Low-wavenumber Raman spectra of α-, β-, and γ-phases of glycine at room temperature and of X-phase at 224 K.
Low-wavenumber Raman spectra of aqueous glycine solution during freezing with cooling rate 5 K/min at few typical temperatures.
Low-wavenumber Raman spectra of frozen aqueous glycine solution during annealing at T = 253 K for some selected times. Inset illustrates the temporal dependence of the intensities of ice band maximum (triangles) and β-glycine peak at 111 cm−1 (circles), and an exponential description in the case of β-glycine peak.
Low-wavenumber Raman spectra of aqueous glycine solution quenched to liquid nitrogen and heated to 213 K (thin line is experimental data and thick line is a smoothing curve).
Low-wavenumber Raman spectra illustrating the phase transitions of glycine from glassy to X-phase near 216 K (top panel) and from X- to β-phase near 226 K (bottom panel).
Raman spectra of α-, β-, γ-, and X-phases of glycine at liquid nitrogen temperature.
Powder x-ray diffraction patterns of the sample obtained by cooling aqueous glycine solution at a copper plate (top panel) and of the separated transparent plates of the “glassy phase” (bottom panel). The patterns with the highest intensity of the reflections from the “X-phase” are highlighted by color, to facilitate a comparison of the intensities of the reflections from “X-phase” and ice Ih. The reflections of the “X-phase” are marked by asterisks, the positions of the reflections of β-glycine and ice Ih are shown by ticks at the bottom of the diagrams.
DSC curves of the frozen glycine aqueous solutions obtained at different conditions. (1) a droplet of glycine aqueous solution (20% w/w) was frozen directly in the DSC crucible from room temperature to 153 K (cooling rate 10 K/min) and then measured on heating (“method 3”); (2) the sample prepared by “method 2b” (30% w/w), glassy phase; (3) the sample prepared by “method 1a” (15% w/w); (4) DSC curve from Ref. 78 , scaled to the load of 10 mg; (5) the sample prepared by “method 2a” (30% w/w), mixture “as is,” before the separation of the glassy phase.
X-ray diffraction patterns from the samples of the initially amorphous “glassy phase” (formed from the frozen aqueous glycine solution) annealed at several temperatures. Asterisks are the strongest reflections of the X-phase.
A summary of the sample preparation techniques used for DSC and x-ray diffraction study.
Apparent Raman line positions of α-, β-, γ-, and X-phases of glycine at 78 K.
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