Low Molecular Weight Salts Research Articles

The reactivities of the oxime groups in 4-vinyl- and 2-methyl-5-vinylpyridine copolymers with their n-phenacyloxime derivatives

The acylation kinetics of the oxime group present in poly-4-vinylpyridine and poly-2-methyl-5-vinylpyridine partly quaternized with bromophenacyloxime have been studied. A considerable increase in the nucleophilicity of the oxime groups present in the copolymers has been detected when they were compared with the respective low molecular weight analogues; it was accompanied by an anomalous p K a reduction. We also show that the rate constant for acylation decreases in the copolymers with the quaternization efficiency of the polymer; in contrast with the low molecular weight analogues it also strongly and exclusively depends on the concentration of various low molecular weight salts present in the reaction mixture. All these effects are due to a large extent to the influence of the micro-environment and the electrostatic reaction of the pyridine, having a positive charge with the oxime with its negative charge.

Phénomènes de transport dans les solutions de polyélectrolytes—I. Formulation de Lois limites

On the basis of non-equilibrium thermodynamic principles a description of electrical and mass transport in polyelectrolyte solutions is given. Transport parameters are expressed in terms of frictional coefficients. Attention is paid in the theory to limiting laws when an excess of low-molecular weight salt is present. The frictional coefficients and transport parameters are evaluated for three polyelectrolyte with a linear charge density. It is conclusively demons- trated that the polyion-ionic atmosphere interactions play a major role and it is not possible to neglect the charge effects even at a high salt concentration; most of the computed transport parameters depend in a complex manner on both electrical and hydrodynamic properties of all ionic components of the solution.

The effect of season of growth on the chemical composition of cambial saps of Eucalyptus regnans trees.

Bark was stripped, at monthly intervals, from the stems of ten previously-unsampled trees of Eucalyptus regnans F. Muell. The exposed surfaces of inner phloem and outer xylem yielded phloem and cambial saps which were rapidly frozen. After freeze drying to determine the contents of water and dry-matter, the samples were extracted with 80% ethanol. The main components in this extract are low molecular weight carbohydrates and salts of inorganic acids. The carbohydrates comprise stachyose, raffinose, sucrose, galactinol, glucose, fructose, myo-inositol and galactose; sucrose is invariably the major component. The amounts of all components varied widely during the sampling period. Multiple regression analyses showed that season of growth has a significant effect on sucrose, glucose, fructose, total sugars and soluble dry-matter, maxima being recorded near the beginning of autumn and spring, and minima near the beginning of winter and summer; that oligosaccharide and myoinositol contents are significantly related to atmospheric temperature; and that rainfall has a significant effect on the hexose and total sugar contents, saps from the xylem surfaces being more affected than those from the phloem surfaces. The translocated photosynthates in E. regnans appear to be oligosaccharides of the raffinose family and sucrose. Significant negative correlations between oligosaccharides and both sucrose and myoinositol, and significant positive correlations between sucrose and both glucose and fructose, are consistent with enzymic hydrolysis and resynthesis of most di- and oligosaccharides. The biosynthetic demands of developing secondary tissues and/or the fluctuations in composition of sieve-tube assimilates appear to control the composition of the sugars in the saps. Oligosaccharides and sucrose may function as soluble reserve substances as well as translocated photosynthates. It is possible that myoinositolis a key component in the interconversion processes of the sugars; experiments with radioactive sugars tend to lend support to this contention, especially during winter conditions.

Scattering of light by charged colloidal particles in salt solutions

In the interpretation of light scattering by colloidal electrolytes in salt solutions the interaction between the colloidal particles and the low molecular weight ions has to be taken into account. When fluctuation theory is applied for the derivation of a light-scattering equation, nonelectroneutral fluctuations may be neglected in most cases. The total light scattering can be split into three contributions, one due to density fluctuations, one due to concentration fluctuations in the low molecular weight components, and one due to the colloidal particles. In the last-named contribution the (usually negative) adsorption of the low molecular weight salts by the colloid is included. This can be taken into account in good approximation by using in the light-scattering equations the refractive index increment at constant chemical potential and not at constant concentrations of the other components of the system. This quantity can be measured directly in membrane equilibria or it can be calculated from concentration differences in a membrane equilibrium combined with the more usual refractive index increments at constant concentrations. The theoretical treatment is confirmed by measurements of light scattering and membrane equilibria with half-neutralized polymethacrylic acid in 0.1 M sodium halide solutions and in a few other salts. The correction on the molecular weight varies from 10% in NaF to 25% in NaI and amounts even to 45% in 0.01 M (NH 4) 6Mo 7O 24.