Theoretical studies of the radiation products of hydroxyproline

The radiation products of hydroxyproline have been investigated using densi ty functional theory. In the resulting radicals, the choice of the apical r ing atom is found to be dependent on the nature and strength of the intramo lecular hydrogen bonding. The observed hyperfine couplings previously assig ned to two zwitterionic conformers of the hydroxyproline primary radical an ion are found to be better described by its nonzwitterionic isomers and cor responding neutral protonated isomers. Similarly, the observed hyperfine co uplings for radicals formed by cleavage of the C-alpha-N bond (deamination) are in closest agreement with those calculated for their neutral forms. Th eoretical proton hyperfine couplings support the experimental assignment of the radical cation formed by decarboxylation and the radicals resulting fr om hydrogen abstraction from the C-2 and C-3 positions. The proton hyperfin e couplings are sensitive to the conformations bf the radicals, which, in t urn, are highly dependent upon the extent of intramolecular hydrogen bondin g.