Screening of nucleation conditions using levitated drops for protein crystallization

The growth of suitable protein crystals is an essential step in the structure determination of a protein by X-ray crystallography. At present, crystals are mostly grown using trial-and-error procedures, and protocols that rapidly screen for the crystal nucleation step are rare. Presented here is an approach to minimize the consumption of precious protein material while searching for the nucleation conditions. Acoustically levitated drops of known protein concentration (0.25-1.5-microL volumes) are injected with crystallizing agents using piezoelectric flow-through dispensers (ejecting 50-100-pL droplets at 1-9000 droplets/s). A restricted number of crystallizing agents representing three classes are used: poly(ethylene glycol), salts, and the viscous alcohol 2-methyl 2,4-pentanediol. From a digitized picture of the levitated drop volume, calculations are performed giving the concentrations of all components in the drop at any time during a "precipitation experiment". Supersaturation is the prerequisite for crystal nucleation, and protein precipitation indicates high supersaturation. A light source illuminates the levitated drop, and protein precipitation is monitored using right-angle light scattering. On the basis of these intensity measurements and the volume determination, precipitation diagrams for each crystallizing agent are constructed that give the protein/crystallizing agent concentration boundaries between the minimum and the maximum detectable protein precipitation. Guided by the concentration values obtained from such plots, when approaching the supersaturation region, separate crystallization drops are mixed and allowed to equilibrate under paraffin oil. At conditions in which microcrystals can be observed, the nucleation tendency of the macromolecule is confirmed. Optimization of crystallization conditions can then follow. Proteins tested include alcohol dehydrogenase and D-serine dehydratase. Alcohol dehydrogenase, known to crystallize easily, was used to evaluate whether the ultrasonic field inhibits nucleation. Details are given for the screening procedure of D-serine dehydratase, an enzyme earlier found to be difficult to crystallize reproducibly. The time and material-saving qualities of this method are emphasized, since a range of conditions can quickly be screened using small amounts of protein to roughly determine solubility characteristics of a protein before crystallization trials are initiated.     

Measurement of Density and Structural Short-Range Order of Levitated Liquid Metals

The determination of thermophysical properties and structure of undercooled metallic melts must be accomplished by contactless methods due to the high reactivity of the material. It has been shown that electromagnetic levitation provides high-purity conditions to allow deep undercooling. The density and thermal expansion of a levitated drop can be derived from volume measurements using a charge-coupled device (CCD) camera and a digital image processing system. Combining levitation with extended x-ray absorption fine structure (EXAFS) spectroscopy leads to the possibility of studying the local structure of the liquid in a wide temperature range including the deeply undercooled regime.     

纳米锡粉的制备及分散稳定性研究

为了使纳米锡粉在乙二醇水溶液中良好稳定地分散,通过直流电弧等离子体蒸发法制备平均粒径为106 nm的纳米锡粉,以十二烷基硫酸钠、六偏磷酸钠、聚乙二醇为分散剂研究纳米锡粉在乙二醇水溶液中的分散性能,分析分散时间、分散剂类型及含量对锡粉分散性能的影响。结果表明,不同分散剂的加入对锡粉颗粒在乙二醇水溶液中的分散稳定性都有所提高,随着超声时间的延长和分散剂浓度的增大,粉体的分散效果先增强后减弱;纳米锡粉在乙二醇水溶液中的最佳分散工艺是加入质量分数为3%的十二烷基硫酸钠,超声时间为60 min。     

Concentration and size separation of DNA samples at liquid-liquid interfaces

This report introduces a new analytical concept utilizing the mass transfer resistance of a liquid-liquid interface to concentrate and separate DNA samples. DNA molecules can be electrophoretically accumulated at a liquid-liquid interface of an aqueous two-phase system (ATPS) of poly(ethylene glycol) (PEG) and dextran, two polymers that form two immiscible phases in aqueous electrolyte solutions. The detachment of DNA from the interface into the other phase can be triggered by increasing the applied electric field. We experimentally study the size dependence of the detachment process for a broad spectrum of DNA fragments. In a regime where the coiling of the chains does not play a significant role, the process shows a linear dependence on the diffusion coefficient, with shorter DNA chains detaching at lower electric field strengths than larger ones. The concept may enable novel separation protocols for preparative and analytical purposes.     

Study on Heat Transfer and Flow Characteristic Under Phase-Change Process of an Acoustically Levitated Droplet

Acoustic levitation is one of the levitation technique which is expected to be used for analytical chemistry and manufacturing new materials. Thus, it is important to gather the knowledge about acoustically levitated droplet. The purpose of this study is to investigate the heat transfer and flow behavior under phase change process of an acoustically levitated droplet. The following results were obtained from experiments. Evaporation process and external flow structure of the levitated droplet is visualized by a high speed camera and it is found that they differ by the type of fluid. Toroidal vortices are observed near the surface of the ethanol solution droplet. Heat transfer coefficient is estimated from the volume change and temperature gradient. It is substantially higher than that estimated by the existing experimental correlation.     

Influencing Factors of Levitation Drift Caused by Magnet Vibration

In a levitated high-temperature superconducting system, the drift of levitated body due to vibration of the permanent magnet or an alternating magnetic field is a key and fatal subject in its applications. In this paper, the levitation drift caused by a PM vibration is investigated by a vibration measurement system. The influences of critical current density, levitation gap, weight of the levitated body, voltage across the shaker (amplitude of vibration), cooling height, etc. on the levitation drift have been measured, respectively. In the end, several methods which can reduce the levitation drift are presented and compared; the most reliable method is enhancing the critical current density of the superconductors.     

Iron-included carbon nanocapsules coated with biocompatible poly(ethylene glycol) shells

Nanoparticles of iron carbides wrapped in multilayered graphitic sheets (carbon nanocapsules) were synthesized by electric plasma discharge in an ultrasonic cavitation field in liquid ethanol and purified by selective oxidation and magnetic separation. The particles had 100–200 nm in diameter after centrifuging for 10 min at 4000 rpm. Carbon nanocapsules were covered by wispy poly(ethylene glycol) PEG coating about 7–10 nm in thickness. The number of PEG chains coated on carbon nanocapsules could be estimated as 9.15%. The values of saturation magnetization Ms and coercivity Hc of purified carbon nanocapsules without PEG coating were 112 emu g⁻¹ and 75 Oe respectively. Magnetically soft carbon nanocapsules with a poly(ethylene glycol) coating on the surface may possibly be used as biocompatible magnetic nanoparticles in medical applications.     

Aspects of high-temperature pyrometry for measurements in ultrahigh vacuum

Containerless materials processing of liquid metals with the use of electromagnetic levitation requires contactless temperature measurement by pyrometry. For high temperatures and under high-vacuum conditions, the vapor pressure of the levitated metal drop increases, leading to evaporation losses of the sample material. This flux condenses on the cold parts of the experimental apparatus including the window in front of the pyrometer. As a result, the intensity of radiation reaching the pyrometer decreases, which is erroneously interpreted as a decrease in temperature. Several methods to protect the pyrometer against contamination have been proposed. In this paper, we report experimental tests of the concepts of shielding windows and mirror optics placed into the optical path between the sample and the pyrometer. Temperature measurements with a periscopic mirror system are also presented.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

External Flow of an Acoustically Levitated Droplet

One of the major recent advances for experiments in containerless processing is acoustic levitation. Although there are a lot of previous studies for acoustic levitation, characteristic of external flow of an acoustically levitated droplet is not experimentally examined enough. In this study, external flow field has been observed by using high speed camera and Particle Image Velocimetry. In the case of any levitated droplet at a velocity antinode of standing wave, toroidal vortex are generated around levitated droplet. It is found that toroidal vortex around a levitated droplet is strongly affected by viscosity of levitated samples and input voltage. In terms of water droplet, as input voltage is decreased, location of toroidal vortex is moved from bottom to top of levitated samples.     

pH值对聚乙二醇渗透材料的影响及NMR的分析

为了探讨聚乙二醇(PEG)渗透材料在不同pH条件下的性能,用NaOH溶液和稀盐酸调节PEG渗透材料的pH值.采用核磁共振研究不同pH值条件对PEG结构的影响.研究表明:当pH值在2~8时,PEG渗透材料放置7d可以保持稳定的pH值;在酸性条件下,由于PEG中的O对酸中H+形成作用,削弱了O原子对与O间接相连的-CH2基团的引力,使该-CH2基团中的H原子的化学位移向低场偏移,但PEG的结构不变;在pH值大于8的条件下,氢键的形成导致线状的PEG发生立体扭结,从而产生沉淀.因此,在pH值为2~8的范围内,可以稳定使用PEG渗透材料.     

Interfacial properties of immiscible Co–Cu alloys

Using electromagnetic levitation under microgravity conditions, the interfacial properties of an Cu₇₅Co₂₅ alloy have been investigated in the liquid phase. This alloy exhibits a metastable liquid miscibility gap and can be prepared and levitated in a configuration consisting of a liquid cobalt-rich core surrounded by a liquid copper-rich shell. Exciting drop oscillations and analysing the frequency spectrum, both surface and (liquid–liquid) interfacial tension can be derived from the observed oscillation frequencies. This paper briefly reviews the theoretical background and reports on a recent experiment carried out on board the TEXUS 44 sounding rocket.     

The surface tension of steels

Over many years NPL has carried out measurements of surface tension of steels using the levitated drop method. Much of this work has been to study variations in weld profile brought about by changes in Marangoni flow patterns in the liquid pool, and many of these data have remained unpublished. 49 ferritic and austenitic steels are compared, and relationships for surface tension, and the coefficient of surface tension against temperature, based on sulphur content of the steel, are presented. Data has been reassessed using the Cummings correction to allow for the effects of the levitation forces.     

热致相分离法EVOH微孔膜的制备和形态

选择乙烯的摩尔分数为38％的乙烯-乙烯醇的共聚物(EVOH)为原料，聚乙二醇(PEG)为稀释剂，采用热致相分离方法(TIPS)制备了亲水性高分子微孔膜．用扫描电子显微镜观测了微孔膜的形态．结果表明，分相的方式及微孔的大小由聚合物的含量及冷却速度决定．EVOH含量越少，则越易发生液-液相分离；冷却速度越慢，则微孔的尺寸也越大、EVOH摩尔分数为60％时，如果冷却速度很慢，则发生液-固相分离；如果冷却速度较快，则可同时观察到液-固相分离和液-液相分离的形态．     

Analysis of a high Tc superconducting levitation systemwith vibration isolation control

This paper presents a method for controlling vibrations of a levitated high Tc superconducting body subjected to base disturbances. To have the control forces, an actuator consisting of a permanent magnet with an electromagnet was presented. The analytical solution for calculating levitation forces due to the permanent magnet and the control currents in the electromagnet was obtained. The levitation forces obtained coincide with the previously published results. The equation of motion of the levitated body subjected to base disturbances under the control was presented. Nonlinear vibrations of the body were first discussed; then the method of vibration isolation control using the direct disturbance cancellation combining the velocity feedback control was investigated. Numerical calculations were carried out for the levitation forces, with respect to the levitated body subjected to harmonic or pulse base excitations. It was clarified that the present method Is valid for controlling nonlinear systems like the magnetically levitated superconducting body     

Observation of the Field,Current and Force Distributions in an Optimized Superconducting Levitation with Translational Symmetry

The superconducting levitation realized by immersing the high-temperature superconductors (HTSs) into nonuniform magnetic field is deemed promising in a wide range of industrial applications such as maglev transportation and kinetic energy storage. Using a well-established electromagnetic model to mathematically describe the HTS, we have developed an efficient scheme that is capable of intelligently and globally optimizing the permanent magnet guideway (PMG) with single or multiple HTSs levitated above for the maglev transportation applications. With maximizing the levitation force as the principal objective, we optimized the dimensions of a Halbach-derived PMG to observe how the field, current and force distribute inside the HTSs when the optimized situation is achieved. Using a pristine PMG as a reference, we have analyzed the critical issues for enhancing the levitation force through comparing the field, current and force distributions between the optimized and pristine PMGs. It was also found that the optimized dimensions of the PMG are highly dependent upon the levitated HTS. Moreover, the guidance force is not always contradictory to the levitation force and may also be enhanced when the levitation force is prescribed to be the principle objective, depending on the configuration of levitation system and lateral displacement.     

Design of a Large Oxygen Magnetic Levitation Facility

The present magnetic levitation facility offers an alternative to space means for studying fluids and especially liquid oxygen that exhibits important safety requirements. The station has great use flexibility. Thus it enables us to study hydrodynamic instabilities (acceleration and deceleration phase) and also to focus on thermal exchanges (nuclear and film boiling) and transition phase of fluids under reduced gravity such as Lunar, Martian or micro-gravity. The volume of liquid oxygen levitated is about two litres with a resulting acceleration less than 0.1 m/s². Besides the aspect ratio of the working cell can be changed.     

Shape Oscillations in Levitated He II Drops

We describe experiments to study the shape oscillations of levitated He II drops. Drops of approximately 0.5 cm diameter are levitated magnetically with a superconducting solenoid, and shape oscillations are induced with an ac electric field. We have measured the damping of shape oscillations as a function of temperature. The damping rate is compared to that predicted by a two fluid, hydrodynamic model, which takes account the effect of the motion in the vapor. The effects of condensation and evaporation on the motion of the drop are also considered.     

致孔剂对PVDF-g-PNIPAAm温度敏感膜成膜过程及膜性能的影响

采用热力学相图和超声时域反射法研究了致孔剂聚乙二醇(PEG)对聚偏氟乙烯-g-聚N-异丙基丙烯酰胺(PVDF-g-PNIPAAm)成膜过程的影响。结果表明,在PVDF-g-PNIPAAm/DMF/H2O成膜体系中添加PEG后,促进了成膜体系的分相,体系变得更不稳定。加入PEG后,使得PVDF-g-PNIPAAm/DMF/H2O成膜体系的成膜速度加快,体系更容易发生瞬时液液分相,导致膜孔尺寸增加,纯水通量提高,但温度响应性能不明显。     

Reduction in the initial-burst release by surface crosslinking of PLGA microparticles containing hydrophilic or hydrophobic drugs

Sustained-release approaches are emerging for the delivery of drugs from polymer encapsulation. However, the most persistent problem that remains is the initial burst release of the drug, which can exceed the toxic limits. Dexamethasone, a hydrophobic drug, was encapsulated in poly(lactide-co-glycolide) (PLGA) microparticles using the solvent evaporation method. The drug release profile of these microparticles was studied and the initial burst was reduced by crosslinking of the microparticle surface using ethylene glycol dimethacrylate and tri(ethylene glycol) dimethacrylate. Due to surface crosslinking, an additional diffusional resistance was created, which prevented easy dissolution of the drug into the release medium and brought about a substantial reduction in the initial burst release. Moreover, the time required for reaching a stationary-state release was also observed to be delayed, prolonging the sustained drug delivery. This concept was further tested with a hydrophilic drug, the sodium salt of dexamethasone phosphate, encapsulated in PLGA polymer microparticles and was observed to reduce the burst release as well. For synthesizing the polymer microparticles containing dexamethasone, an o/w microemulsion and solvent evaporation technique was used; whereas, for those containing dexamethasone phosphate, w/o/o/o phase separation/coacervation technique was used. The surface crosslinking was performed by ultraviolet radiation.     

The Influence of Excitation Frequency on Magnetic Levitation Systems with a High-T c Superconductor

In this paper we present a numerical analysis of dynamic features of the levitation system generated by an interaction between a levitated permanent magnet (PM) and a high-T _c superconductor (HTSC) excited by an oscillatory external source. The obtained results show that the value of the frequency (f _free) of the PM displacement in the case of the levitation system generated by an interaction between a levitated PM and a fixed HTSC is equal at the resonance frequency (f _re) of the levitation system generated by an interaction between a levitated PM and HTS excited by an oscillatory external source and the resonance frequency (f _re) is mainly dependent upon the cooling position (Z ₀) and the mass of the PM. The numerical problem in this paper is solved by using the control volume method (CVM).