Coordination of semiquinone and superoxide radical anions to the zinc ion in SOD model complexes that act as the key step in disproportionation of the radical anions.
Reactions of imidazolate-bridged CuII-ZnII heterodinuclear and CuII-CuII homodinuclear complexes, [CuIIZnII(bdpi)(CH3CN)2](ClO4)3 x 2CH3CN (1) and [CuII2(bdpi)(CH3CN)2](ClO4)3 x CH3CN x 3H2O (2) (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole), with the p-benzosemiquinone radical anion (Q*-) have been examined to provide mechanistic insight into the role of the ZnII ion in copper-zinc superoxide dismutase (Cu,Zn-SOD). The addition of less than one equivalent of Q*- to a deaerated solution of 1 or 2 in propionitrile at -80 degrees C results in the oxidation of Q*- accompanied by the appearance of a new absorption band at 585 nm due to the CuI-Q complex (3 or 4), the absorbance of which increases linearly with the increase in Q*- concentration. Both the resonance Raman spectra of 3 and 4 exhibit a strong resonance-enhanced Raman band at 1580 cm(-1), which can be assigned to a CO stretching vibration in the CuI-Q complexes. Further addition of Q*- to a deaerated solution of 3 in propionitrile results in the reduction of Q*-, whereas no reduction of Q*- occurs with 4, which does not contain the ZnII ion. Thus, the coordination of Q*- to the ZnII ion is essential for the reduction of Q*- by the CuI ion in 3. The coordination of O2*- and Q*- to the ZnII ion has been confirmed by the electronic and ESR spectra of the O2*- and Q*- complexes with mononuclear ZnII complexes, [ZnII[MeIm(Py)2](CH3CN)](ClO4)2 (5) and [ZnII[MeIm(Me)2](H2O)](ClO4)2 (6) (MeIm(Py)2 = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)2 = (1-methyl-4-imidazolylmethyl)bis(6-methyl-2-pyridylmethyl)amine). The binding energies of O2*- with the ZnII ion in 5 and 6 have been evaluated from the deviation of the g values of the ESR spectra from the free spin value.
Ohtsu
H
H
Department of Material and Life Science, Graduate School of Engineering, Osaka University, CREST JAPAN Science and Technology Corporation, Suita.
Fukuzumi
S
S
D000838:Anions; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D011809:Quinones / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013482:Superoxide Dismutase / Q000737:chemistry*; D013481:Superoxides / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
D000838:Anions; D011809:Quinones; D013481:Superoxides; D013482:Superoxide Dismutase; D015032:Zinc