Dr. Kris F. Tesh
Director, Macromolecular Products,
Rigaku Americas Corporation
Abstract:
There have been many experiments dealing with improving the diffraction
quality of crystals. This tends to lead to extensive crystallization
screens, fine matrix screens, successive attempts at cryo-annealing, and
other ideas related to the production of better crystals and improved freeze
conditions. Classical approaches involving altering hydration levels such
as changing salt or buffer concentration, adding of PEG or sugars to the
drop solutions, and dehydrating crystal in air or progressive vapor
diffusion above a gradient of solution concentration suffer from lack of
control of rate of dehydration/hydration or reproducibility of the
experiment and results. But, what does one do when the bag of tricks has no
more tools? Or what is to be done when there are no other improvements from
classical treatments of the crystal? We propose one additional
idea to manipulate the humidity environment to improve the actual crystal
properties as it relates directly to diffraction. The ProterosR Free
Mounting System (FMS) uses computer driven relative humidity changes on a
bare crystal to affect the physical properties in the crystal, thus
resulting in better diffraction and data sets. Since relative humidity is
accurately determined within the software, it is also easily reproduced.
Likewise, the FMS can be used to establish the humidity environment about a
crystal so that other tasks like crystal orientation in the loop or removal
of the adsorbed mother liquid can be safely performed. We will show some of
the revolutionary images and results we have found using the FMS to improve
diffraction, even from otherwise useless crystals.
