Crystal glycine

The phase composition of glycine crystal forms during the drying step of a wet granulation process has been studied, and a model developed for the phase conversion reactions [88], X-ray powder diffraction was used for qualitative analysis, and near-infrared spectroscopy for quantitative analysis. It was shown that when glycine was wet granulated with microcrystalline cellulose, the more rapidly the granulation... 

Fig. 36. Structure of a-glycine crystals. Projection along the c-axis. A and B are proposed sites for the Cu(II) impurities. (Adapted from Ref. 58)...

Figure 28. Morphologies of glycine crystals (a) pure (b)-(d) grown in the presence of (I>) R, (c) S, (d) R.S a-amino acids.

Figure 30. Optical microscope pictures of the 010 faces of a glycine crystal after partial dissolution in the presence of (fl)-alanine (a) (010) face (6) (0T0) face.

Figure 40. Morphology of glycine crystals (a) theoretical (b) observed (glycine obtained by. sublimation).

Fig. 7-15.—Another packing drawing of the glycine crystal (Albrecht and Corey).

Akers, M. J., Milton, N., Bryn, S. R., Nail, S. L. Glycine crystallization during freezing the effects of salt form, pH, and ionic strength. Pharm Res 12 1457-1461 (1995). 

The occurrence of reduction of symmetry is of particular importance in the mirror symmetry breaking process of racemic a-amino acids, accomplished with the assistance of crystals of glycine grown at interfaces. When grown from aqueous solutions, glycine crystallizes in its centrosymmetric a-polymorph (space group P2 /n). This crystal is composed from chiral... 

One may envisage that such conglomerates of crusts of glycine crystals might be spread to yield enantio-enriched environments, as in the mechanism proposed by Welch [68]. 

Diastereoisomeric interactions between chiral surfaces of non-chiral crystals and chiral molecules present in solution are demonstrated by the formation of etch pits. Etch pits were only formed on the (010) face of an a-glycine crystal partially dissolved in an undersaturated solution containing D-alanine, whereas the (0-10) face does not exhibit etch pits, Fig. 7a [69]. 

Fig. 6 Photographs of white crusts and yellow crusts of glycine crystals grown at the air/aqueous solution interface in the presence of Ne-(2,4-dinitrophenyl)-L-lysine and leucine in ratios of L/D > 1 and L/D < 1, respectively. The white crystals exposed their (010) faces towards the solution whereas the yellow crystals exposed their (0-10) faces...

Fig. 7 a Photographs of the (010) and (0-10) faces of plate-like a-glycine crystals after etching in the presence of D-alanine b The (010) and (0-10) faces of a cleaved a-glycine crystal subsequently etched in the presence of DL-alanine... 

Fig. 8 Glycyl-glycine crystals grown in the presence of DL-glycyl-leucine. a Photographs and morphology b Enantiomeric HPLC analyses of samples taken from single crystals cut at the + b and - b poles and sample from the whole crystal (left to right)...

Although these experiments did not provide the desired systems needed to amplify chirality, they were helpful in elucidating the stereochemical mechanism of the role played by additives in the early stages of crystal nucleation. This information was instrumental to the elaboration of appropriate model systems for the amplification of chirality, such as the generation of homochiral lysine via crystals of nickel/caprolactam [131] and the auto catalytic process of the spontaneous segregation of racemic enantiomers of amino acids in aqueous solutions assisted by centrosymmetric glycine crystals grown at interfaces. 

In Sect. 2.3 we showed that when glycine crystals are grown at the air/aqueous solution interface in the presence of DL-a-amino acids, only one of its enan-tiotopic faces, e.g. (010), is exposed to the solution and so it picks up (together with glycine) only the D-a-amino acids, thus converting the centrosymmetric host glycine into chiral mixed crystals. By symmetry, crystals exposing their (0-10) face towards the solution occlude only the L-enantiomers, Scheme 5. 

Combined operation of the hydrophobic and kinetic effects using nonmixtures of L/D-leu of 53 47 (6% ee) in a total concentration of 2.4% wt/wt of glycine resulted in the formation of a crust of floating glycine crystals containing only D-leu, thus enriching the initial L-leu ee of the solution, Fig. 13 [133-135],... 

Glycine crystal at the interface with (by chance) the (01 0) face towards the solution... 

The excess of hydrophobic Z)a-amino acids induces preferential orientation of new glycine crystals with again their (010) faces towards the solution... 

Li, L. Rodriguez-Hornedo, N. Growth kinetics and mechanisms of glycine crystals. J. Cryst. Growth 1992, 121, 33-38. 

M., and Leiserowitz, L. Centrosymmetric crystals for the direct assignment of the absolute configuration of chiral molecules. Application to the a-amino acids by their effect on glycine crystals. J. Amer. Chem. Soc. 105, 6615-6621 (1983). 

Figure 7.20 K-Ala adds to the (010) face and prevents the growth of the glycine crystal along the +b-axis. The (010) face becomes dominant because growth along the other faces is faster now. S-Ala has the same effect in the — b direction R,S-v4/a in b directions. Enantiopolar crystals of achiral glycine add S-alanine to pro-S crystal faces and R-alanine to pro-R faces ". ...

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