Topical review introduction

In this issue, we are pleased to present the first invited topical review in the field of magnetic resonance. This field has recently gained prominence in Molecular Physics by a special issue on modern electron paramagnetic resonance (EPR) spectroscopy [1] and two invited new views articles by Lynette Cegelski and Courtney Reichhardt on solid-state nuclear magnetic resonance (NMR) for bacterial biofilms [2] and by Sebastian Hiller and Sina Reckel on perspectives of solution-state NMR for structural and functional studies of integral membrane proteins [3]. Although neither bacterial biofilms nor integral membrane proteins belong to the traditional realm of Molecular Physics, magnetic resonance methods for their study depend on thorough understanding of quantum systems, in this case spin systems, and interpretation of the results depends to some extent on the understanding of statistical mechanics. These aspects are often neglected when reviews or research articles in the field of magnetic resonance are published in ‘general interest’ journals, where the underlying physics is often considered by both reviewers and editors as ‘too technical’. Molecular Physics provides a home to articles that provide a solid fundament for research, independent of fads.

The topical review by Walter Köckenberger, co-authored by Alexander Karabanov and Grzegorz Kwiat- kowski on spin dynamics simulations of solid effect dynamic nuclear polarisation (DNP) is an example for such fundamental work. DNP is currently a very active field with some of the applications receiving much publicity. At the same time, the underlying physics is not fully understood. Many of the efforts for optimising DNP are thus empirical rather than based on knowledge of the real bottlenecks in polarisation flow from electron to nuclear spins. One of the problems is the co-existence of different theoretical approaches to the problem, with each of them considering some aspects and none of them (yet) considering all relevant aspects. The group of Walter Köckenberger has strongly contributed to a thorough description of one regime of DNP, where the solid effect dominates polarisation transfer. The topical review in this issue consolidates the results and establishes a framework for discussing the relaxation effects that strongly influence the level of steady-state nuclear polarisation.

Polarisation transfer between electron spins [4–6] or from electron to nuclear spins [7,8] is a much discussed topic in Molecular Physics. In spin chemistry, further complexity arises from coupling between spin dynamics and chemical reaction dynamics [9–11]. In this context an invited new views article by Till Biskup has discussed time-resolved EPR as a tool for understanding the radical pair intermediates in cryptochromes that arise from sequential electron transfer after optical excitation [12].

Molecular Physics continues to encourage the submission of original research papers in all areas of magnetic resonance spectroscopy and spin chemistry and will be proud to publish work that enhances our understanding of spin dynamics and its influence on spectroscopic, chemical, and biological phenomena.