Hydrogen bonding. Part 41.1 Factors that influence the distribution of solutes between water and hexadecylpyridinium chloride micelles

Abstract

The partition of 46 compounds between water and hexadecylpyridinium chloride (CPC) micelles at 298 K has been correlated through eqn. (i), using the water–CPC partition coefficients of Christian and co-workers. These 46 compounds include cyclohexane, pentan-1-ol and 44 varied aromatic compounds. The water–CPC micelle partition coefficient is denoted as K(CPC), and the solute explanatory variables, or descriptors, are R₂ the excess molar refraction, π₂^H the dipolarity/polarizability, Σα₂^H and Σβ₂^O the hydrogen-bond acidity and basicity, and V_x the McGowan characteristic volume in units of (cm³ mol^-1)/100. The number of solutes is n, the correlation coefficient is r, the standard deviation is sd, and the F-statistic is F. The main factors that influence partition are solute hydrogen-bond basicity that reduces partition into the CPC micelles, and solute volume that increases partition. It can be deduced from eqn. (i) that CPC micelles behave as though they are highly polar, of very high hydrogen-bond basicity and of moderate hydrogen-bond acidity and hydrophobicity. Comparison with water–alcohol partitions indicates that CPC micelles are as hydrophobic as water-saturated pentanol. Analysis of log K values for water to CPC and to sodium dodecyl sulfate (SDS) micelles, using scaled particle theory, shows that the main factor leading to larger log K values in the CPC system is an increase in dispersion interactions between solute and the CPC pseudophase.The coefficients in eqn. (i) are the same in sign and similar in magnitude to those previously reported by Quina and co-workers for partition between water and hexadecyltrimethylammonium bromide micelles and for partition between water and dodecyltrimethylammonium bromide micelles.