Solvatochromic Parameters and Preferential Solvation Behavior for Binary Mixtures of 1,3-Dialkylimidazolium Ionic Liquids with Water

Binary mixtures of 1,3-dialkylimidazolium based ionic liquids (ILs) and water were selected as solvent systems to investigate the solute-solvent and solvent-solvent interactions on the preferential solvation of solvatochromic indicators at 25℃. Empirical solvatochromic parameters, dipolarity/polarizability (π^*), hydrogen-bond donor acidity (α), hydrogen-bond acceptor basicity (β), and Reichardt's polarity parameters (E_T^N) were measured from the ultraviolet-visible spectral shifts of 4-nitroaniline, 4-nitroanisole, and Reichardt's dye. The solvent properties of the IL-water mixtures were found to be influenced by IL type and IL mole fraction (x_IL). All these studied systems showed the non-ideal behavior. The maximum deviation to ideality for the solvatochromic parameters can be obtained in the xIL range from 0.1 to 0.3. For most of the binary mixtures, the π^* values showed the synergistic effects instead of the E_T^N, α and β values. The observed synergy extent was dependent on the studied systems, such as the dye indicator and IL type. A preferential solvation model was utilized to gather information on the molecular interactions in the mixtures. The dye indicator was preferentially solvated on the following trend: IL >IL-water complex >water.     

Preferential Solvation in Mixed Solvents X. Completely Miscible Aqueous Co-Solvent Binary Mixtures at 298.15 K

Summary.  The Kirkwood-Buff integrals for 18 completely miscible aqueous co-solvent binary mixtures have been recalculated from thermodynamic data, and the volume-corrected preferential solvation parameters derived from them are presented. Also presented are these latter quantities for 15 additional such mixtures, for which the volume correction has not been applied previously. The self-interaction of the water, the mutual interaction of the water and the co-solvent, and the self-interaction of the co-solvent at infinite dilution derived from these integrals and parameters are then discussed. The systems studied include aqueous hydrogen peroxide, methanol, ethanol, 1- and 2-propanol, 2-methyl-2-propanol, 2,2,2-trifluoroethanol, 1,1,1,3,3,3-hexafluoro-2-propanol, ethane-1,2-diol, glycerol, 2-methoxyethanol (at 313 and 343 K), 2-ethoxyethanol, 2-butoxyethanol, 2-aminoethanol, N-methyl- and N,N-dimethyl-2-aminoethanol, tetrahydrofuran, 1,4-dioxane, acetone, formic, acetic, and propanoic acids, piperidine, pyridine, acetonitrile, formamide, N-methyl- and N,N-dimethylformamide, N-methylacetamide, N-methylpyrrolidin-2-one (at 303 K), hexamethyl phosphoric triamide, dimethylsulfoxide, and tetramethylenesulfone (at 303 K). Received January 10, 2001. Accepted (revised) February 20, 2001     

Preferential Solvation of Acetic Acid in Binary Mixtures of Carbon Tetrachloride–Cyclohexane and Carbon Tetrachloride–1,2-Dichloroethane

The partition of acetic acid between aqueous solutions and various binary mixtures of carbon tetrachloride + cyclohexane and carbon tetrachloride + 1,2-dichloroethane were carried out at 30.0 °C. The nonlinear dependence of both the monomer partition coefficient and the dimerization constant on the mole fraction composition has been rationalized in terms of preferential solvation of the various solvation sites of the involved species. Two and four polar sites were identified for the monomer and dimer forms, respectively. The solvation preference is controlled by the relative polarities of the binary solvent components, being, in general, higher for the monomer sites compared to the dimer ones. The dimer is almost equally stable in various carbon tetrachloride + 1,2-dichloroethane mixtures, and the variation of dimerization constants with changing binary composition arises mainly from the monomer solvation stabilization.     

Preferential solvation in three component systems: Evaluation of Kirkwood-Buff parameters

The extent of local excess or deficiency of a component solvent near the solute in a mixed binary solvent has been calculated using the Hall formalism for the Kirkwood-Buff equation. The possibility of calculation of the two solute-solvent Kirkwood-Buff parameters using the values is discussed. A model calculation using literature data for preferential solvation in mixed binary solvents is presented. The solute-solvent and solvent-solvent interactions and the relative size of the solvents are also shown to be relevant factors in determining the values.     

Study of Microheterogeneity in Acetonitrile–Water Binary Mixtures by using Polarity‐Resolved Solvation Dynamics

The solvation dynamics of three coumarin dyes with widely varying polarities were studied in acetonitrile–water (ACN–H₂O) mixtures across the entire composition range. At low ACN concentrations [ACN mole fractions (X_ACN)≤0.1], the solvation dynamics are fast (<40 ps), indicating a nearly homogeneous environment. This fast region is followed by a sudden retardation of the average solvation time (230–1120 ps) at higher ACN concentrations (X_ACN≈0.2), thus indicating the onset of nonideality within the mixture that continues until X_ACN≈0.8. This nonideality regime (X_ACN≈0.2–0.8) comprises of multiple dye‐dependent anomalous regions. At very high ACN concentrations (X_ACN≈0.8–1), the ACN–H₂O mixtures regain homogeneity, with faster solvation times. The source of the inherent nonideality of the ACN–H₂O mixtures is a subject of debate. However, a careful examination of the widths of time‐resolved emission spectra shows that the origin of the slow dynamics may be due to the diffusion of polar solvent molecules into the first solvation shell of the excited coumarin dipole.     

Shape-Controlled First-Row Transition Metal Vanadates for Electrochemical and Photoelectrochemical Water Splitting

Transition metal vanadates (MVs) possess abundant electroactive sites, short ion diffusion pathways, and optical properties that make them suitable for various electrochemical (EC) and photoelectrochemical (PEC) applications. While these materials are commonly used in energy storage devices like batteries and capacitors, their shape-controlled 1D and 2D morphologies have gained equal popularity in water splitting (WS) technology in recent times. This review focuses on recent progress made on various first-row (3d, 4 s) transition metal vanadates (t-MVs) having controlled one-dimensional (fiber, wire, or rod) and two-dimensional (layered or sheet) morphologies with a specific emphasis on copper vanadates (CuV), cobalt vanadates (CoV), iron vanadates (FeV), and nickel vanadates (NiV). The review covers different aspects of shape-controlled 1D and 2D t-MVs including optoelectrical properties, wet chemistry synthesis, and electrochemical (EC-WS) and photoelectrochemical water splitting (PEC-WS) performance in terms of onset potential, overpotential, and long-term stability or high cyclic performance. The review concludes by providing some possible thoughts on how to promote the water-splitting attributes of shape-controlled t-MVs more effectively.     

Solvation Effect of Li+ on the Voltammetric Properties of [PMo12O40]3−. Part 2: Comparative Studies on the Preferential Solvation in Acetonitrile+S and Acetone+S Mixtures

For [PMo₁₂O₄₀]^3?, the presence of Li⁺ produced a two‐electron wave at nearly the same potential as the first one‐electron wave in acetonitrile or acetone. The voltammetric behavior of [PMo₁₂O₄₀]^3? in a binary mixture of acetonitrile and solvent S was compared with those in a mixture of acetone and S. When the donor number (DN) of S>20, the first two‐electron wave was converted into one‐electron waves in such binary mixtures. The conversion occurred at lower mole fractions of S in an acetonitrile+S mixture than in an acetone+S mixture. The ⁷Li NMR results showed that the preferential solvating ability of Li⁺ with S was greater in the former mixture. A linear relationship was found between the iso‐solvation point x_iso(S) and the reciprocal of the difference between the DNs of S and acetonitrile, which gave the basis to explain the anomalies observed for a mixture of acetonitrile and H₂O.     

Solvation of 4-nitropyrazoles according to UV spectroscopy data

The dependence of the energies of intramolecular charge-transfer electron transitions in 1,3,5-trimethyl-4-nitropyrazole, 4-nitropyrazole, and its anion on the dielectric and acidbase properties of solvents was analyzed. The dipole moments of these species in the excited state are larger than those in the ground state. The nonspecific solvation is accomplished through dipole-dipole interactions. 4-Nitropyrazole, which possesses acidic properties, is also solvated by the mechanism of hydrogen bonding with the solvent, which acts as a base. The strength of the hydrogen bond increases on going from the ground to the electron-excited state. The 4-nitropyrazole anion is a base, and its hydrogen bonds with the solvent are stronger in the ground state. The mechanism of specific solvation of the molecule and the anion of 4-nitropyrazole during electronic excitation is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 867–869, April, 1997.     

Preferential solvation effects in the electrochemistry and charge-transfer spectra of cyanoiron(II) complexes

The energies of the charge-transfer bands and the redox potentials of substituted cyanoiron complexes are strongly influenced by preferential solvation effects in water-acetonitrile mixed solvents, exhibiting a linear dependence with respect to the acceptor number scale. The dependence increases with the number of cyanide ligands in the complexes.     

Vibrational Spectroscopic Study on Ion Solvation and Association of Lithium Perchlorate in 4-Methoxymethyl-ethylene Carbonate

Solvation interaction and ion association in solutions of lithium perchlorate/4-methoxymethyl-ethylene carbonate （MEC） have been studied by using Infrared and Raman spectra as a function of concentration of lithium perchlorate. The splitting of ring deformation band and ring ether asymmetric stretching band, and the change of carbonyl stretching band suggest that there should be a strong interaction between Li^＋ and the solvent molecules, and the site of solvation should be the oxygen atom of carbonyl group. The apparent solvation number of Li^＋ was calculated by using band fitting technique. The solvation number was decreased from 3.3 to 1.1 with increasing the concentration of LiClO4/MEC solutions. On the other hand, the band fitting for the ClO4^- band revealed the presence of contact ion pair, and free ClO4^- anion in the concentrated solutions.     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

Solvation thermodynamic mapping of molecular surfaces in AmberTools: GIST

The expulsion of water from surfaces upon molecular recognition and nonspecific association makes a major contribution to the free energy changes of these processes. In order to facilitate the characterization of water structure and thermodynamics on surfaces, we have incorporated Grid Inhomogeneous Solvation Theory (GIST) into the CPPTRAJ toolset of AmberTools. GIST is a grid‐based implementation of Inhomogeneous Fluid Solvation Theory, which analyzes the output from molecular dynamics simulations to map out solvation thermodynamic and structural properties on a high‐resolution, three‐dimensional grid. The CPPTRAJ implementation, called GIST‐cpptraj, has a simple, easy‐to‐use command line interface, and is open source and freely distributed. We have also developed a set of open‐source tools, called GISTPP, which facilitate the analysis of GIST output grids. Tutorials for both GIST‐cpptraj and GISTPP can be found at ambermd.org. © 2016 Wiley Periodicals, Inc.     

电化学阻抗谱测定环氧涂膜吸水率

The amount of water sorption of an epoxy coating can be determined approximately by measuring the electrochemical impedance spectra of both an Al electrode coated with the epoxy film and a preliminary wetted Al electrode covered tightly with the epoxy film. By comparing the double layer capacity of these two electrodes, the amount of water sorption can be estimated. The resistivity of the electrolytic solution in the film may by thousands times larger than that of the bulk solution. This is due to the fact that the cross-section area of the water passages in the film is of molecular size. The short-distance interaction between the ions and the wall of the water passage retards the transport of the ions seriously. The structure of the water passages is discussed.     

电化学氧化法去除苯酚研究

利用氯碱厂报废的DSA电极电解苯酚,结果显示:此电极对一定浓度的苯酚溶液有较好的去除效果.按影响电解效果各主要因素进行筛选,最佳实验条件为:电流密度30mA/cm2,pH10,支持电解质浓度10mg/L,苯酚浓度10mg/L.电解2h后,CODcr的去除率为66.7%,吸光度去除率为90%.     

Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K

Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium bromide, Pr₄NBr, and tetrapentylammonium bromide, Pen₄NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu₄NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me₄NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds increases systematically in going from Me₄NBr to Pen₄NBr.     

普鲁士蓝膜电化学行为的EQCM研究

应用循环伏安法于铂电极上电化学沉积PB膜,并由电化学石英晶体微天平技术(EQCM)原位测量了PB膜电沉积过程的频率响应.研究表明,沉积液中添加邻菲咯啉对PB膜结构有影响.有邻菲咯啉参与沉积的PB Pt/QCM电极对H2O2的电催化还原性能优于不含邻菲咯啉沉积液制备的PB Pt/QCM电极.     

Solvation Dynamics of a Single Water Molecule Probed by Infrared Spectra—Theory Meets Experiment

The dynamics and energetics of water at interfaces or in biological systems plays a fundamental role in all solvation and biological phenomena in aqueous solution. In particular, the migration of water molecules is the first step that controls the overall process in the time domain. Experimentally, the dynamics of individual water molecules is nearly impossible to follow in solution, because signals from molecules in heterogeneous environments overlap. Although molecular dynamics simulations do not have this restriction, there is a lack of experimental data to validate the calculated dynamics. Here, we demonstrate a new strategy, in which the calculated dynamics are verified by measured time‐resolved infrared spectra. The coexistence of fast and slow migrations of water molecules around a CONH peptide linkage is revealed for a model system representative of a hydrate peptide.     

多肽中氢键强度的理论研究

用B3LYP/6-31G^*法优化了多肽分子的几何构型,计算了各个构型的电荷分布和氢键酸度,进而对多肽分子中的氢键强度进行了研究.结果表明,多肽分子中氢键的强度同时取决于形成氢键的H…O原子间距R和N-H…O之间的键角β;多肽分子倾向于形成R值小、β值大的大环氢键.3₁₀螺旋结构的多肽分子中的氢键具有协同效应,分子越大,分子中氢键越多,氢键的协同效应越强.     

水在纤维素水凝胶中的存在状态及对纤维素结晶的影响

制备了高度水合状态的纤维素凝胶, 研究了水在凝胶中的存在状态及其对纤维素结晶的影响. 结果表明, 水在纤维素水凝胶中存在非冻结水、 可冻结水和自由水3种状态. 非冻结水饱和含量为一般纤维素吸附水中不可冻结水的5倍以上, 高达1.6 g/g. 纤维素在水合状态下结晶受到抑制, 随着水含量的减小, 结晶会趋于完善. 在环境温度下, 当纤维素中只存在非冻结水时, 其与纤维素分子链间氢键作用力不稳定, 对纤维素结晶抑制作用较弱, 纤维素结晶比较完善, 导致纤维素断裂时表现为脆性断裂. 水介质的引入有望为纤维素的利用开发提供一种新的思路.     

Solvation of amides of carboxylic acids in aqueous solutions of ethylene glycol

Enthalpies of solution of amides of formic, acetic, and propionic acids with different degrees of N-substitution in aqueous solutions of ethylene glycol were measured at 298.15 K. The concentration of ethylene glycol did not exceed 4 mol kg^–1. The reasons for increasing endothermic values of the enthalpies characterizing the amide transfer from water to a mixed aqueous-organic solvent on going from primary to tertiary amides and from formamides to the corresponding acetamides are discussed. The enthalpic coefficients of pair interactions between amides and ethylene glycol in water were calculated. The endothermicity of the interaction of the alkyl groups of the amide molecules with ethylene glycol results in positive values of the coefficients. The coefficient values increase with the enhancement of the hydrophobic properties of hydrophilic non-electrolytes (urea, formamide, ethylene glycol) due to an increase in the contribution of the hydrophobic component and a decrease in the contribution from the interaction of the polar groups of amides to the total interaction.