Free radicals formed by exposure of pyrimidine solids to sodium atoms: an electron spin resonance study.

Sodium atoms have been deposited on various pyrimidine powders under high vacuum at 77 degrees K and the electron spin resonance spectra of the resulting free radicals have been observed. Generally, the spectra show that the electron of the Na goes into a molecular orbital of the pyrimidine ring and the Na+ ions become attached to a carbonyl oxygen of the resulting pyrimidine anion. In 5-fluorouracil and 5-chlorouracil, however, the halogen is evidently abstracted by the Na to form NaF or NaC1 and the neutral uracil radical. Thymine shows evidence for H-addition radicals as well as the Na+-[thymine]-complex. The H source for the addition radicals may be an H-2-0 impurity in the sample, with which the Na atoms combine to release the H atoms. In addition to a resonance with g equals 2.00 from the pyrimidine anion radical, broad resonances with g greater than 2 were observed for 5-bromouracil, 5-chlorouracil and 5-iodouracil, as well as for alloxan and cytosine. These resonances, generally unstable at room temperature, are believed to arise from electrons trapped in interstitial sties or vacancies in the lattice.

Duke Scholars

Author G. Allan Johnson Radiology