Apparent Molal Volumes and Heat Capacities of Some Tetraalkylammonium Bromides, Alkyltrimethylammonium Bromides, and Alkali Halides in Aqueous Glycerol Solutions

Abstract

The densities and volumetric specific heats of some tetraalkylammonium bromides, alkyltrimethylammonium bromides, and some alkali halides (0.02 to 0.5 aquamolal) were measured in 0 to 30 wt.% glycerol in water with a flow densimeter connected in series with a flow microcalorimeter at 24 and 25 °C respectively. The derived volumes and heat capacities of transfer of the electrolytes from water to glycerol–water mixtures are consistent with the corresponding transfer functions from water to D2O and from water to urea–water mixtures, and suggest that structural interactions are reduced in aqueous glycerol solutions. The volumes and heat capacities of micellisation of n-nonyltrimethylammonium bromide were determined in water, glycerol–water mixtures, urea–water mixtures, and in D2O. Both the transfer and the micellisation study indicate that glycerol behaves in an analogous manner to urea. An effect other than a simple alteration of the water structure must be invoked to account for their different effects on protein stability.