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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
Author(s) -
Ohtsu Hideki,
Fukuzumi Shunichi
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20011119)7:22<4947::aid-chem4947>3.0.co;2-e
Subject(s) - chemistry , imidazolate , disproportionation , raman spectroscopy , superoxide , zinc , ion , photochemistry , electron paramagnetic resonance , imidazole , medicinal chemistry , crystallography , inorganic chemistry , stereochemistry , nuclear magnetic resonance , organic chemistry , enzyme , physics , optics , catalysis
Reactions of imidazolate‐bridged Cu II −Zn II heterodinuclear and Cu II −Cu II homodinuclear complexes, [Cu ii Zn ii (bdpi)(CH 3 CN) 2 ](ClO 4 ) 3 ⋅ 2 CH 3 CN ( 1 ) and [Cu ii 2 (bdpi)(CH 3 CN) 2 ](ClO 4 ) 3 ⋅ CH 3 CN ⋅ 3 H 2 O ( 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 Zn II 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 °C results in the oxidation of Q .− accompanied by the appearance of a new absorption band at 585 nm due to the Cu I −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 Cu I −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 Zn II ion. Thus, the coordination of Q .− to the Zn II ion is essential for the reduction of Q .− by the Cu I ion in 3 . The coordination of O 2 .− and Q .− to the Zn II ion has been confirmed by the electronic and ESR spectra of the O 2 .− and Q .− complexes with mononuclear Zn II complexes, [Zn ii {MeIm(Py) 2 }(CH 3 CN)](ClO 4 ) 2 ( 5 ) and [Zn ii {MeIm(Me) 2 }(H 2 O)](ClO 4 ) 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 O 2 .− with the Zn II ion in 5 and 6 have been evaluated from the deviation of the g ∥ values of the ESR spectra from the free spin value.