Premium
PHOTO‐CIDNP STUDY OF PYRIMIDINE DIMER SPLITTING II: REACTIONS INVOLVING PYRIMIDINE RADICAL ANION INTERMEDIATES
Author(s) -
Pouwels Petra J. W.,
Kaptein Robert,
Hartman Rosemarie F.,
Rose Seth D.
Publication year - 1995
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1995.tb09872.x
Subject(s) - pyrimidine , cidnp , dimer , chemistry , pyrimidine dimer , photochemistry , ion , radical , stereochemistry , organic chemistry , biochemistry , dna , dna damage
A series of photo‐CIDNP (chemically induced dynamic nuclear polarization) experiments were performed on pyrimidine monomers and dimers, using the electron‐donor N α‐acetyltryptophan (AcTrp) as a photosensitizer. The CIDNP spectra give evidence for the existence of both the dimer radical anion, which is formed by electron transfer from the excited AcTrp* to the dimer, and its dissociation product, the monomer radical anion. The AcTrp spectra are completely different from those obtained with an oxidizing sensitizer like anthraquinone‐2‐sulfonate, because of different unpaired electron spin density distributions in pyrimidine radical anion and cation. In the spectra of the anti (1,3‐dimethyluracil) dimers, polarization is detected that originates from a spin‐sorting process in the dimer radical pair, pointing to a relatively long lifetime of the dimer radical anions involved. Although the dimer radical anions of the 1,1′‐trimethylene‐bridged pyrimidines may have a relatively long lifetime as well, their protons have only very weak hyperfine interaction, which explains why no polarization originating from the dimer radical pair is detected. In the spectra of the bridged pyrimidines, polarized dimer protons are observed as a result of spin sorting in the monomer radical pair, from which it follows that the dissociation of dimer radical anion into monomer radical anion is reversible. A study of CIDNP intensities as a function of pH shows that a pH between 3 and 4 is optimal for observing monomer polarization that originates from spin‐sorting in the monomer radical pair. At higher pH the geminate recombination polarization is partly cancelled by escape polarization arising in the same product.