Characterization of dioxygenated cobalt(II)-carnosine complexes by Raman and IR spectroscopy.
Raman and IR studies are carried out on carnosine (beta-alanyl-L-histidine, Carnos) and its complexes with cobalt(II) at different metal/ligand ratios and basic pH. Binuclear complexes that bind molecular oxygen are formed and information regarding the O-O bridge is obtained from the Raman spectra. When the Co(II)/Carnos ratio is <or=1, peroxobinuclear complexes are the predominant species and two forms (monobridged and dibridged) are identified by the presence of two Raman peaks in the nuO-O region (750-850 cm(-1)). These peroxo complexes can be oxidized to yield a superoxo complex when the metal slightly exceeds the Carnos concentration, and there are consequent shifts of the nuO-O band to higher wavenumbers. In addition, the chelated species in the 2 : 1 Co(II)/Carnos system is found to bind oxygen to a lesser degree. With respect to the coordination sites, each Co(II) ion of the binuclear dioxygenated complexes is bound to one oxygen atom and four nitrogen atoms: N(pi) and N(tau) of two Carnos molecules, the peptide, and the terminal amino nitrogen atoms. Conversely, when the metal/ligand ratio is 2, in addition to the dioxygenated complexes, a complex is formed in which the imidazole moiety of Carnos binds two different cobalt ions because the N(pi) and N(tau) nitrogens are both deprotonated.
Torreggiani
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A
Centro di Studio Interfacoltà sulla Spettroscopia Raman, Department of Biochemistry, University of Bologna, Via Belmeloro 8/2, 40126 Bologna, Italy.
Taddei
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P
Fini
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D002336:Carnosine / Q000737:chemistry* / Q000378:metabolism; D002614:Chelating Agents / Q000737:chemistry; D003035:Cobalt / Q000737:chemistry* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000378:metabolism; D008024:Ligands; D046911:Macromolecular Substances; D008958:Models, Molecular; D009584:Nitrogen / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D010455:Peptides / Q000737:chemistry; D011522:Protons; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013237:Stereoisomerism
D002614:Chelating Agents; D007093:Imidazoles; D008024:Ligands; D046911:Macromolecular Substances; D010455:Peptides; D011522:Protons; D003035:Cobalt; D002336:Carnosine; D009584:Nitrogen; D010100:Oxygen