Photo-CIDNP study of the splitting of the dinucleotidecis, syn-thymine dimer with reduced flavin as a sensitizer: Evidence for a thymine radical anion intermediate

Abstract

Abstraer. Photochemically induced dynamic nuclear pola¡ (photo-CIDNP) studies were performed on the splitting of c/s,syn 2'-deoxythymidylyl-(3'~5')-2'-deoxythymidine eyelobutane dimer (cs-dTp[]dT), using redueed flavin asa sensitizer. This system serves as a model for the light-indueed repair mechanism of thymine dimers in DNA by the enzyme photolyase. The CIDNP spectrum shows en¡ absorption of the two C6-H protons of the corresponding monomer dTpdT, which demonstrates that a thymine radical anion is involved in the splitting of the dimer. This is supported by a similar C1DNP spectrum that is obtained with the electron-donor N~-acetyl tryptophan as a sensitizer. This result suggests that the light-induced splitting of thymine dimers in DNA by photolyase also proceeds via the thymine radical anion. The small difference in intensity of the two CIDNP signals belonging to the C6-H protons shows that the unpaired electron in the monomer radical has a slight preferente for the thymine moiety at the 5' terminus.

NMR application for a study of reversible photochemical kinetics: A multisite case

“…If all protons in site i are labeled at a given moment, we will find the equations giving us the concentration n i of chemical form S i . The equations for the concentrations are given by [2] and [3].…”

“…In particular, NMR is used to measure quantum yields for irreversible photochemical reactions (1) and, in addition, NMR branch of photochemically induced polarization of nuclei provides detection of short-lived radicals arising in flash photolysis of substances (2). Being a well-developed NMR tool, dynamic NMR spectroscopy (DNMR) is commonly used to obtain kinetic parameters of dark reversible chemical reactions in solutions (5,6).…”

“…The study of photochemical reactions is one of the many interesting applications of nuclear magnetic resonance (NMR) spectroscopy (1)(2)(3)(4). In particular, NMR is used to measure quantum yields for irreversible photochemical reactions (1) and, in addition, NMR branch of photochemically induced polarization of nuclei provides detection of short-lived radicals arising in flash photolysis of substances (2).…”

NMR applications for a study of converted photochemical processes kinetics

“…Three different experimental procedures for the definition of the effective tate constants and the quantum yield of responses ate considered.One of the numerous applications of nuclear magnetic resonance (NMR) spectroscopy is the study of photochemical reactions [1][2][3][4][5]. The use of NMR for investigating the quantum yields of irreversible photochemical reactions [1] is widely known.…”

“…The use of NMR for investigating the quantum yields of irreversible photochemical reactions [1] is widely known. Besides, photochemicaUy induced dynamic polarization of nucleus allows one to examine [2,3] the short-lived radical alternate corpuscles which appear as a result of flash photolysis of substances. Recently it was shown that with the help of dynamic NMR (DNMR), the reversible photochemical processes [6][7][8] can be investigated in situ.…”