Dresden 2009 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 37: Biopolymers (joint session CPP/BP)
CPP 37.11: Vortrag
Donnerstag, 26. März 2009, 17:15–17:30, ZEU 114
Photo-CIDNP study of transient radicals of Met-Gly and Gly-Met peptides — Olga Morozova1, Sergey Korchak2, Hans-Martin Vieth2, and •Alexandra Yurkovskaya1,2 — 1International Tomography Center, Institutskaya 3a, Novosibirsk, Russia — 2FB Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin
Photo-reactions of methionine containing dipeptides, glycylmethionine (Gly-Met) and methionylglycine (Met-Gly) were studied by time-resolved Chemically Induced Dynamic Nuclear Polarization (CIDNP) a method particularly sensitive to short-lived radical species. In aqueous solution we established several competing reaction pathways following triplet quenching of the photosensitizer 4-carboxybenzophenone depending on the pH: for Gly-Met electron transfer from the sulfur atom takes place, also from the terminal amino group. Two channels of triplet quenching are distinguishable also for Met-Gly: electron transfer from the amino group and from the sulfur atom, here with the formation of a cation radical with a three electron two center S-N bond. At pH<pKa of the terminal amino group Met-Gly forms a linear S-centered radical succeeded by a five-membered cyclic radical. At pH>pKa both peptides form aminium radicals by electron transfer from their N-terminal amino group with deprotonation to the aminyl radical. The radicals were characterized using the dependence of CIDNP on the magnetic field. The potential of the CIDNP techniques in studying other complex biological radical reactions will be discussed. Financial support by the RFBR projects # 08-03-00539, EU FP6 projects "Bio-DNP" and MIF2-CT-2006-022008 is acknowledged.