Superoxide radical anion adduct of 5,5-dimethyl-1-pyrroline W-oxide (DMPO). 1. the thermodynamics of formation and its acidity

Frederick A. Villamena, John K. Merle, Christopher M. Hadad, Jay L. Zweier

Research output: Contribution to journalArticlepeer-review

Abstract

The nitrone 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been the most widely used spin trap for the detection of transient free radicals in chemical, biological, and biomedical research using electron paramagnetic resonance (EPR) spectroscopy. A density functional theory (DFT) approach was used to predict the thermodynamics of formation of the superoxide anion/hydroperoxyl radical (O 2./.O 2H) adduct of DMPO as well as its pK a in aqueous systems. At the B3LYP/6-31+G(d,p)//B3LYP/6-31G(d) level, we predicted (in the gas phase and with a polarizable continuum model (PCM) for water) three conformational minima for both the DMPO-O 2 - and DMPO-O 2H adducts. Using DFT and the PCM solvation method, the pK a of DMPO-O 2H was predicted to be 14.9 ± 0.5. On the basis of free energy considerations, the formation of DMPO-O 2H at neutral pH proceeds via initial addition of O 2. to DMPO to form the DMPO-O 2 - adduct and then subsequent protonation by water (or other acidic sources) to form DMPO-O 2H. Under acidic conditions, the addition of .O 2H to DMPO is predicted to be more exoergic than the addition of O 2. and is consistent with available experimental kinetic data.

Original languageEnglish (US)
Pages (from-to)6083-6088
Number of pages6
JournalJournal of Physical Chemistry A
Volume109
Issue number27
DOIs
StatePublished - Jul 14 2005
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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