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Abstract

Densities of the sodium arsenate aqueous solution with the molality varied from (0.04165 to 0.37306) mol · kg−1 were determined experimentally at temperature intervals of 5 K from 283.15 K to 363.15 K and ambient pressure using a precise Anton Paar Digital vibrating-tube densimeter. The apparent molar volumes (Vϕ), thermal expansion coefficient (α) and partial molar volume (V¯B) were obtained based on the results of density measurement. The 3D diagram of apparent molar volume against temperature and molality as well as the diagram of thermal expansion coefficient and partial molar volume against molality were plotted, respectively. On the basis of the Pitzer ion-interaction equation of apparent molar volume model, the Pitzer single-salt parameters ((βM,X(0)v,βM,X(1)v,βM,X(2)v and CM,Xv,MX=Na3AsO4) and their temperature-dependent correlation F(i, p, T) = a 1 + a 2ln(T/298.15) + a 3(T – 298.15) + a 4/(620 – T) + a 5/(T – 227) (where T is temperature in Kelvin, ai is the correlation coefficient) for Na3AsO4 were obtained on account of the least-squares method. Predictive apparent molar volumes agree well with the experimental values, and those results indicate that the single-salt parameters and their relational coefficients of temperature-dependence for Na3AsO4 obtained are reliable.

Abstract

Group theoretical arguments are used to find the subgroup corresponding to symmetry reduction along a particular irreducible representation of a group. The results are used to guide the search for stationary points on the potential energy surface of hydrated copper(I) ion at the HF/6-31G∗, HF/6-31+G∗, HF/6-311+G∗, MP2/6-31G∗, MP2/6-31+G∗, MP2/6-311+G∗, B3LYP/6-31G∗, B3LYP/6-31+G∗, and B3LYP/6-311+G∗ levels. The better levels give the most stable coordination number of two. The effect of desymmetrization on the Cu-O distances and stretching frequencies has been examined.

Abstract

The use of dielectric relaxation spectroscopy (DRS) for studying electrolyte solutions is reviewed, focussing on the authors’ investigations over the last three decades. It is shown that this often-overlooked technique provides powerful insights into the nature of ion-ion and ion-solvent interactions. DRS is revealed to be particularly useful for detection of weak ion association and, due to its unique ability to detect solvent-separated species, the quantitation of ion pairing. It is demonstrated that DRS correctly determines chemical speciation for ion-paired systems where major spectroscopic techniques (NMR, Raman, UV-vis) fail. DRS also provides important insights into ion solvation. In aqueous solutions, it has been used to build up a coherent set of ‘effective’ hydration numbers for ions based on the dynamics of proximate water molecules, and has a unique ability to detect ‘slow’ water resulting from hydrophilic and hydrophobic hydration of solutes. DRS has been especially useful for characterising the behaviour of ionic liquids (ILs), e.g. showing they possess rather low dielectric constants and, surprisingly, contain no significant concentrations of ion pairs. Neat ILs and their mixtures with molecular solvents are shown by ultra-broadband DRS to exhibit extremely complicated behaviour especially at frequencies in the THz region.

Abstract

Characterization of structural heterogeneity of liquid solutions and the pursuit of its nature have been challenging tasks to solution chemists. In the last decade, an emerging method called excess spectroscopy has found applications in this area. The method, combining the merits of molecular spectroscopy and excess thermodynamic functions, shows the ability to enhance the apparent resolution of spectra, provides abundant information concerning solution structures and intermolecular interactions. In this review, the thinking and mathematics of the method, as well as its developments, are presented first. Then, research progress related to the exploration of the method is thoroughly reviewed. The materials are classified into two parts, small-molecular solutions and ionic liquid solutions. Finally, potential challenges and the perspective for further development of the method are discussed.

Abstract

Various toxic metal ions were successfully removed from solid matrix into supercritical CO2 (scCO2) by open-chain crown ether bridged diphosphates at 313.15 K and 20 MPa, these diphosphates with different ester side chains and different length of ethylene oxide bridge group are highly soluble in supercritical CO2. The extraction efficiency (E%) of heavy metals is between 55 and 89%. Mulliken charge distribution of ligand’s P=O coordination group was calculated to indicate the stability of metal complex. The ligand structure effects and the rationale for different selectivity were discussed. In addition, binding property of these diphosphates towards the alkaline earth metals was further studied following the same extraction procedures. Alkaline earth metal ions Ca2+, Sr2+ and Ba2+ were extracted with E% at 49–74%, 50–73% and 16–64%, respectively. DFT calculations were performed to investigate the interaction energy of the complexes and the correlation with the E% was discussed.

Abstract

Entecavir, triphosphorylated in liver cells, is an antiviral reagent against Hepatitis B virus (HBV). The reagent inhibits reverse transcription of RNA inside the virus capsid. In the present study, free energy profile of an Entecavir triphosphate (ETVTP) molecule has been calculated when it passes through pores of the capsid along two- and three-fold rotational symmetry axes in order to investigate permeation pathway of the reagent to the inside of the capsid. The calculations have been done based on thermodynamic integration (TI) method combined with all-atomistic molecular dynamic (MD) calculations. A free energy minimum of −19 kJ/mol was found at the entrance of the pore from the outside along the three-fold symmetry axis. This stabilization is from the interaction of negatively charged ETVTP with positively charged capsid methionine residues. This excess free energy concentrates of the reagent at the entrance of the pore by a factor of about 2000. A free energy barrier of approximately 13 kJ/mol was also found near the exit of the pore to the inside of the capsid due to narrow space of the pore surrounded by hydrophobic wall made by proline residues and negatively charged wall by aspartic acid residues. There, ETVTP is partially dehydrated in order to pass through the narrow space, which causes the great free energy loss. Further, the negatively charged residues produce repulsive forces on the ETVTP molecule. In contrast, in the case of the pore along the two-fold symmetry axis, the calculated free energy profile showed shallower free energy minimum, −4 kJ/mol at the entrance in spite of the similarly high barrier, 7 kJ/mol, near the exit of the pore.

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