Nitrosyliron complexes with mercapto-purines and -pyrimidines studied by Nuclear Magnetic and Electron Spin Resonance Spectroscopy

The formation of dinitrosyliron complexes with mercapto-purines and -pyrimidines has been studied by e.s.r. and n.m.r. spectroscopy. The binding sites were established by the aid of computer-simulated spectra and of isotopic substitution with 15NO. The sulphur atom complexed with the iron only if ionized. Hindered tautomerism caused complexation via the imidazole nitrogen atoms in mercaptopurines. Two complexes were present at pH 7 in mercaptopyrimidines. A nine-line e.s.r. spectrum was attributed to a complex with two base molecules bonded to the iron atom, one via N-3 and the other via S-. A quintet was attributed to a complex with two bases bonded via S-.