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Free keywords:
serial femtosecond crystallography; X−ray free−electron lasers; macromolecular crystallography; anti−settling; sample delivery instruments
Abstract:
Serial femtosecond crystallography (SFX) using X−ray free−electron laser (FEL)
sources has the potential to determine the structures of macromolecules beyond
the limitation of radiation damage and without the need for crystals of sufficient
size for conventional crystallography. In SFX, a liquid microjet is used to inject
randomly oriented crystals suspended in their storage solution into the FEL
beam. Settling of crystals in the reservoir prior to the injection has been found to
complicate the data collection. This article details the development of an antisettling
sample delivery instrument based on a rotating syringe pump, capable of
producing flow rates and liquid pressures necessary for the operation of the
injector. The device has been used successfully with crystals of different
proteins, with crystal sizes smaller than 20 mm. Even after hours of continuous
operation, no significant impairment of the experiments due to sample settling
was observed. This article describes the working principle of the instrument and
sets it in context with regard to the experimental conditions used for SFX. Hit
rates for longer measuring periods are compared with and without the
instrument operating. Two versions of the instrument have been developed,
which both deliver sample at a constant flow rate but which differ in their
minimum liquid flow rates and maximum pressures
