Superoxide radical anion adduct of 5,5-dimethyl-1-pyrroline N-oxide. 5. Thermodynamics and kinetics of unimolecular decomposition.
The unimolecular decomposition of the superoxide radical anion adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO), 5-carbamoyl-5-methyl-1-pyrroline N-oxide (AMPO), 5-ethoxycarbonyl-5-methyl-1-pyrroline N-oxide (EMPO), and 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO) were computationally investigated by using PCM/BHandLYP/6-311G(d,p)//B3LYP/6-31G(d) and PCM/ROMP2/cc-PVDZ//B3LYP/6-31G(d) levels of theory. Results indicate that the O-O bond scission for nitrone-O(2)H to form the hydroxyl radical and the biradical is endoergic, and that the ring-opening step to form the nitrosoaldehyde is highly exoergic. The energy barriers for the O-O bond scission and ring-opening processes indicate that the former is the rate-limiting step of the reaction. The overall energetics for DMPO-O(2)H decomposition in the presence and absence of explicit water interactions was found to be the most preferred; however, no significant differences in the energetics of decomposition among the various isomers of AMPO-O(2)H, EMPO-O(2)H, and DEPMPO-O(2)H were observed.
Department of Pharmacology and Center for Biomedical EPR Spectroscopy and Imaging, The Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, Ohio 43210, USA. frederick.villamena@osumc.edu
Frederick A
FA
Villamena
D003497:Cyclic N-Oxides / Q000737:chemistry*; D007700:Kinetics; D011789:Quantum Theory; D013481:Superoxides / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
D003497:Cyclic N-Oxides; D014867:Water; D013481:Superoxides; C017245:5,5-dimethyl-1-pyrroline-1-oxide