METHOD OF PACKING ANALYSIS FOR THE SOLUTION OF THE CRYSTAL STRUCTURE OF CYCLO (GLY-L-TYR-GLY)2.2H2O

Abstract

This  paper  describes the  development of a  new technique  for the  solution fo crystal structures from packing  considerations using contact distance criteria,  knowing  approximately  the  shape  of  the  molecule.  The  method  is  applied  to  a  complicated structure,  namely,  that  of  a cyclic  hexapeptide,  cyclo  (GZy-LTyr-GLy),.  2H20, which crystallizes in the  triclinic  space group  P1.  Although  this  is  a  difficult  space  group  for  solution  by  conventional  method,  it  turns  out to be particularly facile  for  the  new  method. The trial  structure  thus obtained could be refined  by  a  series  of  successive  SFLS  refinement,  increasing  the  number of reflections used for  the  refinement  at  each  stage.