Computational Study of the Formation of Short Centrosymmetric N-center dot center dot center dot S Supramolecular Synthon and Related Weak Interactions in Crystalline 1,2,4-Triazoles

A comprehensive analysis of the crystal packing and the energetic features of a series of four biologically active molecules belonging to the family of substituted 4-(benzylideneamino)-3-(4-fluoro-3-phenoxyphenyl)-1H-1,2,4-triazole-5-(4 H)-thione derivatives have been performed based on the molecular conformation and the supramolecular packing. This involves the formation of a short centrosymmetric R-2(2)(8) NH...S supramolecular synthon in the solid state, including the presence of CH...S, CH...O, CH...N, CH...F, CH...Cl, CF...FC, CCl...ClC, and CH...pi intermolecular interactions along with pp stacking to evaluate the role of noncovalent interactions in the crystal. The presence of such synthons has a substantial contribution toward the interaction energy (-18 to -20 kcal/mol) as obtained from the PIXEL calculation, wherein the Coulombic and polarization contribution are more significant than the dispersion contribution. The geometrical characteristics of such synthons favor short distance, and the population of related molecules having these geometries is rare as has been obtained from the Cambridge Structural Database (CSD). Furthermore, their interaction energies have been compared with those present in our molecules in the solid state. The topological characteristics of the NH...S supramolecular synthon, in addition to related weak interactions, CH...N, CH...Cl, CF...FC, and CCl...ClC, have been estimated using the quantum theory of atoms in molecules (QTAIM). In addition, an analysis of the Hirshfeld surface and associated fingerprint plots of these four molecules also have provided a platform for the evaluation of the contribution of different atom...atom contacts, which contribute toward the packing of the molecules in solids.

Experimental determination and theoretical correlation for the solubilities of dicarboxylic acid esters in supercritical carbon dioxide

The synthesis of high molecular weight esters such as bis (2-ethylhexyl) sebacate is of significance for its use as a lubricant. This ester is synthesized by the transesterification of dimethyl sebacate with 2-ethylhexanol. Therefore, the solubilities of bis (2-ethylhexyl) sebacate and dimethyl sebacate were determined at 308-328 K at pressures of 10-18 MPa in supercritical carbon dioxide. The solubility of dimethyl sebacate was always higher than bis (2-ethylhexyl) sebacate at a given temperature and pressure. The Mendez-Teja model was used to verify the self-consistency of data. Further, a new semi-empirical model with three parameters was developed using the solution theory coupled with Wilson activity coefficient. This model was used to correlate the experimental data of this work and solubilities of many high molecular weight esters reported in the literature. (C) 2015 Elsevier B.V. All rights reserved.

Fluctuation theory of Rashba Fermi gases: Gaussian and beyond

Fermi gases with generalized Rashba spin-orbit coupling induced by a synthetic gauge field have the potential of realizing many interesting states, such as rashbon condensates and topological phases. Here, we address the key open problem of the fluctuation theory of such systems and demonstrate that beyond-Gaussian effects are essential to capture the finite temperature physics of such systems. We obtain their phase diagram by constructing an approximate non-Gaussian theory. We conclusively establish that spin-orbit coupling can enhance the exponentially small transition temperature (T-c) of a weakly attracting superfluid to the order of the Fermi temperature, paving a pathway towards high T-c superfluids.

Organic fluorine involved intramolecular hydrogen bonds in the derivatives of imides: NMR evidence corroborated by DFT based theoretical calculations

The rare occurrence of intramolecular hydrogen bonds (HBs) of the type N-H center dot center dot center dot F-C is detected in the derivatives of imides in a low polarity solvent by using multi-dimensional and multinuclear NMR experiments. The observation of (1h)J(FH), (2h)J(FN), and (2h)J(FF), where the spin magnetization is transmitted through space among the interacting NMR active nuclei, provided strong and unambiguous evidence for the existence of intra-molecular HBs. The variation in the chemical shifts of labile protons depending on physical conditions, such as the solvent dilution and the systematic alteration of temperature confirmed the presence of weak interactions through intramolecular HBs in all the investigated fluorine substituted molecules. The self or cross dimerization of molecules is unequivocally discarded by the analysis of the rates of diffusion obtained using pseudo-two dimensional DOSY experiments. The Density Function Theory (DFT) calculations based on the Quantum Theory of Atoms In Molecules (QTAIM) and Non Covalent Interaction (NCI), are in close agreement with the NMR experimental findings.

Anomalous reduction in domain wall displacement at the morphotropic phase boundary of the piezoelectric alloy system PbTiO3-BiScO3

A comparative study of field-induced domain switching and lattice strain was carried out by in situ electric-field-dependent high-energy synchrotron x-ray diffraction on a morphotropic phase boundary (MPB) and a near-MPB rhombohedral/pseudomonoclinic composition of a high-performance piezoelectric alloy (1-x) PbTiO3-(x)BiScO3. It is demonstrated that the MPB composition showing large d(33) similar to 425 pC/N exhibits significantly reduced propensity of field-induced domain switching as compared to the non-MPB rhombohedral composition (d(33) similar to 260 pC/N). These experimental observations contradict the basic premise of the martensitic-theory-based explanation which emphasizes on enhanced domain wall motion as the primary factor for the anomalous piezoelectric response in MPB piezoelectrics. Our results favor field-induced structural transformation to be the primary mechanism contributing to the large piezoresponse of the critical MPB composition of this system.