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.
Villamena
Frederick A
FA
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
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