Abstract
Precise and convenient crystal reorientation is of experimental importance in macromolecular crystallography (MX). The development of multi-axis goniometers, such as the ESRF/EMBL mini-κ, necessitates the corresponding development of calibration procedures that can be used for the setup, maintenance and troubleshooting of such devices. While traditional multi-axis goniometers require all rotation axes to intersect the unique point of the sample position, recently developed miniaturized instruments for sample reorientation in MX are not as restricted. However, the samples must always be re-centred following a change in orientation. To overcome this inconvenience and allow the use of multi-axis goniometers without the fundamental restriction of having all axes intersecting in the same point, an automatic translation correction protocol has been developed for such instruments. It requires precise information about the direction and location of the rotation axes. To measure and supply this information, a general, easy-to-perform translation calibration (TC) procedure has also been developed. The TC procedure is routinely performed on most MX beamlines at the ESRF and some results are presented for reference.
Highlights
Multi-axis goniometers have long been common in both the realm of small-molecule crystallography as well as in the early years of macromolecular crystallography (MX), as summarized by Helliwell (1992)
A renewed focus on miniaturization and collision prevention has led to the development of devices that integrate seamlessly with many positioning systems designed for MX (McCarthy et al, 2009; Wang et al, 2008; Jain & Stojanoff, 2007; Shi et al, 2006; Skinner & Sweet, 1998)
Since the direction vector d0É normal to the rotation plane can be known a priori from rotation calibration (Paciorek et al, 1999), only the location of the rotation axis t0É that is the centre of the circular path of the point needs to be determined
Summary
Multi-axis goniometers have long been common in both the realm of small-molecule crystallography as well as in the early years of macromolecular crystallography (MX), as summarized by Helliwell (1992). Every reorientation must be followed by a translational re-centring to keep the sample in the axis of the beam This design does not offer a unique point of intersection for all of the rotation axes, and the multi-axis goniometer head must be supported by a reliable translation stage as a result. When - and ’-rotation settings are nonbased algorithms [i.e. automatic or three-click centring for zero and a 2 f; ’g rotation is applied on any of those axes, single-axis goniometer heads (Lavault et al, 2006; Jain & the location of the sample in the translation space changes as Stojanoff, 2007)] to allow for rapid calibration of inverse- well. The new translation vector can be expressed by following the sequence of rotating back the axis to 0, applying the ’ rotation and rotating to its new position as t ð!;2 ;’2 Þ
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