Antimicrobial Colloidal Complexes of Lysozyme with Bio-Based Surface Active Ionic Liquids in Aqueous Medium.

Bio-based surface-active ionic liquids (SAILs) have been synthesized and investigated for their complexation with lysozyme (LYZ) in an aqueous medium to develop antimicrobial SAIL-LYZ colloidal complexes. The synthesized SAILs, [Cho][Sar] and [Cho][Doc], are comprised of choline ([Cho]+) and lauryl sarcosinate ([Sar]-) or deoxycholate ([Doc]-). The constituent anions of the investigated SAILs are structurally dissimilar and thus resulted in contrasting complexation behavior toward LYZ, as suggested by the results obtained from different techniques. The interfacial behavior is monitored using tensiometry. Zeta-potential, turbidity, and dynamic light scattering results provide insights into the complexation phenomenon in bulk. The observations made from fluorescence and circular dichroism (CD) spectroscopy give information about the alterations in the inherent structure of LYZ. The thermodynamics of the binding of SAILs with LYZ is monitored using isothermal titration calorimetry (ITC). Computer simulations have been utilized to determine the preferential binding site of SAILs on LYZ, which supports the results obtained from different techniques. Interestingly, LYZ complexed with the investigated SAILs, which are non-antimicrobial, is found to exhibit enhanced antimicrobial activity depending upon the concentration regime of the used SAIL. In this way, we have developed new antimicrobial colloidal complexes of SAILs and LYZ. The present study provides useful insights to synthesize new bio-based SAILs to be utilized for creating colloidal formulations applicable in enzyme/protein stabilization, storage, and other biomedical applications.