Interactions of anionic surfactants with poly(ethylene oxide) and bovine serum albumin polymers: effect of the counterion hydrophobicity

The interactions and properties of resulting complexes between poly(ethylene oxide) (PEO) and surfactants with different head groups, such as sulfates, carboxylate and phosphate has been investigated. Also investigated was the effect of counterion for PEO-dodecyl sulfate surfactants with lithium (LDS), sodium (SDS), cesium (CDS) and tetramethylammonium (TMADS). Special attention was given to the hydrophobic effect of the counterion TMA(+) on the binding. Studies were extended to bovine serum albumin (BSA)-dodecyl sulfate surfactant systems which were then compared with the conventional behavior of the PEO-SDS system. Electrical conductance measurements were used in order to characterize changes of parameters such as the critical aggregation concentration (cac), polymer saturation point (psp), degree of ionization and the amount of surfactant binding to polymer. The mean sizes of the aggregates were determined by the steady-state fluorescence quenching technique. The results are rationalized in terms of a mechanism of interaction which assumes that mean driving forces which, by exclusion of the others, must reside in the head group of surfactant and premicelles which always specifically coordinate with the polymer chain in those cases in which cac depression occurs. Evidence of the existence of premicelle was provided by following the effect of PEO concentration on the first-order rate constant-surfactant concentration profiles, in the presence of SDS, of acid-catalyzed hydrolysis of a moderated hydrophobic substrate, di-n-butyl benzaldehyde acetal. (C) 1999 Elsevier Science B.V. All rights reserved.