Hydration of clays at the molecular scale: the promising perspective of classical density functional theory

We report here how the hydration of complex surfaces can be efficiently studied, thanks to recent advances in classical molecular density functional theory. This is illustrated on the example of the pyrophyllite clay. After presenting the most recent advances, we show that the strength of this implicit method is that: (1) it is in quantitative or semi-quantitative agreement with reference all-atom simulations (molecular dynamics here) for both the solvation structure and energetics, and (2) the computational cost is two to three orders of magnitude less than in explicit methods. The method remains imperfect in that it locally overestimates the polarisation of water close to hydrophylic sites of the clay. The high numerical efficiency of the method is illustrated and exploited to carry out a systematic study of the electrostatic and van der Waals components of the surface–solvent interactions within the most popular force field for clays, CLAYFF. Hydration structure and energetics are found to weakly depend upon the electrostatics. We conclude on the consequences of such findings on future force-field development.     

FastGrow: on-the-fly growing and its application to DYRK1A

Journal of Computer-Aided Molecular Design - Fragment-based drug design is an established routine approach in both experimental and computational spheres. Growing fragment hits into viable ligands...     

Dehydrogenative Silylation of Alcohols Under Pd-Nanoparticle Catalysis

Pd-nanoparticle-catalyzed dehydrogenative coupling between various hydrosilanes and alcohols was shown to provide silyl ethers in good and reproducible yields. The synthetic methodology is effective for a wide range of simple and bulky silanes and secondary alcohols, while keeping various other functional groups intact. The procedure also exhibits high selectivity for the silylation of primary versus secondary alcohols in 1,2-diols, and allows the successive silylation of alkynols and hydrogenation of the triple bond to afford Z-alkenols in good yields.     

Influence of Silica Support Size on the Polymerisation of Ethylene Using a Supported Metallocene Catalyst

In the current work, we will focus on the influence of support properties on the activity and molecular weights of polyethylene produced with a metallocene supported on silica treated with MAO. It is demonstrated that relatively small changes in the size of the silica particles have a profound effect on the activity of the growing particles, and that not all particles in a given batch of catalyst behave in the same manner.     

Single and binary self-assembled monolayers of phenyl- and pentafluorophenyl-based silane species, and their phase separation with octadecyltrichlorosilane

In this paper, we first present the study of the formation of phenyltrichlorosilane film and self-assembled monolayers of phenylalkyltrichlorosilane (PATCl), pentafluoro-phenylalkyltrichlorosilane (PFATCl), and a mixture of the two, on silicon covered by its native oxide. These monolayers are shown to grow in two steps with characteristic time constants. The first step is characterized by a similar time constant of growth for all the studied trichlorosilane molecules and attributed to chemisorption. The second step corresponds to the arrangement between molecules, accelerated by the presence of the short alkyl chain (3-4 carbon atoms), and by mixing phenyl and pentafluoro-phenyl terminal moieties, which is accounted for by hydrogen bonding CH···FC and/or attractive quadrupolar interactions within a face-to-face phenyl/pentafluoro-phenyl alternating stack arrangement. Such results should allow improvement of intermolecular stacking within conjugated molecular domains, which is particularly important for molecular electronic devices. In the second part, we studied how PATCl, PFATCl, and their mixture phase separate with octadecyltrichlorosilane (OTS) molecules in various ratios. The way to improve phase separation was studied modifying aromatic ring to ring as well as aromatic-aliphatic interactions. OTS island size and coverage are shown to be smaller with the aromatic phase that involves stronger ring to ring interactions, i.e., attractive interactions between the phenyl species by mixing phenyl and pentafluoro-phenyl rings. The best phase separation is obtained with PFATCl as the aromatic molecule. If nanoislands of aromatic molecules could not be observed in these experiments, we show that they are attainable by mixing OTS and aromatic small organotriethoxysilanes whose grafting kinetics is slower. These results pave the way to the control improvement of the composition and nanostructuration of SAMs, essential for their further use within molecular devices.     

Promoter Activation in Δhfq Mutants as an Efficient Tool for Specialized Metabolite Production Enabling Direct Bioactivity Testing

Natural products (NPs) from microorganisms have been important sources for discovering new therapeutic and chemical entities. While their corresponding biosynthetic gene clusters (BGCs) can be easily identified by gene‐sequence‐similarity‐based bioinformatics strategies, the actual access to these NPs for structure elucidation and bioactivity testing remains difficult. Deletion of the gene encoding the RNA chaperone, Hfq, results in strains losing the production of most NPs. By exchanging the native promoter of a desired BGC against an inducible promoter in Δhfq mutants, almost exclusive production of the corresponding NP from the targeted BGC in Photorhabdus, Xenorhabdus and Pseudomonas was observed including the production of several new NPs derived from previously uncharacterized non‐ribosomal peptide synthetases (NRPS). This easyPACId approach (easy Promoter Activated Compound Identification) facilitates NP identification due to low interference from other NPs. Moreover, it allows direct bioactivity testing of supernatants containing secreted NPs, without laborious purification.     

A complete study of CO2 line parameters around 4845 cm for Lidar applications

A diode laser spectrometer was used in the Groupe de Spectrométrie Moléculaire et Atmosphérique of Reims (France) to study CO₂ line intensities, self-broadening coefficients and air-pressure-broadening coefficients near 2.063 μm. The spectral region ranging from 4843 to 4848 cm⁻¹, which is suitable for the measurement of atmospheric carbon dioxide (CO₂) mixing ratios was studied using a new generation-commercial diode laser from Nanoplus. Three lines of the (20°1)_III←(0 0 0) band of CO₂ have been studied. The results of intensity measurements and self-broadening coefficients are compared with previous determinations and available databases. Furthermore, the air-broadening coefficients for these transitions are also reported and analyzed. Finally, these new parameters are used for the measurement of atmospheric CO₂ mixing ratio with the 2 μm heterodyne differential absorption Lidar from the Laboratoire de Météorologie Dynamique at Palaiseau (France). These new parameters demonstrate a dramatic improvement of the retrieved atmospheric CO₂ concentrations.     

Thermodynamic study of the protonation of dimethyldodecylamine N-oxide micelles in aqueous solution at 298 K. Establishment of a theoretical relationship linking critical micelle concentrations and pH

Dodecyldimethylamine N-oxide (DDAO) is a zwitterionic surfactant with acid-base properties. The proton dissociation constant of this surfactant was determined by a novel potentiometric method at "controlled chemical potential" of the proton using a classical pH-glass electrode. When the DDAO was in its monomeric form, the pKa was about 5, consistent with the value commonly reported in the literature. However, a unique proton dissociation constant specific to the micellar form of this surfactant could not be obtained. We found that the acid-base behavior of the DDAO micelles depended on their environment. Indeed, we were able to establish thermodynamic relations linking the critical micellar concentration to the degree of protonation of the micelles. The experimental values were in good accordance with this model.