Berlin 2005 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 30: POSTER: Chemical physics
CPP 30.13: Poster
Tuesday, March 8, 2005, 16:30–18:30, Poster TU D
Structure and Magnetic Resonance Parameters of the Cation-Radicals of Methionine as Studied by the CIDNP Magnetic Field Dependence — •Sergey Korchak1,2, Konstantin Ivanov2, Alexandra Yurkovskaya2, and Hans-Martin Vieth1 — 1Department of Physics, Free University of Berlin, D-14195 Berlin, Germany — 2International Tomography Center of SB RAS, 630090, Institutskaya 3a, Novosibirsk, Russia
Radical intermediates as they play a key role in many photoreactions often elude spectroscopic characterization because of their high reactivity resulting in a lifetime too short for direct observation. An indirect method exploiting the dynamic spin polarization created in the paramagnetic reaction stage and conserved in the diamagnetic reaction product circumvents this problem. Such a Chemically Induced Dynamic Nuclear Polarization (CIDNP) formed in the reactions of methionine (Met) and N-acetylmethionine (NMet) with triplet excited 4-carboxybenzophenone (CBP) was measured in an external magnetic field of 0-7 Tesla in neutral and basic aqueous solution. The results show that at a pH above 9, the Met cation radical exists in a cyclic form with a two-center three-electron bond between the nitrogen and sulfur atoms, whilst at pH below 9 the Met cation radical has a linear structure. Cation radicals of NMet are formed in linear structure only. By comparing the experimental results with model calculations the g-factors and the hyperfine constants of the cyclic and linear cation radicals were determined. Experimental method and simulation technique will be discussed.