Marcus Cross-relationship Probed by CIDNP Study of Degenerate Electron Exchange Reactions of Short-lived Radicals | Chapter 3 | Chemical and Materials Sciences: Research Findings Vol. 5

The time-resolved CIDNP method can provide information about degenerate exchange reactions (DEEs) involving short-lived radicals. The purpose of this study is to probe the applicability of the Marcus cross-relation, with better accuracy provided through knowledge of the temperature dependences of the corresponding DEE rate constants. In the temperature range from 8 to 65 °C, the DEE reactions of the guanosine-5′-monophosphate anion GMP(-H)− with the neutral radical GMP(-H)•, of the N-acetyltyrosine anion N-AcTyrO− with a neutral radical N-AcTyrO•, and of the tyrosine anion TyrO− with a neutral radical TyrO• were studied. The setup for the time-resolved CIDNP experiments was based on a Bruker DRX200 NMR spectrometer (Bruker Corporation, Billerica, MA, U.S.; magnetic field 4.7 Tesla, resonance frequency of protons 200 MHz). In all the studied cases, the radicals were formed in the reaction of quenching triplet 2,2′-dipyridyl. The reorganisation energies were obtained from Arrhenius plots. The rate constant of the reductive electron transfer reaction in the pair GMP(-H)•/TyrO− was determined at T = 25 °C. Rate constants of the GMP(-H)• radical reduction reactions with TyrO− and N-AcTyrO− anions calculated by the Marcus cross-relation differ from the experimental ones by two orders of magnitude. The rate constants of several other electron transfer reactions involving GMP(-H)−/GMP(-H)•, N-AcTyrO−/N-AcTyrO•, and TyrO−/TyrO• pairs calculated by cross-relation agree well with the experimental values. The rate of nuclear paramagnetic relaxation was found for the 3,5 and β-protons of TyrO• and N-AcTyrO•, the 8-proton of GMP(-H)•, and the 3,4-protons of DPH• at each temperature. In all cases, the dependences of the rate of nuclear paramagnetic relaxation on temperature are described by the Arrhenius dependence. These findings demonstrate that time-resolved CIDNP, with microsecond resolution, provides a powerful approach for studying the kinetics of DEE reactions and validating theoretical models of electron exchange.

 

 

Author(s) Details

Maksim P. Geniman
International Tomography Center SB RAS, 630090 Novosibirsk, Russia and Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russia.

 

Olga B. Morozova
International Tomography Center SB RAS, 630090 Novosibirsk, Russia.

 

Nikita N. Lukzen
International Tomography Center SB RAS, 630090 Novosibirsk, Russia and Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russia.

 

Günter Grampp
Institute of Physical and Theoretical Chemistry, Graz University of Technology, Stremayrgasse, 9, A-8010 Graz, Austria.

 

Alexandra V. Yurkovskaya
International Tomography Center SB RAS, 630090 Novosibirsk, Russia.

 

 

Please see the book here :- https://doi.org/10.9734/bpi/cmsrf/v5/5922