Accurate determination of solvation free energies of neutral organic compounds from first principles.

The main goal of molecular simulation is to accurately predict experimental observables of molecular systems. Another long-standing goal is to devise models for arbitrary neutral organic molecules with little or no reliance on experimental data. While separately these goals have been met to various degrees, for an arbitrary system of molecules they have not been achieved simultaneously. For biophysical ensembles that exist at room temperature and pressure, and where the entropic contributions are on par with interaction strengths, it is the free energies that are both most important and most difficult to predict. We compute the free energies of solvation for a diverse set of neutral organic compounds using a polarizable force field fitted entirely to ab initio calculations. The mean absolute errors (MAE) of hydration, cyclohexane solvation, and corresponding partition coefficients are 0.2 kcal/mol, 0.3 kcal/mol and 0.22 log units, i.e. within chemical accuracy. The model (ARROW FF) is multipolar, polarizable, and its accompanying simulation stack includes nuclear quantum effects (NQE). The simulation tools' computational efficiency is on a par with current state-of-the-art packages. The construction of a wide-coverage molecular modelling toolset from first principles, together with its excellent predictive ability in the liquid phase is a major advance in biomolecular simulation.

Recent advances in functionalized micro and mesoporous carbon materials: synthesis and applications.

Functionalized nanoporous carbon materials have attracted the colossal interest of the materials science fraternity owing to their intriguing physical and chemical properties including a well-ordered porous structure, exemplary high specific surface areas, electronic and ionic conductivity, excellent accessibility to active sites, and enhanced mass transport and diffusion. These properties make them a special and unique choice for various applications in divergent fields such as energy storage batteries, supercapacitors, energy conversion fuel cells, adsorption/separation of bulky molecules, heterogeneous catalysts, catalyst supports, photocatalysis, carbon capture, gas storage, biomolecule detection, vapour sensing and drug delivery. Because of the anisotropic and synergistic effects arising from the heteroatom doping at the nanoscale, these novel materials show high potential especially in electrochemical applications such as batteries, supercapacitors and electrocatalysts for fuel cell applications and water electrolysis. In order to gain the optimal benefit, it is necessary to implement tailor made functionalities in the porous carbon surfaces as well as in the carbon skeleton through the comprehensive experimentation. These most appealing nanoporous carbon materials can be synthesized through the carbonization of high carbon containing molecular precursors by using soft or hard templating or non-templating pathways. This review encompasses the approaches and the wide range of methodologies that have been employed over the last five years in the preparation and functionalisation of nanoporous carbon materials via incorporation of metals, non-metal heteroatoms, multiple heteroatoms, and various surface functional groups that mostly dictate their place in a wide range of practical applications.

Towards first-principles molecular design of liquid crystal-based chemoresponsive systems.

Nematic liquid crystals make promising chemoresponsive systems, but their development is currently limited by extensive experimental screening. Here we report a computational model to understand and predict orientational changes of surface-anchored nematic liquid crystals in response to chemical stimuli. In particular, we use first-principles calculations to evaluate the binding energies of benzonitrile, a model for 4'-pentyl-4-biphenylcarbonitrile, and dimethyl methylphosphonate to metal cation models representing the substrate chemical sensing surface. We find a correlation between these quantities and the experimental response time useful for predicting the response time of cation-liquid crystal combinations. Consideration of charge donation from chemical species in the surface environment is critical for obtaining agreement between theory and experiment. Our model may be extended to the design of improved chemoresponsive liquid crystals for selectively detecting other chemicals of practical interest by choosing appropriate combinations of metal cations with liquid crystals of suitable molecular structure.

Insights into the interaction between CH2F2 and titanium dioxide: DRIFT spectroscopy and DFT analysis of the adsorption energetics.

Difluoromethane (CH2F2, HFC-32) has been proposed as a valid replacement for both CFCs and HCFCs (in particular HCFC-22), and nowadays it is widely used in refrigerant mixtures. Due to its commercial use, in the last years, the atmospheric concentration of HFC-32 has increased significantly. However, this molecule presents strong absorptions within the 8-12µm atmospheric window, and hence it is a greenhouse gas which contributes to global warming. Heterogeneous photocatalysis over TiO2 surface is an interesting technology for removing atmospheric pollutants since it leads to the decomposition of organic compounds into simpler molecules. In the present work, the adsorbate-substrate interaction between CH2F2 and TiO2 is investigated by coupling experimental measurements using DRIFT spectroscopy to first-principle simulations at DFT/B3LYP level. The experimental results confirm that CH2F2 interacts with the TiO2 surface (∼80% rutile, 20% anatase) through both F and H atoms and show that the DRIFT technique is well suited to study the adsorption of halogenated methanes over semiconductor surfaces. DFT calculations are carried out by considering different periodicities and surface coverages, according to a structure involving an acid-base interaction between the F and Ti(4+) atoms as well as an H-bond between the CH2 group and an O(2-) ion. Lateral effects and energetics are analyzed in the limit of low coverage according to a procedure taking into account the binding, interaction, and distortion energies. The simulation at the different surface coverages and periodicities suggests similar decomposition pathways for the different investigated ensemble configurations.

Facile synthesis of palladium right bipyramids and their use as seeds for overgrowth and as catalysts for formic acid oxidation.

Controlling the shape and thus facets of metal nanocrystals is an effective way to enhance their performance in catalytic reactions. While Pd nanocrystals with a myriad of shapes have been successfully prepared with good uniformity and in high yield, Pd right bipyramids (RBPs) that have a singly twinned structure have been elusive. We report a facile route based on polyol reduction for the synthesis of Pd RBPs with purity >90% and sizes controlled in the range 5-15 nm. The success of our synthesis relies on the use of iodide ions to manipulate the strength of an oxidative etchant and selectively cap the Pd{100} facets. The as-prepared RBPs could serve as seeds to generate a set of Pd nanocrystals with novel shapes and structures. The RBPs also exhibited enhanced catalytic activity toward formic acid oxidation, with a current density 2.5 and 7.1 times higher than those of the single-crystal Pd nanocubes (which were also mainly covered by {100} facets) and commercial Pd black, respectively.

Adsorption of difluoromethane on titanium dioxide: investigation of the FTIR spectra and quantum-mechanical studies of the adsorbate-substrate structures.

The interaction of difluoromethane (CH(2)F(2)) with the TiO(2) surface (P25 Degussa) at room temperature has been studied by Fourier-transform infrared spectroscopy for the first time. From the comparison between the adsorption characteristics and the gas-phase spectra it can be deduced that the molecule adsorbs through an acid-base interaction between one F atom and the surface Lewis acid site (Ti(4+)) and an H-bond between the CH(2) group and the surface Lewis basic site (OH(-) or O(2-)). In order to obtain more information about the orientation geometry and the variation of the molecular structural parameters, a quantum-mechanical investigation at DFT/B3LYP level has been also performed, considering the anatase (101) surface and focusing on the O(2-) as Lewis basic site. The resulting adsorbate-substrate structures involve the formation of an acid-base interaction between one F atom and the Ti(4+) ion and differ for the number of the involved H-bonds. According to the scaled vibrational frequencies, the simulated adsorption model which better agrees with the experimental data corresponds to that in which the CH(2) group interacts with the surface by only one H-bond.