Effect of ketoprofen-based ionic liquids on secondary structure and thermal stability of human serum albumin

Abstract

This is the first study on the interactions of ionic liquids (ILs) composed of cations amino acid esters and anion ketoprofen (KETO) with human serum albumin (HSA). The effect of the ILs on the thermal unfolding of the HSA was negligible in comparison with that of the KETO. For the IL series, the denaturating transitions tend to shift to lower temperatures by 1–3 °C. The secondary structure analyses have shown that KETO, [L-LeuOEt][KETO] and [L-ValOBu][KETO] cause folding, and HSA molecule becomes more coiled. In the presence of [L-ValOPr][KETO] and [L-ValOiPr][KETO], HSA structure although partially unfolded seemed very close to that of the native protein. In contrast, [L-ValOEt][KETO] induces the same conformational changes of HSA as ketoprofen. For the latter, we performed binding assays and we found that the affinity of the HSA to bind the IL is comparable to that for the ketoprofen. The estimated binding constants were 3.1 × 104 and 1.4 × 104 L mol−1 for ketoprofen and [L-ValOEt][KETO], respectively. This study on KETO-ILs could be a basis to the development of a new drug formulation.