Luminescence Studies of the Ligand Exchange Between Two Phenanthroline Complexes and Bovine Serum Albumin

Abstract

The interactions between bovine serum albumin (BSA) and two Cu(II) phenanthroline complexes were studied by fl uorescence and UV-visible absorption spectroscopy. The obtained results confi rm that the phen ligand (phen = 1,10-phenanthroline) is dissociated from the two complexes and moves into the hydrophobic cavity of BSA and that the M-L complexes (M = Co 2+ , Cu 2+ ; L = Hlact, imda; Hlact = lactic acid, H 2 imda = iminodiacetic acid) coordinate with the amino acids on the surface of the peptide in the solution. This mode of action signifi cantly inhibits the denaturation of BSA. The calculated distance between the BSA and the two complexes suggests that the energy transfer from the excited state of BSA to a complex occurs with high effi ciency.Keywords: ligand exchange, phenanthroline, bovine serum albumin, fl uorescence spectrum.Introduction. Protein interactions have a fundamental function in many biochemical processes in both healthy and diseased states, including critical functions in signal transduction, immune reaction, cell cycle control, differentiation, and protein folding. To understand, probe, and manipulate biological systems effectively, studying the infl uence of small molecules or inhibiting protein interactions through selective recognition is necessary [1][2][3][4][5]. Small metal complexes can potentially combine fl exibly in ligands and can be designed to access a wide and diverse range of coordination geometries, optical isomers, and electronic states. This fl exibility can be used to enable or prevent coordination of the metal complex to protein side chains or substrates [6][7][8][9]. At present, many research papers have reported the interaction between the complexes and bovine serum albumins (BSA) [9, 10-14], most of which were conducted using fl uorescence spectroscopy. Dynamic and static quenching constants, binding sites, binding force, and binding distance between the complexes and BSA have been calculated, and the results showed that the complex quenched the fluorophore of BSA by forming ground state complexes in a solution, thereby perturbing the environment surrounding tryptophan or tyrosine residues of BSA.In a previous work, we studied the i nteraction between complexes and BSA with the use of IR spectroscopy and found that the ligands in the complexes could be replaced by the amino acids in BSA [15,16]. In order to demonstrate whether the experiment result is correct, we investigated the interaction between BSA and complexes 1 and 2 via fl uorescence, UV spectroscopy, and the dialysis method {1 = [Co(Hlact) 2 (phen)]·2H 2 O[15], 2 = [Cu(imda)(phen)]·H 2 O [17], Hlact = lactic acid, phen = 1,10-phen anthroline, imda = iminodiacetic acid}, and further investigated whether or not the mode will have an impact on protein denaturation.Experimental. All manipulations were carried out in open air. All chemicals were commercial analytical reagents and used without further purifi cation. Nanopure-quality water was used throughout this work. The pH was measured using a potentiometric met...

Reactions of Medicinal Gold(III) Compounds With Proteins and Peptides Explored by Electrospray Ionization Mass Spectrometry and Complementary Biophysical Methods

“…Indeed, after the mixing of HSA and Au 2 phen, the formation of a precipitate occurs, most probably an adduct between HSA and the aromatic ligand lost from Au 2 phen. On the other hand, the formation of adducts between HSA and 1,10-phenanthroline systems was already reported in literature (Lin and Shen, 2017).…”