There can be no doubt that playing with spins is a lot of fun! If one is lucky enough to have access to the necessary tools to play with nuclear spins and with their associated magnetic moments, then the game becomes not only fun but also extremely interesting and useful. A very high and very homogenous static magnetic field as well as smaller magnetic fields oscillating in the range of radio frequencies are necessary. They can then be used to perturb nuclear spins and enable one to learn about their interactions as well as about their motions. For example we can ask nuclear spins questions about their chemical environment, how many other spins are close in space or connected through chemical bonds, and which fluctuations they experience. In other words, playing with nuclear spins can provide structural and dynamic information on complex molecules with resolution at the atomic scale. This was actually realized soon after nuclear magnetic resonance was discovered. What was probably more difficult to imagine at the time was the large number of applications that this simple idea of playing with nuclear spins would find in the future. Technological improvements in the instrumentation, progress in understanding how to describe spin dynamics, development of new experiments, improvements in sample preparation and isotopic labeling strategies have stimulated the continuous progress of NMR spectroscopy.
It is interesting to remember the initial feelings when approaching this area of research about twenty years ago. The level of sophistication reached by NMR spectroscopy seemed so high that it seemed that hardly any room could be left for further developments. Fortunately this was not true. New challenges emerging in different scientific fields in parallel to new technological improvements in NMR instrumentation have stimulated the development of a large array of new experiments that continue to surprise us and that further expand the range of applications of NMR spectroscopy. The consensus now is that this trend will continue for the forseeable future.
Considering, for example, the application of NMR spectroscopy to the study of biological macromolecules, recent progress has focused on areas where NMR can provide additional unique information that is difficult to access with other tools. Indeed, NMR spectroscopy allows one to study molecules in different aggregation states such as solution, solid state, sedimented solutes, or various kinds of aggregates with high biomedical relevance. The common and complementary aspects of solution and solid-state magic-angle-spinning (MAS) NMR spectroscopy can be used to access information on a wide variety of biological systems. NMR also offers a unique opportunity to study macromolecules at atomic resolution in environments as complex as whole cells. Moreover, NMR spectroscopy can provide unique information not only the structural features but also on local dynamics, enabling us to study highly flexible macromolecules such as unfolded or intrinsically disordered proteins, which are currently attracting the attention of the scientific community, as well. The improved instrumental sensitivity achieved in recent years now enables us to perform direct detection of heteronuclei also for biomolecular applications, to reduce the duration of NMR experiments and thus study fast processes, or to introduce additional indirect dimensions in NMR experiments to achieve greater resolution and thus tackle more complex systems. A variety of different NMR observables, including paramagnetic effects on nuclear shifts and relaxation rates, provide very detailed information.
The applications of NMR go well beyond the field of biological macromolecules. As an example of how NMR can be useful in many other areas of chemistry, several studies focusing on materials are also included. Thus, without being exhaustive, this special section features a variety of different interesting news in the field. We, the guest-editors, Isabella C. Felli (University of Florence, Italy) and Martin Wilkening (University of Graz, Austria), hope that this will contribute to stimulating creativity when playing with nuclear spins and stirring up new ideas to continue in this exciting and creative scientific field.