Spectroscopic investigation of the interaction between copper (II) 2-oxo-propionic acid salicyloyl hydrazone complex and bovine serum albumin

Binding Studies of AICAR and Human Serum Albumin by Spectroscopic, Theoretical, and Computational Methodologies

The interactions of small molecule drugs with plasma serum albumin are important because of the influence of such interactions on the pharmacokinetics of these therapeutic agents. 5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) is one such drug candidate that has recently gained attention for its promising clinical applications as an anti-cancer agent. This study sheds light upon key aspects of AICAR’s pharmacokinetics, which are not well understood. We performed in-depth experimental and computational binding analyses of AICAR with human serum albumin (HSA) under simulated biochemical conditions, using ligand-dependent fluorescence sensitivity of HSA. This allowed us to characterize the strength and modes of binding, mechanism of fluorescence quenching, validation of FRET, and intermolecular interactions for the AICAR–HSA complexes. We determined that AICAR and HSA form two stable low-energy complexes, leading to conformational changes and quenching of protein fluorescence. Stern–Volmer analysis of the fluorescence data also revealed a collision-independent static mechanism for fluorescence quenching upon formation of the AICAR–HSA complex. Ligand-competitive displacement experiments, using known site-specific ligands for HSA’s binding sites (I, II, and III) suggest that AICAR is capable of binding to both HSA site I (warfarin binding site, subdomain IIA) and site II (flufenamic acid binding site, subdomain IIIA). Computational molecular docking experiments corroborated these site-competitive experiments, revealing key hydrogen bonding interactions involved in stabilization of both AICAR–HSA complexes, reaffirming that AICAR binds to both site I and site II.

Elucidation of binding mechanism of dibutyl phthalate on bovine serum albumin by spectroscopic analysis and molecular docking method

Dibutyl phthalate has been illegally used in beverages and directly affects the human health. Herein, the interaction occurred between dibutyl phthalate and bovine serum albumin was studied. The experimental results demonstrated that dibutyl phthalate could bind to bovine serum albumin and statically quench the intrinsic fluorescence of this protein. Circular dichroism measurements proved that the binding of dibutyl phthalate would lead to an obvious decrease of α-helix content in the bovine serum albumin. Molecular docking analysis clarified the fluorescence quenching mechanism, size distribution and zeta potential variation, conformational change of BSA, the site marker competitive fluorescence quenching and the interaction mechanism of dibutyl phthalate to bovine serum albumin. This work provided a useful information for the binding of dibutyl phthalate to protein.

Synthesis of morin-zinc(II) complex and its interaction with serum albumin

A morin-zinc(II) complex (MZ) was synthesized and its interaction with bovine serum albumin (BSA) were studied by molecular spectroscopy including fluorescence emission spectra, UV-visible spectra, circular dichroism (CD) spectra, three-dimensional fluorescence spectra, and synchronous fluorescence spectra. The interaction mechanism of BSA and MZ was discussed by fluorescence quenching method and Förster non-radiation energy transfer theory. The thermodynamic parameters ΔHθ, ΔGθ, ΔSθ at different temperatures were calculated and the results indicate the interaction is an exothermic as well as entropy-driven process. Hydrogen bond forces played the most important role in the reaction. The fluorescence probe experiment showed that the binding site of MZ is in subdomain IIA of BSA and the distance between BSA and MZ is 3.17 nm at normal body temperature. The conformation changes of BSA in presence of MZ were investigated by CD spectra and three-dimensional fluorescence spectra.

Spectroscopic studies on the binding of cobalt(II) 1,10-phenanthroline complex to bovine serum albumin

The binding interaction of the cobalt(II) 1,10-phenanthroline complex (Co(phen) (3) (2+) , phen = 1,10-phenanthroline) with bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV-Vis absorption and circular dichroism measurements under simulative physiological conditions. The experiment results showed that the fluorescence intensity of BSA was dramatically decreased owing to the formation of Co(phen) (3) (2+) -BSA complex. The corresponding association constants (K (a)) between Co(phen) (3) (2+) and BSA at four different temperatures were calculated according to the modified Stern-Volmer equation. The enthalpy change (DeltaH degrees ) and entropy change (DeltaS degrees ) were calculated to be -2.73 kJ mol(-1) and 82.27 J mol(-1) K(-1), respectively, which suggested that electrostatic interaction and hydrophobic force played major roles in stabilizing the Co(phen) (3) (2+) -BSA complex. Site marker competitive experiments indicated that the binding of Co(phen) (3) (2+) to BSA primarily took place in site I of BSA. A value of 4.11 nm for the average distance r between Co(phen) (3) (2+) (acceptor) and tryptophan residues of BSA (donor) was derived from Förster's energy transfer theory. The conformational investigation showed that the presence of Co(phen) (3) (2+) resulted in the change of BSA secondary structure and induced the slight unfolding of the polypeptides of protein, which confirmed the microenvironment and conformational changes of BSA molecules.