Solvent effect on the synthesis of monodisperse amine-capped Au nanoparticles

A remarkable solvent effect in a single-phase synthesis of monodisperse amine-capped Au nanoparticles is demonstrated.Oleylamine-capped Au nanoparticles were prepared via the reduction of HAuCU by an amine-borane complex in the presence of oleylamine in an organic solvent.When linear or planar hydrocarbon(e.g.,n-hexane,n-octane,1-octadecylene,benzene,and toluene) was used as the solvent, high-quality monodisperse Au nanoparticles with tunable sizes were obtained.However,Au nanoparticles with poor size dispersity were obtained when tetralin,chloroform or cyclohexane was used as the solvent.The revealed solvent effect allows the controlled synthesis of monodisperse Au nanoparticles with tunable size of 3-10 nm.     

A study of solvent effects on the stereoselectivity of Diels-Alder reactions through molecular surface electrostatic potentials

Statistical models for the study of solvent effects on the endo/exo selectivity of Diels-Alder reactions using molecular surface electrostatic potentials was obtained. The models show that hydrogen bond interactions of solvent molecules favor the predominance of the endo isomer for the reaction of methyl acrylate, methyl methacrylate and methyl trans-crotonate with cyclopentadiene whereas the effect of solvophobicity seems to be negligible.     

Determination of hydrogen ion activity in various binary dimethylformamide/water and ternary dimethylformamide/dioxane/water solvent systems

The practical pH values in dimethylformamide/water and dimethylformamide/dioxane/water solvent mixtures measured by a pH meter standardized against aqueous buffer solutions do not lie on the conventional scale of hydrogen ion activity referred to the standard state in the corresponding medium (pa^*_H). The values can be converted to pa^*_H by introducing a correction term δ. Values of δ were determined at 25°C. Simple interpolation equations are derived to express the variation of δ with solvent composition. In the ternary mixtures, the results show that the composite medium effect, described by a parameter b=dδ/du, (where u depends on the solvent composition), depends on the ratio of the organic solvent concentrations.     

Dilute solution behaviour of progressively hydrolyzed polyacrylamide in water-N, N dimethylformamide mixtures

The intrinsic viscosities [η’s] of anionic (hydrolyzed; low and high carboxyl content) and nonionic polyacrylamide (unhydrolyzed) were measured in water-N, N dimethylformamide mixtures at various temperatures. Non-polyelectrolyte behavior of low carboxyl content polyacrylamide was observed in mixed solvent system. The plots of [η] vs. solvent composition in a mixed solvent system pass through minima for both high as well as low carboxyl content polymers but through a maximum for nonionic polyacrylamide. Observed minimum for charged polymers may be attributed to the loss of polymer sites available to interact with solvent for H-bonding interaction between neighboring amide and the acid groups. The maximum for nonionic polymer at the particular solvent composition arises for the most powerful cosolvent effect. Existence of two antagonistic effects is apparent in [η] values of nonionic polymer at various temperatures. Huggins constant (K_H) also indicates a significant variation of cosolvency as a function of solvent composition. Activation parameters of viscous flow were calculated using Frenkel-Eyring equation. The volume related parameter and the shape factor were also computed. Shape factor data indicate that polymer molecules are more or less rigid spheres and are not affected by temperature and composition of solvent.     

Effect of solvent on chain propagation and termination reaction rates in radical polymerization

The radical polymerizations of acrylamide and methacrylamide and of acrylic, methacrylic and fluoroacrylic acids have been studied in various solvents. The nature of the solvent affects the overall rate due to changes in k_p and E_p. It has been shown that the effect of solvent also depends on the nature of the monomer. A possible explanation of the observed behaviour is discussed.     

Prediction and experimental verification of the salt effect on the vapour–liquid equilibrium of water–ethanol–2-propanol mixture

Experimental vapour–liquid equilibria of water–ethanol–2-propanol saturated with NaNO₃, NaCl, KCl and containing 0.05 mol CH₃COOK/mol total solvent compared well with those predicted by Tan–Wilson and Tan–non-random two liquid (NRTL) models for multicomponent solvent–solute mixture using a set of solvent–solvent interaction parameters obtained from the regression of the vapour–liquid equilibrium of the solvent mixture without the dissolved solute and a set of solute–solvent interaction parameters calculated from the bubble points of the individual solvent components saturated or containing the same molar ratio of solute/total solvents as the mixture. The results also showed that a solvent component i is salted-in or out of the liquid phase relatively more than solvent component j would depend on whether A_sj/A_si (Tan–Wilson model) or exp(τ_is−τ_js) (Tan–NRTL model) is less or greater than 1. This is consistent with earlier publications on the effect of dissolved solutes (electrolytes and non-electrolytes) on the binary solvents mixtures. These findings confirmed that Tan–Wilson and Tan–NRTL models for multicomponent solvent–solute system can provide an accurate and rapid screening of electrolytes and non-electrolytes for their suitability in facilitating solvent separation by salt distillation of ternary solvent mixtures simply by determining the relative ratios of the solute–solvent interaction parameters from the respective bubble points of the solvent components containing the dissolved solute. The results also suggest that this may also be extended to other multicomponent solvent mixtures.     

Effect of total degree of substitution on molecular parameters of cellulose acetate

An attempt was made to establish for cellulose acetate (CA) the relationship between the molecular properties, the total degree of substitution 〈〈F〉〉 and the degree of solvation. For this purpose, the comprehensive solution data for CA with 〈〈F〉〉 = 0.49-2.92 in previous papers were analyzed. In addition, the strength of the solvation was estimated from the chemical shift of O-acetyl- and hydroxyl-protons in NMR spectra and the number of the solvated solvent molecules at infinite dilution (s_o) was determined from the adiabatic compressibility. The strength of solvation and s_o increased with the dielectric constant ? of the solvent. The close correlation between s_o, the unperturbed chain dimension A and the free draining effect was demonstrated; these three quantities and the exponent a in the Mark-Houwink-Sakurada equation attained their maximum at $\text{〈〈F〉〉 ? 2.5}$, if CA is dissolved in dimethylacetamide. The characteristic variation of the chain rigidity, estimated from A, and of the draining effect with ? of the solvent and 〈〈F〉〉 can be reasonably explained by the solvation. The cellulose molecule dissolved in a hypothetical non-polar (? = 1) solvent was shown to be a freely rotating chain, by duplicated extrapolation A for CA to 〈〈F〉〉 = 0 and to ? = 1.     

Protolytic properties of lignin in binary mixtures of water with aprotic solvents

Acid dissociation constants for three main types of phenol structural fragments of lignin in binary mixtures of water with N,N-dymethylformamide, dimethyl sulfoxide, and 1,4-dioxane were determined by spectrophotometric potentiometric titration. The effect of solvent on lignin protolytic properties was examined on the basis of the Kamlet-Taft principle of linear relationship of free solvation energies. It was found that nonspecific interactions with solvent make the dominating contribution to the effect of the medium.     

Influence of van der Waals interactions on volumetric properties of cholesterol in solvents of linear structure

The densities of solutions of cholesterol in several primary amines and 1-chloroalkanes have been measured at T=298.15 K. The values of partial molar volumes of cholesterol have been calculated and the effect of solute–solvent and solvent–solvent interactions on the partial molar volume of cholesterol have been discussed. For the solvents studied the increase of alkyl chain length enhances the dispersion solvent–solvent interactions and weakens (per one cholesterol molecule) the contribution of dispersion forces in the solute–solvent interactions. Both effects bring about an increase in the partial molar volume of cholesterol with increasing the alkyl chain length. The relation between interaction volume of cholesterol (s.p.t. calculation) and the alkyl chain length have been also discussed.     

The enthalpies of formation of copper(II) complexes with nicotinamide in aqueous ethanol and DMSO

The enthalpies of complex formation between nicotinamide and copper(II) perchlorate in aqueous ethanol and dimethylsulfoxide (DMSO) were determined calorimetrically. The maximum exothermic effect was observed in a solvent with ～0.1 mole fractions of DMSO. The exothermic effect of complex formation increased as the concentration of ethanol grew. The role played by solvation in the thermodynamic characteristics of monoligand complex formation was considered. The influence of solvent composition on Δ_r H ^o was largely related to the resolvation of the ligand donor atom.     

Solvent effect on regioselectivity of epoxide ring opening in styrene oxide by O- and N-nucleophiles in neutral and basic media

The results of ring opening in styrene oxide by alcohols, amines, amino alcohols, and diamines were generalized. On low polarizing ability of the solvent, the main direction of the process is the formation of normal α-substituted products. The solvent effect on regioselectivity of the reaction was studied for N,N-diethylethylenediamine. The ratio of products correlates well with the value of dielectric constant for mixed aqueous-organic solvents and with the parameters of polarity E _T and AN for neat solvents.     

Solvent effect on electron transfer reactions: Comparison of homogeneous and heterogeneous electron exchange between V3+ and V2+ in water +t-butanol mixtures

The kinetics of homogeneous and heterogeneous electron exchange V³⁺/V²⁺ was investigated in 1 M HClO₄, water +t-butanol, mixed solvent solutions (x_t-but. varied from 0 to 0.65). Non-monotonic heterogeneous and monotonic homogeneous variations of the rate constants were observed. The solvent effect on the work of bringing the reactants from infinite separation to the reaction site was estimated with the Gouy-Chapman and Debye-Hückel approximations respectively. The homogeneous kinetics data were next used to calculate the reorganization energy in the heterogeneous reaction, λ_het. Finally the influence of the solvent composition on the rate of the electrode reaction was separated into surface and bulk effects.     

The solvent effect on the reaction constants of tert-butyl radical addition to 2-substituted allyl chlorides

The ρ values of free radical S_H2′ reactions have been determined in various solvents. The correlation of Hammett ρ with Taft's π* gives a W value of 0.70. The W value is a measure of susceptibility of the reaction constant to change in solvent polarity. However, the W value is 2.64 in the dissociation reactions of substituted benzoic acids. The free radical reactions are less susceptible to the solvent effect than ionic reactions and this could be rationalized in terms of the partial charge formed in the transition state of free radical reaction is less than that of heterolytic reaction. The ρ values in S_H2′ reactions might not reflect truly the partial charge separation at transition state, however, it might be a measure of the susceptibility of the reaction to the electronic effect of the substituents.     

Enthalpic and entropic contributions to substituent effects for the ionization of meta- and para-nitrobenzoic acids in water-dimethylsulphoxide mixtures at 25°C

Enthalpic and entropic contributions to substituent effects for the ionization of m-and p-nitrobenzoic acids are examined, ranging from pure water to 0.8 mole fraction DMSO. The effect of the medium on the substituent and reaction constants is explained in terms of solute—solvent interactions. No structure-breaking effect was found.     

Solvent effect on stretching vibration frequencies of the N-H and O-H groups of diphenylamine and phenol in complexes with various proton acceptors: Cooperative effect

Solvent effect on the stretching vibration frequencies of the O-H and N-H groups in complexes of phenol and diphenylamine with bases in aprotic and proton-donor solvents was studied by IR spectroscopy. Linear correlations of high quality were obtained between the frequencies of hydrogen-bonded O-H and N-H groups in these complexes in aprotic solvents and a new solvent parameter, S _VW. The cooperative effect of a proton-donor solvent on the strength of hydrogen bonds in complexes of phenol and diphenylamine with bases was evaluated. It was demonstrated for the first time that the cooperative effect in the examined systems can lead to both strengthening and weakening of hydrogen bonds.     

Stereoselective glycosylation using the long-range effect of a [2-(4-phenylbenzyl)oxycarbonyl]benzoyl group

Highly α-selective glucosylation was effected by virtue of the solvent effect of cyclopentyl methyl ether and the long-range assistance of bulky 6-O-protective groups. Higher α-selectivity was obtained by the use of this solvent in comparison to conventional diethyl ether. α-Selectivity was further improved with the influence of 6-O-substituents, such as TBDPS and phthaloyl groups, the latter being mono esterified with a bulky alcohol.     

The impact of the cononsolvency effect on poly (N-isopropylacrylamide) based microgels at interfaces

The paper addresses the effect of solid interfaces on the cononsolvency effect for poly(N-iso propylacrylamide) based microgels containing different contents of the co-monomer allyl acetic acid (AAA). The cononsolvency effect is studied by dynamic light scattering (DLS) in solution and with atomic force microscopy (AFM) at surfaces against different mixtures of water and organic solvent (ethanol, iso-propanol, and tetrahydrofuran). For the studies at interfaces, the microgels are spin coated on silicon wafers that are precoated with poly(allylamine hydrochloride) (PAH). The minimum in particle volume due to cononsolvency shows a pronounced shift from 10–20 % of organic solvent to 40–50 % after deposition at the Si/PAH wafer. The strong shift indicates an increase of water to organic solvent ratio within the gel at the surface with respect to the bulk solution. In order to understand the increase of water to organic solvent ratio, shrinking/reswelling AFM experiments for different spin-coating conditions and under ambient conditions are carried out. Spin coating from water instead from different solvent mixtures has no effect on the cononsolvency. In ambient conditions, the cononsolvency effect disappears     

Effect of the distance moved by the solvent on the rf values in circular chromatography

1. The effect of the distance travelled by the solvent on the R_F values of the amino acids subjected to circular paper chromatography has been studied under various conditions with two solvents: (i) Phenol-water, which is less volatile and (ii) butanol-acetic acid-water which is more volatile. The R_F values with both the solvents are almost independent of the distance travelled by the solvent. It is essential in all these experiments to control perfect saturation inside the chamber in order to get reproducible R_F values. 2. The increase in R_F values reported by RAO and GIRI¹ with distance of travel of the solvent appears to be clue to lack of necessary saturation inside the chamber. The same defect seems to liave vitiated the experiments of rao and BERI⁶ wlio also reported very high R_F values. 3. Butanol-acetic acid-water of the composition 4 : 1 : 1⁹ is suggested as a good solvent for practical purposes.     

Molecular complexes of several aromatic hydrocarbon-ketone systems

The association constants (K_AD) between several aromatic hydrocarbons and several ketones were determined by a NMR spectrometric method in carbon tetrachloride as a solvent. Thermodynamic parameters for the formation of complexes for benzene-acetone and benzene-actophenone are also reported. The effect of competing complexation with the solvent is discussed. A new equation, which was derived without assuming that the concentration of one solute is far greater than that of the other, was used for the computation of the K_AD-values.