title: Peculiar reactivity of a di-imine copper(II) complex regarding its binding to albumin protein.
abstract: A set of four di-imine copper(II) complexes containing pyridine, pyrazine and/or imidazole moieties, [Cu(apyhist)H2O](2+) 1 (apyhist = 2-(1H-imidazol-4-yl)-N-(1-(pyridin-2-yl)ethylidene)ethanamine), [Cu(apzhist)OH](+) 2 (apzhist = 2-(1H-imidazol-4-yl)-N-(1-(pyrazin-2-yl)ethylidene)ethanamine), [Cu(apyepy)OH](+) 3 (apyepy = 2-(pyridin-2-yl)-N-(1-(pyridin-2-yl)ethylidene)ethanamine), and [Cu(apzepy)H2O](2+) 4 (apzepy = N-(1-(pyrazin-2-yl)ethylidene)-2-(pyridin-2-yl)ethanamine), were investigated regarding their capability of interacting with serum albumin (human, HSA and bovine, BSA), by using spectroscopic techniques, CD, UV/Vis and EPR. Like other similar di-imine copper(II) complexes, most of them showed an expected preferential insertion of the metal ion at the primary N-terminal site of the protein, very selective for copper and characterized by a CD band at 560 nm. Further insertion of the copper ion at a secondary site is expected when using an excess of the metal. However, one of these studied complexes, [Cu(apyhist)H2O](2+) 1, exhibited anomalous behaviour interacting only at this secondary metal binding site of albumin, characterized by a CD band at 370 nm, and attributed to the coordination of copper at the Cys34 pocket. Analogous experiments with HSA previously treated with N-ethyl-maleimide (NEM), that oxidizes the protein Cys34 residue and obstructs the metal coordination, verified these results. Additional data obtained by EPR spectroscopy complemented those results. DFT calculations, considering some structural and electronic characteristics of such series of di-imine ligands and of the corresponding copper complexes, suggested molecular recognition of the apyhist ligand at the protein cavity as a feasible explanation for this unexpected and peculiar behaviour of complex 1.
authors: Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil.
authors: Vivian C
authors: VC
authors: Silveira
authors: Mariana P
authors: MP
authors: Abbott
authors: Maurício
authors: M
authors: Cavicchioli
authors: Marcos B
authors: MB
authors: Gonçalves
authors: Helena M
authors: HM
authors: Petrilli
authors: Leandro
authors: L
authors: de Rezende
authors: Antonia T
authors: AT
authors: Amaral
authors: David E P
authors: DE
authors: Fonseca
authors: Giovanni F
authors: GF
authors: Caramori
authors: Ana M da Costa
authors: AM
authors: Ferreira
mesh_terms: D000818:Animals; D002417:Cattle; D003300:Copper / Q000737:chemistry*; D006801:Humans; D007093:Imidazoles / Q000737:chemistry; D007097:Imines / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011719:Pyrazines / Q000737:chemistry; D011725:Pyridines / Q000737:chemistry; D017382:Reactive Oxygen Species / Q000737:chemistry; D012709:Serum Albumin / Q000378:metabolism*
chemical_list: D007093:Imidazoles; D007097:Imines; D008024:Ligands; D009942:Organometallic Compounds; D011719:Pyrazines; D011725:Pyridines; D017382:Reactive Oxygen Species; D012709:Serum Albumin; D003300:Copper; C029899:imidazole; C023666:pyridine