Section 5.1.2.1. Introduction to crystal mounting

Once crystals have been obtained and visually characterized, the next procedure involves the transfer of a selected crystal to an appropriate mounting device so that the crystal may be characterized using X-rays. Macromolecular crystals are generally obtained from and stored in a solution containing the precipitant or precipitants and other substances such as uncrystallized protein or other macromolecules. The object is to mount the crystal in such a way that it is undamaged by cracking, drying out, dissolving etc. during this operation. In some cases, the crystal may have been stored in a solution containing volatile solvents. Alternatively, the crystals may have been grown at a temperature lower than room temperature and therefore may require special handling in order to avoid crystal deterioration. In other cases, it may be desirable to prepare the crystal for study at cryogenic temperatures. This section deals with the mounting of crystals for all these conditions and concentrates on the mounting of crystals for diffraction experiments at or just below room temperature. Procedures such as `flash cooling' are used to reduce radiation damage. Crystal-mounting techniques for cryogenic experiments are covered in detail in Part 10 and are only mentioned briefly here. In general, the most difficult part of mounting macromolecular crystals is the transfer of the crystal from a holding solution to a suitable mount. A capillary or, if cryogenic experiments are to be carried out, a cryoloop should be used.