Thermodynamic Analysis of the Nonspecific Interaction of Sodium Dodecyl Sulfate with Swollen Bio-Gel Beads

Abstract

In frontal gel chromatography on Bio-Gel P-2, sodium dodecyl sulfate (SDS) at the concentrations below its critical micelle concentration (cmc) showed anomalously high partition coeffics (K^obs_av) indicative of strong interactions with the swollem gel phase; further, K^obs_av was found to increase with concentration and temperature. This preferential partition of SDS in the Bio-Gel phase was analyzed in analyzed in terms of the transfer free energy of SDS from the mobile phase (0.1M NaCl) to the swollen Bio-Gel phase. The results showed that the overall transfer process is promarily governed by hydrophobic free energy arising from the anomalous nature of hydrated water in the gel matrix; that is, in highly hydrated water “iceberg” formation is evidently limited and the hydrophobic free energy is accordingly lowered, resulting in the preferential patition of SDS in the swollen Bio-Gel phase. The increase in the negativity of transfer free energy with concentration, though relatively small, indicated a definite tendency for the formation of SDS clusters in the gel phase. Finally, a model illustrating the states of SDS molecules in the gel matrix is preseented, which may also be pertinent to SDS-protein and SDS-amylose complexes.