Transient Intermediates in Intramolecularly Photosensitized Pyrimidine Dimer Splitting by Indole Derivatives

Abstract

Abstract— Intramolecularly photosensitized pyrimidine dimer splitting can serve as a model for some aspects of the monomerization of dimers in the enzyme‐substrate complex composed of a photolyase and UV‐damaged DNA. We studied compounds in which a pyrimidine dimer was covalently linked either to indole or to 5‐methoxyindole. Laser flash photolysis studies revealed that the normally observed photoejection of electrons from the indole or the 5‐methoxyindole to solvent was diminished by an order of magnitude for indoles with dimer attached (dimer‐indole and dimer‐methoxyindole). The fluorescence lifetime of dimer‐indole in aqueous methanol was 0.85 ns, whereas that of the corresponding indole without attached dimer (tryptophol) was 9.7 ns. Similar results were obtained for the dimer‐methoxyindole (0.53 ns) and 5‐methoxytryptophol (4.6 ns). The quantum yield of dimer splitting for the dimer‐methoxyindole (φ287K7 = 0.08) was only slightly greater than the value found earlier for the dimer bearing the unsubstituted indole (4>2K7= 0.04). Transient absorption spectroscopy also revealed lower yields of indole radical cations following laser flash photolysis of dimer‐indole compared to the indole without attached dimer. Dimer‐methoxyindole behaved similarly. These results are interpreted in terms of an enhanced rate of radiationless relaxation of the indole and methoxyindole excited singlet states in dimer‐indoles. The possible quenching of the indole and methoxyindole excited states via electron abstraction by the covalently linked dimer is discussed.

Solvent Dependence of Pyrimidine Dimer Splitting in a Covalently Linked Dimer‐indole System

“…Previous studies have been carried out on dimer-indole systems in which a relatively long and flexible linker connected the dimer and indole. Extensive quenching of indole fluorescence was observed in such systems , as well as considerable shortening of the indole fluorescence lifetime (Young et al, 1988). These results, along with the observation of greatly 789 reduced production of solvated electrons by indoles with dimers attached, were indicative of efficient intramolecular electron transfer from excited indole to dimer.…”

Efficient Photosensitized Splitting of Thymine Dimer by a Covalently Linked Tryptophan in Solvents of High Polarity

“…In another indole-dimer system, 15, which has a longer spacer and a dimer derived from thymine and orotic acid, [25] a more efficient splitting reaction occurred in water (Φ = 0.081) than in ethanol (Φ = 0.068). The corresponding values of Φ were 0.06 and 0.24 for 13 [10] and 0.02 and 0.12 for 14 [15] in the two solvents, respectively.…”

A Deoxyribozyme, Sero1C, Uses Light and Serotonin to Repair Diverse Pyrimidine Dimers in DNA

“…[28][29][30][31] From a series of key experiments, Young et al, Kim and Rose, and Hartzfeld and Rose have reported that the dielectric constant of the intervening medium separating the charges is a key parameter for successful photoreactivation. Thus, highly nonpolar or hydrophobic intervening media have been linked to high quantum yields of photoreactivation, [32][33][34] and it has been proposed that extant photolyase enzymes likewise provide hydrophobic active sites to suppress charge recombination. 17,18,[28][29][30][31] Provision of a hydrophobic binding/active site is a property that is easily accessible to RNA and DNA.…”