Man Nien Schuchmann1, Heinz-Peter Schuchmann1, Wolfgang Knolle2, Justus von Sonntag2, Sergey Naumov2, Wen-Feng Wang3,Clemens von Sonntag1
1 Max-Planck-Institut fur Strahlenchemie, Stiftstrasse 34-36, P.O. Box 101365, D-45413 Mulheim an der Ruhr, Germany,
2 Institut fur Oberflachenmodifizierung, Permoserstrasse 15, D-04303 Leipzig, Germany,
3 Shanghai Institute for Nuclear Research, P.O. Box 800-204 Shahghai 201800, China
Hydroxyl radicals react with thiourea (and its tetramethyl derivative) yielding dimeric radical cations which are characterized by strong absorptions at 400 nm (450 nm). An analysis of the kinetics of the buildup of these absorptions gives evidence for the intermediacy of OH-adducts and the monomeric radical cations. The dimeric radical cations are also generated in the reactions of triplet-excited maleimide with these thioureas. Moreover, in acid solutions even reducing radicals such as the H atom and a-hydroxyalkyl radicals give rise to these intermediates in full yields, albeit displaying different kinetics. Potential mechanistic implications are discussed. The dimeric thiourea radical cations are strong oxidants and readily oxidize the anions of phenol and 2’-deoxyguanosine. The solvated electron gives rise to an intermediate which is rapidly protonated by water (pKa > 11). Quantum-mechanical calculations support the assignment of the 400 nm (450 nm) absorption to the respective dimeric thiourea radical cation.