ESR characteristics of one-electron reduced thymine in monomer, oligomer, and polymer derivatives.

ESR spectra have been recorded of one-electron reduced thymine (T.-) trapped in a variety of thymine derivatives and matrices. Most of the data were taken at Q-band microwave frequencies on 12 M LiCl glasses containing oligo(T) varying from 2 to 18 nucleotides in length. A nonlinear least-squares simulation program was used to simulate the ESR spectra, resulting in a parameter set that can be used to generate T.- powder spectra at X- and Q-band frequencies. Although it is not possible to identify a unique set of g and hyperfine tensors, it is possible to establish boundaries for these interactions and propose a parameter set that is likely and reasonable. As the trapping molecule is varied from TdR to oligo(T) to poly(T), there are small changes in the interaction parameters. The changes are not large enough to account for the differences between hfc values determined from DNA fiber data versus hyperfine coupling values measured from monomer systems. The analysis also indicates that, in these systems, T.- does not protonate between 4 and 77 K at neutral pH.