Arrangement of water molecules in cavities and channels of the lattice of [Phe4Val6]antamanide dodecahydrate.

Publisher Website
Google Scholar
Abstract
The synthetic, biologically active, [Phe4Val6] analog of natural antamanide was crystallized from a solution containing calcium nitrate, acetone and acetonitrile. The crystal does not contain any Ca2+ but does contain 12 water molecules per peptide molecule. The conformation of this dodecahydrate is identical to the trihydrate crystallized from n-hexane/methyl acetate. The packing in both crystals is very similar, governed by parallel bands of phenyl and pyrrolidine ring stacking and by continuous channels for the solvent molecules, water in this case and n-hexane/methyl acetate in the previous study. The 2 structures are not ideally isomorphous, since the c cell parameter differs by more than 1.0 .ANG. in the 2 cells. There are 3 functions for H2O molecules: the 3 intrinsic H2O molecules in the interior of the peptide ring, the H2O bound to the exposed C.dbd.O groups and the H2O molecules that fill space in the solvent channels. There are no direct H-bonds between neighboring peptide molecules and there are only 2 intramolecular NH.cntdot..cntdot..cntdot.O.dbd.C bonds (of the 5 .fwdarw. 1 type).