Optical studies of the soret effect. Part IV. Entropies and heat capacities of transfer of solutions of sarcosine, dimethylglycine and betaine and their relation to solvent–solute interactions

Abstract

Soret coefficients for aqueous solutions of isoelectric sarcosine, dimethylglycine and betaine have been measured over concentration ranges from about 0·1 molal upwards at mean temperatures of 25 and 35°. Entropies and heat capacities of transfer have been calculated and the results discussed in relation to other physical data on these and related solutions. In spite of its highly polar nature betaine, unlike other amino-acids, has a negative heat capacity of transfer which is attributed to a combination of the loss of solvation sites as –NH₃⁺ is replaced by–NMe₃⁺ and to ‘structure-building’ in the solvent by the N-methyl groups.