Open AccessFree radicals formed by exposure of pyrimidine solids to sodium atoms: an electron spin resonance study.
Author(s) -
G. Allan Johnson
Publication year - 1975
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.72.3.974
Subject(s) - chemistry , radical , electron paramagnetic resonance , thymine , pyrimidine , uracil , photochemistry , ion , resonance (particle physics) , hyperfine structure , crystallography , stereochemistry , nuclear magnetic resonance , dna , atomic physics , organic chemistry , biochemistry , physics
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.