Electron Spin Resonance Spectroscopy Studies on Reduction Process of Nitroxyl Radicals used in Molecular Imaging

Abstract

Electron spin resonance (ESR) spectroscopy studies on the reduction process of nitroxyl radicals were carried out for 1mM concentration of 14N-labeled nitroxyl radicals in 1 mM concentration of ascorbic acid as a function of time. The half life time and decay rate were estimated for 1mM concentration of 14N labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. From the results, the increase in half life time and decrease in decay rate were calculated for TEMPONE compared with TEMPO and TEMPOL radicals, which indicates the higher stability of TEMPONE radical. The observed radical scavenging activity is also higher for TEMPONE radical. The ESR spectrum was also recorded for 1mM concentration of 14N-labeled nitroxyl radicals in pure water and the ESR parameters, line width, hyperfine coupling constant, g-factor, signal intensity ratio and rotational correlation time were obtained. These results indicate that the TEMPONE radical has narrowest line width and fast tumbling motion compared with TEMPO and TEMPOL. Therefore, this study reveals that the TEMPONE radical can act as a good redox sensitive spin probe for molecular imaging.