mesostructures with vertical channels, and even more challenging is their functionalization while maintaining accessible the selected surface groups. Combining the electrochemically assisted deposition of ordered and oriented azide-functionalized mesoporous silica with alkyne-azide click chemistry enables such nanostructured and vertically aligned hybrid films to be obtained with significant amounts of active organic functional groups, as illustrated for ferrocene and pyridine functions. A good level of mesostructural order was obtained, namely up to 40% of organosilane in the starting sol. The method could be applied to a wide variety of functional groups, thus offering numerous new opportunities for applications in various fields.

Wood decay fungi have complex detoxification systems that enable them to cope with secondary metabolites produced by plants. Although the number of genes encoding for glutathione transferases is especially expanded in lignolytic fungi, little is known about their target molecules. In this study, by combining biochemical, enzymatic and structural approaches, interactions between polyphenols and six glutathione transferases from the white-rot fungus Trametes versicolor have been demonstrated. Two isoforms, named TvGSTO3S and TvGSTO6S have been deeply studied at the structural level. Each isoform shows two distinct ligand-binding sites, a narrow L-site at the dimer interface and a peculiar deep hydrophobic H-site. In TvGSTO3S, the latter appears optimized for aromatic ligand binding such as hydroxybenzophenones. Affinity crystallography revealed that this H-site retains the flavonoid dihydrowogonin from a partially purified wild-cherry extract. Besides, TvGSTO6S binds two molecules of the flavonoid naringenin in the L-site. These data suggest that TvGSTO isoforms could interact with plant polyphenols released during wood degradation.