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SHELXL: Difference between revisions
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<b>SADI_54 0.04 FE SG_6 FE SG_9 FE SG_39 FE SG_42</b><br> | <b>SADI_54 0.04 FE SG_6 FE SG_9 FE SG_39 FE SG_42</b><br> | ||
restrains the bond lengths in the FeS<sub>4</sub> unit to be equal, but without a target value, with an esd of 0. | restrains the bond lengths in the FeS<sub>4</sub> unit to be equal, but without a target value, with an esd of 0.04 Å. The central iron atom is in residue number 54 and the four cystein sulfurs are all in different residues. The SADI 'similar distance' restraints provide a convenient way of restaining all sulfate ions in the structure to be regular tetrahedra with approximately equal S-O distances: <br> | ||
<b>SADI_SO4 S O1 S O1 S O3 S O4<br> | |||
SADI_SO4 O1 O2 O1 O3 O1 O4 O2 O3 O2 O4 O3 O4</b><br> | |||
For a disordered sufate on a symmetry axis it may be necessary to use the EQIV instruction to enable symmetry equivalent to be included in such restraints (explained in Sheldrick (2008) ''Acta Crystallogr''. '''A64''', 112-122).<br> | |||
<b>FLAT_* 0.3 O_- CA_- N C_- CA</b><br> | <b>FLAT_* 0.3 O_- CA_- N C_- CA</b><br> | ||
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<b>CHIV_PRO 31 CA</b><br> | <b>CHIV_PRO 31 CA</b><br> | ||
would cause the chiral volumes of all proline CA atoms to be restrained to free variable number 3, which itself is allowed to refine. In this way reasonable geometrical restraints can be applied even when the target values are unknown. By restraining distances to be equal to a free variable using DFIX, a standard deviation of the mean distance may be calculated rigorously using full-matrix least-squares algebra. | would cause the chiral volumes of all proline CA atoms to be restrained to free variable number 3, which itself is allowed to refine. In this way reasonable geometrical restraints can be applied even when the target values are unknown. By restraining distances to be equal to a free variable using DFIX, a standard deviation of the mean distance may be calculated rigorously using full-matrix least-squares algebra.<br> | ||
== Twinned crystals == | == Twinned crystals == | ||