Functional metallomacrocycles and their polymers. 25. Kinetics and mechanism of the biomimetic oxidation of thiol by oxygen catalyzed by homogeneous (polycarboxyphthalocyaninato)metals

H. Shirai, H. Tsuiki, E. Masuda, T. Koyama, K. Hanabusa, N. Kobayashi

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96 Citations (Scopus)

Abstract

The oxidation of 2-mercaptoethanol (RSH) catalyzed by (polycarboxyphthalocyaninato)metal acid (M-papc, M = Fe(III), Co(II), Ni(II), Cu(II), pa = -(COOH)2, -(COOH)4, -(COOH)8) in the presence of molecular oxygen has been studied in aqueous homogeneous solution at pH 7.0 and at 25°C. The catalytic effects of M-papc have been determined the oxygen consumption in the reaction mixture with a Warburg respirometer. The central metal ions and the number of carboxylate ions on M-papc affected the catalytic activities for the aerobic oxidation of RSH. (Octacarboxyphthalocyaninato)iron(III) and -cobalt(II) are remarkably effective catalysts. (Dicarboxyphthalocyaninato)metals and Ni(II)- as well as Cu(II)-phthalocyanine derivatives are less effective catalysts. The kinetics of the aerobic oxidation catalyzed by (octacarboxyphthalocyaninato)iron(III) and -cobalt(II) have been characterized in terms of a bisubstrate Michaelis-Menten rate law (k5 = 600-800 min-1, at pH 7.0, 25°C). The rate law and spectral experiments indicate that the catalyzed reactions proceed via the formation of a ternary activated complex where RS- and O2 reversibly coordinate with the central metal on the phthalocyanine rings. The activation parameters were also determined for this reaction at pH 7.0 and at 25°C. The catalytic activities followed the order of Co(II)-oapc > Fe(III)-oapc > Co(II)-tapc = Fe(III)-tapc. Differences in catalytic ability have been explained in terms of the aggregation and spin state of metallophthalocyanine derivatives in aqueous solution at pH 7.0. The (tetracarboxyphthalocyaninato)cobalt(II) covalently bound to poly(2-vinylpyridine-co-styrene), despite of being a heterogeneous system, is a remarkably effective catalyst (k5 = 2210 min-1) because of polymer effects.

Original languageEnglish
Pages (from-to)417-423
Number of pages7
JournalJournal of physical chemistry
Volume95
Issue number1
DOIs
Publication statusPublished - 1991 Jan 1

ASJC Scopus subject areas

  • Engineering(all)
  • Physical and Theoretical Chemistry

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