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PubMed2005

The balance between charge transfer and non-charge transfer pathways in the sensitization of singlet oxygen by pi pi* triplet states.

A charge transfer (CT) channel and a non-CT deactivation channel, both leading to formation of O(2)((1)Sigma (g)(+)), O(2)((1) Delta(g)) and O(2)((3)Sigma(g)(-)), compete in the quenching of triplet states by O(2). Recent studies by our group demonstrated that these channels are described by rather simple and general quantitative relations. In the present paper we use the detailed kinetic data on the quenching by O(2) of pi pi* triplet sensitizers of three homologous aromatic series in CCl(4) to derive a parameter, which describes the balance between CT and non-CT deactivation. This quantity, p(CT), is the relative contribution of CT mediated deactivation and is easily calculated for a sensitizer of known triplet energy from its quenching rate constant. The parameter p(CT) quantitatively describes the balance between both deactivation channels without requiring any knowledge of oxidation potentials. It is shown how the variation of p(CT) influences the efficiencies and the rate constants of O(2)((1)Sigma(g)(+)), O(2)((1)Delta(g)) and O(2)((3)Sigma(g)(-)) formation in the quenching process.

Carbon Tetrachloride↗

PubMed2000

The decomposition of peroxynitrite does not yield nitroxyl anion and singlet oxygen.

In a recent article [Khan, A. U., Kovacic, D., Kolbanovsky, A., Desai, M., Frenkel, K. & Geacintov, N. E. (2000) Proc. Natl. Acad. Sci. USA 97, 2984-2989], the authors claimed that ONOO(-), after protonation to ONOOH, decomposes into (1)HNO and (1)O(2) according to a spin-conserved unimolecular mechanism. This claim was based partially on their observation that nitrosylhemoglobin is formed via the reaction of peroxynitrite with methemoglobin at neutral pH. However, thermochemical considerations show that the yields of (1)O(2) and (1)HNO are about 23 orders of magnitude lower than those of ( small middle dot)NO(2) and ( small middle dot)OH, which are formed via the homolysis of ONOOH. We also show that methemoglobin does not form with peroxynitrite any spectrally detectable product, but with contaminations of nitrite and H(2)O(2) present in the peroxynitrite sample. Thus, there is no need to modify the present view of the mechanism of ONOOH decomposition, according to which initial homolysis into a radical pair, [ONO( small middle dot) ( small middle dot)OH](cage), is followed by the diffusion of about 30% of the radicals out of the cage, while the rest recombines to nitric acid in the solvent cage.

Animals↗

PubMed2006

Sensitized photooxidation of furanoeremophilane with singlet oxygen and their biogenetic relationship.

In an attempt to explore the biogenetic relationship of furanoeremophilane derivatives and eremophilan-8alpha,12-olides, produced in Ligularia and their structure-activity relationship, we studied the photosensitized oxidation of furanoeremophilane-type sesquiterpenes. Under the condition of several solvents solution Irradiation with a 200 W incandescent lamp of furanoeremophilan-14beta,6alpha-olide isolated from Ligularia vellerea, in various solutions with methylene blue, rose bengal, toluidine blue and safranine T gave several products. The products were isolated by chromatographic procedure and their structures were elucidated as eremophilan-14beta,6alpha,8alpha,12-diolide derivatives by NMR, IR and MS methods. A reaction mechanism has been proposed.

Animals↗

PubMed1998

Homogenous repair of singlet oxygen-induced DNA damage in differentially transcribed regions and strands of human mitochondrial DNA.

Photoactivated methylene blue was used to damage purified DNA and the mitochondrial DNA (mtDNA) of human fibroblasts in culture. The primary product of this reaction is the DNA lesion 7-hydro-8-oxo-deoxyguanosine (8-oxo-dG). The DNA damage was quantitated using Escherichia coli formamidopyrimidine DNA glycosylase (Fpg) in a gene-specific damage and repair assay. Assay conditions were refined to give incision at all enzyme-sensitive sites with minimal non-specific cutting. Cultured fibroblasts were exposed to photoactivated methylene blue under conditions that would produce an average of three oxidative lesions per double-stranded mitochondrial genome. Within 9 h, 47% of this damage had been removed by the cells. This removal was due to repair rather than to replication, cell loss or degradation of damaged genomes. The rate of repair was measured in both DNA strands of the frequently transcribed ribosomal region of the mitochondrial genome and in both strands of the non-ribosomal region. Fpg-sensitive alkali-resistant oxidative base damage was efficiently removed from human mtDNA with no differences in the rate of repair between strands or between two different regions of the genome that differ substantially with regard to transcriptional activity.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed1993