Photochemical excitation (l> 350 nm) of chloro[meso-tetrakis(2,6-dichloroporphyrin]iron (III) Fe(III)(TDCPP)Cl] and chloro[meso-tetra(a,a,a,a-pivalamidophenyl)porphyrin]-iron (III) [Fe(III)(Tpiv)PPCl] induces the oxidation of coordinated N-(4-chlorophenyl)-N'-hydroxyguanidine (1) by molecular oxygen, to give iminoxyl radicals and the Fe(II)O2 adduct. This complex can be accumulated in significant amounts using [Fe(III)(TpivPP)Cl]. The primary photoproducts give rise to secondary reactions that lead to the formation of N-(4-chlorophenyl)urea (2) as the main end product of 1. The conversion of 1 into 2 is accompanied by the formation of NO, as revealed both by an ESR spin trapping technique and in the form of its stable end-products NO2- and NO3-. The presence of 1-methyl imidazole coordinated in axial position has a significant positive effect on the photoinduced production of 2 and NO from the hydroxyguanidine 1. The observation that radical scavengers inhibit the photooxidation process strongly supports the possibility that the reaction pathway resembles a radical-type autooxidation mechanism, where the very fast reaction of O2 with the ferrous porphyrin in the presence of the photogenerated iminoxyl radical should yield an iron-peroxo intermediate as precursor of the urea 2 and NO.
Oxidation of N-4-chlorophenyl-N′-hydroxyguanidine to N-(4-chlorophenyl)urea and nitric oxide by photoexcited iron porphyrins
MOLINARI, Alessandra;
2004
Abstract
Photochemical excitation (l> 350 nm) of chloro[meso-tetrakis(2,6-dichloroporphyrin]iron (III) Fe(III)(TDCPP)Cl] and chloro[meso-tetra(a,a,a,a-pivalamidophenyl)porphyrin]-iron (III) [Fe(III)(Tpiv)PPCl] induces the oxidation of coordinated N-(4-chlorophenyl)-N'-hydroxyguanidine (1) by molecular oxygen, to give iminoxyl radicals and the Fe(II)O2 adduct. This complex can be accumulated in significant amounts using [Fe(III)(TpivPP)Cl]. The primary photoproducts give rise to secondary reactions that lead to the formation of N-(4-chlorophenyl)urea (2) as the main end product of 1. The conversion of 1 into 2 is accompanied by the formation of NO, as revealed both by an ESR spin trapping technique and in the form of its stable end-products NO2- and NO3-. The presence of 1-methyl imidazole coordinated in axial position has a significant positive effect on the photoinduced production of 2 and NO from the hydroxyguanidine 1. The observation that radical scavengers inhibit the photooxidation process strongly supports the possibility that the reaction pathway resembles a radical-type autooxidation mechanism, where the very fast reaction of O2 with the ferrous porphyrin in the presence of the photogenerated iminoxyl radical should yield an iron-peroxo intermediate as precursor of the urea 2 and NO.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
