Ion association and ultrasonic relaxation in hydrogen-bonding solvents: 1:1 Electrolytes in 2-propanol at 25°C

Ultrasonic absorption measurements have been carried out in aqueous solutions of Bu₄NCl, Bu₄NBr, Bu₄NI, Me₄NCl, and LiCl in 2-propanol over the frequency range 15–250 MHz. A single relaxation frequency was observed for each system. All the data were found to be consistent with a 2-step association mechanism in which the rate-determining step was the diffusion of the ions to form a solventseparated ion pair, followed by rapid desolvation to form the contact ion pair. Measured association rate constants were very nearly those predicted for a diffusion-controlled process.     

Simultaneous diffusion of ions and ion pairs across liquid membranes

The flux of tetrabutylammonium nitrate (Bu₄ NNO₃) across a liquid membrane of n-heptyl cyanide varies with the salt concentrations in dilute solution, but with the concentration squared in more concentrated solution. The results are consistent with a mechanism which includes parallel diffusion of ions and ion pairs. This type of behavior, which will be common in homogeneous membranes of low dielectric constant, is a form of facilitated diffusion in which the salt acts as its own carrier.     

有机硅活性中间体的研究 II. 一些含环丙基的有机硅化合物的合成及其结构

用锂有机物的方法合成了四种含有环丙基有机硅化合物,对上述每种化合物中可能存在着的立体异构进行了分离和和构型测定。     

Photometric titration of small quantities of metals with ethylenediaminetetra-acetic acid

A commercially available photometric titration apparatus has been used for the determination ofAl, Ba, Bi, Ca, Cd, Co, Mg, Mn, Ni and Zn in the 4-20 mug range and of Hg in the 16-32 mug range. Pooled standard deviations (32 determinations) of between 0.09 and 0.15 mug were found for all the metals except Ba (0.20 mug) and Hg (0.44 mug, 24 determinations).     

Predicting water-to-cyclohexane partitioning of the SAMPL5 molecules using dielectric balancing of force fields

Alchemical transformation of solutes using classical fixed-charge force fields is a popular strategy for assessing the free energy of transfer in different environments. Accurate estimations of transfer between phases with significantly different polarities can be difficult because of the static nature of the force fields. Here, we report on an application of such calculations in the SAMPL5 experiment that also involves an effort in balancing solute and solvent interactions via their expected static dielectric constants. This strategy performs well with respect to predictive accuracy and correlation with unknown experimental values. We follow this by performing a series of retrospective investigations which highlight the potential importance of proper balancing in these systems, and we use a null hypothesis analysis to explore potential biases in the comparisons with experiment. The collective findings indicate that considerations of force field compatibility through dielectric behavior is a potential strategy for future improvements in transfer processes between disparate environments.     

Diffusion of symmetrical and spherical solutes in protic,aprotic, and hydrocarbon solvents

The diffusion coefficients of a series of symmetrical tetraalkyltins (tetramethyltin, tetraethyltin, tetrapropyltin, tetrabutyltin, tetradodecyltin) of the gases argon, krypton, xenon, methane, and tetramethylmethane and of carbon tetrachloride and tetraethylmethane in hexane, decane, and tetradecane at 25°C have been determined using the Taylor dispersion technique. Diffusion coefficients for the gases in acetone, 2-propanol, 1-butanol, and 1-octanol were also determined. Deviations from the predictions of Stokes' law were found to be large, and the magnitude of the deviation can be directly related to solute size. The predictions of the Hubbard-Onsager equation were tested using the diffusion data.     

Ionic association in hydrogen-bonding solvents

Studies on ionic association in hydrogen-bonding solvents including water, aliphatic alcohols, fluorinated alcohols, formamide, ethylene glycol, and propanol-acetone mixtures are compared. Data were derived from measurements of conductivity, ultrasonic absorption, and viscosity of electrolyte solutions and diffusion of nonelectrolytes. It is concluded that electrolyte solvents can be divided into three categories according to whether they solvate effectively cations only, anions only, or both cations and anions. Water and most other hydrogenbonding solvents constitute the third class, a group in which patterns of ionic aggregation are very similar. Fluorinated alcohols belong to the second class, showing significantly different ion-pairing behavior.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

The conductance of bile salt-lecithin-water mixtures

The conductance of aqueous solutions of sodium glycodeoxycholate and sodium taurodeoxycholate displays a complex concentration dependence (0–0.5 C) with a maximum and minimum occurring in dilute solutions. This behavior can be related to physiologic concentrations observed in hepatic and gallbladder bile and interpreted in terms of anion dimerization and ultimately micellization. The addition of lecithin in 1:2 or 1:5 molar ratios results in micellization at lower concentration, disappearance of the maximum and minimum in the conductance curve, and a decrease in the total conductance.     

Submicro determination of cobalt, manganese or nickel in organometallic compounds

Methods for the determination of cobalt, manganese or nickel in samples of organometallic compounds weighing 30-100 mug have been developed. Spectrophotometric determination following digestion with nitric and sulphuric acids in a sealed tube is recommended, all results obtained from the analysis of standard compounds being within +/-0.4% absolute error. Digestion in an open tube with perchloric and sulphuric acids gives slightly low results for cobalt and nickel compounds and is inappropriate for manganese compounds.