title: Can the ebselen derivatives catalyze the isomerization of peroxynitrite to nitrate?
abstract: The reaction of ebselen and its derivatives (1-7) with peroxynitrite anion (ONOO(-); PN) has been studied in gas phase and in aqueous, dichloromethane, benzene, and cyclohexane solutions using B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) and PCM-B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) approaches, respectively. It was shown that the reaction of 2 (R=H) with PN proceeds via 2 + PN --> 2-PN --> 2-TS1 (O-O activation) --> 2-O(NO(2)(-)()) --> 2-SeO + NO(2)(-) pathway with a rate-determining barrier of 25.3 (14.8) kcal/mol at the NO(2)(-) dissociation step (numbers presented without parentheses are enthalpies, and those in parentheses are Gibbs free energies). The NO(3)(-) formation process, starting from the complex 2-O(NO(2)(-)()), requires by (7.9) kcal/mol more energy than the NO(2)(-) dissociation process and is unlikely to compete with the latter. Thus, in the gas phase, the peroxynitrite --> nitrate isomerization catalyzed by complex 2 is unlikely to occur. It is shown that the NO(3)(-) formation process is slightly more favorably than the NO(2)(-) dissociation process for complex 4, with a strongest electron-withdrawing ligand R=CF(3). Therefore, complex 4 (as well as complex 6 with R=OH) is predicted to be a good catalyst for peroxynitrite <--> nitrite isomerization in the gas phase. Solvent effects (a) change the rate-determining step of the reaction 2 + PN from NO(2)(-) dissociation in the gas phase to O-O activation, which occurs with barriers of (13.9), (8.4), (8.4), and (8.2) kcal/mol in water, dichloromethane, benzene, and cyclohexane, respectively, and (b) significantly reduce the NO(2)(-) dissociation energy, while only slightly destabilizing the NO(3)(-) formation barrier, and make the peroxynitrite <--> nitrate isomerization process practically impossible, even for complex 4.
authors.affiliation: Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA. dmusaev@emory.edu
authors.forename: Djamaladdin G
authors.initials: DG
authors.lastname: Musaev
authors.forename: Yurii V
authors.initials: YV
authors.lastname: Geletii
authors.forename: Craig L
authors.initials: CL
authors.lastname: Hill
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Hirao
mesh_terms: D000838:Anions; D001393:Azoles / Q000737:chemistry*; D002384:Catalysis; D005979:Glutathione Peroxidase / Q000737:chemistry / Q000378:metabolism; D054833:Isoindoles; D007536:Isomerism; D008958:Models, Molecular; D008968:Molecular Conformation; D009566:Nitrates / Q000737:chemistry*; D016566:Organoselenium Compounds / Q000737:chemistry*; D030421:Peroxynitrous Acid / Q000737:chemistry*; D012997:Solvents; D013816:Thermodynamics
chemical_list: D000838:Anions; D001393:Azoles; D054833:Isoindoles; D009566:Nitrates; D016566:Organoselenium Compounds; D012997:Solvents; D030421:Peroxynitrous Acid; C042986:ebselen; D005979:Glutathione Peroxidase