Polymorphism and molecular conformations of non-protonated α-amino acids

The stereochemistry of non-protonated α-amino acids was examined using the data available in the literature for polymorphic crystals of those substances. The object of the study was to ascertain the extent to which such molecules are capable of exhibiting substantial changes in their geometry. We have found that, in the currently available data base, there are two domains: those exhibiting small (or nearly negligible) variations in conformations and those exhibiting medium to disturbingly large internal divergences in stereochemical parameters. Given the information provided by the authors, on how the crystals were obtained, it is impossible to arrive at any useful conclusions on the relationship between crystal preparation and the resulting stereochemistry of the molecules present in that polymorph.