X-Ray Diffraction Spectra of Glycine.

Abstract

There still remains some uncertainty 1 as to whether the needle-like crystals of glycine (produced by precipitation with alcohol from aqueous solution) are identical with the plate form of the crystals (produced by crystallization from water).

This investigation attempts to throw some light on the problem by making use of X-ray diffraction patterns; the powder method was employed.

Glycine from 4 different sources, as follows, was used. A—Prepared by Pfanstiehl. B—Prepared by Eastman Kodak Company. C—Prepared at the Biochemistry Department of this University by the formaldehyde method. 2 D—“Dunn No. 1, 1927,” prepared by the reaction of monochloracetic acid and ammonia. The samples, after thorough drying, were divided into 3 groups and diffraction patterns taken as follows:

Group I. Each sample was photographed without any preliminary treatment except drying and grinding. The spectra of samples A, B, and C were exactly the same. The spectrum of sample D was different.

Group II. A part of each sample was dissolved in water and the crystals separated by slow evaporation to dryness. This produced the plate form of the crystals. The diffraction patterns were identical, and the same as the spectra of samples A, B, and C of group I. The difference observed in sample D of group I had disappeared.

Group III. A part of each sample of group I was dissolved in water and the needle shaped crystals formed by adding absolute alcohol. All 4 spectra of this group were alike but slightly different from the spectra of Group I. With more complete drying, however, a change took place in the crystals with the result that the spectra became identical with those of Group II. The 3 types of spectrum are shown in Figure I.