Absolute solvation free energy of Li+ and Na+ ions in dimethyl sulfoxide solution: a theoretical ab initio and cluster-continuum model study

The solvation of the lithium and sodium ions in dimethyl sulfoxide solution was theoretically investigated using ab initio calculations coupled with the hybrid cluster-continuum model, a quasichemical theory of solvation. We have investigated clusters of ions with up to five dimethyl sulfoxide (DMSO) molecules, and the bulk solvent was described by a dielectric continuum model. Our results show that the lithium and sodium ions have four and five DMSO molecules into the first coordination shell, and the calculated solvation free energies are -135.5 and -108.6 kcal mol(-1), respectively. These data suggest a solvation free energy value of -273.2 kcal mol(-1) for the proton in dimethyl sulfoxide solution, a value that is more negative than the present uncertain experimental value. This and previous studies on the solvation of ions in water solution indicate that the tetraphenylarsonium tetraphenylborate assumption is flawed and the absolute value of the free energy of transfer of ions from water to DMSO solution is higher than the present experimental values.     

Effect of the composition of dimethyl sulfoxide–acetonitrile solvent on the stability of silver(I) complexes with 2,2'-bipyridyl

The effect of composition of the dimethyl sulfoxide–acetonitrile solvent on the shift in complexation equilibrium of silver(I) and 2,2'-bipyridyl was studied potentiometrically at 298.15 K. The stability of mono- and bis(bipyridyl) complexes of silver(I) was found to rise with increasing acetonitrile content in the mixed solvent. The difference in changes in the solvation state of the central and complex ions (the solvation effect of ions) was found to make a major contribution to the changes in stability of silver(I) complexes with 2,2'-bipyridyl in dimethyl sulfoxide–acetonitrile binary solvent.     

Solution behavior of methyl cellulose mixtures with poly(<Emphasis Type="Italic">N</Emphasis>-vinylformamide) in water and dimethyl sulfoxide

The rheological properties of diluted and moderately concentrated solutions of methyl cellulose mixtures with poly(N-vinylformamide) in water and dimethyl sulfoxide are investigated. Negative deviations of the viscosities of these solutions from the additive values are observed and explained by different mechanisms of solvation of macromolecules with water and dimethyl sulfoxide. Incompatibility of the polymers in a common solvent is discovered. This circumstance leads to the formation of a new system of hydrogen bonds and rearrangement of the structural organization of solutions.     

Enthalpies of glycylglycinate ion transfer from water to water-dimethyl sulfoxide solvent

The thermal effects of sodium glycylglycinate dissolution are determined calorimetrically at 298.15 K, and the enthalpies of glycylglycinate ion transfer from water to water-dimethyl sulfoxide solvent are calculated for compositions between 0.00 and 0.99 mole fractions of dimethyl sulfoxide. It is shown that when the concentration of the nonaqueous component is increased, the endothermicity of glycylglycinate ion transfer in the solution is considerably enhanced, weakening the solvation of anions.     

Thermochemical behaviour of crown ethers in the mixtures of water with organic solvents: Part VII. Enthalpy of solution of 15-crown-5 and benzo-15-crown-5 in the mixtures of water with acetone at 298.15 K

Enthalpy of solution of crown ethers (15-crown-5 and benzo-15-crown-5) in water-acetone mixtures have been measured within the whole range of mole fraction at 298.15 K. The obtained data have been compared with those of the solution enthalpy of both crown ethers in the mixtures of water with dimethyl sulfoxide. The replacement of SO group with CO in the molecule of the organic solvent brings about an increase in the exothermic effect of the solution of 15-crown-5 and benzo-15-crown-5 ethers, especially in the mixtures with a medium water content. The observed effect is connected with the preferential solvation of the molecules of both crown ethers by acetone molecules in the water-acetone mixtures. The process of preferential solvation of 15-crown-5 and benzo-15-crown-5 ethers does not take place in the water-dimethyl sulfoxide mixture.     

Acrylic thermoplastic elastomers and comb-shaped poly(methyl methacrylate) via the macromonomer technique

Comb-shaped poly(methyl methacrylate) (PMMA) and poly(butyl acrylate) (PnBuA) grafted with PMMA were prepared by radical copolymerization of ω-methacryloyl-PMMA with MMA and nBuA, respectively. The comb-shaped PMMA is characterized with respect to radius of gyration by using gel permeation chromatography equipped with a multi-angle laser light scattering detector. The radical copolymerization of the macromonomer with nBuA in toluene follows complex kinetics. The dependence of the relative reactivity of the macromonomer on absolute concentration and on the ratio of comonomers may be explained by preferential solvation of comonomers by segments of their own kind (“bootstrap effect”) or even micelle formation. However, there is no clear evidence for the formation of micelles in toluene. In contrast, NMR studies show micelle formation in the preferential solvent dimethyl sulfoxide. The graft copolymers are transparent thermoplastic elastomers. Phase separation is demonstrated by differential scanning calorimetry and morphological studies.     

Carbohydrates Exhibit a Distinct Preferential Solvation Pattern in Binary Aqueous Solvent Mixtures

Molecular dynamics simulations reveal the entire solvation shell around a model disaccharide dissolved in the binary 1:3 molar mixture of dimethyl sulfoxide and water becomes distinctly structured (see drawing). Such preferential solvation is due to the large number of hydroxyl groups and the rich network of hydrogen bonds of a disaccharide formed with the solvent.     

Site-specific solvation determined by intermolecular nuclear Overhauser effect--measurements and molecular dynamics

Site-specific solvation has been determined by intermolecular NOE measurements between solvent and solute. The experimental effect is shown on the four compounds 2-butanol, L-alanyl-L-tryptophan (Ala-Trp), adenosine and the disodium salt of adenosine 5'-monophosphate (5'-AMP) in the two solvents water and dimethyl sulfoxide (DMSO). The strength of NOE transfer correlates with the average distribution of solvent molecules around the corresponding solvation sites represented by the number of solvent molecules in a first solvation sphere, which can be obtained from molecular dynamics simulations in water. Saturation transfer between exchanging protons explains some deviations from this correlation. The NOE transfer measurements provide information on specific solute-solvent interactions and contribute to a better understanding of solvation phenomena. On the basis of a distinct relationship between steric solvation hindrance and the strength of NOE transfer, the application of such measurements for conformational analysis has been demonstrated for the first time.     

Formation and photochemistry of organic sulfur compound–chlorine atom complexes

Photochemical reactions of organic sulfur compounds (CH₃SCH₃, C₂H₅SCH₃ and C₂H₅SC₂H₅)–chlorine atom complexes have been studied using a combined pulse radiolysis-laser flash photolysis technique. Excitation of all complexes has resulted in photobleaching with a similar quantum yield (0.37±0.07), independent of solvent polarities and concentration of solutes. The results were compared with previous studies of the analogous dimethyl sulfoxide (DMSO)–Cl complexes. It is concluded that the significant change of photobleaching quantum yields of the excited DMSO–Cl complex observed in the DMSO-CCl₄ mixed solvent is mainly due to the specific solvation effect of DMSO for cations.     

Thermodynamics of the solvation and phase distributions of 2,2′-dipyridyl in acetonitrile-DMSO-hexane and methanol-DMSO-hexane systems

The Gibbs energies of 2,2′-dipyridyl when transferred from dimethyl sulfoxide to its mixtures with acetonitrile and methanol are determined from the distribution of substance between immiscible phases. It is found that moving from dimethyl sulfoxide to acetonitrile and methanol weakens the solvation of 2,2′-dipyridyl due to a change in the solvation of amino groups and the hydrocarbon substituent, which is reflected in a reduction in the entropy component of the Gibbs energy.     

Stability of copper(II) complexes with nicotinate ion in water solutions of ethanol and dimethyl sulfoxide

The stability constants of copper(II) complexes with nicotinate ion in water–ethanol and water–dimethyl sulfoxide mixtures are determined potentiometrically at 25.0 ± 0.1°C at ionic strength of 0.25 (NaClO4). The stability of the copper(II) nicotinate complex significantly increases with ethanol content in the solution, thus making it possible to control the biologically important process by varying the solvent composition. The increase in DMSO concentration causes a less noticeable rise in stability, with its maximum observed at 0.1 dimethyl sulfoxide mole fractions. A comparative analysis of the findings and stability constants of Cu²⁺ complexes with pyridine-type ligands is carried out. The results are discussed using the solvation thermodynamics approach.     

Elucidation of the thermochemical properties of triphenyl- or tributyl-substituted Si-, Ge-, and Sn-centered radicals by means of electrochemical approaches and computations

Redox potentials of a number of triphenyl- or tributyl-substituted Si-, Ge-, or Sn-centered radicals, R(3)M(*), have been measured in acetonitrile, tetrahydrofuran, or dimethyl sulfoxide by photomodulated voltammetry or through a study of the oxidation process of the corresponding anions in linear sweep voltammetry. For the results pertaining to the Ph(3)M(*) series (including literature data for M = C), the order of reduction potentials follows Sn > Ge > C > Si, while for the two oxidation potentials, it is C > Si. The effect of the R group on the redox properties of R(3)Sn(*) is pronounced in that the reduction potential is more negative by 490 mV in tetrahydrofuran (390 mV in dimethyl sulfoxide) when R is a butyl rather than a phenyl group. The experimental trends have been substantiated through quantum chemical calculations, and they can be explained qualitatively by considering a combination of effects, such as charge capacity being most pronounced for the heavier elements, resonance stabilization present for the planar Ph(3)C(*) and all R(3)M(+)(), and finally a contribution from solvation. The solvation of R(3)M(-) is observed to be relatively strong because of a rather localized negative charge in the pyramidal geometry. However, there is no evidence in the calculations to support the existence of covalent interactions between solvent and anions. The solvation of R(3)M(+)() is relatively weak, which may be attributed to the planar geometry around the center atom, leading to more spread out charge than that for a pyramidal geometry. Although the calculated solvation energies based on the polarizable continuum model approach exhibit the expected trends, they are not able to reproduce the experimentally derived values on a detailed level for these types of ions. An evaluation of the general performance of the continuum model is provided on the basis of present and previous studies.     

Effect of the composition of an acetonitrile-dimethyl sulfoxide solvent on stability of the silver(I) complexes with 18-crown-6 ether

The effect of the composition of an acetonitrile-dimethyl sulfoxide (AN-DMSO) mixed solvent on the stability of silver(I) complexes with 18-crown-6 ether (18C6) is studied by potentiometry. An insignificant increase in the stability of [Ag18C6]⁺ (0.34 log units) is observed on going from acetonitrile to dimethyl sulfoxide. The effect of solvation on the shift of complex formation equilibrium is considered.     

钪-铬天青S-阳离子表面活性剂的显色反应及有机溶剂化效应的研究

本文系统地研究了八种有机溶剂对钪(Ⅲ)-铬天青S-长链季铵盐多元络合物显色反应的溶剂化效应。结果表明不加有机溶剂时,Sc-CAS-OtTAB络合物的摩尔吸光系数为1.4×10⁵升/摩尔·厘米,当适量有机溶剂如甲醇或二甲基甲酰胺存在时,该体系的摩尔吸光系数可提高到3.2×10⁵升/摩尔·厘米。拟定了可以用于直接测定烯土氧化物和镧钪铁氧体中微量钪的分光光度法。测定了钪多元络合物的组成及溶剂化数,探讨了溶剂化效应的机理。     

Molecular dynamics study of the solvation of an alpha-helical transmembrane peptide by DMSO

A 10-ns molecular dynamics study of the solvation of a hydrophobic transmembrane helical peptide in dimethyl sulfoxide (DMSO) is presented. The objective is to analyze how this aprotic polar solvent is able to solvate three groups of amino acid residues (i.e., polar, apolar, and charged) that are located in a stable helical region of a transmembrane peptide. The 25-residue peptide (sMTM7) used mimics the cytoplasmic proton hemichannel domain of the seventh transmembrane segment (TM7) from subunit a of H(+)-V-ATPase from Saccharomyces cerevisiae. The three-dimensional structure of peptide sMTM7 in DMSO has been previously solved by NMR spectroscopy. The radial and spatial distributions of the DMSO molecules surrounding the peptide as well as the number of hydrogen bonds between DMSO and the side chains of the amino acid residues involved are extracted from the molecular dynamics simulations. Analysis of the molecular dynamics trajectories shows that the amino acid side chains are fully embedded in DMSO. Polar and positively charged amino acid side chains have dipole-dipole interactions with the oxygen atom of DMSO and form hydrogen bonds. Apolar residues become solvated by DMSO through the formation of a hydrophobic pocket in which the methyl groups of DMSO are pointing toward the hydrophobic side chains of the residues involved. The dual solvation properties of DMSO cause it to be a good membrane-mimicking solvent for transmembrane peptides that do not unfold due to the presence of DMSO.     

两个Menschutkin反应溶剂效应的比较

Menschutkin反应是研究得较多的亲核取代反应之一,对溶剂的动力学效应也进行了广泛和深入的研究,并获得了巨大的成功,但因溶剂对反应速率的影响因素众多,且又错综复杂。