Rheological and Molecular Dynamics Simulation Studies of the Gelation of Human Serum Albumin in Anionic and Cationic Surfactants

Abstract

Abstract We report the gelation of human serum albumin (HSA) of 5–12 wt.% concentrations in 0–0.15 M aqueous solutions of a cationic surfactant, cetyltrimethylammonium bromide (CTAB), or an anionic surfactant, sodium dodecyl sulfate (SDS), under isothermal and nonisothermal conditions. Under both conditions, the initial increase in the CTAB concentration (up to 0.075 M) accelerated HSA gelation (marked by decreasing gel times (tgel) for the isothermal case or gel temperatures (Tgel) for the nonisothermal case), whereas increasing the SDS concentration inhibited HSA gelation (i.e., increasing tgel or Tgel). The increase and decrease in HSA gelation by CTAB and SDS, respectively, reached a maximum at a surfactant/protein molar ratio of 100. Rheological properties, i.e., storage modulus (G’) and loss modulus (G’’), exhibited mechanically stable behavior of HSA/CTAB gels over the covered concentration range, whereas HSA/SDS gels exhibited decreasing mechanical properties with increasing SDS concentrations. Molecular dynamics simulation showed that the greater rate of the unfolding of the HSA structure in CTAB than in SDS was behind the rapid gelation kinetics of HSA in CTAB compared with SDS. Our result establishes that cationic CTAB and anionic SDS surfactants exert wide-ranging control over the rheological and kinetic properties of HSA hydrogels.