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Located in the Edward & Shirley Stokes Open Chemistry Laboratory, our single-crystal diffractometer at SUU is a copper sealed-tube system coupled with a Breeze CCD detector, manufactured by Bruker AXS.The system is equipped with an Oxford cryostream to hold samples at defined temperatures during diffraction experiments. It is housed in a stand-alone cabinet of leaded-glass. To the left is a water-chilling system which removes heat produced within the X-ray tube run at 40,000 volts during data collection.
Crystals of small organic molecules or inorganic compounds are often analyzed at room temperature because they are composed of tightly-packed molecules that form a relatively durable solid material.
Crystals of proteins are typically about half aqueous solvent, with the molecules held together in a lattice by relatively weak crystal contacts. Large solvent channels between protein molecules often allow diffusion of small molecules throughout the crystals. Because of these tenuous interactions that hold them together, protein crystals are very delicate and can easily be mashed by an eyelash as they are manipulated under a microscope. They are also damaged by X-ray exposure at room temperature.
Therefore protein crystals are transferred to a cryoprotected buffer, suspended in a microscopic loop, and flash-cooled in liquid nitrogen. During data collection of the diffraction patterns, protein crystals are held at a temperature of 100 K (-173 ⁰C) using a cryostream which approaches the crystal from the top as shown in the images. A video camera is coupled to an aligned microscope to visualize and center the sample in the finely-focused beam, and can be seen above the X-ray tube. The X-ray tube is on the right, and the monochromatic X-ray beam is directed through the collimator and then through the crystal. A small piece of lead acts as a beam-stop by absorbing this main beam. Diffracted photons are collected on the BREEZE detector on the left. The CCD chip is held at -25 ⁰C to reduce thermal noise during data collection.
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