Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 12: POSTER Colloids, Nanoparticles and Self-Organizing Systems

CPP 12.29: Poster

Tuesday, March 28, 2006, 17:00–19:00, P3

Electron and Hydrogen Transfer Reactions in the Photolysis of Aromatic Amino Acids Studied by CIDNP — •Karsten Miesel and Hans-Martin Vieth — Department of Physics, Free University of Berlin, Arnimallee 14, D-14195 Berlin, Germany

The near UV photolysis of N-acetyl tyrosine (NATyrOH) and N-acetyl tryptophan (NATrpH) in aqueous solutions was investigated by field dependent chemically induced dynamic nuclear polarisation (FD-CIDNP) and its time dependence in high magnetic field (TR-CIDNP). For both amino acids, ionisation is most efficient in basic solutions yielding a solvated electron (e⁻_aq) and the amino acid radicals NATyrO^• and NATrpH^•+. As the primary event, monophotonic ionisation occurring from singlet excited precursors is identified, leading to a characteristic maximum in their CIDNP field dependencies. Simulations of the field dependencies allowed the determination of g-factors of the amino acid radicals. Concomitantly, some side reactions were investigated, such as decarboxylation and the formation of L-DOPA in the photolysis of tyrosine. The radical precursors are identified and a reaction scheme is presented. The observation of strong ¹H-CIDNP on the solvent peak (HDO) in the photolysis of NATyrO⁻ is attributed to H-transfer between the o-benzosemiquinone radical and NATyrO^•, and subsequent deprotonation of NATyrOH. An equivalent mechanism is proposed to occur in the photolysis of NATrpH.