Hydrogen bonding. Part 40. Factors that influence the distribution of solutes between water and sodium dodecylsulfate micelles

Abstract

The partition of 132 assorted compounds between water and sodium dodecyl sulfate (SDS) micelles at 298 K has been correlated through eqn. (i). The mol fraction water–SDS micelle partition coefficient is denoted as K_x, and the solute explanatory variables, or descriptors, are R₂ the excess molar refraction, π^H₂ the dipolarity/polarizability, ∑α^H₂ and ∑β^O₂ the hydrogen-bond acidity and basicity, and V_x the McGowan characteristic volume. The number of solutes is denoted as n, the correlation coefficient as ρ, the standard deviation as sd, and the F-statistic as F. log K_x= 1.201 + 0.542 R₂– 0.400 π^H₂– 0.133 ∑α^H₂– 1.580 ∑β^O₂+ 2.793 V_X(i), n= 132, ρ= 0.9849, sd = 0.171, F= 817.

The two main factors that influence partition are solute hydrogen-bond basicity that reduces partition into micelles, and solute volume that increases partition. It may be deduced from eqn. (i) that SDS micelles behave as though they are highly polar, of quite high hydrogen-bond acidity (although not as high as water) and of about the same hydrogen-bond basicity as water. Comparison with water–alcohol partitions indicates that SDS micelles are as hydrophobic as water-saturated isobutanol. It is also shown that water–octanol partition coefficients, as log K_oct do not correlate well with log K_x for the 132 varied solutes, but that a double regression in log K_oct and V_x is a useful equation for the estimation of log K_x values. log K_x= 1.129 + 0.504 log K_oct+ 1.216 V_x(ii), n= 132, ρ= 0.9755, sd = 0.215, F= 1269.