Character of the thermal motion of water molecules according to the data on quasielastic incoherent scattering of slow neutrons

The paper discusses the applicability of quasi-crystalline approximation to describing the thermal motion of water molecules in their normal and supercooled states. The problem is subjected to the critical analysis of experimental data on incoherent scattering of slow neutrons based on theories developed by Singwi-Sjolander [1] and Oskotsky [2] modified to duly take into account the limited applicability range of diffusion approximation. The applicability conditions of quasi-crystalline approximation are shown to be consistently satisfied only when water is in supercooled state and within a narrow temperature range above the melting temperature.     

Anomalous Density and Permittivity Effects on the Structure of Water

The relationship between the structural peculiarities of the hydrogen bond net and the anomalous behavior of density and dielectric permittivity of water is investigated. The degree of ordering in the network of hydrogen bonds is described in terms of the structural functions, among which the most important ones are tetrahedricity and the mean number of hydrogen bonds per molecule. The temperature dependence of the number of hydrogen bonds per molecule is discussed in terms of the analysis of the experimental temperature dependences of density and permittivity of water on the saturation line. The estimated density of hexagonal ice at the melting point is reproduced in terms of the concepts suggested for analysis; the estimate is rather close to the experimental value. Possible applications of the new approach are discussed.     

Temperature dependence of density, thermal expansion coefficient and shear viscosity of supercooled glycerol as a reflection of its structure

The relationship of the microstructure of supercooled, highly viscous glycerol to the temperature dependence of its density, thermal expansion coefficient, and shear viscosity are discussed. The character of this temperature dependence at the transition from low viscosity state to the solid amorphous state (solidified state without nuclei) is described with help of function psi, which can be interpreted as the effective number of degrees of freedom responsible for the change of viscosity of glycerol over a broad range; these degrees of freedom are those related to the alpha-relaxation process. It is shown that the change in effective activation energy of the viscosity is completely determined by the parameter psi. The change in the shear viscosity of glycerol due to the influence of the solid-phase nuclei is considered. It is shown that the introduction of the parameter phi, equal to the specific volume occupied by the nuclei of the solid phase, together with psi provides a natural explanation of the temperature dependence of density and thermal expansion coefficients of glycerol in its liquid, solid amorphous, glassy, and crystal states. The peculiarities of the temperature dependence of phi(T) and psi(T) for glycerol and o-terphenyl are compared.     

Profiling primaquine metabolites in primary human hepatocytes using UHPLC‐QTOF‐MS with 13C stable isotope labeling

Therapeutic efficiency and hemolytic toxicity of primaquine (PQ), the only drug available for radical cure of relapsing vivax malaria are believed to be mediated by its metabolites. However, identification of these metabolites has remained a major challenge apparently due to low quantities and their reactive nature. Drug candidates labeled with stable isotopes afford convenient tools for tracking drug‐derived metabolites in complex matrices by liquid chromatography‐tandem mass spectrometry (LC‐MS‐MS) and filtering for masses with twin peaks attributable to the label. This study was undertaken to identify metabolites of PQ from an in vitro incubation of a 1:1 w/w mixture of ¹³C₆‐PQ/PQ with primary human hepatocytes. Acquity ultra‐performance LC (UHPLC) was integrated with QTOF‐MS to combine the efficiency of separation with high sensitivity, selectivity of detection and accurate mass determination. UHPLC retention time, twin mass peaks with difference of 6 (originating from ¹³C₆‐PQ/PQ), and MS‐MS fragmentation pattern were used for phenotyping. Besides carboxy‐PQ (cPQ), formed by oxidative deamination of PQ to an aldehyde and subsequent oxidation, several other metabolites were identified: including PQ alcohol, predictably generated by oxidative deamination of PQ to an aldehyde and subsequent reduction, its acetate and the alcohol's glucuronide conjugate. Trace amounts of quinone‐imine metabolites of PQ and cPQ were also detected which may be generated by hydroxylation of the PQ/cPQ quinoline ring at the 5‐position and subsequent oxidation. These findings shed additional light on the human hepatic metabolism of PQ, and the method can be applied for identification of reactive PQ metabolites generated in vivo in preclinical and clinical studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Contribution of H-bond vibrations to heat capacity of water

The origin of the anomalously large value of the heat capacity of liquid water is discussed. Comparing the temperature dependence of the heat capacities for water with those for argon and hydrogen sulfide, we separate contributions of the translational and rotational degrees of freedom. The residual part is considered as being caused by the specific contributions of the transversal vibrations of H-bonds. The estimate for the number of H-bonds per molecule is obtained from the analysis of this contribution. This estimate is in quite good agreement with the estimates which follow from the analysis of the specific volume, heat of evaporation, and kinematic shear viscosity.     

Water dimer dipole moment

The peculiar properties of the behavior of effective polarizability of water molecules in its saturated vapor are discussed on the basis of the experimental data on the static dielectric constant. It is taken into account that in the region 273 K < T < 485 K there is a mixture of monomers and dimers in the water vapor. The comparison of the theoretical and experimental expressions for the effective polarizability shows that the dipole moment of water dimer is connected with the dipole moment of monomer via relation: d _D = √2d _m. The relative value of the irreducible pair contributions to the polarizability of the dimer is determined.     

Heat capacity and cluster structure of saturated water vapor

The value and temperature dependence of the heat capacity of saturated water vapor are studied. It is shown that the behavior of the heat capacity is determined by the formation of dimers, tetramers, and higher-order clusters, and by excitation of the hydrogen bond vibrations within these clusters. The temperature regions that correspond to water vapor as (a) a mixture of monomers and dimmers and (b) as a mixture of monomers, dimmers, and tetramers, are determined.     

The role of two-particle effects in the behavior of refraction of single-component liquids and two-component solutions

The role of irreducible two-particle contributions to the refraction properties of liquids and solutions has been studied. Two-particle contributions to the polarization vector of the system are calculated by electrostatics methods, which can be explained by weak deformations and overlaps of the electron shells of atoms and molecules. It is shown that, when the two-particle effects are taken into account, the constant of molecular refraction for binary solutions becomes a weakly nonadditive function of the constant of refraction of the components. It is shown by the example of aqueous solutions of ethanol and methanol that our values of the refractive indices and constants of refraction of the solutions are in good agreement with the experimental data.