Spin-selective recombination reactions of radical pairs: Experimental test of validity of reaction operators

Maeda, Kiminori; Liddell, Paul A.; Gust, Devens; Hore, P. J.

doi:10.1063/1.4844355

Cited by 20 publications

(33 citation statements)

References 44 publications

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“…Of particular interest to us is the paper by Jones and Hore [27] who derived their reaction operator using Kraus maps [16]. The Jones-Hore equation predicts a different singlet-triplet dephasing rate to the conventional approach of Haberkorn's and has been the subject of a recent experiment aimed at discriminating the two models [31]. This experiment showed the Jones-Hore equation to be inconsistent with the measured dephasing rate.…”

Section: Arxiv:150604213v2 [Quant-ph] 20 Aug 2015mentioning

confidence: 99%

“…k S + k T , rather than the average predicted by L H (or L K ). Despite being perceived by Jones and Hore to be too small a difference to be detectable in an experiment [27], Maeda and colleagues have recently managed to place the two models under experimental scrutiny [31] using pulsed electron paramagnetic resonance spectroscopy [47]. We briefly review some key elements of this experiment below.…”

Section: Theoretical Modelsmentioning

confidence: 99%

“…[31] uses radical pairs in a modified version of the carotenoid-porphyrinfullerene triad molecule of Ref. [4].…”

Section: Experimental Discriminationmentioning

confidence: 99%

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Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

et al. 2016

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Classical chemical kinetics use rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, or in other words, a reaction which contain only incoherent transitions. A prominent example reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator which determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts a recombination dephasing rate consistent with recent experiments [J. Chem. Phys. 139, 234309 (2013)], in contrast to previous work by Jones and Hore [Chem. Phys. Lett. 488, 90 (2010)]. The standard radical-pair reaction has conventionally been described by either a normalised density operator incorporating both the radical pair and reaction products, or by a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalised and refers only to radical-pair states. Generalisations to include additional dephasing processes and an arbitrary number of sites are also discussed.

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Section: Arxiv:150604213v2 [Quant-ph] 20 Aug 2015mentioning

confidence: 99%

Section: Theoretical Modelsmentioning

confidence: 99%

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Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

et al. 2016

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“…There is much exciting work in this area [97] and it is fascinating to consider whether these more 'quantum' models may be useful in the analysis of olfaction and enzyme reaction rates. It is less obvious how environmental vibrations contribute in magnetoreception; however, it has been experimentally shown that the environment does not disguise any effect [91], and it is likely that the D/A pair that encode the field are held at relative orientations optimal for the effect transduction ( figure 13) which is of course determined by the host protein.…”

Section: (A) Environment Helpsmentioning

confidence: 99%

“…Figure 15. Reaction mechanism (b) and two-dimensional structures of the carotenoid (C)-porphyrin (P)-fullerene (F) system (a) that demonstrates the 'chemical compass' principle, from [91]. Interconversion between singlet and triplet pair is shown [C •+ − P − F…”

Section: Bird Magnetoreceptionmentioning

confidence: 99%

Quantum effects in biology: golden rule in enzymes, olfaction, photosynthesis and magnetodetection

Brookes

2017

Proc. R. Soc. A.

112

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Despite certain quantum concepts, such as superposition states, entanglement, 'spooky action at a distance' and tunnelling through insulating walls, being somewhat counterintuitive, they are no doubt extremely useful constructs in theoretical and experimental physics. More uncertain, however, is whether or not these concepts are fundamental to biology and living processes. Of course, at the fundamental level all things are quantum, because all things are built from the quantized states and rules that govern atoms. But when does the quantum mechanical toolkit become the best tool for the job? This review looks at four areas of 'quantum effects in biology'. These are biosystems that are very diverse in detail but possess some commonality. They are all (i) effects in biology: rates of a signal (or information) that can be calculated from a form of the 'golden rule' and (ii) they are all protein-pigment (or ligand) complex systems. It is shown, beginning with the rate equation, that all these systems may contain some degree of quantum effect, and where experimental evidence is available, it is explored to determine how the quantum analysis aids in understanding of the process.

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Spin Dynamics in Radical Pairs

Lewis

2018

Springer Theses

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The coherent spin dynamics of radical pairs play a crucial role in their reactions, which consequently cannot be described by a simple kinetic scheme. Instead, simulations of the spin dynamics are required in order to predict the rate and outcome of radical pair reactions, and especially their response to the application of a magnetic field. Unfortunately, the number of spin states of the radical pair increases exponentially with the number of nuclear spins, making deterministic quantum mechanical simulations of realistic radical pairs difficult.To overcome this difficulty, this thesis begins by presenting an efficient stochastic quantum mechanical method capable of describing a radical pair with as many as 20 nuclear spins, which we use to analyse spin-dependent charge recombination rates along molecular wires. This enables us to identify the mechanism of charge recombination of both the singlet and triplet states of the wire by determining their relative contributions to the overall recombination rate.We then derive an approximate semiclassical theory which allows to treat the spin dynamics of much larger radical pairs, since the time required for a semiclassical calculation scales linearly with the number of nuclear spins, rather than exponentially. Using this method, we reproduce the results of the first experiments to show that the outcome of a radical pair reaction may be influenced by an Earthstrength magnetic field, and calculate the anisotropy in the singlet recombination yield of the radical pair thought to be responsible for avian magnetoreception.We show that our semiclassical theory reduces to the earlier Schulten-Wolynes theory under two additional approximations, and use this simpler theory to reveal that singlet-triplet dephasing plays an important role in the spin dynamics of polaron pairs in the semiconducting polymer layer of organic light emitting diodes. We derive a new expression which relates the magnetic field dependence of the electroluminescence and conductance observed in these materials to the singlet yield of the radical pair recombination reaction, which we confirm produces better agreement with experimental data than the relationships used previously.Thanks to Prof. Peter Hore for all of his expert advice on spin dynamics, and for putting us on the right track time after time.Thanks to Joseph Lawrence and Tom Fay for being excellent colleagues and for a whole host of bright ideas about oLEDs and molecular wires.I would like to thank Susannah Worster for her helpful explanations of Redfield theory and other descriptions of relaxation, and Hamish Hiscock for his comments on Chapter 5, as well as their invaluable help in tackling spin dynamics with me.Huge thanks must go to my parents, Joy and Andy, and my brother Mark, for encouraging, challenging, and supporting me throughout my academic career.Thank you to my loving wife Hannah, who has taken a great interest in my research, patiently listened to all of my jelly baby-based explanations of quantum chemistry, and selflessly given her ...

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Spin-selective recombination reactions of radical pairs: Experimental test of validity of reaction operators

Cited by 20 publications

References 44 publications

Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

Quantum effects in biology: golden rule in enzymes, olfaction, photosynthesis and magnetodetection

Spin Dynamics in Radical Pairs

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