https://www.ks.uiuc.edu/Publications/Papers/PDF/RITZ2000/RITZ2000.pdf

A Model for Photoreceptor-Based Magnetoreception in Birds

Electron transfer in biological molecules provides both insight and inspiration for developing chemical systems having similar functionality. Photosynthesis is an example of an integrated system in which light harvesting, photoinduced charge separation, and catalysis combine to carry out two thermodynamically demanding processes, the oxidation of water and the reduction of carbon dioxide. The development of artificial photosynthetic systems for solar energy conversion requires a fundamental understanding of electron-transfer reactions between organic molecules. Since these reactions most often involve single-electron transfers, the spin dynamics of photogenerated radical ion pairs provide important information on how the rates and efficiencies of these reactions depend on molecular structure. Given this knowledge, the design and synthesis of large integrated structures to carry out artificial photosynthesis is moving forward. An important approach to achieving this goal is the development of small, functional building blocks, having a minimum number of covalent bonds, which also have the appropriate molecular recognition sites to facilitate self-assembly into a complete, functional artificial photosynthetic system.

Energy, charge, and spin transport in molecules and self-assembled nanostructures inspired by photosynthesis.

Although it has been known for almost half a century that migratory birds can detect the direction of the Earth's magnetic field, the primary sensory mechanism behind this remarkable feat is still unclear. The leading hypothesis centers on radical pairs—magnetically sensitive chemical intermediates formed by photoexcitation of cryptochrome proteins in the retina. Our primary aim here is to explain the chemical and physical aspects of the radical-pair mechanism to biologists and the biological and chemical aspects to physicists. In doing so, we review the current state of knowledge on magnetoreception mechanisms. We dare to hope that this tutorial will stimulate new interdisciplinary experimental and theoretical work that will shed much-needed additional light on this fascinating problem in sensory biology.

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The Radical-Pair Mechanism of Magnetoreception.

Migratory birds travel vast distances each year, finding their way by various means, including a remarkable ability to perceive the Earth's magnetic field. Although it has been known for 40 years that birds possess a magnetic compass, avian magnetoreception is poorly understood at all levels from the primary biophysical detection events, signal transduction pathways and neurophysiology, to the processing of information in the brain. It has been proposed that the primary detector is a specialized ocular photoreceptor that plays host to magnetically sensitive photochemical reactions having radical pairs as fleeting intermediates. Here, we present a physical chemist's perspective on the “radical pair mechanism” of compass magnetoreception in birds. We outline the essential chemical requirements for detecting the direction of an Earth-strength ≈50 μT magnetic field and comment on the likelihood that these might be satisfied in a biologically plausible receptor. Our survey concludes with a discussion of cryptochrome, the photoactive protein that has been put forward as the magnetoreceptor molecule.

https://www.pnas.org/content/pnas/106/2/353.full.pdf

Chemical magnetoreception in birds: The radical pair mechanism

Issues associated with the exposure of patients to strong, static magnetic fields during magnetic resonance imaging (MRI) are reviewed and discussed. The history of human exposure to magnetic fields is reviewed, and the contradictory nature of the literature regarding effects on human health is described. In the absence of ferromagnetic foreign bodies, there is no replicated scientific study showing a health hazard associated with magnetic field exposure and no evidence for hazards associated with cumulative exposure to these fields. The very high degree of patient safety in strong magnetic fields is attributed to the small value of the magnetic susceptibility of human tissues and to the lack of ferromagnetic components in these tissues. The wide range of susceptibility values between magnetic materials and human tissues is shown to lead to qualitatively differing behaviors of these materials when they are exposed to magnetic fields. Mathematical expressions are provided for the calculation of forces and torques.

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Safety of Strong, Static Magnetic Fields

ions was studied by Margulis et al.156 These authors used solvent mixtures of water or ethanol with glycerol to obtain very highly viscous solvents. Varying the temperature and the solvent composition, they showed that the MFEs are determined by the value of T/q. MFEs on the free radical yield (determined by flash spectroscopy) or on the permanent bleaching reaction (determined by continuous photolysis) became detectable only at T/q values smaller than 10 K/cP. At room temperature this corresponds to viscosities larger than 20 cP. In the systems investigated by Margulis et (cf. Table 8). The magnetic field causes an increase of free radical yield, which results from a suppression of tripletsinglet transitions by a magnetic field. The MFD curves are of the case 2 type, which is taken as evidence for a contribution of the relaxation mechanism. Remarkably, Margulis et al. also found MFEs on the second-order recombination rate constant in the case of riboflavin semiquinone radicals and benzophenone ketyl radicals. The second-order bulk recombination rate is slowed down by the magnetic field, demonstrating that F pairs behave rather like geminate triplet pairs, which has also been confirmed in many CIDNP investigations. MFEs in the photochemistry of quinoline and isoquinoline derivatives have been reported by Hata et al.318-320 Photochemical hydrogen abstractions by the ring nitrogen from the solvent ethanol are believed to be the primary reactions in the photoreactions of 1isoquinolinecarbonitrile (7) and 4-methylquinoline-2carbonitrile (9). For the reaction of 7 (eq 46) the

/pdf/magnetic-field-effects-in-chemical-kinetics-and-related-4k3mf64iio.pdf

Magnetic field effects in chemical kinetics and related phenomena

Magnetic Field Effects in Chemical Kinetics and Related Phenomena

/pdf/investigation-of-triplet-exciplex-dynamics-by-magnetic-field-1vxnbe9e2s.pdf

Thomas Ulrich

Papers

Magnetic field effects in chemical kinetics and related phenomena

Magnetic Field Effects in Chemical Kinetics and Related Phenomena

Investigation of Triplet Exciplex Dynamics by Magnetic Field Effects due to the Triplet Mechanism

Magnetic-field-dependent recombination kinetics of geminate radical pairs in reversed micelles of variable size

Control of photo-electron-transfer induced radical production by micellar cages, heavy-atom substituents and magnetic fields