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In this work, various atomic charge schemes including natural bond orbital (NBO), electrostatic potential based (CHELPG), and σ -hole model charges were applied in the OPLS-AA force field to investigate their effects on the thermophysical and structural properties of iodobenzene and its derivatives. Molecular dynamics simulations presented in this work show that the studied structural and thermophysical properties are in good agreement with experiments when the CHELPG charge was coupled with the OPLS-AA force field. Also, the arrangement of iodobenzene derivatives in the liquid phase was investigated via combined radial/angular distribution functions (CDFs) analyses and halogen-bonding theory. The most probable orientation of iodobenzene derivatives at the liquid/vacuum interface was assigned by atom density profile and bivariate orientational distribution maps. For all studied iodobenzene derivatives, benzene rings are oriented such that the iodine atoms tend toward the vacuum phase. [Display omitted] • The effect of different partial atomic charges of iodobenzene derivatives is investigated by MD simulation.. • Structure of liquid iodobenzene derivatives is predicted using halogen-bonding theory. • Most probable orientation of iodobenzene derivatives at liquid/vacuum interface is determined. [ABSTRACT FROM AUTHOR]

Abstract: A series of high quality 1-alkyl-3-methylimidazolium-based ionic liquids are synthesized and used for studying their surface tension. The capillary rise method is used for measuring the surface tension of I−, Cl−, PF6 −, and BF4 − salts in the temperature range 298–393K. The capillary apparatus is evacuated and sealed under vacuum. The experimental results show that surface tension of these compounds depend systematically on temperature. For ionic liquids containing a butyl alkyl chain, the contribution of the anion to the surface tension is found to be in the order of I− >Cl− >PF6 − >BF4 −. As the chain length of the alkyl group is increased, the surface tension decreases and approaches the surface tension of alkyl fluids of the same chain length. The surface entropy decreases smoothly as the chain length increases while the surface energy decreases rather sharply. This resembles the behavior of normal liquids, molten salts, and molten metals. Comparison with literature suggests that the complete removal of water and dissolved atmospheric gases as well as sufficient thermal equilibrium would produce a highly correlated and thus accurate surface tension of ionic liquids. [Copyright &y& Elsevier]

A simple and reliable colorimetric method for the quantitative determination of citalopram (CIT) enantiomers in aqueous solution using gold nanoparticles as a colorimetric probe was presented. S-citalopram induced aggregation of citrate capped AuNPs resulted in a decrease in the plasmon absorption at 520 nm and the formation of a broadened surface plasmon band around 600–700 nm. The results show that the colorimetric system possesses a very well selectivity toward S-citalopram compare to the R-citalopram as evidenced by the fact that there is the same color change from S-citalopram and (RS)-citalopram, and significant UV–vis spectral shift. The experimental conditions were optimized and the results show that S-citalopram can be determined in a linear range 2.5 × 10 −6 –6.0 × 10 −4 M with correlation coefficients of 0.9963 and limit of detection 2.1 × 10 −6 M. [ABSTRACT FROM AUTHOR]

In this paper, properties of binary mixture of polar portions of the crude oil are studied by classical molecular dynamics simulation. Particularly, the bulk and the interface of pyridine (and its alkyl derivatives) mixture with n -octane are studied, including density and structure in bulk as well as their molecular orientations at the liquid–vapor interface. Initial simulations of density profile and interfacial properties are to validate the force field applied. Additionally, the structure of solution of pyridine derivatives in bulk and at the interface is studied. As a result, the derivatives with long alky chain (of low surface tension) approaches to the surface while those with short chain (of high surface tension) aggregate in the solution and avoid approaching the surface. Finally, the molecular orientations of pyridine and alkyl derivatives are investigated in the bulk and at interface by the intrinsic bivariate orientational maps. [ABSTRACT FROM AUTHOR]

Abstract: Viscosities of ionic liquids were correlated with two linear relations. The first one presents the temperature dependence of imidazolium-, pyridinium-, pyrrolidinium-, quaternary ammonium-, and nicotinium-based ionic liquids with high accuracy. The second one is a linear relation between logarithm of surface tension and fluidity involving the characteristic exponent ϕ, and fits the ionic liquids uniquely with ϕ =0.30. Our previously measured surface tension data of ionic liquids and literature''s were used in this study. The dependence of surface tension–fluidity relation of the imidazolium-based ionic liquids on the anion type is likely disappeared as alkyl chain length increases. [Copyright &y& Elsevier]