Kinetic study and theoretical analysis of hydroxyl radical trapping and spin adduct decay of alkoxycarbonyl and dialkoxyphosphoryl nitrones in aqueous media

Frederick A. Villamena, Christopher M. Hadad, Jay L. Zweier

Research output: Contribution to journalArticle

Abstract

Spin-trap development is important because of limitations that still exist among the currently used nitrone spin traps. This study correlates the experimental kinetic data with theoretical calculations, a novel approach that could be helpful in the future design of new spin traps. The kinetics of hydroxyl radical (.OH) trapping and spin adduct decay of the alkoxycarbonyl-nitrones 5-ethoxycarbonyl-5-methyl-l-pyrroline N-oxide (EMPO) and 5-butoxycarbonyl-5-methyl-l-pyrroline N-oxide (BocMPO) as well as the dialkoxyphosphoryl-nitrones 5-diethoxyphosphoryl-5-methyl-l-pyrroline N-oxide (DEPMPO) and 5-diisopropyloxyphosphoryl-5-methyl-1-pyrroline N-oxide (DIPPMPO) have been investigated and compared with those of unsubstituted 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Kinetic investigation was performed by the steady-state generation of .OH from H2O2 by UV photolysis in the presence of a nitrone. Apparent rate constants of .OH trapping by EMPO, BocMPO, DEPMPO, and DIPPMPO in competition with ethanol are all comparable, with kapp values ranging from 4.99 ± 0.36 to 4.48 ± 0.32 M-1 s-1 and the commonly used spin trap 5,5-dimethyl-l-pyrroline N-oxide (DMPO) having a lower kapp of 1.93 ± 0.05 M-1 s-1. Half-lives of the .OH adducts of EMPO, DEPMPO, and DIPPMPO are much longer (t1/2 = 127-158 min) than those of DMPO and BocMPO with half-lives of only 55 and 37 min, respectively. Geometry optimizations, frequency analyses, and single-point energies of the nitrones and their corresponding spin adducts were determined at the B3LYP/6-31G*//HF/6-31G* level to rationalize the experimental results.

Original languageEnglish (US)
Pages (from-to)4407-4414
Number of pages8
JournalJournal of Physical Chemistry A
Volume107
Issue number22
DOIs
StatePublished - Jun 5 2003
Externally publishedYes

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hydroxyl radicals
Hydroxyl Radical
Oxides
adducts
trapping
Kinetics
oxides
kinetics
decay
traps
pyrroline
nitrones
half life
Photolysis
Rate constants
photolysis
Ethanol

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Kinetic study and theoretical analysis of hydroxyl radical trapping and spin adduct decay of alkoxycarbonyl and dialkoxyphosphoryl nitrones in aqueous media. / Villamena, Frederick A.; Hadad, Christopher M.; Zweier, Jay L.

In: Journal of Physical Chemistry A, Vol. 107, No. 22, 05.06.2003, p. 4407-4414.

Research output: Contribution to journalArticle

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abstract = "Spin-trap development is important because of limitations that still exist among the currently used nitrone spin traps. This study correlates the experimental kinetic data with theoretical calculations, a novel approach that could be helpful in the future design of new spin traps. The kinetics of hydroxyl radical (.OH) trapping and spin adduct decay of the alkoxycarbonyl-nitrones 5-ethoxycarbonyl-5-methyl-l-pyrroline N-oxide (EMPO) and 5-butoxycarbonyl-5-methyl-l-pyrroline N-oxide (BocMPO) as well as the dialkoxyphosphoryl-nitrones 5-diethoxyphosphoryl-5-methyl-l-pyrroline N-oxide (DEPMPO) and 5-diisopropyloxyphosphoryl-5-methyl-1-pyrroline N-oxide (DIPPMPO) have been investigated and compared with those of unsubstituted 5,5-dimethyl-1-pyrroline N-oxide (DMPO). Kinetic investigation was performed by the steady-state generation of .OH from H2O2 by UV photolysis in the presence of a nitrone. Apparent rate constants of .OH trapping by EMPO, BocMPO, DEPMPO, and DIPPMPO in competition with ethanol are all comparable, with kapp values ranging from 4.99 ± 0.36 to 4.48 ± 0.32 M-1 s-1 and the commonly used spin trap 5,5-dimethyl-l-pyrroline N-oxide (DMPO) having a lower kapp of 1.93 ± 0.05 M-1 s-1. Half-lives of the .OH adducts of EMPO, DEPMPO, and DIPPMPO are much longer (t1/2 = 127-158 min) than those of DMPO and BocMPO with half-lives of only 55 and 37 min, respectively. Geometry optimizations, frequency analyses, and single-point energies of the nitrones and their corresponding spin adducts were determined at the B3LYP/6-31G*//HF/6-31G* level to rationalize the experimental results.",
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