The effect of dodecyl trimethylammonium bromide on the formation of methemoglobins and hemichrome

Abstract

The interaction of n-dodecyl trimethylammonium bromide (DTAB), a cationic surfactant, with human and greylag goose ( Anser anser) hemoglobins (Hbs) has been studied using various methods, such as a potentiometric technique using a DTAB-selective membrane electrode, UV–Vis spectrophotometry in the absence and the presence of 100 mM NaCl, isothermal titration microcalorimetry at buffer condition of 50 mM Tris, pH 7.2 and 1 mM EDTA. Binding isotherms were obtained from the potentiometric technique and using the Wyman binding potential model, apparent binding constants were calculated. Thermodynamic parameters were obtained for two sets of binding sites from the Hill equation. Binding of DTAB molecules induced the unfolding of hemoglobin accompanied with exposure of the heme pocket and facilitating the oxidation of heme. The concentration of metHb increases and oxyHb and deoxyHb decrease due to the interaction of DTAB–Hb complexes. Increasing the temperature and ionic strength, in the presence of DTAB, increases the autoxidation of oxyhemoglobin. The met process is enhanced by electrostatic contributions induced by the initial ionic binding and subsequently the hemichrome is increased by the hydrophobic effect that is induced by a second set of DTAB binding sites.