A beginner's guide to nuclear magnetic resonance: from atomic spies to complex 3D structures at the heart of structural biology

The 'Beginner's Guides' are an ongoing series of feature articles, each one covering a key technique and offering the scientifically literate, but not necessarily expert audience, a background briefing on the underlying science of a technique that is (or will be) widely used in molecular bioscience. The series will cover a mixture of techniques, including some that are well established amongst a subset of our readership but not necessarily familiar to those in different specialisms. This 'Beginner's Guide' covers nuclear magnetic resonance. Nuclear magnetic resonance (NMR) provides a way to explore the 3D structures of macromolecules in much more biologically relevant conditions and does this by taking advantage of the quantum mechanical property of some nuclei---nuclear spin. Here, we discuss how nuclear spin can be harnessed to provide information on the 3D structure of macromolecules in solution and how new thinking is leading to a revolution in drug discovery.

Magnetic Systems

The chapter explains that up to this point the discussion has centered on some basic concepts of condensed matter physics as viewed through the illustrative lenses of familiar systems: liquids, crystals, and glasses. The chapter now turns to another important class of materials: magnetic systems, which are regarded as materials possessing properties that can be altered or manipulated through the application of an external magnetic field. The chapter introduces the basics of solid state magnetism, starting with the quantum mechanical property of spin, and showing how the familiar phenomenon of ferromagnetism—as well as the less familiar but equally important ones of antiferromagnetism and paramagnetism—arises. This is a necessary prelude to understanding the idea of what a spin glass is.

MONOGAMY OF ENTANGLEMENT, N-REPRESENTABILITY PROBLEMS AND GROUND STATES

Monogamy of entanglement is a quantum mechanical property that limits quantum correlations shared among many parties. In an example strongly interacting spin system we examine approaches for approximating the ground state energy both from above and below by mean-field and N-representability methods, respectively. Due to strong competition among the terms in the Hamiltonian, the resulting ground-state wavefunction, although is entangled, does not possess entanglement that is proportional to the system size, thus obeying the monogamy of entanglement.