Studies in molecular packing analysis

Abstract

A procedure has been proposed whereby the techniques of conformational analysis and molecular packing analysis be combined to predict the crystal structure of cyclic oligopeptides. Computer programs have been developed for conformational analysis of such molecules. The known crystal structure of the tetrapeptide cyclo (L-O-t-butylseryl-β-alanyl-glycyl-L-β-methoxyasparagyl) was correctly predicted. The conformation of the depsipeptide pithomycolide, cyclo (L-N-methylalanyl-L-valyl-D-3-oxy-3-phenylpropionyl-D-3-oxy-3-phenylpropionyl-L-2-oxy-3-methylbutyryl), has been extensively analysed, but analysis of the crystal structure was not successful. The crystal structures of the polymorphs of ice have been subjected to molecular packing analysis, at pressures from 0 kbar to 25 kbar, assuming interaction between the molecules according to the ST2 potential function. Some aspects of the relative stability of the various phases can be explained, but it appears that long range coulombic effects are being exaggerated by this potential function.