Space groups isomorphous replacement methods

In order to understand the interactions between these bis-intercalating drugs and IMA more fully, we have crystallized several complexes of them and undertaken the structure determination by x-ray diffraction technique. One of the crystal forms diffracts to 1.6 A resolution with a space group of F222. The crystal structure was determined by the multiple isomorphous replacement method using three different heavy atom derivatives. The structure was refined to an R-factor of 19% and there were moderate number of solvent molecules clearly visible. The crystal... 

If two isomorphous derivatives in which the replaceable atoms have considerably different diffracting powers are available, an improved form of this method can be used. Strychnine sulphate pentahydrate and the corresponding selenate form isomorphous monoclinic crystals of space group C2 Bokhoven, Schoone, and Bijvoet (1951) solved the centrosymmetric b projection by the straightforward method first used... 

If two heavy-atom derivatives can be crystallized which preserve the space group and unit cell size of a large protein, then the structure can be solved directly this method of multiple isomorphous replacement was used by Perutz152 and Kendrew153 to solve the first two protein structures by laborious, decade-long film methods hemoglobin and myoglobin. 

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