Sequence and structural determinants of amyloid fibril formation

Amyloid fibril formation is a process that represents an essential feature of the chemistry of proteins and plays a central role in human pathology and the biology of living organisms. In this Account, we shall describe some of the recent results on the sequence and structural determinants of protein aggregation. We shall describe the factors that govern aggregation of unfolded peptides and proteins. We shall then try to summarize the factors that pertain to the aggregation of partially structured states and will show that even fully folded states of proteins have an ability to aggregate into at least early oligomers with no need to undergo substantial conformational changes.     

煤溶胀动力学与热力学的研究

以煤溶胀机理、氢键等为基础,从热力学和动力学方面综述了煤溶胀的本质,讨论了溶剂性质、氧化、温度、煤粉粒度及热处理对溶胀动力学的影响。结果表明：溶胀过程中,表观活化能和速率常数不仅与溶剂分子的空间属性有关,还受溶剂分子形状的影响;混合溶剂的协同效应极大地提升了溶胀速率,增大了表观活化能;抽提煤的干燥条件不同及煤经过氧化后,溶胀机理均会发生明显改变。最后详细介绍了煤溶胀技术对煤分子结构的影响及在煤液化方面的应用。     

Designed amyloid beta peptide fibril - a tool for high-throughput screening of fibril inhibitors

Amyloid beta peptide (Abeta) fibril formation is widely believed to be the causative event of Alzheimer's disease pathogenesis. Therapeutic approaches are therefore in development that target various sites in the production and aggregation of Abeta. Herein we present a high-throughput screening tool to generate novel hit compounds that block Abeta fibril formation. This tool is an application for our fibril model (Abeta(16-37)Y(20)K(22)K(24))(4), which is a covalent assembly of four Abeta fragments. With this tool, screening studies are complete within one hour, as opposed to days with native Abeta(1-40). A Z' factor of 0.84+/-0.03 was determined for fibril formation and inhibition, followed by the reporter molecule thioflavin T. Herein we also describe the analysis of a broad range of reported inhibitors and non-inhibitors of Abeta fibril formation to test the validity of the system.     

Direct observation of amyloid fibril growth, propagation, and adaptation

Amyloid fibrils form through nucleation and growth. To clarify the mechanism involved, direct observations of both processes are important. First, seed-dependent fibril growth of beta2-microglobulin (beta2-m) and amyloid beta peptide was visualized in real time at the single fibril level using total internal reflection fluorescence microscopy combined with the binding of thioflavin T, an amyloid-specific fluorescence dye. Second, using atomic force microscopy, ultrasonication-induced formation of beta2-m fibrils was shown, indicating that ultrasonication is useful to accelerate the nucleation process. Third, with the proteolytic fragment of beta2-m, propagation and a transformation of fibril morphology was demonstrated. These direct observations indicate that template-dependent growth and structural diversity are key factors determining the structure and function of amyloid fibrils.     

Inhibition of cytotoxicity and amyloid fibril formation by a D-amino acid peptide that specifically binds to Alzheimer's disease amyloid peptide

Alzheimer's disease (AD) is a progressive neurodegenerative disorder. The 'amyloid cascade hypothesis' assigns the amyloid-beta-peptide (Abeta) a central role in the pathogenesis of AD. Although it is not yet established, whether the resulting Abeta aggregates are the causative agent or just a result of the disease progression, polymerization of Abeta has been identified as a major feature during AD pathogenesis. Inhibition of the Abeta polymer formation, thus, has emerged as a potential therapeutic approach. In this context, we identified peptides consisting of d-enantiomeric amino acid peptides (d-peptides) that bind to Abeta. D-peptides are known to be more protease resistant and less immunogenic than the respective L-enantiomers. Previously, we have shown that a 12mer D-peptide specifically binds to Abeta amyloid plaques in brain tissue sections from former AD patients. In vitro obtained binding affinities to synthetic Abeta revealed a K(d) value in the submicromolar range. The aim of the present study was to investigate the influence of this d-peptide to Abeta polymerization and toxicity. Using cell toxicity assays, thioflavin fluorescence, fluorescence correlation spectroscopy and electron microscopy, we found a significant effect of the d-peptide on both. Presence of D-peptides (dpep) reduces the average size of Abeta aggregates, but increases their number. In addition, Abeta cytotoxicity on PC12 cells is reduced in the presence of dpep.     

Kinetics and thermodynamics of paclitaxel extraction from plant cell culture

We investigated the effect of temperature on the efficiency of paclitaxel extraction from biomass. In addition, kinetic and thermodynamic studies of this extraction process were performed. The concentration of extracted paclitaxel increased with increasing extraction temperature and extraction time. When the experimental data were applied to various kinetic models, the hyperbolic model (second-order model) was the most appropriate. The predictive model was developed to predict the concentration of extracted paclitaxel at different temperatures at a given time. The Gibbs free energy change was determined to be negative, while enthalpy change and entropy change were positive. These results indicate that this extraction process is spontaneous, endothermic, and irreversible.     

Kinetics and thermodynamics of sulfuric acid-mediated cleavage of substituted diaryl sulfones

The cleavage of di-p-tolyl sulfone with concentrated sulfuric acid has been shown to occur at elevated temperatures (>120°C). The products were confirmed as the corresponding sulfonic acids by gas chromatography-mass spectrometry analysis of the sulfonate ester derivatives. The cleavage reactions of a series of di-p-substituted diaryl sulfones with sulfuric acid have been studied. A method using a double end-point titration has been used to quantify the amounts of sulfonic acid formed as the reactions proceed. These data have been used to construct second-order rate plots over a range of temperatures and to determine rate constants for the cleavage reactions. The second-order rate plots showed good linearity. Activation energies were determined from Arrhenius plots of the second-order rate constants over a range of temperatures. The presence of electron-donating groups decreases the activation energy of the reaction, whereas the presence of electron-with-drawing groups increases the activation energy of the reaction.     

铷、铯的分离提取方法及其研究进展

近年来,关于重稀碱金属铷、铯的开发和利用逐渐得到了广泛的关注,主要总结了铷、铯分离提取方法的现状,归纳了铷、铯分离提取的主要方法和最新进展,此外还对于铷、铯的分离提取方法的发展趋势进行了评论,认为离子交换法和萃取法对工业化分离提取铷、铯具有经济意义。     

Elucidating amyloid beta-protein folding and assembly: A multidisciplinary approach

Oligomeric, neurotoxic amyloid protein assemblies are thought to be causative agents in Alzheimer's and other neurodegenerative diseases. Development of oligomer-specific therapeutic agents requires a mechanistic understanding of the oligomerization process. This is a daunting task because amyloidogenic protein oligomers often are metastable and comprise structurally heterogeneous populations in equilibrium with monomers and fibrils. A single methodological approach cannot elucidate the entire protein assembly process. An integrated multidisciplinary program is required. We discuss here the synergistic application of in hydro, in vacuo, and in silico methods to the study of the amyloid beta-protein, the key pathogenetic agent in Alzheimer's disease.     

大孔吸附树脂纯化草木樨香豆素的动力学和热力学

通过静态吸附和解吸实验筛选出纯化草木樨香豆素的大孔吸附树脂,确定了HPD300树脂纯化香豆素的吸附动力学模型、等温吸附模型和热力学参数,并通过动态吸附和解吸实验优化其工艺条件。结果表明:HPD300树脂对香豆素的吸附量大、解吸率高、吸附速度快,其吸附动力学可用拟二级动力学方程很好地描述,等温吸附过程可用Langmu ir方程较好地拟合,其吸附是一个自发、放热的物理吸附过程,在优化的条件下产物中香豆素的纯度大于90%,回收率高于90%。研究表明:HPD300树脂是一种分离纯化草木樨香豆素的理想树脂,可用于大规模分离纯化草木樨香豆素。     

Kinetics and thermodynamics of the phosphine adsorption on the modified activated carbon

The kinetics and the thermodynamics of phosphine (PH₃) adsorption on the modified activated carbon have been explained for the adsorption process of PH₃. This study investigated the kinetic and thermodynamic properties of PH₃ adsorption on the activated carbon impregnated with 5% HCl solution. The thermodynamic properties including PH₃ adsorption isotherm and adsorption heat were separately investigated at 20°C, 70°C, 90°C. The results showed that the Freundlich-type isotherm equation described the isotherms well. The adsorption capacity increased with increasing temperature between 20°C and 70°C. Between 70°C and 90°C, the adsorption capacity decreased obviously with increasing temperature. The adsorption capacity reached the maximum at 70°C. By analyzing the results of the kinetics and the thermodynamics, we found that the adsorption of PH₃ was dominated by physical adsorption at the lower temperature (20°C). Then with increasing temperature, chemical adsorption gradually dominated in the adsorption process. The adsorption capacity decreased at above 70°C is due to the exothermic effects in the process of adsorption.     

Kinetics and thermodynamics of oxygen chemisorption on an industrial vanadium oxide catalyst

The chemisorption of oxygen on an industrial vanadium pentoxide/potassium sulphate catalyst has been studied in the temperature range 300-353°C by a gravimetric technique. Agreement of equilibrium data with the Langmuir and Freudlich equations is not entirely satisfactory. The kinetic measurements suggest that at least two mechanisms are involved in oxygen chemisorption under certain conditions. At low coverage Langmuir or Elovich kinetics are followed reasonably closely although a pressure dependence is apparent suggesting dissociation into oxygen atoms before a final chemisorbed state is reached. Diffusion is suggested as the possible ratedetermining process at higher coverage. Langmuir analysis of the kinetics as equilibrium is approached shows that an unexpected pressure dependence also exists in this region.     

Amide inequivalence in the fibrillar assembly of islet amyloid polypeptide

Amyloid fibers are aggregated, yet highly ordered, beta-sheet-rich assemblies of misfolded proteins. Order is established in such systems following profiles indicative of nucleation-dependent assembly. Nucleation dependence suggests that specific interactions, such as long-range contacts and/or strand registration, are critical to establishing initial fiber structure. Here, we show that amino acids at selected positions participate in key interactions that modulate the pathway of amyloid fiber formation by the hormone, islet amyloid polypeptide (IAPP). Specifically, we investigated the role of amide side-chain interactions in the process of IAPP assembly. We mutated five of the asparagine side chains in IAPP and assessed their effects on the kinetics of assembly. We find that the asparagine amide side chains strongly dictate the ability of IAPP to form fibers. In particular, the elimination of two specific asparagines results in near and total loss of amyloid, respectively. Interestingly, the two asparagines are located in a recently identified domain with alpha-helical bias. These sensitivities are unusual for IAPP, as IAPP is generally tolerant to mutation. Here, we demonstrate this mutational tolerance by assessing 10 alterations at five distinct sites. In all cases, the constructs form fibers on timescales perturbed by less than a factor of two compared with wild-type protein. These findings indicate the presence of key specific interactions that are the determinants of IAPP amyloid formation.     

Kinetics and thermodynamics of Cu(II) adsorption on oil shale wastes

The oil shale waste material, retorted shale, was utilized as an adsorbent for Cu(II) removal from aqueous solution. The kinetics and thermodynamic adsorption was investigated during a series of batch adsorption experiments. The removal efficiency was controlled by solution pH, temperature, initial ion concentration and contact time. Two simple kinetic models, pseudo-first-and second-order, were used to investigate the adsorption mechanisms. The pseudo-second-order chemical reaction kinetics provides the best correlation with the experimental data. Langmuir and Freundlich models were used to fit the equilibrium data, which showed that Langmuir best-fitted these data. Thermodynamic parameters such as free energy, enthalpy and entropy were calculated to predict the nature of the adsorption process.     

离子交换树脂吸附TP5的热力学和动力学研究

针对凝胶型阳离子交换树脂对TP5的吸附行为,研究了间歇反应中TP5水溶液的吸附热力学与动力学特性。热力学研究表明,TP5在所用树脂上的吸附平衡数据符合Langmu ir吸附等温方程。在283.15~303.15 K之间,TP5的质量浓度在10 g/L时,离子交换树脂对TP5的吸附过程可分两个阶段,第一阶段受液膜扩散控制,第二阶段主要吸附过程受颗粒扩散的控制。利用TP5在不同条件下的动态吸附性能实验,考察了pH值、温度、溶液初始浓度、搅拌转速等因素的影响。采用两相阻力模型描述了TP5在离子交换介质中的动态吸附性能,通过计算得到了TP5在吸附剂颗粒中的颗粒扩散系数,有助于进一步研究小肽在吸附过程中的传质现象。     

Co-pyrolytic behaviors of biomass and polystyrene: Kinetics,thermodynamics and evolved gas analysis

The pyrolytic degradation mechanism of chestnut shell (CNS) and its blend with waste polystyrene (PS) were investigated. Individual pyrolysis behavior of samples obtained separately was compared with those of the blends using a combined TGA/MS/FT-IR system. To elaborate kinetic analysis and to determine kinetic parameters, distributed activation energy model (DAEM) was used. The average activation energy of co-pyrolytic decomposition reaction was 191.6 kJ/mol, while the activation energy of the pyrolysis of CNS and PS was 175.2 and 208.9 kJ/mol, respectively. Friedman and Flynn-Wall-Ozawa iso-conversional methods were applied and the results were found to be consistent with the models. To express the presence of complex reaction mechanisms and the interactions of the radicals, thermodynamic parameters were also calculated. Finally, the pathways for main volatiles were established, and their relationship with the pyrolytic degradation was suggested.     

Pd/SiO_2杂化材料在空气气氛中热分解的动力学和热力学研究

为了研究Pd/SiO_2杂化材料的热力学性能,以正硅酸乙酯、甲基三乙氧基硅烷为前驱体,氯化钯为钯源,采用溶胶-凝胶法制备Pd/SiO_2杂化材料。采用TG-DTG技术对其进行热分析,利用KAS和FWO法计算热分解活化能Ea,根据主曲线法确定热分解的机理函数,并计算峰温下不同升温速率时的平均活化焓ΔH≠、活化熵ΔS≠、活化Gibbs自由能ΔG≠。结果表明,Pd/SiO_2杂化材料的热分解过程分为3个阶段。第1阶段为水分子和醇的挥发,第2阶段为未完全水解反应物的分解和Pd~(2+)的还原/氧化,第3阶段为甲基的分解和部分Pd0的氧化。3个阶段的ΔG≠、ΔH≠值均随着温度的升高而增加,其值都大于0。Pd的负载增大了甲基热分解反应阶段的活化能。