Design of an inverted spindle axis for frozen crystal screening and storage

For biological macromolecules, X-ray diffraction data collection at temperatures close to that of liquid nitrogen greatly reduces radiation damage and allows an almost unlimited number of data to be collected from a single crystal. Single-axis instruments are common and are very often configured with the spindle axis vertical and pointed upwards (e.g. the R-axis image-plate diffractometer from Molecular Structure Corporation). This geometry allows a crystal to be frozen after it is mounted, but it is difficult to use prefrozen crystals or to remove and store crystals once an initial set of data has been collected. Such prescreening is very useful for efficient synchrotron data collection. In this paper, a device is presented that accomplishes an inversion of the spindle axis, allowing easy transfer of crystals to and from liquid nitrogen and a data collection run with Φ sweeps. This device is readily interchangeable with the standard goniometer mount.