Crystal Structure Of Betulin Ethanol Solvate

The crystal structure of the 1:1 ethanol betulin solvate, a widely spread natural compound, is determined. The betulin solvate crystallizes in orthorhombic symmetry in the P2₁2₁2₁ space group, Z= 4. The unit cell parameters are as follows: a = 7.0159(1) ?, b = 12.4425(2) ?, c = 33.7500(5) ?; V = 2946.22(8) ?³. Betulin molecules are hydrogen bonded to each other and ethanol molecules, as a result of which the layers are distinguished in the structure, which are perpendicular to the crystallographic direction. Inside the layer, all molecules are hydrogen bonded, while the layers are linked by van der Waals interactions.     

Pressure Effect on the Crystal Structure of Na2C2O4: Deformation Anisotropy During Hydrostatic Compression and Phase Transition at 3.8 GPa

Variation of the unit cell parameters of Na₂C₂O₄ is investigated by powder diffractometry in diamond anvils when hydrostatic pressure is increased to 6.5 GPa. Anisotropic distortion of the structure was observed up to about 3.8 GPa, whereupon a transition to an unknown polymorphous modification occurred. Before the phase transition, the compression was maximal in the direction perpendicular to close-packed layers formed by oxalate ions. Minimal compression was observed in the direction of the specific crystallographic axis b. The anisotropy of compression at elevated pressure is similar, but not identical, to the anisotropy of compression of the same structure at reduced temperature.     

Kinetic-morphological peculiarities of solid-state isomerization of complexes

The thermal solid-state isomerizations of Copy₂Cl₂ (py=pyridine), Nien₂(NO₂)₂ and Nien₂(NCS)₂ (en=ethylenediamine) were studied by thermal analysis, thermomicroscopy, X-ray diffraction and IR-spectroscopy. It was shown that the reactions proceed by nuclear formation and growth. The kinetic-morphological peculiarities of the processes suggest that the process-determining stage is a phase stage, i. e. structural transformation. The topography and kinetics of processes are therefore determined by the crystal structures of the initial material and the reaction product, and by the contact conditions at the interface. The stress relaxation processes affect the morphology of the products and the kinetics of the transformation.

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Zusammenfassung Thermische Isomerisierungsreaktionen in fester Phase wurden durch thermische Analyse, Thermomikroskopie, Röntgenbeugung und IR-Spektroskopie an CoPy₂Cl₂ (Py=Pyridin), Nien₂(NO₂)₂ und Nien₂(NCS)₂ (en=Ethylendiamin) untersucht. Es wird gezeigt, dass die Reaktionen durch Keimbildung und Wachstum ablaufen. Die kinetischen und morphologischen Charakteristika der Prozesse weisen darauf hin, dass der geschwindigkeitsbestimmende Schritt ein Phasenschritt, d. h. eine Strukturumwandlung ist. Deshalb sind Topographie und Kinetik der Vorgänge durch die Kristallstrukturen des Ausgangsstoffe und des Reaktionsprodukts und durch die Kontaktbedingungen an der Grenfläche bestimmt. Die Spannungsrelaxationsprozesse beeinflussen die Morphologie der Produkte und die Umwandlungskinetik.

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, , ₂l₂, Nien₂(NO₂)₂ Nien₂(NCS)₂, en= , = . , . - , . , . .

     

Effect of High Pressure on the Polymorphs of Paracetamol

Effect of hydrostatic pressure on the two (I – monoclinic and II – orthorhombic) polymorphs of paracetamol was studied by X-ray diffraction in the diamond anvil cell at pressures up to 4.5 GPa (for the monoclinic form) and up to 5.5 GPa (for the orthorhombic form). The two groups of phenomena were studied: (i) the anisotropic structural distortion of the same polymorph, (ii) transitions between the polymorphs induced by pressure. The anisotropy of structural distortion of polymorphs I and II was well reproducible from sample to sample, also from powder samples to single crystals. The bulk compressibility of the two forms was shown to be practically the same. However, a noticeable qualitative difference in the anisotropy of structural distortion was observed: with increasing pressure the structure of polymorph II contracted in all the directions showing isotropic compression in the planes of hydrogen-bonded molecular layers, whereas the layers in the structure of the polymorph I expanded in some directions. Maximum compression in both polymorphs I and II was observed in the directions normal to the molecular layers. The transitions between the polymorphs induced by pressure were poorly reproducible and depended strongly on the sample and on the procedure of increasing/decreasing pressure. No phase transitions were induced in the single crystals of the monoclinic polymorph at pressures at least up to 4GPa, although a partial transformation of polymorph I into polymorph II was observed at increased pressure in powder samples. Polymorph II transformed partly into the polymorph I during grinding. The transformation could be hindered if grinding was carried out in CCl₄. This revised version was published online in August 2006 with corrections to the Cover Date.     

New composites of betulin esters with arabinogalactan as highly potent anti-cancer agents

Betulin and its esters are the natural compounds with high in vitro cytotoxicity toward many cancer cells. However, the poor water solubility of these compounds has limited their applications. We prepared new composites of betulin esters using two methods, namely ball-milling of the mixtures of betulin esters with arabinogalactan and preparation of thin films of these mixtures by evaporating the aqueous solutions. These composites revealed higher water solubility as compared with the initial substances without losing the structural integrity and functionality. As a result, the new composites have shown much higher inhibitory effects against different cancer cell lines such as Ehrlich ascites carcinoma cells and lung carcinoma cells (A549) in comparison with the initial substances. The cell viability studies based on Annexin V and Propidium iodide probes have confirmed the high proapoptotic effect of betulin ester derivatives against cancer cells.     

Diffusional-kinetic model of the joint dissolution of interacting poorly soluble substances

A model of the dissolution and interaction of two poorly soluble substances with the formation of a readily soluble product was developed. The kinetic characteristics of the process were described for the dissolution of two solid substances in a planar slit between them filled with a solvent and for the dissolution of intensely stirred suspension of particles of two substances.     

XPS study of pharmacological substances mechanochemically immobilized on the surface of alumina

Piroxicam and meloxicam nanocomposites with alumina were synthesized by mechanochemical treatment of medicinal substances mixed with the oxide. X-ray photoelectron spectroscopy demonstrated that interaction of the components during mechanical activation proceeds via binding the amide and sulfate groups in the molecules of medicinal substances with the active sites of alumina surface. XPS studies confirmed the formation of “core-shell” composites with the shell represented by medicinal substances distributed over the support surface.