Effect of Furosemide on denaturation of lysozyme in the presence of ionic surfactant at different temperatures

The thermodynamics of Furosemide–lysozyme interaction has been studied using conductivity in combination with viscosity, density and speed of sound measurements. Lysozyme binds preferentially with Furosemide in the presence of surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB). A number of physico-chemical parameters viz. critical micelle concentration (CMC), standard enthalpy of micellization ( Δ H m ° ) , standard entropy of micellization ( Δ S m ° ) , standard free energy of micellization ( Δ G m ° ) , apparent molar volume (ϕv), apparent molar adiabatic compressibility (ϕk) and relative viscosity (ηr) have been calculated from experimentally measured conductivity (κ), density (d), speed of sound (v) and viscosity (η). The critical micelle concentration data were found to pass through a broad minimum at 303 K, which tends to become sharp with the increase in the [lysozyme] in case of SDS. Whereas for CTAB, CMC values, in general increase with the temperature and decrease with the increase in concentration of lysozyme. Experiments at different lysozyme concentrations and in the presence of surfactants suggest the predominant involvement of electrostatic interactions in the complexation process of Furosemide with lysozyme in the presence of SDS which induce unfolding of lysozyme as the surfactant concentration approaches its critical micelle concentration value, and non-specific interaction behaviour of Furosemide with lysozyme in the presence of CTAB.