Abstract
Oxidation of cobalt(II) nitrosyl complexes of porphyrins (P), chlorins (C), and isobacteriochlorins (iBC) yields CoIINO π-cation radicals. The radicals are stable and recyclable to the parent compound without loss of NO. The oxidized species have been characterized by electrochemistry, visible and infrared spectroscopy, and electron spin resonance (ESR). Interest in these intermediates is prompted by the presence of iron Cs or iBCs in enzymes that catalyze the reductions of nitrite to ammonia or nitric oxide (nitrite reductases) and the recent identification of cobalt iBC in sulfite reductases, enzymes which are also capable of nitrite reduction. The optical spectra of the CoIINO radicals resemble those previously obtained on oxidation of FeIINOC and iBC and lend support to the assignment of those ESR-silent species as FeIINOC+ and iBC+ π-cation radicals. As found in other series with the same macrocycles (FeIINO, FeIIICl, Zn, H2), the CoIINO complexes become progressively easier to oxidize as the porphyrin is saturated (P <C <iBC, easiest). In all three species, the Co-NO bonds remain bent, suggestive of some Co-NO- character. The C and iBC radicals exhibit ESR features characteristic of "a1u" radicals that include spin delocalization onto the metal. Similar spin profiles may rationalize the ESR spectra of presumed "a1u" porphyrin radicals in oxidized chloroperoxidase, catalase, and cytochrome P450.
| Original language | English |
|---|---|
| Pages (from-to) | 7665-7669 |
| Number of pages | 5 |
| Journal | Journal of the American Chemical Society |
| Volume | 107 |
| Issue number | 25 |
| Publication status | Published - 1985 |
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Cobalt(II) nitrosyl cation radicals of porphyrins, chlorins, and isobacteriochlorins. Models for nitrite and sulfite reductases and implications for A1u heme radicals. / Fujita, Etsuko; Chang, C. K.; Fajer, Jack.
In: Journal of the American Chemical Society, Vol. 107, No. 25, 1985, p. 7665-7669.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Cobalt(II) nitrosyl cation radicals of porphyrins, chlorins, and isobacteriochlorins. Models for nitrite and sulfite reductases and implications for A1u heme radicals
AU - Fujita, Etsuko
AU - Chang, C. K.
AU - Fajer, Jack
PY - 1985
Y1 - 1985
N2 - Oxidation of cobalt(II) nitrosyl complexes of porphyrins (P), chlorins (C), and isobacteriochlorins (iBC) yields CoIINO π-cation radicals. The radicals are stable and recyclable to the parent compound without loss of NO. The oxidized species have been characterized by electrochemistry, visible and infrared spectroscopy, and electron spin resonance (ESR). Interest in these intermediates is prompted by the presence of iron Cs or iBCs in enzymes that catalyze the reductions of nitrite to ammonia or nitric oxide (nitrite reductases) and the recent identification of cobalt iBC in sulfite reductases, enzymes which are also capable of nitrite reduction. The optical spectra of the CoIINO radicals resemble those previously obtained on oxidation of FeIINOC and iBC and lend support to the assignment of those ESR-silent species as FeIINOC+ and iBC+ π-cation radicals. As found in other series with the same macrocycles (FeIINO, FeIIICl, Zn, H2), the CoIINO complexes become progressively easier to oxidize as the porphyrin is saturated (P <C - character. The C and iBC radicals exhibit ESR features characteristic of "a1u" radicals that include spin delocalization onto the metal. Similar spin profiles may rationalize the ESR spectra of presumed "a1u" porphyrin radicals in oxidized chloroperoxidase, catalase, and cytochrome P450.
AB - Oxidation of cobalt(II) nitrosyl complexes of porphyrins (P), chlorins (C), and isobacteriochlorins (iBC) yields CoIINO π-cation radicals. The radicals are stable and recyclable to the parent compound without loss of NO. The oxidized species have been characterized by electrochemistry, visible and infrared spectroscopy, and electron spin resonance (ESR). Interest in these intermediates is prompted by the presence of iron Cs or iBCs in enzymes that catalyze the reductions of nitrite to ammonia or nitric oxide (nitrite reductases) and the recent identification of cobalt iBC in sulfite reductases, enzymes which are also capable of nitrite reduction. The optical spectra of the CoIINO radicals resemble those previously obtained on oxidation of FeIINOC and iBC and lend support to the assignment of those ESR-silent species as FeIINOC+ and iBC+ π-cation radicals. As found in other series with the same macrocycles (FeIINO, FeIIICl, Zn, H2), the CoIINO complexes become progressively easier to oxidize as the porphyrin is saturated (P <C - character. The C and iBC radicals exhibit ESR features characteristic of "a1u" radicals that include spin delocalization onto the metal. Similar spin profiles may rationalize the ESR spectra of presumed "a1u" porphyrin radicals in oxidized chloroperoxidase, catalase, and cytochrome P450.
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M3 - Article
AN - SCOPUS:0001219383
VL - 107
SP - 7665
EP - 7669
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 25
ER -