High Magnetic Fields in Chemistry

Abstract

Recent applications of large (∼ 1 T -∼ 30 T) magnetic fields in modern chemical research are reviewed. Magnetic field effects of chemical relevance appear on the levels of quantum mechanics, thermodynamics, and macroscopic forces. Quantum mechanical magnetic field effects are governed by the Zeeman interaction and are borne out as static and dynamic effects in spectroscopy and in chemical kinetics. Magnetic circular dichroism (MCD) spectroscopy and magnetic fluorescence quenching in the gas phase serve to illustrate the former, while radical pair spin chemistry is representative of the latter. The principles of the radical pair mechanism are outlined and highfield applications are illustrated in some detail for photo-induced electron transfer reactions of some transition metal complexes. Thermodynamic effects concern the magnetization of chemical samples, which is the focus of magnetochemistry or -more modern -molecular magnetism, and the equilibrium of chemical reactions. Representative examples of both aspects are described. Finally, the exploitation of orientational forces caused by the magnetic anisotropy of larger particles (from macromolecules to micro-crystals) is exemplified. Crystal growth in a magnetic field may hold a potential for achieving better control of the quality of protein crystals for structural analysis.

Effects and Mechanisms of Interaction of Electromagnetic Fields on Cells

“…According to the spin conservation rule, the kind of product depends on the state of atoms (excited singlet or triplet) at the moment of the reaction. [5] Microwave magnetic fields can lead to resonant transitions between triplet states of molecules, affecting the reaction kinetics that proceeds via triplet formation. In general, magnetic fields can influence on spin-dependent chemical reactions.…”

The magnetoelectrochemical switch

“…These spin chemistry effects (23) can occur in a wide range of applied fields, depending on the thermodynamic or quantum mechanical mechanism involved. The smallness of the Zeeman splitting magnetic energy can require rather large magnetic fields (of the order of 10 T) to impact the reaction (24). The hyperfine field, typically of the order of 0.1 T, can also significantly modify the lifetime of radical species, in the so-called "normal magnetic field effect," extensively studied for photosynthesis.…”

Magnetic Field and Temperature Dependencies Shed Light on the Recombination Kinetics of a Transition Metal Donor/Acceptor System

“…As for ET systems in general, the energetics and the distance between the donor (D) and acceptor (A) components are cardinal quantities determining the kinetics of the system. − Spin processes may be a further factor influencing ET kinetics. In contrast to hyperfine induced spin conversion prevailing in organic systems (>1 ns), − in compounds containing transition metals, spin processes can have an impact on picosecond ET dynamics, as shown in an exemplary way for oxazine 1/ferrocene. − These ultrafast spin processes may play a role in biological systems involving radical pair (RP)-type intermediates, where one part is a paramagnetic metal ion, as in a vitamin B 12 analogue. , …”