High-sensitivity measurements of weak magnetic field effects

The study of spin chemistry and, in specific, magnetosensitivity has been growing in importance in recent years. Not only has there been great advances in the field of magnetic field effects (MFEs) on biological reactions, but also on their applications in semiconductor and polymer science. Many chemical systems exhibit sensitivity to comparatively weak magnetic fields by a variety of mechanisms. The most prevalent of such magnetic field effect (MFE) mechanisms in solution is the radical pair (RP) mechanism, which will be investigated in this work. Chapter 1 will introduce ideas behind the RP-based magnetosensitivity: the quantum mechanics of spin, the theory of long-range electron transfer, chemical kinetics and finally the RP-mechanism itself. The chapter will conclude by describing the magnetosensitivity of flavin-based systems investigated in this work. A significant part of this work revolved around the understanding, using and development of the methodology involved. Chapter 2 will discuss some of the mathematical and computational methods used throughout this work. The methods covered are the time-frequency analysis, fitting, numerical solutions to differential equations and analysis of uncertainty. The examples used throughout this chapter have been selected to illustrate important points of their respective subjects, but also to be relevant to understanding other parts of this work. Chapter 3 will make use of some of the methodology described in the previous chapter and talk about the development and theoretical treatment of a modulated fluorescence experiment - ModMARY. The chapter will conclude by showcasing the methodology developed to measure a fluorescent exciplex-based system traditionally investigated by ModMARY pyrene / 1,3-dicyanobenzene. The work done in this chapter is the basis of a publication led by the author. The flavin-based system often used in magnetosensitivity studies of biological systems is the solution of flavin mononucleotide (FMN) and hen egg-white lysozyme (HEWL). This system is well known, but not fully understood. The interactions of freely diffusing FMN within a crystal lattice of HEWL has been investigated in Chapter 4, by confocal laser-scanning microscopy (CLSM). The principle of CLSM, as well as the data analysis methodology developed, will be discussed. Then, the spatiotemporal evolution of the MFE of FMN in HEWL crystals will be explored. The work in this chapter is part of a joined publications with Dejéan et al. MFEs can be probed optically not only by fluorescence, as investigated in the aforementioned chapters, but also by absorption techniques. The understanding and development of broadband cavity-enhanced absorption spectroscopy (BBCEAS), and its application to measurements of solution-based cryptochrome samples will be discussed in Chapter 5. The systems of most interest in the field of magnetoreception are the cryptochrome molecules - flavin-binding proteins proposed as the source of the avian magnetic sense. The methodology from previous chapter will be used in Chapter 6 to measure the samples of cryptochrome proteins from five different animal species and their selected mutants. This data will be compared and its implications will be discussed. The work is a part of a joined publications with Xu et al.