Spectroscopic Characteristics of Thymine Dimers

Cyclobutane pyrimidine dimers (CPDs’), a photoreactive product formed from the exposure of DNA to UV light, are a precursor that if not repaired by the bodies CPD-photolyases can ultimately lead to cell death or skin cancer. The DNA lesions in question form through a carbon-carbon bond split between two (adenine-thymine) bonds and a [2+2] photocycloaddition reaction between the thymines, one of four stereoisomers of cyclobutane thymine dimer(CTD) can be formed. After irradiation of thymine monomer in aqueous solution, HPLC was used to isolate each stereoisomer, after which NMR, FTIR, and Raman spectroscopy was used to identify the cis-syn, cis-trans, anti-syn and anti-trans peaks. It was found two of the chiral stereoisomers could not be separated under reverse phase HPLC conditions used. The intensity of the three respective peaks still indicates a favor in formation of the Trans-dimers due to steric hindrance and for possible unknown mechanistic reasons.