Interaction of the La(III)–Morin Complex with Human Serum Albumin

Abstract

Lanthanum (La) is one of the most reactive rare earth elements, whose carbonate had been approved by the FDA for marketing as a treatment drug for hyperphosphatemia. In this paper, a complex of La with the natural active compound morin was synthesized and identified. The interaction between synthesized complex (LaMO) and human serum albumin (HSA) was studied by multiple spectroscopic methods. It was found that LaMO has an efficient interaction with HSA through hydrogen bonds and van der Waals forces, with formation of the LaMO–HSA complex in its ground state. The reaction led to quenching of HSA’s fluorescence and the quenching follows a static quenching mechanism. The binding constants, reference state enthalpy change (ΔH θ), Gibbs energy change (ΔG θ) and entropy change (ΔS θ) were calculated at four different temperatures. Fluorescence probe techniques were used to identify the binding location. The results showed that LaMO competes with warfarin for Sudlow’s site I in subdomain IIA of HSA, an acknowledged site marker. Meanwhile, circular dichroism spectrum measurements revealed changes of HSA’s secondary structure in the presence of LaMO, which implies that LaMO is potentially bioactive. The study involves research about the pharmacologic mechanism of rare earth metal coordination compounds and can provide basic data for their safety evaluation.