SQUEEZE - An effective cure for the disordered solvent syndrome

IMPORTANT:
Large voids currently require significant computing at the stage where the size and shape of the solvent accessible void is determined. The reflection data and FFT-arrays are stored in memory, i.e. large structures may require large amounts of memory. The WinGX implementation may not be large enough to cope with many problems.

This option is initiated by typing "CALC SQUEEZE" . The reflection file name.HKL is required. The results are found in:
(a) a list file giving details of the calculations
(b) a modified reflection file (name.HKA) against which the ordered structure parameters can be refined (the solvent contribution has been eliminated from the reflection data.)

The general procedure has been described in more detail, see P. v.d. Sluis and A.L. Spek (1990) as the 'BYPASS procedure'. The 'difference-map' improvement potential of this technique is demonstrated for small molecule structures. The technique should also work for protein data. However, this has not been tested by us as yet with PLATON/SQUEEZE. Current design features may cause problems when tried.

• The record length of the '.HKA' file has been increased above 80 to accomodate additional data (the exact details are not fixed)
• The SHELXL-TWIN instruction is not available as yet in PLATON.

Current conditions for applicability are:

• Reasonable data-resolution (say 25 degrees Mo).
• Structure of the known part completed, together with H-atoms.
• No more than 26 'voids' in the unit-cell.
• Disorder density should be well outside the VanderWaals surface of the known structure.
• The area to be 'SQUEEZED' should not be too large (say less than in the order of 30% of the unit-cell volume.