Open AccessElectron Spin Resonance of Pteridine Radicals and the Structure of Hydropteridines
Author(s) -
Ehrenberg Anders,
Hemmerich Peter,
Müller Franz,
Pfleiderer Wolfgang
Publication year - 1970
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1970.tb01121.x
Subject(s) - radical , chemistry , delocalized electron , electron paramagnetic resonance , pteridine , hyperfine structure , resonance (particle physics) , electron transfer , crystallography , unpaired electron , photochemistry , nuclear magnetic resonance , atomic physics , organic chemistry , physics , enzyme
Cations of monohydropteridine radicals have been obtained in solution and investigated by electron spin resonance. The hyperfine pattern of these signals as well as that of previously described trihydropteridine radical cations has been computed to agreement with experiment. The first mentioned radicals are shown to have 5,8‐H 2 Pter + ‐structure, whereas the latter are 5,6,7,8‐H 4 Pter + . Substitutions in the pyrimidine part of the system (positions 1–4) do not affect the spin distribution essentially in any case. In monohydropteridine the unpaired electron is delocalized over the whole pyrazine part of the system (positions 5–8), whereas in trihydropteridines it is mainly confined to N(5) and possibly to the bridge carbons. The biochemical implications of pteridine radicals are discussed. While two‐electron oxidoreduction, implying 7,8‐dihydropteridine, is thermodynamically irreversible, one‐electron oxidoreduction appears to be intermediate in the systems Pter/5,8‐H 2 Pter on the one hand, and 6,7‐H 2 Pter/H 4 Pter on the other hand, thus permitting rapid electron transfer. Hence, it is reasonable to assume that trihydropteridine radicals might be of biological importance, though clearly not as the strongly acidic cations described here, but maybe in the stabilized form of metal complexes. In this context, existence, stability and eventual biological importance of the various dihydropteridine isomers is discussed.