Is choline kosmotrope or chaotrope?

Abstract

Abstract Several well-known criteria and techniques such as B coefficient obtained from Jones-Dole’s equation, structural entropy, volumetric quantities, Hepler’s coefficient or structural volume of the ions, can be used to explain water structuring and nature of interactions in aqueous solutions of any studied substance. However, for certain substances, these parameters give opposite results and classification into structure makers or structure breaker is not so simple. In this paper, the biologically significant nutrient, choline cation (Ch+) has been studied to explain the interactions with water and reliable classification in kosmotropic or chaotropic compounds based on measured physicochemical properties and computer simulations. These properties and nature of the interactions in aqueous choline chloride (ChCl) as widely used food additive have been investigated measuring density and viscosity in the temperature range from T = (293.15 to 313.15) K at atmospheric pressure (p = 1·105 Pa) in the molality range from m = (0.0850 to 0.4990) mol·kg−1 and m = (0.0107 to 0.4990) mol·kg−1, respectively. Also, molecular dynamics (MD) and radial distribution functions (RDFs) have been applied to investigate water structuring in the studied system. The effect of ChCl on the structural organisation of water was studied through apparent molar volumes, partial molar volumes, viscosity B-coefficients and hydration number of ChCl and choline. The structural entropy and entropy of solvation for Ch+ ion was calculated. It was found that hydroxyl group of choline has a negligible contribution to its structure making/breaking properties in water.