26302-80-7Relevant academic research and scientific papers
Reactions of psoralen radical cations with biological substratest
Wood, Paul D.,Mnyusiwalla, Anisa,Chen, Lie,Johnston, Linda J.
, p. 155 - 162 (2007/10/03)
The reactions of several psoralen and coumarin radical cations with biological substrates such as nucleotides, amino acids and alkenes that serve as models for unsaturated fatty acids have been examined. The radical cations were generated by laser photoionization of the parent psoralen or coumarin in aqueous buffer in most cases. Easily oxidized substrates such as tyrosine, tryptophan and guanosine monophosphate react with the 8-methoxypsoralen and several methoxy-substituted coumarin radical cations with rate constants in excess of 2 × 109 M-1 s-1. In each case reaction occurs via electron transfer, as demonstrated by the observation of quencher-derived radical cations or radicals by transient absorption spectroscopy. For other substrates such as histidine, methionine and adenosine monophosphate the measured rate constants are significantly slower and vary with the oxidation potential of both the parent psoralen or coumarin and the quencher, again indicative of electron transfer reactivity. Most of the alkenes studied also react with the psoralen or coumarin radical cations via electron transfer, although there is some evidence for addition for linoleic acid. Product studies carried out using both lamp and laser irradiation in the presence of deoxyguanosine as a radical cation trap lead to the formation of characteristic base-derived Type-I (electron transfer) products. This lends support to our previous hypothesis that photoionization occurs via a monophotonic process and is thus relevant to conditions used in clinical phototherapeutic applications of psoralens. The results demonstrate the relevance of electron transfer chemistry to the use of psoralens and related compounds as photoactivated drugs.
Electron Transfer Reactions of Tryptophan and Tyrosine Derivatives
Jovanovic, Slobodan V.,Harriman, Anthony,Simic, Michael G.
, p. 1935 - 1939 (2007/10/02)
Oxidation of tryptophan, tyrosine, and their derivatives by oxidizing radicals was studied by pulse radiolysis in aqueous solutions at 20 deg C.Rate constants for the oxidation of tryptophan derivatives with .N3 and Br2-. radicals vary from 8x108 to 4.8 x 109 M-1 s-1 and oxidation goes to completion; no pH dependence was observed.Oxidation rate constants for tyrosine derivatives increase upon deprotonation of the phenolic residue at higher pH.Redox potential for the indolyl and phenoxyl radicals were derived from the measured equilibrium constants by using p-methoxiphenol (E7.5 = 0.6 and E13 = 0.4 V), bisulfite (E3 = 0.84 V), and guanosine (E7 = 0.91 V) redox couples as reference systems.The redox potential of the tryptophyl radical was measured by pulse radiolysis and laser photolysis and found, by both techniques, to be E =0.64 V at pH 7.Redox potentials of tryptophan derivatives were found to be dependent on the nature of the side chain possibly due to interaction of the side chain with the nitrogen atom in the pirolle ring.Redox potentials of tyrosine derivatives were found to be independent of the nature of the side chain and higher than the redox potentials of triptophan derivatives.E = 0.85 V and E13 = 0.65 V were measured for the tyrosine/phenoxylradical redox couple at pH 7 and 13, respectively .Electron transfer from tyrosine to tryptophyl radical was found to be slow in neutral media, k = 5x105-1.3 x 106 M-1 s-1, and is suggested to proceed via multiple steps, one of which is proton transfer from tyrosine to tryptophyl radical folowed by electron transfer.
