Recombination yield of geminate radical pairs in low magnetic fields – A Green’s function method

Doktorov, A.B.; Hansen, Martin J.; Pedersen, J. Boiden

doi:10.1016/j.chemphys.2006.07.038

Cited by 3 publications

(4 citation statements)

References 12 publications

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“…34,35 Green's function methods have proved to be efficient for tackling problems in spin chemistry, in particular for analytical studies of small model systems. 33,[36][37][38][39][40][41][42][43] Here, we employ the approach as a numerical tool to predict the recombination efficiency of realistic radical pairs, a task that, at low fields, is intractable by direct solution. For the convenience of the reader and to summarize the essence of the numerical implementation, we outline the theoretical fundamentals.…”

Section: Spin Dynamics Simulationsmentioning

confidence: 99%

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Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

Evans

Kattnig

Henbest

et al. 2016

The Journal of Chemical Physics

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Even though the interaction of a <1 mT magnetic field with an electron spin is less than a millionth of the thermal energy at room temperature (kBT), it still can have a profound effect on the quantum yields of radical pair reactions. We present a study of the effects of sub-millitesla magnetic fields on the photoreaction of flavin mononucleotide with ascorbic acid. Direct control of the reaction pathway is achieved by varying the rate of electron transfer from ascorbic acid to the photo-excited flavin. At pH 7.0, we verify the theoretical prediction that, apart from a sign change, the form of the magnetic field effect is independent of the initial spin configuration of the radical pair. The data agree well with model calculations based on a Green's function approach that allows multinuclear spin systems to be treated including the diffusive motion of the radicals, their spin-selective recombination reactions, and the effects of the inter-radical exchange interaction. The protonation states of the radicals are uniquely determined from the form of the magnetic field-dependence. At pH 3.0, the effects of two chemically distinct radical pair complexes combine to produce a pronounced response to ∼500 μT magnetic fields. These findings are relevant to the magnetic responses of cryptochromes (flavin-containing proteins proposed as magnetoreceptors in birds) and may aid the evaluation of effects of weak magnetic fields on other biologically relevant electron transfer processes.

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Section: Spin Dynamics Simulationsmentioning

confidence: 99%

“…Applications of the method have been documented by Doktorov and co-workers; readers interested in the theoretical details are referred to their work. 33,[36][37][38][39][40][41][42][43] A. Theory…”

Section: Spin Dynamics Simulationsmentioning

confidence: 99%

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

Evans

Kattnig

Henbest

et al. 2016

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…Despite the rather short lifetimes of the transient radicals in a typical system, these reactions have been fairly well understood, owing mostly to their specific properties of spin-selective recombination and sensitivity to an external magnetic field . In particular, it was found that even relatively weak magnetic fields can substantially alter the rates of chemical reactions proceeding via the formation of a spin-correlated radical pair. − Furthermore, it was shown that the spin-selective recombination of the pair can be controlled by an “external” paramagnetic particlea third spin magnetically coupled to the pair partners. , …”

Section: Introductionmentioning

confidence: 99%

“…4 In particular, it was found that even relatively weak magnetic fields can substantially alter the rates of chemical reactions proceeding via the formation of a spin-correlated radical pair. [5][6][7][8][9][10][11][12][13][14][15][16][17] Furthermore, it was shown that the spin-selective recombination of the pair can be controlled by an "external" paramagnetic particlesa third spin magnetically coupled to the pair partners. 18,19 This phenomenon is now commonly referred to as "spin catalysis" and has been experimentally verified for several photochemical, biochemical and radiochemical systems.…”

Section: Introductionmentioning

confidence: 99%

Difficulties in Building Radiation-Generated Three-Spin Systems Using Spin-Labeled Luminophores

Matveeva¹,

Sviridenko²,

Korolev³

et al. 2007

J. Phys. Chem. A

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Aromatic compounds are well-known acceptors of primary radical ions that are formed under high-energy irradiation of nonpolar systems. Thus formed radical ion pairs recombine and produce magnetosensitive fluorescence, which helps study the short-lived radical ions. It was initially suggested that a simple introduction of a spin label into the original arene would allow an easy transition from two-spin to three-spin systems, retaining the experimental techniques available for radical pairs. However, it turned out that spin-labeled arenes often do not produce magnetosensitive fluorescence in the conditions of a conventional radiochemical experiment. To understand the effect of the introduced spin label, we synthesized a series of compounds with the general structure "stable 3-imidazoline radical-two-carbon bridge-naphthalene" as well as their diamagnetic analogues. By use of this set of acceptors, we determined the processes that ruin the observed signal and established their connection with the chemical structure of the compound. We found that the compounds with flexible (saturated) two-carbon bridges between the luminophore and the stable radical moieties exist in solution in folded conformation, which leads to suppression of luminescence from naphthalene due to efficient through-space exchange quenching of the excited state by the radical. Increasing the rigidity of the bridge by introducing the double bond drastically increases the reactivity of the extended pi-system. In these compounds, the energy released upon recombination is spent in radiationless processes of chemical transformations both at the stage of the radical ion and at the stage of the electronically excited molecule.

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General relationships between the kinetic characteristics of bulk and geminate recombination of radicals in solutions

Doktorov,

Lukzen

2023

J Math Chem

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Recombination yield of geminate radical pairs in low magnetic fields – A Green’s function method

Cited by 3 publications

References 12 publications

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

Sub-millitesla magnetic field effects on the recombination reaction of flavin and ascorbic acid radicals

Difficulties in Building Radiation-Generated Three-Spin Systems Using Spin-Labeled Luminophores

General relationships between the kinetic characteristics of bulk and geminate recombination of radicals in solutions

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