非离子型表面活性剂辅助酶水解玉米秸杆蒸爆渣

研究纤维素酶对蒸汽爆破预处理玉米秸杆的水解过程. 实验结果表明,玉米秸杆蒸爆渣中的木质素对纤维素酶存在非生产性吸附,降低了纤维素酶对玉米秸杆蒸爆渣的水解率;通过添加非离子型表面活性剂PEG 6000,减少纤维素酶的非生产性吸附,改善纤维素酶对玉米秸杆蒸爆渣的水解性能;在pH值为4.8,温度为50℃,PEG 6000浓度为3.5g/L的优化条件下,纤维素酶水解玉米秸杆蒸爆渣48h,还原糖水解率和葡萄糖水解率分别为83.61%和64.15%.     

催化加氢不同预处理玉米秸秆制取多元醇的研究

以玉米秸秆为研究对象,采用5%硫酸和5%氢氧化钠对其进行预处理,通过对解聚前后玉米秸秆官能团表征和成分分析,发现酸、碱处理后秸秆中大部分半纤维素和木质素被脱除,其中先碱后酸、先酸后碱处理后秸秆的木质素含量由28.04%分别下降至11.54%和12.14%,而纤维素相对含量由42.02%分别增加到75.12%和77.68%。通过浸渍法制备的非贵金属5%Ni-15%W/MCM-41催化剂用于催化转化预处理秸秆制取多元醇,结果表明:与未经处理的玉米秸秆多元醇得率21.00%相比,先碱后酸、先酸后碱处理的玉米秸秆催化转化多元醇得率分别达到60.72%和61.40%。α-葡萄糖和β-葡萄糖的加氢结果显示乙二醇(EG)和1,2-丙二醇(1,2-PG)得率均相近,说明葡萄糖的旋光构型对催化加氢没有影响。与C6糖加氢产物分布比较,C5糖的产物中除了有EG和1,2-PG,同时还有丙三醇的生成,提出了糖加氢制取多元醇的可能机理。     

底物水解预处理对玉米秸秆发酵生物产氢的影响

水解预处理是影响纤维索类生物质发酵产氢效率的关键因素之一.在批式试验条件下,分别采用乳酸处理(方法A),生物处理(方法B)和生物/乳酸两步处理(方法C)方法对玉米秸秆进行糖化水解预处理;考察了水解预处理对产氢效率的影响.结果表明:经乳酸预处理、生物预处理和乳酸/生物两步处理的玉米秸秆的累积氢产量分别为132 mL/g,...     

棘孢曲霉β-葡萄糖苷酶Ⅰ在毕赤酵母中的表达及烷基糖苷的催化合成

将来自棘孢曲霉(Aspergillus aculeatus NO. F-50)的β-葡萄糖苷酶Ⅰ在毕赤酵母中分泌表达. 初步研究表明, 目的蛋白得到较好表达, 以对硝基酚-β-D-葡萄糖苷(4-Nitrophenyl-β-D-glucopyranoside, pNPG)为底物, 重组β-葡萄糖苷酶Ⅰ酶促反应的最适温度为65 ℃, 最适pH为5.0, 50 ℃下反应发酵上清液中的酶活力可达33.8 U/mL, 蛋白表达量最高可达0.388 mg/mL. 该重组酶可通过逆水解或转糖苷反应催化合成烷基糖苷. 在有机-水双相反应体系中, 初步优化了pH 值、 含水量、 葡萄糖浓度及酶量等条件. 结果表明, 在优化的反应条件下, 丁基、 己基、 辛基和癸基葡萄糖苷最大产率分别为51.4%, 28.8%, 6.9%和3.0%.     

微波辅助DMSO/AmimCl复合溶剂预处理玉米秸秆的酶解影响

为了实现玉米秸秆纤维素的高效糖化, 设计利用微波加热辅助的离子液体1-烯丙基-3-甲基咪唑氯盐(AmimCl)/二甲基亚砜(DMSO)复合溶剂生物质预处理体系, 破坏玉米秸秆天然结构, 提高纤维素酶解效率. 研究发现, 15% (w)DMSO, 110℃, 60 min 及4 g 秸秆/100 g 复合溶剂为最适预处理条件. 在此条件下, 秸秆溶解率、提取率可分别达46.6%和22.9%; 提取物纤维素酶解率14 h 可达71.4%, 相较于天然玉米秸秆的20 h 酶解率12.5%有极大提高. 通过XRD,SEM及¹H NMR 分析发现:秸秆预处理后, 提取物纤维素晶型由Ⅰ 型变为Ⅱ 型, 残渣纤维素相对结晶度明显降低, 有利于纤维素酶解的进行, 达到了生物质预处理的目的; 预处理过程中使用的AmimCl 离子液体经简单回收再生, 结构及秸秆溶解性能未发生变化, 可循环使用. 为玉米秸秆生物质预处理提供了一个新的方案.     

基于酶触发的点击化学反应测定β-葡萄糖苷酶活性

建立了一种新的β-葡萄糖苷酶活性定量检测的方法,其原理是通过β-葡萄糖苷酶对2-O-β-D-葡萄糖基-L-抗坏血酸的特异性水解,释放出抗坏血酸来还原Cu(II),原位生成的Cu(I)催化荧光较弱的香豆素和苄基叠氮进行环加成点击反应,产生高荧光强度的三氮唑,从而利用荧光光谱检测体系荧光强度的变化,反映出β-葡萄糖苷酶的活性.实验结果显示,在1～40U/L范围内,荧光强度增强程度与β-葡萄糖苷酶活性呈线性关系,可实现定量检测,其最低检测限为0.456 U/L.     

高效液相色谱-电喷雾质谱联用测定黄芪黄酮苷酶解产物

高效液相色谱-电喷雾质谱(HPLC-ESI-MS)联用分析黄芪中的黄酮类化合物结果表明黄芪黄酮提取物主要包含毛蕊异黄酮-7-O-β-D-葡萄糖苷、芒柄花苷、9, 10 -二甲氧基紫檀烷-3-O-β-D-葡萄糖苷以及2'-羟基-3',4'-二甲氧基异黄烷-7-O-β-D-葡萄糖苷等黄酮苷,黄芪黄酮提取物经过β-葡萄糖苷酶(1 IU/mL)粗酶液酶解后,HPLC-ESI-MS分析酶解生成产物主要为黄酮苷元毛蕊异黄酮、芒柄花素、3-羟基-9,10 -二甲氧基紫檀烷以及7, 2'-二羟基-3',4'-二甲氧基异黄烷.其中前两种主要的黄酮苷酶解率均达90%以上.酶解后所得产物对DPPH自由基清除率是酶解前的1.4倍.因此,通过β-葡萄糖苷酶水解可以有效地将黄芪黄酮转化为相应的黄酮苷元,大大提高黄芪黄酮提取物的抗氧化活性.     

木质纤维素酶解糖化*

纤维素水解转化为可发酵糖工艺是纤维素乙醇炼制过程中至关重要的环节。酶法水解工艺具有条件温和、副产物少、环境友好等特点,因而受到广泛重视。目前许多学者已针对如何提高木质纤维素酶解效率、降低纤维素酶成本等问题,开展了多种化学、生物技术及工艺耦合的研究。本文综述了近几年木质纤维素酶解领域取得的最新工艺进展和理论研究成果,对原料预处理、多酶复配优化、酶脱附与重复利用、工艺耦合、高固液比反应等方面的研究情况进行了总结,同时展望了木质纤维素酶解工艺的未来发展方向。     

利用高浓度秸秆废弃物发酵产氢

采用高浓度的玉米秸秆(60g·L-1)作为产氢底物,研究了在氢发酵过程中几个关键过程参数对发酵产氢的影响,以期在秸秆废弃物的清洁氢能转化过程中减少发酵废水的生成总量.结果表明,在酸化秸秆浓度为60g·L-1,碳酸氢铵添加量为1.2g·L-1,十六烷基三甲基溴化铵添加量为30mg·L-1,菌株Bacillus sp.FS2011添加量为10%(质量分数),以及初始pH=7.5±0.5、发酵温度(37±1)℃条件下,最大产氢量和产氢速率分别为(79.8±1.5)mL·g-1和3.78mL·g-1·h-1.与使用低浓度秸秆(≤20g·L-1)底物时相比,生成的氢发酵废水总体积减小了约67%.     

秸秆发酵燃料乙醇关键问题及其进展

利用木质纤维素原料生产燃料乙醇是国际公认的难题。本文从秸秆原料组分不均一性出发,分析了秸秆难以高值化原因;进一步分析了秸秆酶解发酵燃料乙醇的关键问题,介绍了有关秸秆原料预处理、纤维素酶生产、秸秆酶解发酵乙醇和产业化示范工程等的进展。秸秆酶解发酵燃料乙醇产业化示范工程具有自主知识产权,为实现我国秸秆转化燃料乙醇的规模化、产业化、低成本生产奠定了基础。     

Kinetics of hydrolysis of some new heterocyclic azomethines

Kinetics of base hydrolysis of new heterocyclic azomethines derived from active methyl quaternary salts and aromatic nitroso compounds were investigated in the presence of 70% (wt/wt) water-methanol. The base hydrolysis of these compounds is strictly first-order with respect to OH^– and azomethine. The rate determining step is suggested to be the attack of the hydroxide ion on the free base. Effects of water content and nature of organic hydroxylic solvent have been studied. It is concluded that specific solute-solvent interactions through dispersion forces play a major role in the base hydrolysis rate of the azomethines investigated. The effect of pH (2.98 – 12.24) on hydrolysis rates of compounds having a diethylamino substituent in the presence of 30% methanol has been studied. In acidic media, the rate determining step is probably the water attack on the protonated substrate.     

A mild hydrolysis of esters mediated by lithium salts

When treated with amine bases such as triethylamine and various lithium salts in wet solvents, esters are efficiently hydrolyzed to the corresponding acids in good yields. Esters incorporating an α- or β-heteroatom with respect to the ester carbonyl group are hydrolyzed rapidly even at room temperature. To further demonstrate the usefulness of this method, one example is provided where hydrolysis of acetylated camphorsultam is mediated by LiBr.     

Identification of hydrolytic metabolites of dyfonate in alkaline aqueous solutions by using high performance liquid chromatography – UV detection and gas chromatography-mass spectrometry

Organophosphorus compounds, becoming the most commonly used pesticides in agriculture, are garnering more interest to be environment and health issues associated with their usage. These compounds run-off into surface water and leach into groundwater supplies where they have been detected. Dyfonate is commonly applied to the soil as an insecticide for the control of variety of insects. However, critical information on the transformation of dyfonate into its hydrolytic byproducts during water treatment is lacking, even though they have been used in the field for a long time. In this study, dyfonate hydrolysis at elevated pH levels, simulating a water treatment operation or similar process, was investigated. Dyfonate, an organophosphorus insecticide used to treat infestations primarily on corn, was investigated due to its greater rate of hydrolysis observed during our screening studies. The hydrolysis of dyfonate was investigated at pH 10, 11, and 12 in phosphate buffered water over the course of 7 days. Two hydrolysis products, thiophenol and phenyl disulfide, were detected. Dyfonate and thiophenol were analysed using high pressure liquid chromatography/UV detection (HPLC/UV), while phenyl disulfide was detected using gas chromatography/mass spectrometry (GC/MS). The relative concentration profiles of dyfonate and its hydrolysis products, as well as their transformation pathways, were also reported. The data from this study will help environmental researchers understanding the hydrolytic pathways of dyfonate and its metabolites at different pHs in a water treatment system.     

The effect of electron-withdrawing properties of substituents on the hydrolysis of some Schiff bases

The dissociation kinetics of the Schiff bases investigated in the present paper [N,N-bis(X-benzylidenes)ethylenediamine], have been examined under basic and acidic conditions, in aqueous medium 25% acetone in water (wt-wt). The base hydrolysis reaction of these compounds was found to follow second-order kinetics, first-order with respect to each of the Schiff base and the hydroxide ions. The rate-determining step is suggested to be the hydroxide ions attack on the free base. The effect of acetone ratio, in hydrolysis medium, has been studied under alkaline conditions. It is deduced that both the hydrogen bonding formation and solvent-solvent interaction have a pronounced role in such hydrolysis reactions. The acid hydrolysis reaction is strictly second-order kinetics, first-order with respect to the Schiff base and also to the hydrogen ions, and the attack of water molecules on the protonated substrate becomes the rate-determining step. A slower rate of the base hydrolysis was observed through the Schiff base II (p-NO₂), on the other hand, a fast acid hydrolysis rate was detected in the case of compound III (p-COOH). Furthermore, from the effect of temperature on the reaction rate, the various thermodynamic parameters have been also calculated and discussed.     

New fluorescent probes for testing combinatorial catalysts with phosphodiesterase and esterase activities

Combinatorial development of new catalysts with phosphodiesterase and esterase activities requires specific fluorescent probes for rapid visual detection of hydrolytic activity. Such fluorescent probes have been synthesized with special attention to solubility in water and stability towards spontaneous hydrolysis at a given pH. The probes reported here include compound 5 based on a fluorescein fluorophore, compound 12 for FRET-detection of phosphodiester hydrolysis and compound 25 based on a quinolinium fluorophore.     

Silicon and phosphorus alkoxide mixture: Sol-gel study by spectroscopic technics

Sol-gel synthesis of mixtures of tetraethoxysilane and a phosphorus alkoxide [P(OEt)₃ or (OEt)₂P-O-P(OEt)₂ or PO(OEt)₃] have been studied by ¹H, ¹³C²⁹Si and ³¹P liquid and solid state NMR, infrared and raman spectroscopies. This study shows different behaviors towards hydrolysis for these three different phosphates and phosphites. P(OEt)₃ almost instantly reacts with water to form an intermediate species HPO(OEt)₂, which slowly evolves first to HPO(OH)(OEt), then to HPO(OH)₂ a few days later. For (OEt)₂P-O-P(OEt)₂, the P-O-P bond is broken when water is added, then the same intermediates are formed faster. PO(OEt)₃ is hydrolyzed much slower than the other alkyl phosphates. After ten months, triethoxyphosphate is quantitatively present in the sol with little PO(OH)(OEt)₂ species. All these hydrolyzed species are well characterized. Only the system which contains the tetraethoxysilane and the triethoxyphosphite P(OEt)₃ forms a few P-O-P and P-O-Si bonds in the gel. Hydrolysis of tetraethoxysilane is much faster than that of phosphorus alkoxides and the conventional Q₂, Q₃ and Q₄ condensed silicon species form the gel three dimensional network.     

二卤二茂钛在水溶液中的水解化学

七十年代末,德国的H.Koepf和P.Koepf-Maier首次证明二氯二茂钛具有抗艾氏腹水癌(EAT)活性后,现在人们又发现了二茂钛衍生物,尤其是二茂钛卤化物对多种肿瘤都具有显著的抑制作用。可以说,二茂钛配合物是继顺铂后又一类型有效的有机金属抗癌剂。现有的研究表明,处量后的二茂钛晶胞中,胞内金属的分布和报导的铂配合物相     

Cr3+的水解聚合作用的研究 Ⅺ.在顺丁烯二酸存在下的水解和聚合

在60℃和恒定离子强度下,用平衡法研究了0.004mol dm^-3Cr(NO₃)₃在三种不同浓度顺丁烯二酸H₂A(0.008,0.010,0.014mol dm^-3的水溶液中的状态,用计算机拟合和p.q.r分析方法得到了[Cr(OH)A₂]^2-,[Cr₂(OH)A₂]⁺[Cr₃(OH)₂A₂]⁺和CrA₃^3-四种水解产物,并计算了其平衡常数,在我们系列工作中研究了在宽广的Cr³⁺和顺丁烯二酸浓度下Cr³⁺的状态,共生成11种配合物,本文对其形成规律进行了讨论.     

Two-stage dilute-acid pretreatment of softwoods

Whole treechips obtained from softwood forest thinnings were pretreated via single-and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity tomaximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.     

Initial design of a dilute sulfuric acid pretreatment process for aspen wood chips

A preliminary process design for dilute sulfuric acid pretreatment of aspen wood chips in order to obtain fermentable sugars has been prepared and subjected to an economic evaluation. The process design was prepared according to experimental data on the kinetics of dilute sulfuric acid prehydrolysis and particle size effects obtained in this study and our previous work. The initial economic evaluation shows woodchips are 56% of the cost of production, whereas the reactor is only 4%, and the comminution operation is just under 10%, indicating that the process economics are extremely vulnerable to feedstock costs and are thus yield-sensitive. Although chances for major cost improvements by modification of the reactor design and finding alternatives to dry milling of aspen chips to small (20–80 mesh) particles needed for acid penetration and enzymatic saccharification are not great, design improvements of the process will necessitate development of a cheaper acid resistant pretreatment reactor and a less energy intensive comminution system. Experimental results on effects of particle size on the dilute acid pretreatment design are presented.