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Low Resolution Phasing
XENON Derivatives

PROTEIN CRYSTALLOGRAPHY
Xenon and Krypton Derivatives for Phasing

We have facilities for using xenon derivatives (at room temp. and 100K) for MIR and Anomalous Dispersion experiments on the protein crystallography stations at the SRS, Daresbury.

Why use xenon? | Properties | History
Developments of the method @ Daresbury | Useful links | Reference list

Why Use XENON?
Problems
XENON Properties
XENON (Xe)
Atomic no 54
Melting point -112
Boiling point -108
Relative density (Gas) 4.5
Relative density (liquid) 1.5
Molecular weight 131
Solubility in water 644 mg/l


Absorption edges (Å and (kev))
K LI LII LIII MI
0.3587 2.2738 2.4293 2.5926 10.8321
(34.5614) (5.4528) (5.1037) (4.7822) (1.1446)

 

anomalous scattering coefficients f' and f'' as a Function of energy
Text file of anomalous scattering coefficients f' and f'' as a Function of energy
HISTORY
1965
Schoenborn et al determine a xenon binding site in sperm whale metmyoglobin by collecting x-ray diffraction data to a resolution of 2.8Å from crystals pressurised to 2.5 atmospheres.
1984
Tilton et al varied the number of bound xenon atoms by altering the sample pressure.
1991
Vitali et al demonstrate the use of xenon as a heavy atom, for the first time, in determining phases for the structure of sperm whale metmyoglobin, with the technique of isomorphous replacement with anomalous scattering (SIRAS).
1994
Schiltz et al use xenon as an alternative to heavy metal derivatives; for the first time calculate phases of a protein of unknown structure using a xenon derivative.
1997
Soltis et al for the first time, demonstrate a method for preparing cry-cooled xenon derivatised protein crystals.
Devlopments @ Daresbury

We now have the equipment to produce xenon derivatives from crystals and collect the anomalous data at room temperature or 100K. The equipment for freezing crystals or producing xenon derivatives can be borrowed for use on any of the PX stations.

For Capilliary Mounted Crystals

We are developing a xenon cell at Daresbury Laboratory for collectiong room temp. data from xenon derivative crystals in the 0 to 25 bar pressure range. It is a very simple but effective device based on a commercially available compression fitting.

Room Temperature Cell Mounted on a Goniometer Head Various Components of the Room Temperature Xenon Cell

left-The Room Temperature Cell Mounted on a Goniometer Head.
right - The Various Components of the Room Temperature Xenon Cell

Schematic Diagram of the Xenon Cell.
Schematic Diagram of the Xenon Cell

Xenon Cell
The Xenon Cell Mounted on the Goniostat of Station 7.2 at the SRS.

For Frozen Crystals

We have acquired an Oxford Cryosystems Xcell for pressurising crystals prior to freezing.

Users of the xenon pressure cell at Daresbury are required to complete a class 3 risk assessment, including a description of the hazard and safe system of work, prior to their beamtime.
http://www.dl.ac.uk/srs/PX/xenon_cell/new_risk.html

Oxford Cryosystems Xcel

Instructions for Using the Oxford Cryosystems Xcell
Future Developments
Explore the possibilities of exploiting absorption edges for MAD and SAD experiments. Xe K-edge 0.3587 Å, Kr K-edge 0.86552 Å.
Acknowledgements

Ethan A Merritt ©1996-1999/ merritt@u.washington.edu / Biomolecular Structure Center at UW

Useful Links
REFERENCES
OTHER REFERENCES

http://www.dl.ac.uk/srs/PX/xenon_cell/reference_list.txt

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