Charge, spin and momentum densities: different faces of this same nature

Abstract

It is well known that the use of synchrotron radiation has revolutionised structural biology and is responsible for the exponential growth of known macromolecular structures in the Protein Data Bank. So onemaywonder if continued progress is possible. The recent developments of beamlines for macromolecular crystallography at the ESRF have had the purpose to make them highly automated. This has enabled the users to screen a multiplum of samples to find the best suited crystal for data collection. The use of crystallization robots tends to yield smaller crystals, which creates an increasing demand for beamlines with small beams to be used for the diffraction experiments. These developmentsmake it possible to study larger andmore complex biological systems, bringing the structural biology closer to the studies of soft condensed matter. We can also observe an increasing interest to complement the diffraction studies with complementarymethods like small angle scattering and imaging. The use of nanometer sized X-ray beams is also in demand for investigations of chemical systems. The use of nanosized beams opens possibilities for an unprecedented spatial resolution that open new scientific possibilities inmaterials science, soft matter chemistry and the characterization of complex chemical systems. The possibility of conducting the experiments at the synchrotron on samples under different thermodynamic conditions has stimulated an avenue of studies of chemical systems under extreme conditions. There is a similar interest in employing the time structure of synchrotron radiation in time resolved studies. The trends in the application of synchrotron radiation in chemistry and biology will be described and illustrated by recent scientific achievements [1].