Spin trapping by 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO): Theoretical and experimental studies

Frederick A. Villamena, Antal Rockenbauer, Judith Gallucci, Murugesan Velayutham, Christopher M. Hadad, Jay L. Zweier

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Abstract

The nitrone 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO) was synthesized and characterized. Spin trapping of various radicals by AMPO was demonstrated for the first time by electron paramagnetic resonance (EPR) spectroscopy. The resulting spin adducts for each of these radicals gave unique spectral profiles. The hyperfine splitting constants for the superoxide adduct are as follows: isomer I (80%), αnitronyl-N = 13.0 G and α β-H = 10.8 G; isomer II (20%), αnitronyl-N = 13.1 G, αβ-H = 12.5 G, and αγ-H = 1.75 G. The half-life of the AMPO-O2H was about 8 min, similar to that observed for EMPO but significantly shorter than that of the DEPMPO-O 2H with t1/2 ∼16 min. However, the spectral profile of AMPO-O2H at high S/N ratio is distinguishable from the spectrum of the OH adduct. Theoretical analyses using density functional theory calculations at the B3LYP/ 6-31+G**//B3LYP/6-31G* level were performed on AMPO and its corresponding superoxide adduct. Calculations predicted the presence of intramolecular H-bonding in both AMPO and its superoxide adduct. The H-bonding interaction was further confirmed by an X-ray structure of AMPO, and of the novel and analogous amido nitrone 2-amino-5-carbamoyl-5-methyl-1-pyrroline N-oxide (NH2-AMPO). The thermodynamic quantities for superoxide radical trapping by various nitrones have been found to predict favorable formation of certain isomers. The measured partition coefficient in an n-octanol/buffer system of AMPO was similar to those of DMPO and DEPMPO. This study demonstrates the suitability of the AMPO nitrone for use as a spin trap to study radical production in aqueous systems.

Original languageEnglish
Pages (from-to)7994-8004
Number of pages11
JournalJournal of Organic Chemistry
Volume69
Issue number23
DOIs
Publication statusPublished - Nov 12 2004

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ASJC Scopus subject areas

  • Organic Chemistry

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