Berlin 2005 – wissenschaftliches Programm
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CPP: Chemische Physik und Polymerphysik
CPP 30: POSTER: Chemical physics
CPP 30.11: Poster
Dienstag, 8. März 2005, 16:30–18:30, Poster TU D
Investigation of field dependent CIDNP in multinuclear radical pairs: Determination of magnetic interaction parameters in tryptophan radicals by comparison with model calculations — •Karsten Miesel1, 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
The magnetic field dependence of chemically induced dynamic nuclear polarisation (1H-CIDNP) formed in reversible electron transfer reaction between triplet excited dyes (2,2’-dipyridyl and anthraquinone-2-sufonate) and N-acetyl-tryptophan in aqueous solutions at varying pH was observed and compared to model calculations. The experiment employs fast field cycling between a variable field of polarization ranging from 0 to 7T and the fixed field of a cryomagnet for high resolution NMR detection. At high field the CIDNP depends on both g-factors and hyperfine interactions (HFI) of the radicals, while at low field it is conditioned solely by HFI. The difference between magnetic resonance parameters for cationic and neutral radicals of tryptophan is discussed. The entanglement of spins in the tryptophan radicals formed at zero magnetic field was unravelled by Fourier-analysing the dependence of the CIDNP spectral pattern on the duration of the NMR rf excitation pulse. This approach provides information about the populations of all involved nuclear spin states and allows verifying the HFI constants obtained from simulations of the CIDNP field dependence.