The effect of diluting crystallization droplets on protein crystallization in vapor diffusion method

In this study, effects of diluting either protein or crystallization agents in the droplets on the success rate of protein crystallization was investigated. Diluting the crystallization agent was found to increase the success rate of protein crystallization. Theoretical analysis showed that, concentration ranges of both protein and crystallization agent that can be scanned during the vapor diffusion process are wider with diluting the crystallization agent than that without dilution, resulting in more opportunities for the crystallization solution to be in the nucleation zone. On the other hand, diluting protein could lead to controversial results depending on the location of the initial concentration relative to that of the nucleation zone in the phase diagram. The method of diluting the crystallization agent is therefore proposed as an alternative modification to the conventional vapor diffusion method for obtaining more crystallization conditions in protein crystallization screening. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of impurities on the crystallization of dextrose monohydrate

The effects of impurities on dextrose monohydrate crystallization were investigated. Crystal nucleation and growth kinetics in the presence of impurities were studied using an in-line focused beam reflectance monitoring (FBRM) technique and an in-line process refractometer. Experimental data were obtained from runs carried out at different impurity levels between 4 and 11 wt% in the high dextrose equivalent (DE) syrup. It was found that impurities have no significant influence on the solubility of dextrose in water. However, impurities have a clear influence on the nucleation and growth kinetics of dextrose monohydrate crystallization. Nucleation and growth rate were favored by low levels of impurities in the syrup.     

Spherulitic branching in the crystallization of liquid selenium

Liquid selenium is a spherulite-forming liquid. In a previous study [G. Ryschenkow and G. Faivre, J. Crystal Growth 87 (1988) 221], several spherulitic modes of crystallization have been observed to coexist, at a given undercooling of the liquid, with the growth of single crystals. The spherulitic modes were thought to be basically due to a mechanism inducing a regular polygonization of crystal during growth (small-angle branching). We present a morphological investigation of the spherulites of selenium, by optical and electron microscopy, which substantiate this conjecture. At medium undercooling of the liquid, the small-angle branching periodically triggers a homoepitaxial large-angle branching. This gives rise to nonringed spherulites. At higher undercooling the spherulites are ringed, which we attribute to the ineffectiveness of the large-angle branching. The existence of several spherulitic modes signifies that several stable regimes of the small-angle branching exist.     

Effect of various external factors and pretransitional phenomena on structural transformations in cholesteric liquid crystals

The publications on low-molecular thermotropic liquid crystals with cholesteric structures have been reviewed. The effect of an applied electric field on cholesteric structures is studied. Bistability of the cholesteric-nematic transition, electric field-induced color textures of cholesteric mixtures, and electro-optics of amorphous cholesteric structures are considered as well as pretransitional (blue and TGB) phases, discotic cholesterics, PDLC films, flexoelectric electro-optics, and photostimulated switching in cholesterics.     

Influence of stirring speed on the crystallization of calcium carbonate

Control over crystal morphology of calcium carbonate (CaCO₃) was investigated by simply changing the stirring speeds in the process of CaCO₃ formation. Scanning electron microscopy (SEM) and powder X‐ray diffraction (XRD) measurements explore the morphology evolution of CaCO₃ at varying stirring speeds. As the stirring speeds increase, rhombohedral calcite, spherical vaterite, and monoclinic crystal with coexistence of calcite phase and vaterite phase were formed, suggesting a facile control over calcium carbonate crystallization in constructing crystals with desired morphology. Moreover, almost pure vaterite spherical particles of narrow particle size distribution were formed at optimum stirring speed. Finally, also elucidated in this work is the mechanism investigation into the construction of various crystal forms via this simple route. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of polyelectrolytes on crystallization of zeolite Y

In this study, the influence of polyelectrolytes on the crystallization of zeolite Y is investigated. The prepared synthesis mixtures are aged at room temperature for 24 h and then left to crystallize. The compositional and structural information are provided by elemental analysis obtained by ICP, X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), particle size analyzer and adsorption and desorption isotherms of nitrogen by a volumetric adsorption instrument. The first group of synthesis studies is conducted by using solutions containing no additive (WA), nonionic (NI), 100% anionic (100A), and 100% cationic (100C) polyelectrolytes. The crystallization temperature and crystallization time are kept at 100 ºC and 48 h, respectively. The experimental results show that nonionic polyelectrolyte has the most influence on the crystallization of zeolite NaY. In the second group of synthesis studies, the effects of polyelectrolytes with various degrees of anionic properties (10%, 50% and 70%) of the same chemical structure are investigated by conducting crystallization experiments at 100 °C for a duration of 48 h. The results suggest that; particle size, crystallinity and BET surface area (S_BET) can be controlled by adding anionic polyelectrolytes to the solution.     

Influence of various conditions of convective mixing of melt on the structure and magnetoresistance of eutectic InSb-NiSb alloys obtained by directional crystallization

The microstructures are analyzed of the eutectic alloys solidified in the quasi-binary InSb-NiSb system under different conditions of convective mixing of melts grown in an ampoule by the Czochralski and directional crystallization methods under earth and microgravity conditions. It is established that growth of the phases in directional solidification of the InSb-NiSb eutectics is determined not only by the diffusion mechanism of the component redistribution at the crystallization front but also by the diffusion-convection mechanism. The comparative analysis of the influence of the crystal microstructure on the value of the magnetoresistance, R _M , is performed for the first time. It is shown that the R _M value of directionally crystallized InSb-NiSb eutectics depends on the density of the NiSb needles, disorder of the eutectic structure, and electrophysical parameters of the matrix.     

Impurity distribution within the diffusion layer in the cluster crystallization model

The impurity distribution in front of the surface of the growing crystal by Czochralski method is considered at the assumption that the crystallization begins in the melt within the diffusion layer by the formation of clusters, i.e. it has an extented nature. The moving force of the crystallization is the supercooling of the melt. The principle distinction from the classical BPS theory is that the concentration profile has no break near the meltcrystal interface and is defined by the impurity concentrations both in the liquid and cluster phases with allowance for their specific volumes.     

Influence of the nucleation time-lag on the activation energy in non-isothermal crystallization

In the present work, the influence of the nucleation time-lag on the non-isothermal glass crystallization is discussed. Differential thermal analysis (DTA) results of an iron-rich glass nucleated by Cr₂O₃ were obtained at different heating rates. The activation energy of crystallization, E_c, and the Avrami parameter, m, estimated by Kissinger's and Ozawa's equations were shown to be dependent on the heating rate. The value of E_c, obtained at 2.5, 5 and 7.5 K/min heating rates was calculated as 299 kJ/mol, while the value of E_c, obtained at 10, 15 and 20 K/min was as 499 kJ/mol. The value of m for ‘low' and ‘high' heating rates were 2.57 and 1.45, respectively. The results were interpreted on the basis of the non-steady state nature of the nucleation process. It was assumed that at high heating rates no nucleation takes place and the crystals grow on a existing fixed number of nuclei; the activation energy of crystal growth, E_g, can be estimated by applying the Kissinger equations. At low heating rates nucleation occurs and the number of nuclei formed is influenced by the heating rate; E_g can be estimated by the Matusita and Sakka equation.     

Influence of seeding of the solutions on the crystallization of fibrillar sodium trimolybdate

An effect of the seeding of solutions on the crystallization of fibrillar sodium trimolybdate is described. The crystallization was studied in three solutions of initial molybdenum concentration C_Mo = 0.250 M and degree of acidity Z = 1.20, 1.25, and 1.33. The abridgment of the total time of the process respects only to the period of nucleation. At the moment of the acidification of the solutions different forms of isopolymolybdates come into existence.     

Influence of UV-exposure on the crystallization and optical properties of photo-thermo-refractive glass

Photo-thermo-refractive (PTR) glass is a photosensitive multi-component silicate glass. Photoinduced crystalline phase precipitation results in refractive index variations in UV exposed areas of PTR glass. The precipitation of silver containing particles which occurs during photo-thermo-refractive process increases the optical absorption of the samples in the range 350 nm to NIR wavelengths and the growth of sodium fluoride crystals and their aggregation increases light scattering in visible and NIR regions. We show that one effect of the UV-exposure is a decrease in the crystallization temperature by ～50 °C compared to the unexposed areas as measured by differential scanning calorimetry, which we attribute to an increase in nucleation rate. Using spectro-photometric measurements, a linear function is fitted to the changes in the amplitude of the absorption band of the silver containing particles versus the UV-dosage. The root mean square scatter of the data from the linear function is better than 0.99 and the slope of the function is 0.32 ± 0.01 cm/J. The IR absorption of PTR sample, measured by laser calorimetry shows that the increase of the absorption in infrared region at 1.1 μm, is due to the tail of the absorption band of silver containing particles having maximum at 465 nm. We finally show that after hyper-development, one effect of UV-exposure at 325 nm on the crystallization kinetics of PTR glasses is a decrease in particle sizes from micron size to nanometers size. But additional investigations demonstrate that smaller dosage UV-exposures (a few tens of milliwatts) increase the optical scattering by one order of magnitude. Optical micrographs taken after UV-exposure and hyper-development reveal the use of smaller dosages enhances nucleation rate without preventing the growth of large crystals and therefore induces higher scattering.     

Molecular dynamics simulation of the crystallization of a liquid gold nanoparticle

Molecular dynamics simulation of the crystallization behavior of a liquid gold (Au) nanoparticle, about 4 nm in diameter, on cooling has been carried out based on the modified embedded-atom-method potential. With decreasing cooling rate, the final structure of the particle changes from amorphous to crystalline via icosahedron-like structure. While the outer shell of the icosahedron-like particle shows crystalline feature with {1 1 1}-like facets, the inner core remains amorphous. It is found that the structure of the fully crystallized particle is polycrystalline face-centered cubic (fcc). The fcc structure of the gold nanoparticle is proved energetically the most stable form.     

Influence of alternating electric fields on the crystallization of barium titanate glasses

The paper is concerned with the question as to how far low-frequency electric fields exert an influence on the crystallization process. The results for a glass of the composition 75 mol.% BaO---TiO₂, 19 mol.% SiO₂, 6 mol.% Al₂O₃ show that the samples which are influenced by electric fields have a higher degree of crystallization than the electrically uninfluenced samples under well-defined annealing conditions.     

Influence of crystallization conditions on the size of cellular and cellular-dendritic substructure

A relationship is shown to exist between the size of the cellular-dendritic substructure and the growth conditions. The dependence of the cell diameter on the crystallization rate is non-monotonic, having a maximum in the region of low solidification rates. Theoretical calculations are compared with experimental data.     

Influence of solvent and crystallization method on the crystal habit of metronidazole

In the present study, metronidazole was crystallized in several solvents, according to both the “cooling crystallization” and the “crystallization by non‐solvent addition”. Particle properties, such as crystal habit, elongation ratio, and mean particle size, were determined by SEM analysis. Structural changes and development of polymorphic forms were excluded by both Differential Scanning Calorimetry (DSC) and X‐Ray Powder Diffractometry (XRPD). Crystal habit (and thus elongation ratio) was typically influenced by both the solvent polarity index and the crystallization method: solvents with higher polarity index tended to promote acicular or stick‐shaped crystals with a high elongation ratio, while isodimensional crystals were promoted by decreasing the polarity index, as was particle aggregation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The crystallization of lysozyme and thaumatin with ionic liquid

Three different ionic liquids (ILs) were used for the crystallization of lysozyme and thaumatin. It would be a promising solvent for applications in protein chemistry, due to its unusual features such as excellent solubility of inorganic and organic materials, enhancement of protein activity and stability, etc. Here, [BMIm][BF₄] was used as precipitants or union-precipitants in the experiments of thaumatin and lysozyme, respectively. And the experimental results indicated that the probability of single crystals appearance was significantly increased with the addition of [BMIm][BF₄].     

Influence of disorder on the diffusion of alkali ions in SiO2- and GeO2-glasses

The frequency factor and activation energy for the diffusion of Na and K in SiO₂-glasses are strongly dependent on the concentration of Na₂O or K₂O respectively. A similar behavior was found for hydrogen diffusion in amorphous metals. In the last case the results are in agreement with theoretical calculations, if a Gaussian distribution of activation energies is assumed which arises from a similar distribution of the potential energy of hydrogen being in equilibrium sites. The equations derived were used in this study to describe the concentration dependence of Na and K diffusion in SiO₂ glasses, because these impurities are dissolved in randomly distributed interstices of different volume as well. The theory yields the two experimental facts that diffusion below the glass transformation temperature is governed by a single activation energy and that concentration profiles of the tracer atoms can be described by a constant diffusion coefficient. A comparison with low temperature results for Na diffusion shows they agree with theoretical predictions and yield the following parameters: most probable value of the activation energy = 59.4 kJ/mol, corresponding frequency factor = 2 × 10^?3 cm²/s and half width of the Gaussian distribution = 25 kJ/mol. The model also predicts a minimum in plots of the chemical diffusivity versus concentration which is in agreement with experimental findings for sodium diffusion in GeO₂.