Superoxide Radical Anion Adduct of 5,5-Dimethyl-1-pyrroline N-Oxide. 4. Conformational Effects on the EPR Hyperfine Splitting Constants

Abstract

Spin trapping has been commonly employed in the detection of superoxide radical anion in chemical and biological systems; hence, accurate interpretation of the hyperfine splitting constants (hfsc's) arising from the O 2 ·-adducts (also referred to as hydroperoxyl (HO 2 · ) radical adducts) of various nitrones is important. In this work, the nature of the relevant hfsc's was investigated by examining the effect of conformational changes in the hydroperoxyl moiety of the O 2 ·-adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO), 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO), 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO), and 7-oxa-1-azaspiro[4.4]non-1-en-6-one N-oxide, (CPCOMPO) on the magnitude of a N , a β-H , and a γ-H . Conformational change around the substituents and their effect on the hfsc's were also explored. Results indicate that a β-H is most sensitive to conformational changes of the hydroperoxyl and substituent groups relative to hfsc's of other nuclei. The orbital overlap between the C-H σ-orbital and the SOMO of the nitroxyl nitrogen plays a crucial factor in determining the magnitude of the a β-H . The hfsc values for the O 2 ·-adducts were predicted with high accuracy by using a low-cost computational method at the PCM(water)/BHandHLYP/EPR-III//B3LYP/ 6-31G* level of theory without taking into account the explicit water interaction.

Review—Quantification of Hydrogen Peroxide by Electrochemical Methods and Electron Spin Resonance Spectroscopy

“…Some of the research groups, using those spin traps and spin probes have commented on specificity and sensitivity, but also critically issued problems and made suggestions for reasonable precautions. 56,[410][411][412][413][414][415][416][417][418][419] A detailed list of available spin traps is regularly updated by the IU-PAC (see https://goldbook.iupac.org/html/S/S05878.html). 420 The catalyzed reduction occurs via two sequential steps of one-electron oxidation of AUR forming two intermediate radicals which are dismutated to regain one AUR and form one colored, fluorescent resorufin.…”

An EPR Study of Superoxide Radicals from Potassium Superoxide Solutions

“…The higher stability of the DEPMPO spin adducts allows for a higher signal-to-noise ratio compared to what can be obtained with another classical spin trap, DMPO, under identical experimental conditions. In addition, the 31 P (I = 1/2) in DEPMPO induces extra line splitting, leading to more complex but also more informative spectra than with DMPO [10].…”

In situ nitroxide‐mediated polymerization of styrene promoted by the N‐tert‐butyl‐α‐isopropylnitrone/bpo pair: ESR investigations

“…To interpret the experimental data, the hyperfine coupling constants (HFCCs)—implicitly, the isotropic HFCCs—were calculated using first principles methods, of which the performance has been assessed in a recent investigation 38. Indeed, due to the impact of electron correlation, the need to employ extended basis sets, and their sensitivity to the surrounding, accurate evaluation of HFCCs is a difficult task 39–57. Thus, the results reported here were obtained using a density functional theory (DFT) approach combining the B3LYP hybrid exchange‐correlation functional and the EPR III basis set58 whereas the effects of the solvent were described using the polarizable continuum model and the integral equation formalism (IEFPCM) 59, 60.…”