Complexation Behavior of β-Lactoglobulin with Surface Active Ionic Liquids in Aqueous Solutions: An Experimental and Computational Approach

Abstract

The nature of functionalization of alkyl chains of imidazolium-based surface active ionic liquids (SAILs) with amide or ester moiety led to contrasting complexation behavior toward the globular protein, bovine serum albumin. This prompted us to further investigate the SAIL-dependent colloidal behavior of another globular protein, β-lactoglobulin (βLG), to probe the origin of varying structural transformations in globular proteins induced by SAILs. Herein, we investigated the colloidal systems of βLG, rich in β-sheet structure, in the presence of four structurally different SAILs using a multitechnique approach. The complexation behavior, both at the air–solution interface and in bulk, is supplemented by different techniques. Docking studies have complemented the obtained experimental results. The specificity of structure, H-bonding ability of SAILs, and inherent structure of protein are found to govern their complexation behavior in terms of size, shape, and polarity of protein–SAIL complexes along with varying degrees of structural alterations in globular proteins. The present work is expected to be very useful in establishing a deep understanding of the structure–property relationship between the nature of proteins and SAILs for their complexation and colloidal behavior for various biomedical applications.

Aqueous colloidal systems of bovine serum albumin and functionalized surface active ionic liquids for material transport

“…A lower value of I 1 /I 3 (1.23) of pyrene in BSA solution as compared to that observed in phosphate buffer (1.71) indicates the adsorption of pyrene in the hydrophobic pockets located on the surface of BSA. 46,56 I 1 /I 3 decreases with a relatively lower slope in all of the investigated systems till C 1 indicating a marginal increase in hydrophobicity of forming MCs due to the adsorption of SAIL ions. At C 1 , I 1 /I 3 value of respective SAIL- Fig.…”

“…Such observations are quiet common in protein/polymer-SAIL systems. 46,48 Further information about the degree of counterion binding (b) and standard free energy of micellization ðDG mic Þ calculated using conductivity measurements (Annexure S2, ESI †) is provided in footnote of Table S3 (ESI †).…”

“…8,[46][47][48][49][50][51][52][53][54][55][56][57] Different proteins such as BSA, Gelatin and blactoglobulin (b-LG) has been investigated for their complexation with SAILs, where the length of alkyl chain and nature of head group of SAIL has been found to exert signicant inuence on complexation behavior of BSA with SAILs. 8,[46][47][48][49]56,57 It is stressed that in most of the investigations, SAILs without any functionalization of ionic head group or alkyl chain have been employed with the exception of few studies. 8,46,48 A contrasting complexation behavior of functionalized SAILs as compared to non-functionalized ones towards BSA, 8 Gelatin 48 and b-lactoglobulin (b-LG) 46 has been observed.…”

“…8,[46][47][48][49]56,57 It is stressed that in most of the investigations, SAILs without any functionalization of ionic head group or alkyl chain have been employed with the exception of few studies. 8,46,48 A contrasting complexation behavior of functionalized SAILs as compared to non-functionalized ones towards BSA, 8 Gelatin 48 and b-lactoglobulin (b-LG) 46 has been observed. Different types of SAILprotein complexes varying in morphology, internal structure and hydrophobicity etc., governed by the nature and extent of varying set of interactions has been observed.…”

“…Aer C 4(cmc) , I 1 /I 3 begin to rise in all the cases indicating a relative increase in the polarity of SAIL-BSA aggregates. It is quite probable that beyond C 4(cmc) , the forming micelles containing high surface charge8,46,48 disintegrate the respective SAIL-BSA ACs into smaller micelle bound/unbound ACs. A similarity in values of I 1 /I 3 in the absence and presence of BSA beyond C 4(cmc) supports the partition of pyrene into the micelle bound to ACs.3.2.3.…”