Systematic study of the interactions of ionic surfactants with protein trypsin in buffer solution pH 3.5, 7.0 and 9.0, ionic strength 10 mM at 298 K was done using the microcalorimetric technique. In this study, anionic surfactant solutions of the sodium n-alkyl sulfates series (C8, C10, C12 and C14) were used. The enthalpy of interaction (ΔintHº) shows that the interaction of the surfactants C8, C10, C12 and C14 with trypsin in the solution pH 3.5 is an endothermic process with the value of ΔintHº decreasing linearly with increasing carbon chain length, which is attributed to the unfolding of the polypeptide chain. In the solution pH 7.0, we observed the same trend except for C14. In the solution pH 9.0, from C10 the enthapy of interaction didn't change with the increasing of the carbon chain length due to unfolding of the polypeptide. We concluded that when trypsin is folded, the enthalpy of interaction shows a linear relationship with the surfactant's hydrophobicity, in agreement with Traube's rule.
surfactants; protein; microcalorimetry
