Initial excited-state structural dynamics of thymine derivatives.
Thymine is one of the pyrimidine nucleobases found in DNA. Upon absorption of UV light, thymine forms a number of photoproducts, including the cyclobutyl photodimer, the pyrimidine pyrimidinone [6-4] photoproduct and the photohydrate. Here, we use UV resonance Raman spectroscopy to measure the initial excited-state structural dynamics of the N(1)-substituted thymine derivatives N(1)-methylthymine, thymidine, and thymidine 5'-monophosphate in an effort to understand the role of the N1 substituent in determining the excited-state structural dynamics and the subsequent photochemistry. The UV resonance Raman spectrum of thymidine and thymidine 5'-monophosphate are similar to that of thymine, suggesting that large masses at N(1) effectively isolate the vibrations of the nucleobase. However, the UV resonance Raman spectrum of N(1)-methylthymine is significantly different, suggesting that the methyl group couples into the thymine ring vibrations. The resulting resonance Raman intensities and absorption spectra are self-consistently simulated with a time-dependent expression to quantitatively extract the initial excited-state slopes, homogeneous and inhomogeneous linewidths, and electronic parameters. These results are discussed in the context of the known photochemistry of thymine and its derivatives.
Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.
Brant E
BE
Billinghurst
Sulayman A
SA
Oladepo
Glen R
GR
Loppnow
D000042:Absorption; D013059:Spectrum Analysis, Raman; D013936:Thymidine / Q000737:chemistry; D013938:Thymidine Monophosphate / Q000737:chemistry; D013941:Thymine / Q000031:analogs & derivatives*; D014466:Ultraviolet Rays
D013938:Thymidine Monophosphate; D013941:Thymine; D013936:Thymidine