蛋白质水解阶段对氨基酸组成分析的影响

水解是蛋白质氨基酸组成分析的重要步骤，水解质量的好坏直接影响到分析结果的正确与否，蛋白质的水解受到很多因素的影响，如温度，时间、水解试剂，添加剂，水解方法等，本文对近10年来蛋白质组成分析中中有关蛋白质水解问题的研究进进行了评述，对最近几年出现的一些新的水解方法如酸性水解中的气相水解，微波辐射水解，膜上蛋白质和印迹水解，聚丙烯酰安凝胶中蛋白质的水解，敏感氨基酸的水解以及水解过程中影响氨基酸外消旋化的因素等作了简要的介绍。     

A simple capillary electrophoresis with electrochemical detection method for determination of the hydrolysis rate constant of chlorogenic acid

A method based on the kinetics stability study on hydrolysis of chlorogenic acid by capillary zone electrophoresis with electrochemical detection (CE-ED) has been developed in this paper. Both cyclic and hydrodynamic voltammograms of chlorogenic acid and its hydrolysis product caffeic acid have been investigated. The conditions for separation of chlorogenic acid and caffeic acid, such as the buffer pH and concentration, the separation voltage, and the injection time have been optimized. Under the optimum CE running conditions, the effects of reaction temperature and pH values of the hydrolysis solutions on the hydrolysis rate constants were further studied. The hydrolysis rate constants of chlorogenic acid were obtained from the concentration change of hydrolysis during the process of hydrolysis. Based on the fact, a simple and economical method for the determination of the hydrolysis rate constant and activation energy of hydrolysis reaction has been developed.     

Intermediates of chemical assembling of oligoorganosiloxanes in hydrolysis of organochlorosilanes

The mechanism of the formation of oligoorganosiloxanes during the hydrolysis of organochlorosilanes was considered. A comparative estimation of a relationship of the degree of conversion of the monomer vs. degree of conversion of functional groups in the homo- and heterofunctional condensation and partial hydrolysis of organochlorosilanes was performed for the first time. In the hydrolysis of diorganodichlorosilanes with either an excess or a deficiency of water, the homofunctional condensation of diorganosilanediols is not the main mode for the chemical assembling of oligoorganosiloxanes. The main intermediates in the route of oligoorganosiloxane formation during organochlorosilane hydrolysis are the incomplete hydrolysis products (organochlorohydroxysilanes). Experimental data suggest that the chemical assembling of oligoorganosiloxanes occurs via the mechanism of organochlorohydroxysilane heterocondensation under usually used conditions of organochlorosilane hydrolysis.     

Studies on Different Hydrolysis Procedures for Drugs of Abuse in Hair

1.IntroductionDrugsofabusehavebecomeamajorprobleminoursocietyinrecentyearsandhaveresultedinwidespreadabuse.Thedetectionofdrugsofabuseinbiologicalsamplesisoneoftheprimaryfunctionsofaclinicalorforensictoxicologylaboratory.Particularlyincaseswheretheres...     

Hydrolysis of fluorosilanes: a theoretical study

Hydrolysis and condensation of simple trifluorosilanes, HSiF3 and MeSiF3, was studied by quantum mechanical methods. Hydrolysis of fluorosilanes is highly endothermic. The Gibbs free energy of the first reaction step in the gas phase is 31.4 kJ/mol, which corresponds to an equilibrium constant of 10(-6). Hydrolysis of the subsequent fluorine atoms in trifluorosilanes is thermodynamically more unfavorable than the first step of substitution. No significant difference in thermodynamics of hydrolysis was found between HSiF3 and MeSiF3. The activation energy for hydrolysis by a water dimer is significantly lower than that for hydrolysis by a water monomer. The former reaction is also less unfavorable thermodynamically, due to a high binding energy of the HF-H2O complex formed as a product of hydrolysis. Self-consistent reaction field (SCRF) calculations show that hydrolysis of trifluorosilanes in aqueous medium has lower activation energy than in the gas phase. It is also thermodynamically less unfavorable, due to better solvation of the products. Homofunctional condensation of HSiF2OH is thermodynamically favored. The equilibrium mixture for hydrolysis/condensation of RSiF3 in water is predicted to contain ca. 2.3% disiloxane (HF2Si)2O, if 100-fold excess of water relative to silane is assumed. Further hydrolysis of (HF2Si)2O is negligible. The thermodynamics of fluorosilane hydrolysis contrasts with that of chlorosilanes, where both hydrolysis and condensation are strongly favorable. Moreover, in the case of trichlorosilanes each subsequent hydrolysis step is more facile, leading to the product of full hydrolysis, RSi(OH)3.     

Kinetics of alkaline hydrolysis of organic esters and amides in neutrally-buffered solution

Reaction rate constants for the hydrolysis of organic esters and amides were determined at temperatures of 100–240°C in aqueous solutions buffered at pH values between 5.5 and 7.3. Experiments are modeled assuming alkaline hydrolysis with a thermodynamic solution model included to account for the temperature dependence of hydroxide ion concentration. In most cases, the ester hydrolysis second order rate constants agree well with published values from experiments in strongly basic solutions at pH values from 11 to 14 and temperatures from 25–80°C, despite the large extrapolations required to compare the data sets. The amide hydrolysis rate constants are about one order of magnitude higher than the extrapolated results from other investigators, but the reaction rate increased proportionally with hydroxide ion concentration, suggesting that an alkaline hydrolysis mechanism is also appropriate. These data establish the validity of the alkaline hydrolysis mechanism and can be used to predict hydrolysis reaction rates in neutrally-buffered solutions such as many groundwater and geothermal fluids.     

液质联用法研究活性黑5的水解产物

用高效液相色谱-质谱联用技术研究活性染料黑5及其水解产物的方法,考察了梯度洗脱对色谱分离及pH对其水解产物的影响;质谱辅助定性了其水解产物。结果表明：pH对活性黑5的水解过程影响非常显著;除了常规的水解产物,还检测到未知水解产物,推测可能在水解过程中还有其它的反应存在。活性染料黑5水解后的毒性升高,从染料及其水解产物的分子结构式来分析,这很可能和活性染料的活性基团变化有关。     

Utilization of cellulose nitrate waste

A two-step procedure for utilization of cellulose nitrate waste accumulated at industrial enterprises of the Russian Federation was suggested and experimentally checked. The procedure involves hydrolysis of cellulose nitrate in alkaline medium and incineration of hydrolysis products. The best reagents for complete hydrolysis of cellulose nitrate are aqueous solutions of sodium hydroxide and sodium carbonate. As demonstrated by thermal analysis and thermodynamic calculations, incineration of cellulose nitrate base hydrolysis products can be performed without using hydrocarbon fuel.     

Effects of hemicellulose and lignin on enzymatic hydrolysis of cellulose from dairy manure

This study focused on the effect of hemicellulose and lignin on enzymatic hydrolysis of dairy manure and hydrolysis process optimization to improve sugar yield. It was found that hemicellulose and lignin in dairy manure, similar to their role in other lignocellulosic material, were major resistive factors to enzymatic hydrolysis and that the removal of either of them, or for best performance, both of them, improved the enzymatic hydrolysis of manure cellulose. This result combined with scanning electron microscope (SEM) pictures further proved that the accessibility of cellulose to cellulase was the most important feature to the hydrolysis. Quantitatively, fed-batch enzymatic hydrolysis of fiber without lignin and hemicellulose had a high glucose yield of 52% with respect to the glucose concentration of 17 g/L at a total enzyme loading of 1300 FPU/L and reaction time of 160 h, which was better than corresponding batch enzymatic hydrolysis.     

Visualization of structural changes in cellulosic substrates during enzymatic hydrolysis using multimodal nonlinear microscopy

Enzymatic hydrolysis of cellulose provides a renewable source of monosaccharides for production of variety of biochemicals and biopolymers. Unfortunately, the enzymatic hydrolysis of cellulose is often incomplete, and the reasons are not fully understood. We have monitored enzymatic hydrolysis in terms of molecular density, ordering and autofluorescence of cellulose structures in real time using simultaneous CARS, SHG and MPEF microscopy with the aim of contributing to the understanding and optimization of the enzymatic hydrolysis of cellulose. Three cellulose-rich substrates with different supramolecular structures, pulp fibre, acid-treated pulp fibre and Avicel, were studied at microscopic level. The microscopy studies revealed that before enzymatic hydrolysis Avicel had the greatest carbon-hydrogen density, while pulp fibre and acid-treated fibre had similar density. Monitoring of the substrates during enzymatic hydrolysis revealed the double exponential SHG decay for pulp fibre and acid-treated fibre indicating two phases of the process. Acid-treated fibre was hydrolysed most rapidly and the hydrolysis of pulp fibre was spatially non-uniform leading to fractioning of the particles, while the hydrolysis of Avicel was more than an order of magnitude slower than that of both fibres.     

A model explaining declining rate in hydrolysis of lignocellulose substrates with cellobiohydrolase I (cel7A) and endoglucanase I (cel7B) of Trichoderma reesei

It is commonly observed that the rate of enzymatic hydrolysis of solid cellulose substrates declines markedly with time. In this work the mechanism behind the rate reduction was investigated using two dominant cellulases of Trichoderma reesei: exoglucanase Cel7A (formerly known as CBHI) and endoglucanase Cel7B (formerly EGI). Hydrolysis of steam-pretreated spruce (SPS) was performed with Cel7A and Cel7B alone, and in reconstituted mixtures. Throughout the 48-h hydrolysis, soluble products, hydrolysis rates, and enzyme adsorption to the substrate were measured. The hydrolysis rate for both enzymes decreases rapidly with hydrolysis time. Both enzymes adsorbed rapidly to the substrate during hydrolysis. Cel7A and Cel7B cooperate synergistically, and synergism was approximately constant during the SPS hydrolysis. Thermal instability of the enzymes and product inhibition was not the main cause of reduced hydrolysis rates. Adding fresh substrate to substrate previously hydrolyzed for 24 h with Cel7A slightly increased the hydrolysis of SPS; however, the rate increased even more by adding fresh Cel7A. This suggests that enzymes become inactivated while adsorbed to the substrate and that unproductive binding is the main cause of hydrolysis rate reduction. The strongest increase in hydrolysis rate was achieved by adding Cel7B. An improved model is proposed that extends the standard endo-exo synergy model and explains the rapid decrease in hydrolysis rate. It appears that the processive action of Cel7A becomes hindered by obstacles in the lignocellulose substrate. Obstacles created by disordered cellulose chains can be removed by the endo activity of Cel7B, which explains some of the observed synergism between Cel7A and Cel7B. The improved model is supported by adsorption studies during hydrolysis.     

First-principle studies of intermolecular and intramolecular catalysis of protonated cocaine

We have performed a series of first-principles electronic structure calculations to examine the reaction pathways and the corresponding free energy barriers for the ester hydrolysis of protonated cocaine in its chair and boat conformations. The calculated free energy barriers for the benzoyl ester hydrolysis of protonated chair cocaine are close to the corresponding barriers calculated for the benzoyl ester hydrolysis of neutral cocaine. However, the free energy barrier calculated for the methyl ester hydrolysis of protonated cocaine in its chair conformation is significantly lower than for the methyl ester hydrolysis of neutral cocaine and for the dominant pathway of the benzoyl ester hydrolysis of protonated cocaine. The significant decrease of the free energy barrier, approximately 4 kcal/mol, is attributed to the intramolecular acid catalysis of the methyl ester hydrolysis of protonated cocaine, because the transition state structure is stabilized by the strong hydrogen bond between the carbonyl oxygen of the methyl ester moiety and the protonated tropane N. The relative magnitudes of the free energy barriers calculated for different pathways of the ester hydrolysis of protonated chair cocaine are consistent with the experimental kinetic data for cocaine hydrolysis under physiologic conditions. Similar intramolecular acid catalysis also occurs for the benzoyl ester hydrolysis of (protonated) boat cocaine in the physiologic condition, although the contribution of the intramolecular hydrogen bonding to transition state stabilization is negligible. Nonetheless, the predictability of the intramolecular hydrogen bonding could be useful in generating antibody-based catalysts that recruit cocaine to the boat conformation and an analog that elicited antibodies to approximate the protonated tropane N and the benzoyl O more closely than the natural boat conformer might increase the contribution from hydrogen bonding. Such a stable analog of the transition state for intramolecular catalysis of cocaine benzoyl-ester hydrolysis was synthesized and used to successfully elicit a number of anticocaine catalytic antibodies.     

Catalysts/cosolvents and general acid catalysts for acceleration of the hydrolysis of osmate(VI) esters

New catalysts/cosolvents as hydrolysis aids and the properties of the catalyst/cosolvent that effect the efficiency of the hydrolysis aid for the hydrolysis of osmate(VI) esters of aliphatic olefins are presented. Also, the effect of pH of the reaction media on the specific and general acid-catalysed hydrolysis of osmate(VI) esters of conjugated aromatic olefins is presented.     

Recovery of enzymes from the insoluble residue of hydrolyzed wood

During the enzymatic hydrolysis of steam-exploded wood, enzymes are adsorbed on both the cellulosic and noncellulosic components. Significant amounts of enzymes are recovered from the spent hydrolysis residue, which consists mostly of lignin, by neutralizing the pH from 4.5, the optimum for hydrolysis.     

水解制备球形TiO2及其水解过程动力学

以硫酸钛(Ti(SO4)2)为前驱物水解得到超细球形TiO2. 研究了水解过程中前驱物浓度和体系温度对水解速率的影响, 并对实验值进行了拟合, 得到水解TiO2的质量分数与水解时间呈良好的指数关系, 根据Avrami方程进一步验证了拟合的可靠性. 分析了水解介质的影响作用, 确定介电常数和zeta电位也是影响水解速率的重要因素, 因此可通过改变溶剂成分来调节介电常数和zeta电位, 从而达到控制Ti(SO4)2水解速率的目的. 实验结果表明, Ti(SO4)2水解制备TiO2的过程中, 较低的前驱物浓度, 较高的水解温度和合适的溶剂体系有利于得到粒径分布窄、分散性好的TiO2.     

Hydrolysis characteristics of tissue fractions resulting from mechanical separation of corn stover

Corn stover has potential as a resource for both fiber and chemical needs if separation strategies can be developed to deal with its heterogeneity. Relative hydrolysis characteristics were assessed for pith (sclerenchyma and parenchyma) and fiber (collenchyma) tissue fractions derived from mechanical separation of corn stover to determine whether classification by tissue type resulted in fractions with different hydrolysis response. The physical characteristics of the tissue fractions were analyzed. The hydrolysis behavior of the fractions was evaluated under both acidic and basic conditions. The results from the hydrolysis experiments are compared with previously reported compositional analysis for the tissue fractions.     

Modeling the catalysis of anti-cocaine catalytic antibody: competing reaction pathways and free energy barriers

The competing reaction pathways and the corresponding free energy barriers for cocaine hydrolysis catalyzed by an anti-cocaine catalytic antibody, mAb15A10, were studied by using a novel computational strategy based on the binding free energy calculations on the antibody binding with cocaine and transition states. The calculated binding free energies were used to evaluate the free energy barrier shift from the cocaine hydrolysis in water to the antibody-catalyzed cocaine hydrolysis for each reaction pathway. The free energy barriers for the antibody-catalyzed cocaine hydrolysis were predicted to be the corresponding free energy barriers for the cocaine hydrolysis in water plus the calculated free energy barrier shifts. The calculated free energy barrier shift of -6.87 kcal/mol from the dominant reaction pathway of the cocaine benzoyl ester hydrolysis in water to the dominant reaction pathway of the antibody-catalyzed cocaine hydrolysis is in good agreement with the experimentally derived free energy barrier shift of -5.93 kcal/mol. The calculated mutation-caused shifts of the free energy barrier are also reasonably close to the available experimental activity data. The good agreement suggests that the protocol for calculating the free energy barrier shift from the cocaine hydrolysis in water to the antibody-catalyzed cocaine hydrolysis may be used in future rational design of possible high-activity mutants of the antibody as anti-cocaine therapeutics. The general strategy of the free energy barrier shift calculation may also be valuable in studying a variety of chemical reactions catalyzed by other antibodies or proteins through noncovalent bonding interactions with the substrates.     

Effect of inhibitors released during steam-explosion pretreatment of barley straw on enzymatic hydrolysis

The influence of the liquid fraction (prehydrolysate) generated during steam-explosion pretreatment (210°C, 15 min) of barley straw on the enzymatic hydrolysis was determined. Prehydrolysate was analyzed for degradation compounds and sugars' content and used as a medium for enzymatic hydrolysis tests after pH adjusting to 4.8. Our results show that the presence of the compounds contained in the prehydrolysate strongly affects the hydrolysis step (a 25% decrease in cellulose conversion compared with control). Sugars are shown to be more potent inhibitors of enzymatic hydrolysis than degradation products.     

生物质半纤维素稀酸水解反应*

半纤维素是木质纤维素类生物质中第二大组分,半纤维素的高效、低成本转化是实现木质纤维素类生物质转化工艺实用化的一个技术关键。稀酸水解技术被广泛应用于水解生物质半纤维素,其对半纤维素糖的转化率高,得到的糖可进一步发酵生产燃料乙醇等。半纤维素还可直接水解制低聚糖等功能性食品和糠醛等化工产品。本文综述了半纤维素稀酸水解反应的研究进展。介绍了半纤维素的基本结构特征,解析了稀酸催化半纤维素水解的反应机理及反应网络,评述了半纤维素水解过程中反应条件等对目标产物的影响,并总结了半纤维素稀酸水解动力学模型。在此基础上,对今后半纤维素稀酸水解反应的研究方向与水解产物的利用进行了展望。     

FT-Raman-Spectroscopic Investigations of the System Glycidoxypropyltrimethoxysilane/Aminopropyltriethoxysilane

The base catalyzed sol-gel process in the system 3-glycidoxypropyltrimethoxysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) is highly interesting for the synthesis of hybrid (inorganic-organic) polymers. FT-Raman spectroscopy with excitation in the near infrared as a versatile tool for in situ measurements was used to monitor the kinetic behavior of the hydrolysis reaction.An unexpected slow-down of the hydrolysis of GPTS recorded at higher temperatures can be attributed to a decrease of the pH-value during hydrolysis caused by silanol groups. After condensation has started, the pH-value reincreases and forces hydrolysis to reaccelerate. The results strongly suggest the existence of a pentacoordinated transition state with a negative charge at the silicon atom during base catalyzed hydrolysis.