Page 79 - Macromolecular Crystallography

68 MACROMOLECULAR CRYS TALLOGRAPHY

Protocol 4.6 Recovery of shock-cooled crystals from the X-ray diffraction camera

Materials (Protocols 4.4 and 4.5). Cool the cryotongs, cryovial, and
Cryotongs vial clamp immersion in liquid nitrogen.
Shallow Dewar flask 2. The cold cryotongs are used to rapidly capture the
Cane mounting pin/loop. This step should be carried out rapidly
so that the crystal leaves the cold stream and enters the
Cryovial
protected (cold) space within the cryotongs in a minimum
Vial clamp
amount of time.
Storage Dewar
3. The cryotongs (with enclosed crystal) is rapidly lifted off
Liquid nitrogen
the goniometer head and plunged into a liquid nitrogen
Gloves bath.
Face shield 4. The magnetic crystal wand is used to capture the
mounting pin.
5. While immersed in liquid nitrogen, the mounting pin
Procedure (attached to crystal wand) is manoeuvred into a cryovial
1. Recovery of crystals from the cold stream involves (which is held with the cooled vial-clamp).
performing the procedure described for the mounting of 6. The recovered crystal (in the cryovial) is secured to a
crystals to X-ray camera but with the steps reversed cryocane, which is stored in a liquid nitrogen storage Dewar.

Protocol 4.7 Storage and transport of macromolecular crystals
Materials Dewar. Allow the ‘dry shipping’ Dewar to stand for several
‘Dry Shipping’ Dewar (Taylor Wharton: Cryo Express and minutes upside down until it is completely empty of liquid
Cryo Flight) (commercial shipping companies will refuse to ship a
Hard case container that contains liquid).
4. Once dry, cryocanes containing cryocooled crystals are
Insulated gloves
transferred from the liquid nitrogen bath to the shipping
Face shield
Dewar. Samples prepared with liquid propane or liquid
nitrogen are handled in the same manner. The temperature
Procedure inside the shipping Dewar should maintain the propane in
1. A ‘dry shipping’ Dewar (at ambient temperature) is the cryovials in solid form.
charged by filling it slowly with liquid nitrogen. Consult the
product literature for specific details. Many commercial shipping companies will accept a properly
2. Once filling is complete, the absorbent is thoroughly prepared shipping Dewar containers for transport around
cooled by the liquid nitrogen (approx 7–8 h). This will the world. Each investigator should check with the shipping
require topping up of the Dewar several times. A properly company of choice about requirements, paperwork,
charged Dewar should be able to stably maintain liquid and cost.
nitrogen on standing.
3. In preparation for shipping, liquid nitrogen from the ‘dry
shipping’ Dewar is decanted into an appropriate storage

minimum symmetry, relevant to macromolecules, of restrictions on its lattice constants, while the cubic
the unit cell for each of the seven crystal systems and system has four three-fold axes along the diagonal
the restrictions imposed on unit cell lattice constants. of the cube, three equal lattice lengths, and three lat-
◦
For example the triclinic system has no symmetry or tice angles equal to 90 . The unit cell in each crystal