For information on how to prepare and ship un-frozen samples, please see the instruction manual on Remote Access at Elevated Temperatures and Controlled Humidity.
A crystal dehydration experiment may improve the diffraction resolution of ill-behaved macromolecular crystals. During these experiments, crystals are equilibrated at decreasing values of relative humidity (RH) in a stepwise fashion. Diffraction images are collected at each step to compare the diffraction quality and resolution.
The Arinax HC-lab is a scientific instrument designed to regulate the relative humidity of macromolecules crystals while mounted on the goniometer. Installed in the same way as a standard cryogenic stream head, the HC-lab blows a controlled humid air stream onto the sample. The air stream is generated by using the Dew Point Method to remove water from a hot and saturated air stream so that it will be at the correct RH when it reaches the crystal. The device provides a user-friendly sample environment to collect data at room temperature without the need of capillary mounting. It also enables crystal dehydration experiments with the aim of improving crystal diffraction.
The HC-lab comprises the machine body connected via a 1.5 m tube to a nozzle, which points the humid stream onto the sample (Figure 1).
Figure 1. Setting of the HC-lab at the SSRL beamlines.
Any RH value between 99.8% and 50.0% can be set using the Humidity control in the Blu-ice Sample Tab interface (Figure 2). If you cannot see the humidity control options, ask your user-support scientist to enable humidity control for your experiment. Once the RH value is set, wait until the air stream reaches this value and it is stable
Figure 2. Humidity Control Tab within the Blu-Ice Sample Tab.
The green area displays the current relative humidity. To change the set point, type a value in the entry box (which will be in red text) then click “Move” to change in set point (the “set point” text will then turn black).
Further integration of the HC-lab control software into the Blu-Ice software is in progress.
Regardless the type of experiment you are planning, the first step is to measure or estimate the RH value of your crystallization solution.
Measuring the RH Starting Point
Estimating the RH Starting Point
Complete datasets may be collected from crystals at optimized humidity. Multiple crystals may be required.
Alternatively, a new rapid nozzle switcher has been recently developed at SSRL that will be installed on some of the crystallography beamlines. Using this device, crystals at optimized humidity can be flash-frozen to collect complete datasets.