Magnetic Field For Orientation Research Articles

Atomic Alignment Effects for the Formation of Excimers RgX* (B, C) in the Reaction of Oriented Rg (3P2, MJ = 2) (Rg = Xe, Kr, Ar) + Halogen(X)-Containing Molecules

Atomic alignment effects for the formation of excimers, RgX* (B, Omega = 1/2) and RgX* (C, Omega = 3/2), in the reaction of Rg ((3)P(2)) (Rg = Xe, Kr, Ar) with halogen (X)-containing molecules (RX) (CH(3)I, CF(3)I, CF(3)Br, NF(3), CHBr(3), CHCl(3), CCl(3)F, and CCl(4)) have been measured by using an oriented Rg ((3)P(2), M(J) = 2) atomic beam at a collision energy of approximately 0.07 eV. The emission intensities for RgX* (B, C) have been measured as a function of the magnetic orientation field direction in the collision frame. The reactant (RX) dependence of the atomic alignment effect is extremely different between the RgX* (B) and the RgX* (C) channels. For RgX* (C), an analogous atomic alignment effect is commonly observed despite the difference of RX and Rg. In contrast, for RgX* (B), the atomic alignment effect shows a diverse dependence on RX and Rg.

Atomic Alignment Effect on the Branching to ArCl* and CCl2* Formation in the Reaction of Oriented Ar(3P2,MJ=2) + CCl4

Atomic alignment effects for the formation of ArCl*(C) and CCl2*(A) in the reaction of Ar((3)P 2) + CCl 4 have been measured by using an oriented Ar( (3)P2, M J=2) beam at a collision energy of 0.08 eV. The emission intensity for ArCl*(C) and CCl2*(A) has been measured as a function of the magnetic orientation field direction in the collision frame. A significant atomic alignment effect is observed for the atom transfer process [ArCl*(C) formation]. Formation of ArCl*(C) is modestly enhanced when the electron angular momentum of the Ar((3)P 2) reactant is aligned along the relative velocity vector, while the excitation transfer process [CCl2*(A) formation] shows little alignment effect.

Steric Effect in the Energy Transfer Reaction of N2 + Rg (3P2) (Rg = Kr, Ar)

Steric effect for the formation of N 2 (B, (3)Pi u ) in the energy transfer reaction of Kr ( (3)P 2) + N 2 has been measured using an oriented Kr ( (3)P 2, M J = 2) beam at a collision energy of 0.07 eV. The N 2 (B, (3)Pi u ) emission intensity was measured as a function of the magnetic orientation field direction in the collision frame. A significant atomic alignment effect on the energy transfer probability was observed. This result was compared with that for the formation of N 2 (C, (3)Pi g ) in the Ar ( (3)P 2) + N 2 reaction. Despite the large difference on the energy transfer cross-section, the atomic alignment dependence for Kr ( (3)P 2) + N 2 is found to be analogous to that for Ar ( (3)P 2) + N 2. It is revealed that the configuration of inner 4p (3p) orbital in the collision frame gives an important role for the stereoselectivity on electron transfer process via the curve-crossing mechanism.

Cryptochrome mediates light-dependent magnetosensitivity in Drosophila

Although many animals use the Earth's magnetic field for orientation and navigation, the precise biophysical mechanisms underlying magnetic sensing have been elusive. One theoretical model proposes that geomagnetic fields are perceived by chemical reactions involving specialized photoreceptors. However, the specific photoreceptor involved in such magnetoreception has not been demonstrated conclusively in any animal. Here we show that the ultraviolet-A/blue-light photoreceptor cryptochrome (Cry) is necessary for light-dependent magnetosensitive responses in Drosophila melanogaster. In a binary-choice behavioural assay for magnetosensitivity, wild-type flies show significant naive and trained responses to a magnetic field under full-spectrum light ( approximately 300-700 nm) but do not respond to the field when wavelengths in the Cry-sensitive, ultraviolet-A/blue-light part of the spectrum (<420 nm) are blocked. Notably, Cry-deficient cry(0) and cry(b) flies do not show either naive or trained responses to a magnetic field under full-spectrum light. Moreover, Cry-dependent magnetosensitivity does not require a functioning circadian clock. Our work provides, to our knowledge, the first genetic evidence for a Cry-based magnetosensitive system in any animal.

Chemical compass model of avian magnetoreception

Approximately 50 species, including birds, mammals, reptiles, amphibians, fish, crustaceans and insects, are known to use the Earth's magnetic field for orientation and navigation. Birds in particular have been intensively studied, but the biophysical mechanisms that underlie the avian magnetic compass are still poorly understood. One proposal, based on magnetically sensitive free radical reactions, is gaining support despite the fact that no chemical reaction in vitro has been shown to respond to magnetic fields as weak as the Earth's ( approximately 50 muT) or to be sensitive to the direction of such a field. Here we use spectroscopic observation of a carotenoid-porphyrin-fullerene model system to demonstrate that the lifetime of a photochemically formed radical pair is changed by application of < or =50 microT magnetic fields, and to measure the anisotropic chemical response that is essential for its operation as a chemical compass sensor. These experiments establish the feasibility of chemical magnetoreception and give insight into the structural and dynamic design features required for optimal detection of the direction of the Earth's magnetic field.

Effect of Molecular Rotation on the Atomic Alignment Dependence in the Oriented Ar (3P2) + CF3H Reaction

Atomic alignment effect for the CF3* formation in the oriented Ar (3P2, MJ = 2) + CF3H reaction has been investigated at different two CF3H beam conditions: effusive and supersonic beams. The chemiluminescence intensity of CF3* was measured as a function of the magnetic orientation field direction in the collision frame. A significant contribution of rank 4 moment was recognized. The cross-section for each magnetic M'(J) substate in the collision frame, sigma|M'(J)|, was determined to be sigma(|M'(J)|=0):sigma(|M'(J)|=1):sigma(|M'(J)|=2) = 1.00:0.84 +/- 0.02:0.88 +/- 0.02 for the effusive CF3H beam condition. The atomic alignment effect was found to significantly depend on the CF3H beam condition. For the supersonic beam condition, sigma(|M'(J)|=0&1) was changed to be smaller than sigma(|M'(J)|=2).

Spontaneous preferences for magnetic compass direction in the American red-spotted newt, Notophthalmus viridescens (Salamandridae, Urodela)

In addition to other sensory modalities, migratory vertebrates are able to use the earths’ magnetic field for orientation and navigation. The magnetic cue may also serve as a reference for other orientation mechanisms. In this study, significant evidence is shown that, even in darkness, newts (Notophthalmus viridescens, Salamandridae) spontaneously align according to the natural or to the deviated earth’s magnetic field lines, thereby demonstrating a magnetic compass sensitivity. All newts preferred compass directions close to east or west or chose the E/W axially and hence sought to maintain a specific angle or axis relative to the magnetic field vector. Such an active alignment is considered an essential precondition for magnetic orientation. When the horizontal magnetic vector was experimentally compensated, animals became disoriented. We infer that the animals have either learned the preferred magnetic direction/axis individually or that these choices are innate and could even be seasonally different as in migrating birds. It is still an unanswered question as to how and where the physical and physiological mechanisms of magnetic transduction and reception take place. The visual system and other light-dependent (radical pairs) mechanisms alone are often claimed to be in function, but this must now be reconsidered given the results from animals when deprived of light. The results may therefore point to putative receptor mechanisms involving magnetite elements in specialized magneto-receptors.

Significant change of alignment effect by dimer formation in the dissociative energy transfer reaction of Ar(P23)+(N2O)n and (H2O)n

An alignment effect in the dissociative energy transfer reaction of Ar((3)P(2))+(X(2)O)(n)(X=N,H) was directly measured using an oriented Ar((3)P(2),M(J)=2) beam. The chemiluminescence intensity of N(2)(B,(3)Pi(g)) for (N(2)O)(n) and OH(A,(2)Sigma(+)) for (H(2)O)(n) was measured as a function of the magnetic orientation field direction in the collision frame. The relative reaction cross section for each magnetic substate in the collision frame, sigma(M(J) (') ), was determined. In both the reaction systems, it is observed that the dimer formation significantly enhances the alignment effect and decreases the reactivity, especially for sigma|1| and sigma|2|. A significant contribution of rank 4 moment is recognized in the dimer reaction.

Steric effect in the energy transfer reaction of Ar(P23)+N2

Steric effect for N2(C,3Piu) formation in the energy transfer reaction of Ar(3P2)+N2 was directly measured by using an oriented Ar(3P2,MJ=2) beam at a collision energy of 0.06 eV. The N2(C,3Piu) chemiluminescence intensity was measured as a function of the magnetic orientation field direction in the collision frame. A significant alignment effect on the energy transfer probability was observed. The relative reactivity for each magnetic substate in the collision frame sigma|MJ'|was determined to be sigma|2|:sigma|1|:sigma(0)=0.50:0.60:1.00. It is suggested that the observed steric effect is primarily due to the favorable configuration of the 3p orbital for the efficient overlap with the 2sigma(u) molecular orbital of N(2).

Further experiments on the relationship between hippocampus and orientation following phase-shift in homing pigeons

Following a clock- or phase-shift of the light–dark cycle, hippocampal lesioned pigeons ( Columba livia) consistently display a larger deviation in vanishing bearings away from the homeward direction compared to intact birds; an effect never seen in unshifted birds. In Experiment 1, control and hippocampal lesioned pigeons oriented similarly after being held 1 week under artificial lighting in the absence of a phase-shift. Housing under artificial light by itself does not result in between group orientation differences. In Experiment 2, control and hippocampal lesioned pigeons oriented equally well under overcast conditions, indicating that both groups had a functional magnetic compass. The between group difference in orientation following phase-shift does not appear to be a consequence of control birds being able to use both the sun and earth’s magnetic field for orientation and the hippocampal lesioned pigeons only being able to use the sun. In Experiment 3, lengthening the time held under 6-h clock-shift from 1 to 2 weeks had no effect on the magnitude of the difference in orientation, but fast shifting produced clearer effects than slow shifting. Taken together, the data suggest that hippocampal lesions alter how a pigeon responds to a rapidly changing light–dark cycle, particularly following a fast-shift manipulation, suggesting an as yet unspecified relationship between the avian hippocampus and the circadian rhythm(s) that regulate sun compass orientation.

Magnetic field effects on biomolecules, cells, and living organisms

This article surveys three major areas of biomagnetic research: (a) the magneto-orientation effect; (b) the role of the geomagnetic field in bird orientation and navigation; and (c) the biological effects of extremely low-frequency magnetic fields. The magneto-orientation effect is caused by diamagnetic anisotropy of highly ordered biological structures, such as visual photoreceptor and chloroplast membranes, in a homogeneous magnetic field of about 10 kG. While it is not possible to orient the individual constituent molecules with such a field because of thermal fluctuation, these ordered structures can be oriented as a whole by virtue of summing the anisotropy over a large number of mutually oriented molecules. While the magneto-orientation effect seems to require the use of unphysiologically strong magnetic fields, certain birds apparently have highly sensitive sensors to detect the geomagnetic field for the purpose of orientation and navigation. However, the advances in this latter field were made mainly in the behavioral studies; the magnetosensors and the neural mechanisms remain elusive. A number of candidates of the sensors are evaluated. We suggest that pecten oculi, which is unique to avian eyes, should not be overlooked for its possible role as a magneto-sensor based on the magneto-orientation effect. Birds primarily use a static (DC) magnetic field for orientation, but recent investigations indicate that weak alternating (AC) magnetic fields with extremely low frequency (ELF) may have hazardous health effects. Such reports are often received with skepticism, because the effects usually involve magnetic energies that are less than the kT energy. However, some of the in vitro studies yield experimental results that are too significant to be ignored. Here, we propose an argument to explain why low-level magnetic fields can be detected without being overshadowed by thermal noises. Relevance of biomagnetic research to the development of biosensors and novel computational paradigms is also discussed.

Wintergoldhähnchen (Regulus regulus) besitzen einen Inklinationskompaß

During autumn migration, orientation tests were performed with Goldcrests in the morning immediately after the birds had been caught. In the local geomagnetic field (vertical component pointing downward), they showed a significant tendency towards 144° SE; in a magnetic field with the vertical component pointing upward, their mean was at 321° NW. This response to an inversion of the vertical component reveals that the Goldcrests used the magnetic field for orientation and that their magnetic compass is an inclination compass as it has been described for several other species of migrants.

Magnetic compass orientation in the subterranean rodentCryptomys hottentotus (Bathyergidae)

To test whether mole-rats Cryptomys hottentotus were able to use the magnetic field for orientation, laboratory experiments were conducted which were based on the animals' spontaneous tendency to build their nests at the same position in a circular arena. In the local geomagnetic field, the animals preferred the SE-sector. When magnetic north was turned by 120 degrees or by 180 degrees, the mole-rats changed their nest position accordingly. This clearly shows that they can use the magnetic field for direction finding.