A SIMPLE APPARATUS FOR TIME-RESOLVED X-RAY-DIFFRACTION BIOSTRUCTURE STUDIES USING STATIC AND OSCILLATING PRESSURES AND PRESSURE JUMPS

A beryllium rod with an internal bore diameter of 1.5 mm and a wall thickness of 2.4 mm constitutes an x-ray compatible cell for hydrostatic pressures rated up to 1800 bar (180 MPa, 26 000 psi) at temperatures up to 90-degrees-C. The system can be used to produce static and oscillating pressures, pressure ramps, and pressure jumps. Pressure is generated by compressing water, the pressure medium, in a syringe-type high-pressure pump. Commercially available pressure valves serve to produce sinusoidal pressure oscillations and pressure jumps for any initial and final pressure between atmospheric pressure and 1800 bar. Typical rise times for a minimally damped and damped pressure jump from atmospheric pressure to 1600 bar are approximately 2 and 5 ms, respectively. A depressurization jump from 450 bar to atmospheric has a decay time of order 5 ms. This equipment has the advantage of being relatively easy to build and to operate. However, it does not provide the fastest possible pressure jumps. The assembly of thermocouples and wire feedthroughs for operation under high pressure is detailed. The apparatus described here has been used in time-resolved x-ray diffraction studies of lipid phase transitions using synchrotron radiation. We anticipate using it to collect static and slow kinetic data on a conventional x-ray source.