化学沉淀法制备超细粉体过程行为

应用硫酸铜还原化学沉淀法制备铜的超细粉体,研究了反应温度、浆液密度和表面活性剂对超细铜粉制备过程行为的影响。试验发现,当反应温度较高时,由于还原反应速度较高,晶核的生成速度急剧增加,晶核数量密度过大,在反应器壁上生成铜箔及大的团聚体;当体系中浆液密度较高时,颗粒由于相互间的碰撞在表面能的作用下团聚成纺锤形的大颗粒。这是两种不同的团聚行为,前者由于生长中的晶核的团聚故称为“核级团聚”,后者是由于生长中的颗粒间的团聚称为“粒级团聚”。在适当的反应条件下,控制适度过饱和度,及适度的成核速率,可以得到均匀的球形铜粉。表面活性剂的加入可有效的防止粒子的团聚。     

Aggregation thermodynamics for asphaltene precipitation

Asphaltene precipitation has been a major concern for petroleum industry due to its adverse effect on upstream production, midstream transportation, and downstream refining. As a complex phenomenon involving solubility, aggregation, and clustering, asphaltene precipitation has been extensively investigated and correlated with empirical models and equations. Based on the insight regarding hierarchical structure of asphaltenes recently elucidated by Mullins, we present a thermodynamic formulation for asphaltene aggregation, the onset of asphaltene precipitation. The thermodynamic formulation accounts for asphaltene aggregation driving force as a two‐step process: (1) molecular asphaltene forming imaginary “nanocrystals”, and (2) “nanocrystals” re‐dissolving as colloidal nanoaggregates. Applying UNIFAC with this thermodynamic formulation, we show semi‐quantitative predictions of asphaltene precipitation in 13 binary solvents with wide varieties of chemical structures and solvent combinations. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1254–1264, 2016     

结晶及沉淀过程中粒子聚结与团聚的研究进展

粒子聚结及团聚是结晶及沉淀过程中重要的二次动力学过程,对最终产品的晶形、粒度分布及纯度影响较大。综述了粒子聚结及团聚过程的机理及其影响因素,讨论了有关数学模型的研究进展,并对聚结与团聚的研究方向进行了展望。     

Sunflower protein precipitation in a tubular precipitator

Isoelectric precipitation of sunflower protein was carried out in a 20 m long, 6 mm internal diameter glass tubular precipitator. Effects of feed flow rate, protein concentration in the feed stream, and mean residence time on particle size distribution (PSD) were studied. The population balance equation (PBE) for the tubular precipitator was solved using the orthogonal collocation multiple shooting method. A simulated annealing method was used to determine the precipitation kinetic parameters for the nucleation rate, growth rate, aggregation rate, and breakage rate from the experimental data. Due to the lack of experimental data on the kinetics of sunflower protein precipitation in the literature, the extracted kinetics from our experiments were used to evaluate the predictive capability of the present model for experiments whose results had not been used to derive the kinetics. The model predictions of the particle size distribution along the tubular precipitator showed better agreement with the experimental data for large particles in comparison to the small particles (< 10 μm).     

Protein separation mechanisms in surfactant precipitation systems

Separation of globular proteins (cytochrome c and ribonuclease A) from buffer using precipitation by sodium bis-(2-ethylhexyl) sulfosuccinate (AOT), and their recovery with a counterionic surfactant, trioctylmethylammonium chloride (TOMAC) was investigated. The molar ratio between AOT and the protein (R) required for complete removal was 17 for cytochrome c, and 22 for ribonuclease A. Finally, three mixtures of the two proteins and lysozyme (studied earlier by us) were used to determine the factors controlling separation: selectivity was a strong function of surface charge distribution, indicating that charge interactions between the surfactant and surface groups of different proteins was driving precipitation.     

Properties of Protein Isolates from Marine Hydrobionts Obtained by Isoelectric Solubilisation/Precipitation: Influence of Temperature and Processing Time

Protein isolates were obtained from marine hydrobionts by the method of isoelectric precipitation with a preliminary stage of protein alkaline solubilisation. Northern blue whiting was chosen as the raw material. Various technological modes of the solubilisation stage were used: the temperature of the reaction mixture was 4 or 20 °C, and the duration was 4 or 16 h. The yield of the product was 44–45% with a high content of the main component (protein) equal to about 95%. It has been shown that a decrease in the temperature and duration of the alkaline solubilisation stage provides the production of protein isolates with good technological properties, a low solubility, high swelling and high emulsifying ability, necessary for its use in the production of functional food products, including therapeutic and prophylactic effects. These technological properties are explained by a change in the composition and structure of the protein, the change being an increase in the content of essential amino acids and the proportion of α-helices in the polypeptide chain. The main patterns obtained will be used to obtain protein isolates from marine molluscs.     

硫酸钙晶体自发沉淀动力学研究

建立了精确测量硫酸钙过饱和溶液在析晶过程中所有离子浓度变化的实验一计算系统。通过测定临界时间与过饱和度之间的关系,得到硫酸钙晶体的表面自由能为21.5mJ/m^2。基于热力学基本理论和经典的沉淀动力学理论,从实验测定值进一步推导出一系列临界状态时的热力学常数。无量纲时间指标Id与时间之间良好的线性关系表明：硫酸钙的析晶过程主要受扩散机制控制。     

Mechanism of Suppression of Protein Aggregation by ��-Crystallin

This review summarizes experimental data illuminating the mechanism of suppression of heat-induced protein aggregation by α-crystallin, one of the small heat shock proteins. The dynamic light scattering data show that the initial stage of thermal aggregation of proteins is the formation of the initial aggregates involving hundreds of molecules of the denatured protein. Further sticking of the starting aggregates proceeds in a regime of diffusion-limited cluster-cluster aggregation. The protective effect of α-crystallin is due to transition of the aggregation process to the regime of reaction-limited cluster-cluster aggregation, wherein the sticking probability for the colliding particles becomes lower than unity.     

Conformational Analysis of Misfolded Protein Aggregation by FRET and Live-Cell Imaging Techniques

Cellular homeostasis is maintained by several types of protein machinery, including molecular chaperones and proteolysis systems. Dysregulation of the proteome disrupts homeostasis in cells, tissues, and the organism as a whole, and has been hypothesized to cause neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and Huntington’s disease (HD). A hallmark of neurodegenerative disorders is formation of ubiquitin-positive inclusion bodies in neurons, suggesting that the aggregation process of misfolded proteins changes during disease progression. Hence, high-throughput determination of soluble oligomers during the aggregation process, as well as the conformation of sequestered proteins in inclusion bodies, is essential for elucidation of physiological regulation mechanism and drug discovery in this field. To elucidate the interaction, accumulation, and conformation of aggregation-prone proteins, in situ spectroscopic imaging techniques, such as Förster/fluorescence resonance energy transfer (FRET), fluorescence correlation spectroscopy (FCS), and bimolecular fluorescence complementation (BiFC) have been employed. Here, we summarize recent reports in which these techniques were applied to the analysis of aggregation-prone proteins (in particular their dimerization, interactions, and conformational changes), and describe several fluorescent indicators used for real-time observation of physiological states related to proteostasis.     

Primary Steps of pH‐Dependent Insulin Aggregation Kinetics are Governed by Conformational Flexibility

Insulin aggregation critically depends on pH. The underlying energetic and structural determinants are, however, unknown. Here, we measure the kinetics of the primary aggregation steps of the insulin monomer in vitro and relate it to its conformational flexibility. To assess these primary steps the monomer concentration was monitored by mass spectrometry at various pH values and aggregation products were imaged by atomic force microscopy. Lowering the pH from 3 to 1.6 markedly accelerated the observed aggregation kinetics. The influence of pH on the monomer structure and dynamics in solution was studied by molecular dynamics simulations, with the protonation states of the titrable groups obtained from electrostatic calculations. Reduced flexibility was observed for low pH values, mainly in the C terminus and in the helix of the B chain; these corresponded to an estimated entropy loss of 150 J mol^?1 K^?1. The striking correlation between entropy loss and pH value is consistent with the observed kinetic traces. In analogy to the well‐known Φ value analysis, this result allows the extraction of structural information about the rate determining transition state of the primary aggregation steps. In particular, we suggest that the residues in the helix of the B chain are involved in this transition state.     

Different Roles of p62 (SQSTM1) Isoforms in Keratin-Related Protein Aggregation

p62/Sequestosome-1 (p62) is a multifunctional adaptor protein and is also a constant component of disease-associated protein aggregates, including Mallory–Denk bodies (MDBs), in steatohepatitis and hepatocellular carcinoma. We investigated the interaction of the two human p62 isoforms, p62-H1 (full-length isoform) and p62-H2 (partly devoid of PB1 domain), with keratins 8 and 18, the major components of MDBs. In human liver, p62-H2 is expressed two-fold higher compared to p62-H1 at the mRNA level and is present in slightly but not significantly higher concentrations at the protein level. Co-transfection studies in CHO-K1 cells, PLC/PRF/5 cells as well as p62⁻ total-knockout and wild-type mouse fibroblasts revealed marked differences in the cytoplasmic distribution and aggregation behavior of the two p62 isoforms. Transfection-induced overexpression of p62-H2 generated large cytoplasmic aggregates in PLC/PRF/5 and CHO-K1 cells that mostly co-localized with transfected keratins resembling MDBs or (transfection without keratins) intracytoplasmic hyaline bodies. In fibroblasts, however, transfected p62-H2 was predominantly diffusely distributed in the cytoplasm. Aggregation of p62-H2 and p62ΔSH2 as well as the interaction with K8 (but not with K18) involves acquisition of cross-β-sheet conformation as revealed by staining with luminescent conjugated oligothiophenes. These results indicate the importance of considering p62 isoforms in protein aggregation disease.     

Isoelectric precipitation of sunflower protein in a tubular precipitator

Isoelectric precipitation of sunflower protein was carried out in a 10-m long, 6-mm internal diameter glass tubular precipitator. The effects of feed flow rate, protein concentration in the feed stream, and volumetric feed ratio of precipitant (HCl aqueous solution) to protein solution on solid protein recovery and particle size distribution were studied. The dispersion range of the tubular precipitator was modelled to predict the experimental results. Calculated initial growth rates of protein particles were found to: increase with increases in feed flow rate and protein concentration in the feed stream, and decrease with increases in volumetric feed ratio.     

Kinetics of precipitation of surfactants. II. Anionic surfactant mixtures

Precipitation kinetics were measured for calcium-induced precipitation of mixtures of two anionic surfactants. The overall time required for precipitation to occur increased dramatically in specific ranges of compositions for the surfactant mixtures when compared to single components. Adsorption of the nonprecipitating surfactant onto the precipitate surface was shown to be responsible for this remarkable synergism. The higher the supersaturation of surfactant monomers, the more rapidly precipitation occurred. Under conditions where both surfactants were supersaturated, precipitation sometimes occurred in stepwise fashion, where crystals of different composition were formed with different induction times. Image analysis of the crystalline precipitate showed that crystal habit was affected when the two surfactants were mixed, indicating that processes such as adsorption and coprecipitation (most likely by inclusion) were occurring. When the crystals were allowed to age in solution for a period of 1 wk, the crystalline phase from the mixed surfactant solutions was found to separate into two types of crystals, which resembled week-old crystals formed from single surfactant systems.     

Inhibition of Amyloid Protein Aggregation Using Selected Peptidomimetics

Aberrant protein aggregation leads to the formation of amyloid fibrils. This phenomenon is linked to the development of more than 40 irremediable diseases such as Alzheimer's disease, Parkinson's disease, type 2 diabetes, and cancer. Plenty of research efforts have been given to understanding the underlying mechanism of protein aggregation, associated toxicity, and the development of amyloid inhibitors. Recently, the peptidomimetic approach has emerged as a potential tool to modulate several protein-protein interactions (PPIs). In this review, we discussed selected peptidomimetic-based approaches for the modulation of important amyloid proteins (Islet Amyloid Polypeptide, Amyloid Beta, α-synuclein, mutant p53, and insulin) aggregation. This approach holds a powerful platform for creating an essential stepping stone for the vital development of anti-amyloid therapeutic agents.     

The Role of Crowded Physiological Environments in Prion and Prion-like Protein Aggregation

Prion diseases and prion- like protein misfolding diseases are related to the accumulation of abnormal aggregates of the normal host proteins including prion proteins and Tau protein. These proteins possess self-templating and transmissible characteristics. The crowded physiological environments where the aggregation of these amyloidogenic proteins takes place can be imitated in vitro by the addition of macromolecular crowding agents such as inert polysaccharides. In this review, we summarize the aggregation of prion proteins in crowded physiological environments and discuss the role of macromolecular crowding in prion protein aggregation. We also summarize the aggregation of prion- like proteins including human Tau protein, human α-synuclein, and human copper, zinc superoxide dismutase under macromolecular crowding environments and discuss the role of macromolecular crowding in prion- like protein aggregation. The excluded-volume effects caused by macromolecular crowding could accelerate the aggregation of neurodegenerative disease-associated proteins while inhibiting the aggregation of the proteins that are not neurodegenerative disease-associated.     

Kinetics of precipitation of surfactants. I. Anionic surfactants with calcium and with cationic surfactants

Isoperibol calorimetry was used to measure the rates of precipitation for aqueous solutions of several anionic surfactants with calcium and of anionic and cationic surfactants. A monomer concentration-dependent supersaturation ratio was used to describe the relative rates of precipitation for the surfactant systems studied. This supersaturation ratio allows for the relative rates of precipitation of any surfactant solution to be compared whether micelles are present in solution or not. In general, as the supersaturation ratio increases, the rate of precipitation decreases and the induction time decreases, bot above and below the critical micelle concentration (CMC). The rate of precipitation of sodium dodecyl sulfate (SDS) with dodecyl pyridinium chloride is much slower than the rate of precipitation of the anionic surfactants with calcium for similar supersaturation ratios. The rate of precipitation of SDS with calcium is slightly faster than the rate of precipitation of sodium octyl benzene sulfonate for similar supersaturation ratios. Studies of precipitate crystals, conducted using image analysis, showed that size and shape dependent on the initial supersaturation, the precipitating surfactant molecule, and the extent of aging (until an equilibrium size and shape was reached). Also, differences in the appearance of crystals formed from solutions above and below the CMC were observed. These were most likely due to the difference in supersaturation of these solutions. The crystals formed due to precipitation of SDS with calcium at a concentration above the CMC formed flat trapezoidal, rhombic and hexagonal shapes. These aged into clusters by 1 wk. For a solution that was precipitated at concentrations beginning below the CMC, the crystals began as elongated and rhombic flat plates and aged into trapezoidal, rhombic, and needle-like structures.     

Kinetics of horseradish peroxidase-catalysed polymerization and precipitation of aqueous 4-chlorophenol

Hydrogen-peroxide oxidoreductase (EC 1.11.1.7) from horseradishes catalyzes the polymerization and precipitation of aromatic compounds from aqueous solutions in the presence of hydrogen peroxide. This process has demonstrated good potential as a technique for the removal of toxic contaminants from wastewaters. Steady-state, fully transient and pseudo-steady-state models of the horseradish peroxidase system have been developed to assist in the under-standing of the dominant mechanisms of inactivation and to aid in the selection and design of an appropriate reactor system. Model validation was performed by comparing model predictions with experimental observations of the polymerization and precipitation of 4-chlorophenol. Good agreement was found between experimental data and predictions of the fully transient and pseudo-steady-state models. The pseudo-steady-state model has the advantage of reduced complexity with a corresponding reduction in computation time required to solve model equations while maintaining the predictive ability of the fully transient model.     

Chemical Biology Toolbox to Visualize Protein Aggregation in Live Cells

Protein misfolding and aggregation is a complex biochemical process and has been associated with numerous human degenerative diseases. Developing novel chemical and biological tools and approaches to visualize aggregated proteins in live cells is in high demand for mechanistic studies, diagnostics, and therapeutics. In this review, we summarize the recent developments in the chemical biology toolbox applied to protein aggregation studies in live cells. These methods exploited fluorescent protein tags, fluorescent chemical tags, and small-molecule probes to visualize the protein-aggregation process, detect proteome stresses, and quantify the protein homeostasis network capacity. Inspired by these seminal works, we have generalized design principles for the development of new detection methods and probes in the future that will illuminate this important biological process.     

Kinetics of precipitation of surfactants. III. Atomic force microscopy of precipitate crystals

The overall time required for precipitation to occur can increase dramatically for surfactant mixtures compared to single components. Atomic force microscopy (AFM) has been used in this study to examine the precipitated surfactant crystals, which gives insight into both the thermodynamics and kinetics of surfactant precipitation. Calcium dodecyl sulfate, Ca(DS)₂ shows regular, layered growth that is consistent with a screw-dislocation crystallization mechanism. Calcium octylbenzene sulfonate, Ca(OBS)₂, forms crystals with uneven, jagged edges. At high magnification, the head groups of both Ca(DS)₂ and Ca(OBS)₂ show hexagonal packing. For mixtures that have surprisingly slow precipitation kinetics, the jagged Ca(OBS)₂ crystals were observed to grow on the layered Ca(DS)₂ crystals. Other surfactant mixtures that exhibited a stepwise rate curve formed crystals with incomplete layers and holes that are not observed with pure surfactants. In general, this type of crystal formation can occur when an impurity is present, which in this case is most likely the second surfactant. This work indicates that interruption of crystal growth by crystallization of a dissimilar supersaturated surfactant onto the first crystal is one explanation for the slower precipitation of surfactant mixtures compared to single surfactants. Entrapment of the nonprecipitating surfactant (inclusion) in the forming crystal of the precipitating surfactant in mixed surfactant systems is another mechanism responsible for the reduction in precipitation rate.