期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1977
卷号：74
期号：7
页码：2602-2606
DOI：10.1073/pnas.74.7.2602
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The synthetic, biologically active, [Phe4Val6] analog of natural antamanide has been crystallized from a solution containing calcium nitrate, acetone, and acetonitrile. The crystal does not contain any Ca2+ ions 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 solvement molecules, water in this case and n-hexane/methyl acetate in the previous study. The two structures are not ideally isomorphous, since the c cell parameter differs by more than 1.0 A in the two cells. There are three functions for H2O molecules: the three intrinsic H2O molecules in the interior of the peptide ring, the H2O bound to the exposed C=O groups, and the H2O molecules that fill space in the solvent channels. There are no direct hydrogen bonds between neighboring peptide molecules and there are only two intramolecular NH-O=C bonds (of the 5 leads to 1 type).
