Nano Archive

Studies on the mechanism of the reaction of tetrakis({1-methylpyridinium-4-yl}porphyrinato)iron(III) pentaperchlorate with hydrogen peroxide

Saha , T. K. and Karmaker, S. and Tamagake, K. (2003) Studies on the mechanism of the reaction of tetrakis({1-methylpyridinium-4-yl}porphyrinato)iron(III) pentaperchlorate with hydrogen peroxide. JOURNAL OF PORPHYRINS AND PHTHALOCYANINES, 7 (9-10). pp. 693-699. ISSN 1088-4246

Full text is not hosted in this archive but may be available via the Official URL, or by requesting a copy from the corresponding author.

Official URL: http://www.worldscinet.com/jpp/07/0710/S1088424603...

Abstract

The reaction of the 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrinatoiron(III) cation, [Fe-III(TMPyP)](5+) (1; prepared as the pentaperchlorate), with hydrogen peroxide (H2O2) in aqueous solution was studied by spectrophotometric methods. The porphyrin 1 was rapidly oxidized with an excess of H2O2 under aerobic conditions to the oxo-iron(IV) porphyrin, [(FeO)-O-IV(TMPyP)](4+) (2), having UV-visible absorption maxima at 436 and 450 nm. Computer deconvolution of the time-resolved absorption spectra revealed that the absorption spectra < 0.5 s were not reproduced well by a simple combination of the two spectra of I and 2, indicating that transient species were formed at the initial stage. Addition of sodium nitrite (NaNO2), which is thought to be a one-electron donor, to the stoichiometric reaction mixture of 1 and H2O2 increased the initial formation rate of 2. The presence of uric acid (UA) caused a significant delay in the formation of 2. The delay of the appearance of 2 was directly proportional to the starting concentration, [UA],, but other kinetic profiles were not changed significantly. Based on these observations and the kinetic analysis, we confirmed the involvement of the oxo-iron(IV) porphyrin radical cation, [(FeO)-O-IV(TMPyP.)](5+) (3), as a compulsory intermediate in the rate-determining step of the overall reaction, 1 + H2O2 --> 2, with a rate constant k = 4.4 x 10(4) M-1 .s(-1). The rate constants for the reaction between 2 and NaNO2, and between 2 and UA were estimated to be 9.0 M-1 .s(-1) and 5.45 x 10(6) M-1 .s(-1), respectively. Copyright (C) 2003 Society of Porphyrins & Phthalocyanines.

Item Type:Article
Subjects:Physical Science > Nanophysics
Physical Science > Nano objects
Material Science > Nanochemistry
Material Science > Nanostructured materials
Divisions:Faculty of Engineering, Science and Mathematics > School of Physics
Faculty of Engineering, Science and Mathematics > School of Chemistry
ID Code:9725
Deposited By:JNCASR
Deposited On:19 Oct 2010 09:58
Last Modified:19 Oct 2010 09:58

Repository Staff Only: item control page