Physico-chemical studies of oppositely charged protein–surfactant system in aqueous solutions: Sodium dodecyl sulphate (SDS)–lysozyme

Sound velocities (v) and densities (d) of sodium dodecyl sulphate (SDS) in various aqueous solutions of lysozyme have been measured over a temperature range of 25–40 °C. The data was used to calculate apparent molar volume (ϕv) and apparent molar adiabatic compressibility (ϕk). These parameters have been examined as a function of surfactant concentration, lysozyme concentration and temperature to understand the consequences of interactions between these two components. Surface tension (γ) measurements were also carried out for the same systems using Man Singh Survismeter. The surface tension data have been used further to calculate the interfacial parameters like, maximum surface excess concentration (Γmax), minimum area per molecule (Amin), standard free energy of adsorption (ΔGad°), surface pressure at CMC (Πcmc) and standard free energy of transfer (ΔGtr°), that have direct bearing on the consequences of such interactions at the molecular level. The work has been extended to include UV-studies for different SDS–lysozyme solutions. A reasonably good qualitative correlation is found to exist with regard to the surfactant–lysozyme interaction obtained from the experimental data, from different techniques.

► v and d of SDS in various aqueous solutions of lysozyme have been measured.
► γ measurements were carried out for the same systems using Man Singh Survismeter.
► ϕv, ϕk and interfacial parameters have been evaluated.
► Studies reveal the formation of charged complex between SDS and lysozyme.
► Lysozyme undergo reasonable conformational change in the presence of SDS.