No abstract

The effect of the addition of short-chain monohydric alcohols (ethanol and propan-2-ol) to the protein:surfactant system lysozyme:sodium dodecyl sulfate (Lz:SDS) in aqueous solution was investigated using a conductometric technique. A second protein:surfactant system, bovine serum albumin:SDS (BSA:SDS) was also investigated so that the effect of a different protein conformation and composition could be compared. The critical aggregation concentration (CAC) of the protein forming the complex and the critical micelle concentration (CMC *) of SDS in the presence of protein, at different alcohol concentrations, were determined. It was found in both cases that the addition of alcohol does not produce a significant change in the CAC, whereas the CMC * displays variation with alcohol concentration that shows an inversion in the ranges 0.05-0.06 ethanol mole fraction and 0.02-0.03 propan-2-ol mole fraction. This suggests that, in contrast with the CAC behaviour, the major factor that drives SDS micellization in the presence of protein is the variation in water structure. Results also suggest that it occurs in the same way for both proteins, where electrostatic interactions are the main force in the formation of the complex. Conversely, hydrophobic interactions play the dominant role at the micellization stage, and only the extent of the interaction between protein:surfactant aggregates and surfactant species seems to depend on protein nature.

The structural and electronic features of the interaction between silica surfaces and surfactants have been studied with high level computational techniques of simulation. Calculations have been performed at the B3LYP level of theory as implemented in the CRYSTAL06 code. Each of the periodic models adopted consists of a conveniently functionalized (001) surface of edingtonite and a layer of tetrametilammonium and other species like water and Clthat mimic the interface between the silica and the surfactant solution moieties, in both acidic and basic media. Different degrees of coverage and hydration have also been considered. Our calculations indicate that besides the electrostatic interactions, polarization and charge-transfer processes play a nonnegligible role in the formation and stability of the silica surface.