Radicals and Radical Pairs in Chemical and Biological Systems

Magnetic fields of different strengths can be applied to chemical and biological systems to study processes involving radicals or radical pairs. This work uses two such techniques, electron paramagnetic resonance (EPR) spectroscopy (≥ 150 mT) in addition to time resolved EPR spectroscopy and time resolved infrared (TRIR) spectroscopy (≤ 37 mT). The former are used to monitor metalloproteins, and the photochemistry of phosphorus oxides, while TRIR spectroscopy is used to record the magnetic field effects on the reaction kinetics of neutral radical pairs. The thesis begins with an introduction and an overview of the experimental techniques and developments. This is followed by an EPR study of the Fe(III) binding proteins, transferrin and lactoferrin and the effect thereon of catecholamine stress hormones. Catecholamines mediate bacterial growth by sequestering iron from the iron binding proteins. The mechanism of iron capture is unknown, however, the current work reveals Fe(III) binding by the catecholamine and supports subsequent reduction as the most likely route. Since catecholamines are also administered therapeutically, the validity of EPR as a diagnostic technique is examined and iron loss from human serum transferrin is observed. Also within this work, experiments are presented in which TRIR spectroscopy is used to investigate factors that affect the development of magnetic field effects for radical pairs in different solutions. This initially involves studies on acylphosphine oxides. In addition to the reported photoprocesses, alternative chemistry is uncovered, which occurs when bisacylphosphine oxide is in solutions where the solvent is sufficiently nucleophilic. The photochemistry is investigated using time resolved EPR and density functional theory calculations to suggest three possible structures that are responsible for the additional radicals observed. Furthermore, encapsulated organic radical pairs in reverse micelles are studied. These experiments, in combination with dynamic light scattering measurements provide insight into the magnitude of the observed magnetic field effects and the differing kinetics of the radical pair in the reverse micelles.