The partitioning of alkanediols into SDS and DTAB micelles from NMR-PRE experiments

The p-values of a number of ,-alkanediols, 1,2-alkanediols, and 1,5-hexanediol and 2,5-hexanediol between D₂O and the micellar phases of anionic sodium dodecylsulfate (SDS) and cationic dodecyltrimethylammonium bromide (DTAB) have been determined using the using a NMR paramagnetic relaxation enhancement experiment (NMR-PRE). From the p-values, mole-fraction based partition coefficients and Gibbs energies of transfer for the alkanediols from the bulk D₂O phase to the micellar phase have been calculated. Differences in the partition coefficients of the ,-alkanediols and the 1,2-alkanediols are discussed in terms of the smaller Gibbs transfer energy per CH₂ group for ,-alkanediols. For the 1,5- and the 2,5-hexanediols, the p-values are substantially smaller than for the other hexanediols in both SDS and DTAB micelles. All of these results are consistent with the location of the two hydroxyl groups on the carbon backbone making a substantial contribution to the thermodynamics of transfer of solubilizates.