Teruyo Yamashita

Differential scanning calorimetric studies on bovine serum albumin IV. Effect of anionic surfactants with various lengths of hydrocarbon chain

Using defatted and SH-blocked bovine serum albumin (BSA), measurements of differential scanning calorimetry (DSC) have been made at pH 7 on the complexes of BSA and a series of sodium alkyl sulfates used were sodium decyl sulfate (SDeS), sodium octyl sulfate (SOS), sodium hexyl sulfate (SHS) and sodium ethyl sulfate (SES). Results obtained were compared with those on the system BSA-sodium dodecyl sulfate (SDS) studied previously. Two peaks P1 and P2 existed in the DSC curve of BSA. These peaks originate in the heat-induced transition of BSA. The pattern of DSC curve changed with the amount of the ligand added, i.e. with the molar mixing ratio ligand/BSA (1). The change for systems BSA-SDeS, BSA-SOS and BSA-SHS was qualitatively the same as that for the system BSA-SDS (2). Interestingly, SES, which is not a surfactant, interacts with BSA. The change for the system BSA-SES was qualitatively the same as that for the system BSA-Na2SO4. All alkyl sulfates suppressed the heat-induced transition at lower concentrations. A linear relationship was obtained for the plots of log(D/A)1 versus log CMC, where (D/A)1 is the molar mixing ratio of anionic surfactant (D) to BSA (A) at which the most heat-stable complex is formed. This suggests that the hydrophobic force has a serious effect on the formation of heat-stable complexes.

Cationic micellar effects on the kinetics of the protolysis of carboxylic acids

Abstract The kinetics of the protolysis of aromatic carboxylic acids solubilized in a micelle of dodecylpyridinium chloride has been studied by the ultrasonic relaxation absorption measurements. The rate constants are dependent on the acid dissociation constant K a and the results are interpreted by means of the Bronsted catalysis law. The micellar catalytic effect is discussed in comparison to those in the acid and base equilibria of carboxylic acids and amines in the micellar solutions. The volume change of the reaction is also found to be dependent on K a .

Micellar effect on the kinetics of the base equilibrium of amino acids studied by the ultrasonic absorption method

Ultrasonic relaxation absorption has been measured in aqueous solutions of amino acids (tryptophan, leucine, glycine, phenylalanine, asparagine) in the absence and in the presence of micelles of sodium dodecylsulphate. The relaxation absorption was ascribed to the base equilibrium of amino acids, and the rate constants, the base dissociation constant, and the volume change of the reaction were obtained. The smaller micellar catalytic effect for the base equilibrium of amino acids, compared to those of amines and ammonia was ascribed to the electrostatic effect of the carboxylate group. The reaction mechanism, including the interactions of amino acid and the SDS micelles, were discussed.