Abstract: A comparative study between two ionic surfactants,namely sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB),for their interactions with bovine serum albumin (BSA) has been made by measurement of fluorescence,ultraviolet absorption,dynamic light scattering and Zeta potential.The results show that,both SDS and DTAB can quench the intrinsic fluorescence of BSA.The quenching constantsK_sv at 298 K are 2.64×10⁴ and 304.21 L/mol,respectively.Synchronous fluorescence spectra and three-dimensional fluorescence spectra show that SDS and DTAB have influences on the conformation of BSA.The fluorescence quenching of BSA by SDS occurs through a mixed static and dynamic quenching mechanism.The thermodynamic parameters reveal that the electrostatic force dominates in the formation of the SDS/BSA complex.DTAB can quench the intrinsic fluorescence of BSA by dynamic quenching,in which the hydrophobic force is dominating.The average binding distance of SDS and DTAB to BSA are calculated to be 2.77 and 4.73 nm.With the combination of results of binding constants,particle size and Zeta potential,it can be concluded that SDS with larger charge density and smaller polar headgroup has stronger binding to BSA under the same conditions.

Key words: ionic surfactant, bovine serum albumin, fluorescence quenching, comparative study