Crystallization from solution crystallography

One question which immediately arises is that of the structure at the surface of polyethylene films produced in this manner. The question of polymer crystallography and morphology has been extensively discussed and documented by Wunder1ich. For the most part, discussion has centered around samples crystallized from solution or produced from the melt under pressure. There are two considerations which make it difficult to extrapolate from this work. 

In spite of their easy interconversion in solution a and p forms of carbohydrates are capable of independent existence and many have been isolated m pure form as crys talline solids When crystallized from ethanol d glucose yields a d glucopyranose mp 146°C [a]o +112 2° Crystallization from a water-ethanol mixture produces p d glucopyranose mp 148-155°C [aj +18 7° In the solid state the two forms do not mterconvert and are stable indefinitely Their structures have been unambiguously con firmed by X ray crystallography... 

Monosodium L-glutamate [142-47-2] C HgNO Na H20 (mol wt 187.13) crystallizes from aqueous solution at room temperature as rhombic prisms. Its stmcture, as deterrnined by x-ray crystallography (6), indicates that the sodium ions are coordinated octahedraHy by four (3a and ly) carboxyl oxygen atoms and two water molecules as follows ... 

Interesting crystals can also be made from supersaturated solutions of Epsom salts (MgS04 7 H20) and alum (KA1(S04)2 - 12 H2Oj, which is used for pickling and is available in the spice section of some grocery stores. Crystal shape directly relates to how the ions or molecules of a substance pack together. In fact, substances are often characterized by the shape of the crystals they form. Crystallography is the study of mineral crystals and their shapes and structure. 

An unusual clathrochelate species [Na+(hpy.hpy.hpy)] e- AN formed by electroreductive crystallization from [Na(bpy.bpy.bpy)]Br acetonitrile solution was characterized hy X-ray crystallography [413],... 

For any chiral drug, establishment of its stereochemical identity is not an insurmountable technical problem, even for enantiopure material. The techniques of X-ray crystallography and NMR spectroscopy will, in general, lead to conclusions of high certainty, at least for the material studied. However, for enantiopure material, it is critical that the relevance of conclusions based on these techniques be correlated to larger batches of material through chiral properties, such as optical rotation. Of the thousands of published determinations of absolute configuration based on X-ray studies, most are unsupported by such data on solutions of the specific crop of crystals from which a few were selected for study. 

George, A., and Wilson, W.W. Predicting protein crystallization from a dilute-solution property. Acta Crystallographica Section D-Biological Crystallography, 1994, 50, p. 361-365. 

Compounds of the type [(Me3Si)2N]3M have been prepared for all of the lanthanide elements except Pm, Tb, Dy, Tm, and Er (4). The synthetic method used in their preparation is nucleophilic substitution with three molar equivalents of lithium -or sodium - bis(trimethylsilyl)amide on the metal trichlorides in tetrahydrofuran. The compounds are rather high melting solids (145-170°C) which can be isolated by crystallization from pentane as long needles or by vacuum sublimation (80-100°C). The binary silylamides are monomeric in refluxing benzene solution, in the gas phase (by mass spectrometry), and in the solid state (by x-ray crystallography, see below). Thus, these compounds are three-coordinate, a unique coordination number for the lanthanide elements. 

---