Inhibiting the fibrillation of serum albumin proteins in the presence of surface active ionic liquids (SAILs) at low pH: Spectroscopic and microscopic study

Abstract

One of the key necessary steps to prevent human neurological disorders is the efficient disruption of protein aggregation or amyloid fibril. In this article, we have explored the effect of three amphiphilic surface active ionic liquids (SAILs), namely 1-methyl-3-octylimidazolium chloride ([C8mim]Cl), 1-dodecyl-3-methyllimidazolium chloride ([C12mim]Cl), and 1-hexadecyl-3-methyllimidazolium chloride ([C16mim]Cl) having concentrations of 5.8, 0.29, and 0.08 mM, respectively, on bovine serum albumin (BSA) and human serum albumin (HSA) fibril. These SAILs have different alkyl chain length attached to the cationic imidazolium headgroups. Interestingly, it is observed that all of the three SAILs exhibit fibril inhibition at room temperature itself as initially evidenced from thioflavin T (ThT) fluorescence assay study. However, C16mimCl is found as the most efficient quencher having highest quenching constant than the other two analogues. In addition, circular dichroism (CD) data give valuable insights into the conformational changes of BSA fibril as a consequence of interaction with SAILs. The field emission scanning electron microscopy (FESEM) and fluorescence lifetime imaging microscopy (FLIM) confirm the inhibitory effect of SAILs. It is evident from fluorescence correlation spectroscopy (FCS) study that 62% fibril is ruptured in the presence of C8mimCl while C12mimCl and C16mimCl completely destroy the fibrillar morphology. So the inhibition efficiency is related to the hydrophobicity associated with the long alkyl chain attached with the cationic imidazolium headgroup of SAILs.