Hydrogen bonding. Part 40. Factors that influence the distribution of solutes between water and sodium dodecylsulfate micelles
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 Kx, and the solute explanatory variables, or descriptors, are R2 the excess molar refraction, πH2 the dipolarity/polarizability, ∑αH2 and ∑βO2 the hydrogen-bond acidity and basicity, and Vx 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 Kx= 1.201 + 0.542 R2– 0.400 πH2– 0.133 ∑αH2– 1.580 ∑βO2+ 2.793 VX(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 Koct do not correlate well with log Kx for the 132 varied solutes, but that a double regression in log Koct and Vx is a useful equation for the estimation of log Kx values. log Kx= 1.129 + 0.504 log Koct+ 1.216 Vx(ii), n= 132, ρ= 0.9755, sd = 0.215, F= 1269.