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)     

Determination of the avrami exponent by non-isothermal analyses

This paper presents a method for a rapid determination of the growth morphologies of glass-forming materials using thermoanalytical techniques (DTA or DSC, respectively). Since this method, which is based on the Johnson-Mehl-Avrami equation, does not require a temperature independent activation energy it is not restricted to low temperature processes like conservative techniques, but can be applied to all temperature ranges of crystallization. Thus it is also possible to study the crystallization caused by cooling from the melt.Analyses of the crystallization process of selenium samples indicate a linear growth in the case of crystallization from the glassy state and a spherulitic growth in the case of crystallization from the melt. The results are discussed and compared with those obtained by means of other techniques.     

Developing a Fluorescence-based Approach to Screening for Macromolecule Crystallization Conditions

Current macromolecule crystallization screening methods rely on the random testing of crystallization conditions, in the hope that one or more will yield positive results, crystals. Most plate outcomes are either clear or precipitated solutions, which results are routinely discarded by the experimenter. However, many of these may in fact be close to crystallization conditions, which fact is obscured by the nature of the apparent outcome. We are developing a fluorescence-based approach to the determination of crystallization conditions, which approach can also be used to assess conditions that may be close to those that would give crystals. The method uses measurements of fluorescence anisotropy and intensity. The method was first tested using model proteins, with likely outcomes as determined by fluorescence measurements where the plate data showed either clear or precipitated solutions being subjected to optimization screening. The results showed a ~83% increase in the number of crystallization conditions. The method was then tried as the sole screening method with a number of test proteins. In every case at least one or more crystallization conditions were found, and it is estimated that ~53% of these would not have been found using a plate screen.     

Structure of KTiOPO<Subscript>4</Subscript> single crystals grown by the top-seeded solution and spontaneous flux crystallization methods

This paper reports on the results of precision X-ray structural investigations of KTiOPO₄ single crystals grown by one method (crystallization from a solution in the melt) in two variants (the spontaneous formation of crystallization centers or top-seeded solution growth during slow cooling of saturated solution melts). It is shown that spontaneous flux crystallization leads to the formation of a larger number of defects. Potassium atoms are found to be disordered. The splitting of the K1 and K2 potassium positions is equal to 0.347(4) and 0.279(3) Å, respectively, for the crystals grown by the top-seeded solution method and 0.308(5) and 0.321(4) Å, respectively, for the crystals grown through the spontaneous flux crystallization.     

Non-isothermal crystallization of PVDF/PMMA blends processed in low and high shear mixers

The morphological, thermal and non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) and its blends with poly(methyl methacrylate) (PMMA) processed in low (LSM) and high (HSM) shear mixers were studied by differential scanning calorimetry (DSC). The processing effect on the PVDF melt and crystallization kinetics was described and the effect of PMMA on the PVDF crystallization was also investigated. The addition of PMMA into PVDF increases of relative B phase content independent of the processing conditions. The validity of the modified Avrami and Kolmogorov–Johnson–Mehl–Avrami (KJMA) models for the non-isothermal crystallization of PVDF/PMMA blends are discussed. The KJMA method described accurately the non-isothermal crystallization behavior. The results showed a shift in the PVDF crystallization/fusion peak to lower temperatures. The activation energies for crystallization of PVDF and its blends evaluated through the isoconversional method using Friedman's approximation were higher for samples processed in the LSM. Differences in the activation energies were related to the ability of the molecular segments to crystallize when reaching the growing crystallization front, confirming that the mixing process has some effect on the interaction between the polymers. On the other hand, the isoconversional methods in combination with the KJMA equation provide better understanding of the kinetics of the crystallization process demonstrated by a strongly dependence of activation energy (Ea), relative crystalline fraction (XT), and global and local Avrami exponents (n and n (XT)).     

Crystallization tests bench

A model of an air-cooled tube (“air-heat saw”) installed in a laboratory tube furnace is presented. The setup (“crystallization tests bench”) allows easy regulation and simultaneous crystallization tests of a series of different crystallization parameters in crucible columns, enabling fast studies of obtaining crystals from materials with unknown crystallization parameters. The relationships between the crystallization rate and parameters of air-cooled tube are given and numerically analyzed. This method can also be applied in crucible or chamber furnaces.     

A numerical study of convection during THM growth of CdTe with ACRT

The accelerated crucible rotation technique (ACRT) is an effective way to increase mixing in the solution zone in travelling heater method (THM) growth and to obtain higher growth rate limits. In this paper, detailed numerical calculations of the combined thermally driven and forced convection during THM growth of CdTe from a Te-rich solution are presented. The effects of various parameters of ACRT on the mixing are considered and a possible optimum cycle for high growth rate limits is given.     

Supersaturation by gelling: Gel-grown single crystals of metal(II)carboxylates

Hydrolysis and polycondensation of tetraalcoxysilanes create both: a crystal growth medium and an alcohol-water mixture with diminished solubility for a lot of compounds. Solvent varying gel crystallization is shown for twenty metal(II)carboxylates in TMOS. The influence of pH-value, salt- and TMOS concentration and combination of this method with cooling crystallization are described.     

A short overview on practical techniques for protein crystallization and a new approach using low intensity electromagnetic fields

This contribution deals with a practical overview of some popular and sophisticated crystallization methods that help increase the success rate of a crystallization project and introduces a newly developed method involving low intensity electromagnetic fields. Aiming to suggest a methodology to follow, the present contribution is divided into two main parts in a logical order to get the best crystals for high resolution X-ray crystallographic analysis. The first part starts with a short review of the chemical and physical fundamentals of each crystallization method through different strategies based on physicochemical approaches. Then, practical non-conventional techniques for protein crystallization are presented, not only for growing protein crystals, but also for controlling the size and number of crystals. These include crystal growth in gels, counter-diffusion, seeding, and macromolecular imprinted polymers (MIPs). The second part shows the effects of coupling low intensity electric fields (in the scale of units of  μAmperes) with weak magnetic fields (in the scale of milli Tesla) applied to protein crystallization. This approach consists of a novel experimental set up, which was used to study the influence of the coupled fields on the crystallization of lysozyme in solution and in gel media. This new approach is based on the classical theories of transport phenomena and offers a more accessible strategy to obtain suitable crystals for X-ray characterization or Neutron diffraction investigations.     

Crystallization of binary melt with a periodically varying rate

The time dependence of the crystallization rate at crystal pulling to the cold zone with a velocity that has a sinusoidal component has been investigated within a one-dimensional time-dependent model of solidification of a diluted binary melt by the net method. It is shown that the regularities that were obtained previously by the analytical method for pulling rates with small oscillations are repeated in many respects when considering oscillations of larger amplitudes. At significant oscillation amplitudes, the time-averaged values of impurity concentration at the interface for the stationary and vibrational crystallization modes may differ by several dozen percent.     

Simplex optimization of protein crystallization conditions

Simplex algorithms have been used to optimize for size, number and morphology of lysozyme and apoferritin crystals. This approach requires fewer experiments than the single-factor-at-a-time method or factorial designs and will be useful in conserving materials on the International Space Station. The simplex method has the possible advantage that it conserves on materials by reducing the number of experiments required to optimize a crystallization system. The process is iterative and exploratory and should allow optimum microgravity conditions to be determined which might very well be different from the optimum conditions on Earth. Because the simplex method uses simple mathematical operations to calculate the next set of crystallization conditions it will be easier for crystal growers to implement than factorial designs. Factorial experiments are based on varying all factors simultaneously at a limited number of factor levels. This results in a model that is used to determine the influence of each factor and their interactions. Factorial design experiments are especially useful at the beginning of an experimental study and as a screening tool to investigate a large number of factors. The simplex method is an optimization method which is model-independent and requires no fitting of models to data. Also, when applied to protein crystal growth the simplex method does not rely on an absolute quality score. Instead, with each iteration a comparison is made to the last experiment and the results are assigned as being “better or worse”. In this study, commercially obtained apoferritin was purified from 65% monomeric apoferritin to 92% monomeric apoferritin by size exclusion chromatography. Simplex optimization found the best apoferritin crystals were obtained at 15 mg/ml apoferritin, 2.0% CdSO₄, 25°C using the hanging drop vapor diffusion method of crystallization and at 24 mg/ml apoferritin, 1.5% CdSO₄, 25°C using the containerless crystallization method. For lysozyme, the simplex method found the best crystals at 19 mg/ml lysozyme, 7.0% (w/v) NaCl, pH 4.0, 25°C using the hanging drop vapor diffusion method of crystallization. For both proteins, the optimum conditions were found with less than ten experiments using very little protein. Finally, we report that the factors to be considered in the successful application of this method to crystallization are the number of variables to be studied, the initial conditions, step size and analysis of crystal quality.     

Design of agitated crystallizers

The evaluation and/or design method for crystallization, based on the system constant B_N, has been applied on crystallization data of various substances published in the literature. A correlation of the B_N values with the relative kinetic exponent of crystallization, n/g, demonstrates that the applicability of the method is independent of the size of equipment, mode of crystallization and mode of supersaturation creation.     

Analysis of the feasibility of Avrami equation to amino acid endcapped PPDO crystallization by using Malek and Mitsuhashi method

Typically, the crystallization kinetics behaviour of biodegradable polyester could be described by the Avrami equation; however, for the appropriate application of this equation, some assumptions are required. Under conventional conditions of isothermal crystallization without nucleating agents, homogeneous nucleation is the key factor for the compatibility of this equation. On account of structural characteristics, the homogeneous nucleation of polymers is possibly affected by several factors. In this study, we investigated the isothermal crystallization of four PPDOs end‐capped with amino acids, followed by the Avrami equation analysis. After employing the method reported by Malek and Mitsuhashi, the L‐Gly‐ end‐capped PPDO and L‐Leu‐, L‐Phe‐end‐capped PPDO crystallized at higher temperatures were not suitable for analysis by the Avrami equation. In addition, this result was substantiated by reasoning the polymer chains’ mobility which could be affected by the terminated amino acids’ steric hindrance and crystallization temperatures, subsequently affecting homogeneous nucleation.     

Growth and interface study of 2 in diameter CdZnTe by THM technique

Growth interface of large diameter CdZnTe ingots grown from Te solution by travelling heater method have been studied. Both macroscopic and microscopic investigations were carried out. The results indicated that the shape of the interface strongly governs the grain growth on the ingot, while the microscopic morphology of the growth interface is responsible for Te inclusions in the grown crystal.     

Influence of Gravitation on the Processes of Heat and Mass Transfer in Solution Crystal Growth by the Travelling Heater Method (THM) (I)

In axially symmetric and planar cases the formulation is given of a two-dimensional hydrodynamic thermodiffusive problem on the crystal PbTe growth from solution by the travelling heater method. The analysis of the one-dimensional thermo-diffusive problem solution is presented. The dependences were obtained of the growing and dissolving interface positions relative to the heater on the heater travel rate for different lengths of solvent zone.     

三聚甲醛存在下EMT分子筛的合成及表征

以硅酸钠为硅源、铝酸钠为铝源,以三聚甲醛(TOX)为有机添加剂,室温下悬浮聚集陈化合成了EMT分子筛.考察了凝胶组成、晶化温度、晶化时间等因素对EMT分子筛合成的影响.采用XRD、FT-IR、SEM、BET、ICP等手段对EMT分子筛进行了表征.结果表明,合成EMT分子筛适宜的条件为:凝胶摩尔组成nNa2O∶nAl2O3∶nSiO2∶nH2O∶nTOX=18.5∶1∶5∶240∶0.5,晶化温度30 ℃,晶化时间72 h,此条件下合成的EMT分子筛,XRD特征峰较强,与典型的EMT分子筛的特征衍射峰相吻合,相对结晶度为80.1;,经ICP分析计算Si/Al=2.01,BET比表面积为80.57 m2/g,孔容和孔径分别为0.03 cm3 /g和2.07 nm,SEM照片显示EMT为球形晶体颗粒团聚状生长,大小均匀,排列紧凑.     

Evaluation of the guided random parameterization method for critical cooling rate calculations

We focus on a recently suggested approach to the calculation of critical cooling rates for glass formation. It is a “random parameterization” method that is guided by a limited number of isothermal scanning calorimetry experiments. However, several assumptions have been made in its derivation that may not mirror the actual crystallization behavior of most supercooled liquids, which may jeopardize the estimation of glass forming ability. We evaluate those assumptions and the applicability of the method is tested for lithium disilicate glass (which displays moderate internal nucleation rates) and dibarium titanium silicate glass (which displays very high internal nucleation rates, similar to those of metallic glasses). Both glasses nucleate homogeneously and exhibit polymorphic crystallization. Our calculations show that some overlooked variables, such as the sample geometry, nucleation induction-times, surface crystallization and the breakdown of the Stokes–Einstein/Eyring equation, have significant roles on the calculated time–temperature–transformation curves during heating experiments. We demonstrate that the proposed random parameterization method can only be used when a glass forming liquid that undergoes internal crystallization is cooled from above its liquidus to various test temperatures. If the sample undergoes predominant surface crystallization or if it is heated to the test temperature several corrections must be made.     

纳米氧化镱对熔融石英析晶动力学机制的影响

本文研究引入纳米氧化镱对熔融石英析晶机制及动力学过程的影响.通过X射线衍射仪(XRD)测试结果分析了纳米氧化镱的引入对熔融石英陶瓷析晶率的影响,采用动力学方法分析了纳米氧化镱的引入对熔融石英陶瓷析晶机制的影响,同时探讨了其等温析晶动力学过程.研究表明,熔融石英陶瓷的晶粒向二维兼有一维及三维的方式生长,引入纳米氧化镱的熔...     

Analysis of the static method of the growth of cadmium sulphide crystals with large temperature gradients

The paper gives an analysis of the thermodynamical conditions of crystallization of cadmium sulphide from the gaseous phase with the use of large temperature gradients in the course of crystal growth. From the achieved results there follows that large temperature gradients with the static method of crystal growth favourably influences the formation of crystallization nuclei and the growth of single crystals. The crystals cultivated under such conditions are comparatively large, their volume being several cm³ and their weight ranging from 40–60 g. These crystals are suitable for photoelectrical and electroacoustical measurements and various technical applications.