Development of polycapillary x-ray optics for macromolecular crystallography.

摘要

One of the most powerful tools available to chemistry, structural biology, and materials science is x-ray crystallography. The technique can yield the three dimensional positions of atoms in a crystalline solid to atomic resolution. This knowledge can lead to an understanding of phenomena as varied as atomic, nuclear, electronic and magnetic interactions in materials science, to binding properties of proteins and recognition of viruses in biochemistry. In particular, there has recently been an explosive growth in the use of crystallography to determine the 3-D structure of biological molecules. Due to the weak interaction of x-rays with most solids, standard x-ray crystallography relies on the ability to generate beams of x-rays with high flux and relatively low angular divergence and cross section, i.e. high brilliance. Incorporation of polycapillary x-ray optics into existing x-ray sources helps to increase the total flux in the beam while maintaining the necessary angular divergence and cross section. The optics can be collimating optics, which yield gains on the order of 5-10 times in flux depending on the equipment used, or slightly focusing optics which further increase flux as much as an order of magnitude by focusing the beam to a minimum on the crystal. Alternatively, these optics can yield x-ray beams with large focusing angles and small spot sizes. This dissertation will discuss the theoretical basis of polycapillary x-ray optics, the application of the optics to macromolecular crystallography, their advantages and disadvantages compared to other types of optics and the re-emergence of a technique for collecting crystallographic data--the "convergent beam" technique.