Current Physical Chemistry - Volume 6, Issue 3, 2016

The effects of applying 5.14, 25.70 and 51.40 MV/cm static external electric fields (EEFs) to oriented selected fatty acids and their mono-, di- and tri-glycerides were computed involve using the HyperChem 8.0 software. The semi-empirical PM3 method was applied for optimization of the conformations of the molecules both without and in the presence of the EEFs. It was found that EEFs only slightly influenced the charge densities, bond lengths and acidities of the fatty acids. The EEFs induced polarization of the C=C bonds depends on the geometry of the carbon chain. In the cis-isomers polarization is directed towards the chain end bearing the carboxyl group, whereas in the trans-isomers it is directed to the opposite end of the carbon chain. EEFs can favor the esterification of fatty acids and in their glycerides it can favor transesterification as well as acid- and base-catalyzed hydrolysis.

Molecular electronics involves the use of molecules as basic electronic building blocks. Conventional electronics has reached its fabrication limits using traditional technology, as many research groups seeking to better understand the transport flow of electrons through molecular systems and molecular devices. The quantum nature of these nanoscale (molecular) devices requires a quantum mechanical description. In the current review, we present a non-equilibrium electron transport theory for atomistic bimetal nanojuctions using density functional theory along with the Lippman-Schwinger equation in scattering approaches. Based upon the aforementioned framework, we have calculated the current-carrying wavefunctions of bimetal nanojuctions, which are the essential ingredients to understanding the non-equilibrium quantum electronic transport phenomena. This allows one to explore the quantum transport characteristics of nanoscale systems such as the current-voltage profile, current-induced forces as well as the shot noise and counting statistics. Moreover, thermoelectric phenomena like the Seebeck coefficients, the thermoelectric figure of merit and the local heating were investigated. Also, the quantum transport and the thermoelectric phenomena have been examined in the case of inelastic vibronic coupling contribution. A simple model based on the tight-binding framework and the non-equilibrium Green's function(NEGF)technique is used to get a further understanding of the underlying physics.

Background: Treatment with antioxidants might theoretically act to prevent the propagation of tissue damage. Enrichment in selenium, the essential microelement, enhances the antioxidant, reducing and free radical scavenging activity of extracts from several mushroom mycelia. The selenium uptake by the mushroom cultures from different systematic groups results in the sulphur atom substitution by selenium in L-methionine to form selenomethionine. Objective: Is to elucidate the theoretical prerequisites for preferential S atom substitution by Se in L-methionine, but not in L-cysteine - another sulphur-containing amino acid. Therewith the reactivity of these α-amino acids is discussed not only with respect to the well-studied inorganic compounds of selenium, but also for the potentially feasible interaction of amino acids with 1,5-diphenyl-3-selenopentanedione-1,5 (I). This is related to the directive regulation of fungal developmental parameters. Method: At the B3LYP/6-311++G(3df,3pd) level of theory with the implementation of NBO analysis and QTAIM, we have performed comparative quantum chemical research in the electronic structure and reactivity of L-cysteine and L-methionine at the initial steps of their interaction with electrophilic reagents. The selected QSAR properties of L-cysteine and L-methionine have been discussed. Results: From the viewpoint of the analysis of natural charge distribution, natural Wiberg bond order, second order perturbation energy, topological electron density characteristics, electron density in highest occupied molecular orbital, dipole moment, molecular size, polarizability of the molecules, and lipophilicity, a theoretical explanation has been presented for the preferable substitution reaction substrate, L-methionine compared with L-cysteine, on sulphur atom replacement by selenium.

Heterocycles are frequently appearing structure-building elements in drug candidates. The present paper investigates the consequences of the replacement of the oxygen atom by a sulfur atom in the isomeric rings of 5OH-oxazole and 5OH-isoxazole. Theoretical calculations at the B97D/aug-cc-pvqz level (with five additional “d” functions on the S atom) and considering the CCSD(T) level at the complete basis set limit followed the structural and concomitant free energy changes for the four title molecules in the isolated state, and in dichloromethane and water solvents. The selected species are subject to both conformational and tautomeric transformations. The polarizable continuum method (PCM) was applied for in-solution geometry optimization and estimation of the free energy components. In addition, explicit solvent Monte Carlo simulations were performed to calculate the relative solvation free energies of selected tautomers. This latter method allows for presenting solute atom - solvent atom radial distribution functions and the estimation of the number solute-solvent hydrogen bonds. The tautomeric preferences for the oxygen and sulfur containing species, which are sometimes different, were discussed and the calculated results were compared with experimental measurements for the structure composition available for 5OH-isoxazole and its methyl derivatives of in water. Potential of mean force curves were calculated for the 5-one tautomers of 5OH-isothiazole in dichloromethane and the possible tautomeric pathways for this solute in a non-protic solvent was discussed.