NEW OPPORTUNITIES IN X RAY CRYSTALLOGRAPHY AT THIRD GENERATION SYNCHROTRON SOURCES. Carl-Ivar Bränden, ESRF, BP 220, F-38043 Grenoble Cedex

Undulators at third generation Synchrotron sources produce parallel, narrow X-ray beams of very high brilliance even at energies as high as 70 keV. These beams open up new opportunities for diffraction and some examples will be presented from recent experiments at ESRF. Conventional optical elements are used to produce a monochromatic beam with as high flux as possible for macromolecular crystallography. Excellent data have been collected from virus crystals with cell dimensions 1110*1110*1547Å and from needle-shaped protein crystals 10 micrometers thick. Circular Bragg-Fresnel lenses have been used to produce beams with focal spot size in the micron or sub-micron range. Such beams have been used in diffraction experiments using diamond anvil cells to study solid hydrogen and oxygen as well as ice at very high pressure. Capillary optics was used in a combined microfluorescence and microdiffraction experiment to study the composition and structure of individual grains of micron size in fly-ash particles. Diamond crystal monochromators are now used in combination with multilayer mirrors to build four independent protein crystallography stations on one beamline for high data collection throughput.

Time-resolved experiments have been made both by multi-bunch energy-dispersive diffraction and by single bunch Laue diffraction. The early process of hydration of cement was studied by energy-dispersive diffraction using high energy to penetrate the 10 mm thick sample and fast data acquisition in the subsecond range. It was found that a previously unknown intermediate phase appears seconds after mixing and disappears again after 2-3 minutes. Photolysis of CO-myoglobin was studied by single bunch Laue diffraction in the pico and nanosecond range. Excellent electron density maps were obtained from a dataset collected by single bunch exposures which last about 50 picoseconds.