Search results for "Crystallization"
showing 10 items of 774 documents
Optical experiments on a crystallizing hard-sphere–polymer mixture at coexistence
2010
We report on the crystallization kinetics in an entropically attractive colloidal system using a combination of time resolved scattering methods and microscopy. Hard sphere particles are polystyrene microgels swollen in a good solvent (radius a=380nm, starting volume fraction 0.534) with the short ranged attractions induced by the presence of short polymer chains (radius of gyration rg = 3nm, starting volume fraction 0.0224). After crystallization, stacking faulted face centred cubic crystals coexist with about 5% of melt remaining in the grain boundaries. From the Bragg scattering signal we infer the amount of crystalline material, the average crystallite size and the number density of cry…
Enantioselective zinc-mediated conjugate addition of terminal alkynes to enones.
2012
Zinc for conjugate alkynylation: The enantioselective conjugate addition of terminal alkynes to 2-arylidene-1,3-diketones in the presence of diethylzinc and a catalytic amount of (R)-VANOL has been developed. The reaction can be applied to different aromatic and heteroaromatic alkynes and enones, giving the expected products in good yield and with enantiomeric excesses up to 91%. The products can be enantiomerically enriched up to 99% ee by crystallization (see scheme).
N,N-Di-n-octyl-N,N-dimethyl and N,N-di-n-nonyl-N,N-dimethyl ammonium cholates: 13C and 15N CPMAS NMR, powder X-ray diffraction and thermoanalytical c…
2009
Abstract N,N-Di-n-octyl-N,N-dimethyl cholate (1) and N,N-di-n-nonyl-N,N-dimethyl ammonium cholate (2) have been prepared by crystallization from equimolar mixtures of sodium cholate and quaternary N,N-di-n-alkyl-N,N-dimethyl (n-octyl or n-nonyl) ammonium bromides. The formed crystalline materials have been structurally characterized by 13C and 15N cross polarization magic angle spinning (CPMAS) NMR, powder X-ray diffraction (PXRD) and thermoanalytical (TGA/DTA and DSC) methods and compared with each other. Powder X-ray diffraction patterns of 1 and 2 reveal clear similarities. Combined with the thermoanalytical data of these structures an existence of two hydrated polymorphs (most probably …
Strong stabilization of amorphous calcium carbonate emulsion by ovalbumin: gaining insight into the mechanism of 'polymer-induced liquid precursor' p…
2011
8 pages; International audience; The impact of the ovo proteins ovalbumin and lysozyme-present in the first stage of egg shell formation-on the homogeneous formation of the liquid amorphous calcium carbonate (LACC) precursor, was studied by a combination of complementing methods: in situ WAXS, SANS, XANES, TEM, and immunogold labeling. Lysozyme (pI = 9.3) destabilizes the LACC emulsion whereas the glycoprotein ovalbumin (pI = 4.7) extends the lifespan of the emulsified state remarkably. In the light of the presented data: (a) Ovalbumin is shown to behave commensurable to the 'polymer-induced liquid precursor' (PILP) process proposed by Gower et al. Ovalbumin can be assumed to take a key rol…
Direct nucleation of calcium oxalate dihydrate crystals onto the surface of living renal epithelial cells in culture
1998
Direct nucleation of calcium oxalate dihydrate crystals onto the surface of living renal epithelial cells in culture. Background. The interaction of the most common crystal in human urine, calcium oxalate dihydrate (COD), with the surface of monkey renal epithelial cells (BSC-1 line) was studied to identify initiating events in kidney stone formation. Methods. To determine if COD crystals could nucleate directly onto the apical cell surface, a novel technique utilizing vapor diffusion of oxalic acid was employed. Cells were grown to confluence in the inner four wells of 24-well plates. At the start of each experiment, diethyloxalate in water was placed into eight adjacent wells, and the pla…
Sialic acid-containing glycoproteins on renal cells determine nucleation of calcium oxalate dihydrate crystals
2001
Sialic acid-containing glycoproteins on renal cells determine nucleation of calcium oxalate dihydrate crystals. Background The interaction between the surfaces of renal epithelial cells and calcium oxalate dihydrate (COD), the most common crystal in human urine, was studied to identify critical determinants of kidney stone formation. Methods A novel technique utilizing vapor diffusion of oxalic acid was employed to nucleate COD crystals onto the apical surface of living cells. Confluent monolayers were grown in the inner 4 wells of 24-well culture plates. To identify cell surface molecules that regulate crystal nucleation, cells were pretreated with a protease (trypsin or proteinase K) to a…
Effect of Composition on the Photoelectrochemical Behavior of Anodic Oxides on Binary Aluminum Alloys
2006
The photoelectrochemical behavior of anodic films on Al alloys, containing titanium, tantalum, and tungsten (valve metals), has been studied as a function of alloy composition and anodizing conditions. Photocurrent spectroscopy has been used to get information on bandgap and the flatband potential values of different mixed oxides. Both insulator-like and semiconducting behavior has been observed for anodic oxides grown on Al-W and Al-Ti alloys dependent on alloy initial composition. Optical bandgap values, E opt g , of different oxides are in accordance with predictions based on the correlation between E opt g and the difference of electronegativities of the oxide constituents, indicating p…
Nikotīnamīda un dikarbonskābju kokristālu tvaikķīmiskas veidošanās izpēte
2016
Nikotīnamīda un dikarbonskābju kokristālu tvaikķīmiskas veidošanās izpēte. Ķeķe A., darba vadītāja vadošā pētniece Dr. chem. Orola L. Bakalaura darbs, 41 lappuses, 27 attēli, 1 tabula, 40 literatūras avoti. Latviešu valodā. Darbā veikta nikotīnamīda kokristālu tvaikķīmiska iegūšana ar dažādām dikarbonskābēm (malonskābi, dzintarskābi, glutārskābi, adipīnskābi, pimelīnskābi, suberīnskābi, azelaīnskābi, sebacīnskābi). Iegūtie kokristāli analizēti, izmantojot pulvera rentgendifraktometrijas metode. Kokristālu pārvēršanās pakāpes noteikšanai izmantoja tādas kvantatīvās analīzes metodes kā pilna profila analīzi un Ritvelda metodi.
Crystal-phagocyte interaction in calcinosis interstitialis.
1984
Based on recent findings indicating the stimulation of the respiratory burst in human neutrophils by crystal phagocytosis, ectopic calcified nodules of a patient with calcinosis interstitialis were exposed to autologous granulocytes and monocytes in vitro. The activity of the respiratory burst was determined by luminol-enhanced chemiluminescence. Controls included amorphous monosodium urate, microcrystalline monosodium urate, hydroxyapatite, and zymosan. Microcrystalline monosodium urate elicited a marked stimulation of both granulocytes and monocytes as did hydroxyapatite in granulocytes. Hydroxyapatite caused no stimulation of monocytes, possibly reflecting selective functional modulation…
Conditioning following powder micronization: influence on particle growth of salbutamol sulfate.
2003
Micronization is a high-energy process that induces changes in the crystallinity of materials. As a result, the crystalline structures on the particles' surface are being destroyed and amorphous areas are formed. After micronization of salbutamol sulfate to be used in dry powder inhalers, only small amounts of amorphous material are produced. Nevertheless, even these small amounts can have important effects on the physical stability of the powder. The amorphous state is thermodynamically unstable and tends to convert to the stable, crystalline state. The recrystallization process of disordered regions on the particles' surface leads to particle growth of milled particles. In this case, brid…