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Kinetic Magnetic‐Field Effect Involving the Small Biologically Relevant Inorganic Radicals NO and O 2 .−
Author(s) -
Karogodina Tatiana Y.,
Dranov Igor G.,
Sergeeva Svetlana V.,
Stass Dmitry V.,
Steiner Ulrich E.
Publication year - 2011
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100178
Subject(s) - chemistry , radical , aqueous solution , kinetic energy , reaction rate constant , magnetic field , yield (engineering) , analytical chemistry (journal) , thermodynamics , computational chemistry , kinetics , physics , organic chemistry , quantum mechanics
Oxidation of dihydrorhodamine 123 (DHR) to rhodamine 123 (RH) by oxoperoxonitrite (ONOO − ), formed through recombination of NO and O 2 .− radicals resulting from thermal decomposition of 3‐morpholinosydnonimine (SIN‐1) in buffered aerated aqueous solution at pH 7.6, represents a kinetic model system of the reactivity of NO and O 2 .− in biochemical systems. A magnetic‐field effect (MFE) on the yield of RH detected in this system is explored in the full range of fields between 0 and 18 T. It is found to increase in a nearly linear fashion up to a value of 5.5±1.6 % at 18 T and 23 °C (3.1±0.7 % at 40 °C). A theoretical framework to analyze the MFE in terms of the magnetic‐field‐enhanced recombination rate constant k rec of NO and O 2 .− due to magnetic mixing of T 0 and S spin states of the radical pair by the Δ g mechanism is developed, including estimation of magnetic properties ( g tensor and spin relaxation times) of NO and O 2 .− in aqueous solution, and calculation of the MFE on k rec using the theoretical formalism of Gorelik at al. The factor with which the MFE on k rec is translated to the MFE on the yield of ONOO − and RH is derived for various kinetic scenarios representing possible sink channels for NO and O 2 .− . With reasonable assumptions for the values of some unknown kinetic parameters, the theoretical predictions account well for the observed MFE.