Micellar properties of pluronics in combination with cationic surfactant and interaction with lysozyme: Thermodynamic evaluation

Physicochemical understanding of surfactant interaction with protein and its effect on the protein structure is essential. We have studied the effect of surfactant mixture [(TTAB + F68) and (TTAB + F127)] on the conformation of model protein hen egg white lysozyme. This work aims to understand if the pluronic can alter the TTAB CMC and its effect on protein. The quantitative investigation of effect of [(TTAB + F68) and (TTAB + F127)] mixture on thermal stability and conformation of protein was accomplished by combination of high sensitivity isothermal titration calorimetry, fluorescence spectroscopy, UV–visible spectroscopy, circular dichroism and differential scanning calorimetry. Early micellization is observed in surfactant mixture [(TTAB + F68) and (TTAB + F127)] in presence of pluronic, therefore the mixed micelles are preferred. The enthalpies of interaction suggest the presence of polar interaction between lysozyme and [(TTAB + F68) and (TTAB + F127)]. Fluorescence spectroscopy, DSC and CD results indicates that, F127 interacts with TTAB and supresses TTAB effect on the protein, while F68 shows no such effect. Further, experimental results are supported by the surfactant's deviation from ideal behaviour calculations, suggesting that TTAB has negative synergism (antagonism/ repulsive interaction) with F68 and positive synergism (attractive interaction) with F127, respectively.