A Biomagnetic Sensory Mechanism Based on Magnetic Field Modulated Coherent Electron Spin Motion

Abstract

Biomagnelism / Electron spin states / Hyperfine interaction Electron transfer processes which generate radical pairs in coherent electron spin states (singlet or triplet) are affected by weak magnetic fields [Schulten et ai, . physik. Chem. Neue Folge 101 (1976) 371]. Based on this finding we suggest a reaction mechanism for a chemical compass which exhibits a sensitivity on the orientation of the geomagnetic field originating from an anisotropy of the hyperfine interaction experienced by unpaired electron spins in a redox process. It is argued that such mechanism may explain the ability of many biological species to orient themselves in the geomagnetic field.

Magnetic orientation of garden warblers ( Sylvia borin ) under 1.4 MHz radiofrequency magnetic field

“…The latter is especially interesting, because the well-documented existence of the magnetic compass in birds remains one of few unambiguous demonstrations of the elusive magnetic sense of animals, the physical and physiological origins of which are still unclear [10]. Based, again, mainly on laboratory experiments with birds, two theoretical models of magnetoreception in terrestrial animals were singled out as the most viable: one involving magnetic nanocrystals of iron oxides [11] and the other based on magneto-sensitive photochemical reactions in the eye [12,13] (the radical-pair model, RPM).…”

The quantum needle of the avian magnetic compass

“…The primary sensory receptors are located in the eyes (2,3,(5)(6)(7), and directional information is processed bilaterally in a small part of the forebrain accessed via the thalamofugal visual pathway. The evidence currently points to a chemical sensing mechanism based on photo-induced radical pairs in cryptochrome flavoproteins in the retina (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Anisotropic magnetic interactions within the radicals are thought to give rise to intracellular levels of a cryptochrome signaling state that depend on the orientation of the bird's head in the Earth's magnetic field (8,9,19).…”

“…The evidence currently points to a chemical sensing mechanism based on photo-induced radical pairs in cryptochrome flavoproteins in the retina (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Anisotropic magnetic interactions within the radicals are thought to give rise to intracellular levels of a cryptochrome signaling state that depend on the orientation of the bird's head in the Earth's magnetic field (8,9,19). In support of this proposal, the photochemistry of isolated cryptochromes in vitro has been found to respond to applied magnetic fields in a manner that is quantitatively consistent with the radical pair mechanism (15).…”

“…The general aim is to determine how the yield of a reaction product depends on the orientation of the reactants with respect to the magnetic field axis. A crucial element in all such calculations is the presence of nuclear spins whose hyperfine interactions are the source of the magnetic anisotropy (8,16). Most studies have focused on idealized spin systems comprising the two electron spins, one on each radical, augmented by one or two nuclear spins (9,(21)(22)(23)(24)(25)(26)(27)34).…”

Chemical magnetoreception in birds: The radical pair mechanism

“…Radical pair reactions were first proposed as a magnetoreceptor by Schulten (18,19), prompted by the findings that avian magnetic orientation is lightdependent-suggesting a photochemical process-and is responsive to the inclination rather than the polarity of the geomagnetic field (20)(21)(22)(23); unlike a magnetic compass needle, birds maintain their orientation when the ambient field vector is reversed (5).…”