Mechanistic and conformational studies on the interaction of human serum albumin with rhodamine B by NMR, spectroscopic and molecular modeling methods

Rhodamine B (RB), an important congeneric form of rhodamine dyes, is widely used as a colorant and tracing agent, and recent studies have shown that it is potentially harmful to wildlife and human health. To assess the toxicity of RB at the molecular level, the interaction between human serum albumin (HSA) and RB was investigated using NMR, multispectroscopic methods in combination with computational approaches. The data of NMR indicated that RB indeed bound to HSA, in which the benzene rings were spatially close to the binding site of HSA. The fluorescence results showed that RB had a moderate binding affinity to HSA and strongly quenched the intrinsic fluorescence of HSA through a static quenching mechanism. Analysis of thermodynamic parameters and the effect of ionic strength revealed that electrostatic, hydrophobic and hydrogen bond interactions played an important role in the complex formation. And the main binding region of RB was located near site I of HSA. Furthermore, the microenvironment and conformation of HSA were changed in the presence of RB, which was confirmed by the results obtained from CD, FT-IR, and synchronous fluorescence. Finally, the optimal binding mode of RB to HSA and the stability of HSA-RB complex were studied through molecular modeling methods. In short, this work would provide significant insights for understanding the transport, distribution and toxicity effect of RB when it spread in human body. (C) 2020 Elsevier B.V. All rights reserved.