Radical-pair reactions as a potential mechanism for a physiological magnetic compass

The Radical Pair Mechanism(RPM) has been proposed to explain the avian magnetic orientation process. The dependence of radical pair reactions on the direction of external magnetic held makes radical-pair reactions potential magnetic sensors. Previous studies have explained why a weak magnetic field may affect radical-pair reactions. However with little knowledge about the radical pairs functioning as magnetic sensors in animals, the mechanism of magnetic orientation has yet to be understood.; In this thesis, we address three interrelated questions about the theoretical basis of the Radical Pair Mechanism as a potential mechanism for a physiological magnetic compass. We first investigate what chemical features would make a radical pair more optimal as a magnetic compass molecule. Calculations of static magnetic field effects were conducted on radical-pair models, from one-proton radical pairs to radical pairs containing up to eight hyperfine couplings. In a second study, we aim to connect calculations on the molecular level to behavioral studies that attempted to disrupt magnetic orientation by attaching magnets to the heads of birds. We study the effects of a second static field turning together with the bird's head to find conditions under which effects from attached magnets in behavioral experiments can be expected. Finally we addressed the question whether one can expect occurrence of resonances at certain frequencies without knowing details of the hyperfine structure. This question is of particular relevance for recent studies that apply weak oscillating magnetic fields in behavioral experiments.; Calculations in this thesis are not only on a specifically chosen radical pair, but more systematically for a wide range of radical pairs types. We investigated effects of a single static field and combined static fields as well as combined oscillating fields. The more systematic nature of the investigations in this thesis allows for conclusions regarding which features of magnetic field effects are general to many radical pairs and which features are specific to particular radical pair types. The calculations in this thesis are not meant to prove or disprove the radical-pair hypothesis. Rather they contribute to the theoretical basis for predictions to be tested in further studies.