Thermus thermophilus木糖异构酶与木糖醇的分子对接及模型分析

在1BXB结构基础上, 通过分子对接方法构建木糖异构酶与抑制剂木糖醇的复合物模型, 为合理设计解除木糖醇对木糖异构酶的抑制及进一步揭示木糖醇对该酶抑制机理提供参考.     

HPLC法测定半纤维素水解液中糖的研究

研究了用ＨＰＬＣ分离测定毛竹水解液中的木糖、阿拉伯糖及葡萄糖等。探讨了试样的净化方法和分离条件，试样经活性炭和ＳｅｐＰａｋＧ８小柱净化，色谱柱为ＹＷＧ－ＮＨ２，１０μｍ，４．６×２５０，流动相为乙腈＋水＝８５＋１５，流量为０．８ｍＬ／ｍｉｎ，获最佳分离。木糖、阿拉伯糖、葡萄糖的平均回收率（％）分别为９９．１、１０１和９５．０，相对标准偏差为１．２５％、１．３９％和１．５３％。     

毛细管区带电泳法分离发酵液中的木糖和木糖醇

 建立了利用毛细管区带电泳分离发酵液中木糖和木糖醇的新方法。研究表明 :采用硼砂缓冲溶液时 ,木糖和木糖醇的分离度随硼砂浓度的增高而加大 ,在室温下硼砂最高浓度为 130mmol/L ;分离度还与溶液的 pH有关 ,在pH 9 5 5处分离度有最大值 ;缓冲液中十六烷基三甲基溴化铵的浓度为 4× 10 -6mmol/L～ 8× 10 -4 mmol/L时对分离度无显著影响 ;在优化的分离条件下 ,木糖和木糖醇可在 6min内基线分离。测定了发酵过程中样品各组分的含量和加标回收率 ,5次测定木糖的相对标准偏差 (RSD)为 1 42 %～ 3 11% ,回收率为 96 0 %～ 10 8 0 % 。     

电膜法生产木糖醇工艺

电膜法生产木糖醇工艺黄玉秀（华南理工大学应用化学系广州５１０６４１）关键词木糖，木糖醇，制备，电还原法１９９６－０９－１０收稿，１９９７－０１－２３修回目前生产木糖醇都用高压加氢法［１，２］．此法工艺流程长，对设备要求高，生产不安全．应用电膜法生产木...     

木糖和木糖醇的色谱模型

利用集总模型，以柱床的物料衡算方程式、吸附等温线模型、传质推动力及初始和边界条件组成木糖、木糖醇的色谱模型，用计算机模拟得到柱中液相浓度分布仿真结果。     

H点标准加入光度法同时测定葡萄糖和木糖

１引言葡萄糖和木糖是自然界中最常见的两种单糖，其结构和化学性质极为相似，用普通方法很难将其分离和分别测定。本文利用硫酸－苯酚与糖的显色反应，采用Ｈ点标准加入法对葡萄糖和木糖不经分离进行同时测定。本法简便、快速、结果准确，已应用于食用纤维的分析。２方法原理在二元混合物（组分为ｘ和ｙ，浓度为ＣｘＣｙ）体系中，将不同量已知浓度的ｘ分别准确加入到一系列混合体系中，然后分别在λ１和λ２处测量其分析信号Ａ１和Ａ２。其表达式为：Ａ１＝ｋｘ１Ｃｘ＋Ｋｙ１Ｃｙ＋Ｋｘ１Ｃｉｘ（１）Ａ２＝ｋｘ２Ｃｘ＋Ｋｙ２Ｃｙ＋ｋｘ…     

高效液相色谱法分析蜂蜜中的糖

本文研究了用四乙撑五胺（简称ＴＥＰＡ）作为胺基改善剂，在硅胶柱上定量分析蜂蜜含糖量的方法，并成功地分离了木糖、果糖、葡萄糖、蔗糖、麦芽糖和乳糖。对操作条件进行了探讨。采用示差折光检测器检测，含０．０１％ＴＥＰＡ的乙腈－水（７７＋２３）作流动相。六种糖的相对标准偏差均小于３．５％。     

反相高效液相色谱法测定吴茱萸及制剂中吴茱萸碱和吴茱萸次碱

用反相高效液相色谱法测定了吴茱萸及制剂中吴茱萸碱和吴茱萸次碱，建立了中药及制剂中吴茱萸碱、吴茱萸次碱分离、测定的色谱方法。色谱条件：ＯＤＳ柱，乙腈＋水＋四氢呋喃＋乙酸（５２＋４８＋１＋０．１）为流动相，紫外检测波长２８０ｎｍ。方法简便、灵敏、准确、快速。     

铕与醛糖及铕与D─核糖、L─氨基酸络合作用的伏安法研究

Ｅｕ（３＋）在ＨＡｃ－ＮａＡｃ（ｐＨ４．６）溶液中与五碳醛糖有弱的络合作用，用循环伏安法和微分脉冲极谱可以观察到Ｄ－核糖，Ｄ－阿拉伯糖，Ｄ－木糖对Ｅｕ（３＋）还原波形的络合影响，使还原和氧化过程变得较为可逆，其中Ｄ－核糖最为明显，而来苏糖无影响．Ｅｕ（３＋）与氨基酸在相同实验条件下有络合作用，且在汞电极上有吸附现象，因此分别加入Ｌ－苯丙氨酸、Ｌ－组氨酸和Ｌ－蛋氨酸等，进一步改善了Ｅｕ（３＋）的波形而接近于可逆氧化－还原过程，其中以Ｅｕ（３＋）－Ｄ－核糖－Ｌ－苯丙氨酸最明确。绘出了在电极表面形成三元络合物的示意图。     

毛细管区带电泳法测定复方芦丁片中芦丁和维生素C的含量

考察了缓冲溶液的pH、背景电解质浓度及分离电压对芦丁、维生素C及苯甲酸分离的影响，建立了以苯甲酸为内标，毛细管区带电泳法快速测定复方芦丁片中芦丁和维生素C含量的新方法。以3g/L硼砂－4g/L硼酸(pH8.18）为运行缓冲液，苯甲酸为内标，在分离电压为25kV，检测波长为254nm的电泳条件下，芦丁、维生素C和内标可在5min实现分离。芦丁的线性方程为：y=2．65x＋0．095（r＝0．9994），线性范围为0．025mg/mL－0．4mg/mL，维生素C的线性方程为：y＝3．1343x＋0．565（r＝0．9991），线性范围0．125mg/mL－1．0mg/mL。方法可用于复方芦丁片的质量控制。     

高效液相色谱法测定大蒜及其制品中的大蒜素

采用人工合成的大蒜素做为标准品，建立了高效液相色谱法直接测定大蒜及其制品中的大蒜素含量的方法。使用Ｓｐｈｃｒｉｓｏｂ　ＯＤＳ２色谱柱，流动相为甲醇＋水＝６０＋４０，检测波长２５４ｎｍ，进样体积２５μＬ。大蒜素最小检测量为 ２．０ ｍｇ／Ｌ，相对标准偏差为２．８％，回收率为９０．４％～１０３．０％，线性范围为 ０～１２０ｍｇ／Ｌ     

Synthesis and characterization of topologically interesting vinyl polymers

A series of macrocyclic poly(2-vinylpyridine)&s were synthesized by high dilution (∼10⁻⁵ M) coupling of the two-ended living precursor dianions with 1, 2- and 1, 4-bis-(bromomethyl)benzene (1, 2- or 1, 4-DBX). SEC measurements indicate that the macrocycles contain less than 5% linear precursor and that the hydrodynamic size of the macrocycles is substantially (∼30%) less than that of the linear precursor. At very low MW, the sizes of macrocyclic and linear polymers differ less, particularly for the case of the 1, 2-DBX product. Viscometry measurements in THF of linear and macrocyclic polymers also indicated substantial size differences of linear and macrocyclic P2VP. The values of the glass transition temperature (T_g) for both the 1, 2- and 1, 4-DBX macrocycles were found to increase with decreasing MW as qualitatively predicted by entropy calculations. Thus, as the degree of polymerization decreases, the macrocyclic chains become conformationally stiffer and this is reflected by higher T_g values. The differences in T_g between linear and macrocyclic P2VP are quite large (∼40K) around a DP of 40 and decrease to values of a few degrees at a DP of around 200. These differences are diagnostically useful in estimating the linear content of the macrocycles below a DP of 100.     

Synthesis and Photoreaction of a-Methylene-γ-Butyrolactone-Psoralen Heterodimers

Three double-headed molecules were synthesized by linking a photoreactive linear (1, 2) or angular (3) furocou-marin via a linear 10- or 5-carbon chain to an electro-philic α-methylene-γ-butyrolactone. The photochemical behavior of these molecules was investigated in ethanol at 365 nm and the photocycloadducts obtained from each compound were isolated and characterized. In all cases, the photoreactivity results showed the 3,4-pyrone double bond of the psoralen (linear or angular) to be the most reactive and [2 + 2] intramolecular photocycloadducts between the 3,4-pyrone and the exomethylenic double bonds were obtained. With compounds 1 and 2, two kinds of intramolecular photocycloadducts were obtained, namely cissyn-exo derivatives in 46% and 36% yield, respectively, and trans-syn-exo derivatives in 14% and 18% yield, respectively. With compound 3, only the trans-syn-exo derivative was obtained in 33% yield.     

固相萃取–高效液相色谱法测定豆芽中4-氯苯氧乙酸钠和6-苄基腺嘌呤的残留量

建立了测定豆芽中4-氯苯氧乙酸钠和6-苄基腺嘌呤的固相萃取–高效液相色谱法。样品以0.1 mol/L的盐酸溶液为提取剂,经C18固相萃取柱净化处理,以乙腈–10 mmol/L乙酸铵水溶液(体积比25∶75)为流动相,Tech Mate C_(18)–ST色谱柱分离,4-氯苯氧乙酸钠和6-苄基腺嘌呤的紫外检测波长分别为228 nm和267 nm,色谱峰面积外标法定量。在0.50~100.00 mg/L浓度范围内,4-氯苯氧乙酸钠的相关系数为0.999 8,精密度在1.3%~8.2%之间(n=6),回收率在103.1%~109.0%之间;在0.05~10 mg/L浓度范围内,6-苄基腺嘌呤相关系数为0.999 9,精密度在0.9%~3.8%之间(n=6),回收率在88.0%~95.4%之间。4-氯苯氧乙酸钠和6-苄基腺嘌呤的检出限(S/N=3)分别为0.24,0.02 mg/kg。该法可以同时完成豆芽中4-氯苯氧乙酸钠和6-苄基腺嘌呤的分析检测。     

芳香族化合物生物降解性的QSBR研究

分别采用线性基团贡献法和人工神经网络法对芳香族化合物的生物降解最大去除率QTOD进行QSBR研究。得到不同基团对生物降解性的贡献顺序为 :C6H5>COOH >OH >CO >CH3 >C1 >NH2>NO2 。线性基团贡献法对于训练组和测试组的预测正确率分别为 86%和 80 % ,总的预测正确率达85 % ;而人工神经网络法的预测正确率分别为 94%、80 %和 92 %。结果表明 ,线性基团贡献法和神经网络法的预测效果均很好 ,而神经网络法的预测更精确。     

Synthesis and flocculation performance of graft and random copolymer microgels of acrylamide and diallyldimethylammonium chloride

Graft (from linear homopolymers) and random (from a linear random copolymer) copolymer microgels of diallyldimethylammonium chloride (DADMAC) and acrylamide were synthesized via a free-radical mechanism using a γ-radiation technique. These copolymer microgels were evaluated as flocculants on a model dilute TiO₂ colloid suspension using a turbidimeter and a disc centrifuge photosedimentometer, and their performances were compared with the linear homopolymers and their blends. It was found that microgels produced after an appropriate irradiation time showed improved flocculation behavior over their nonirradiated linear counterparts. The graft microgels performed better than the corresponding random microgels. For a γ-radiation dosage of 100 krad/h, the graft microgels obtained by irradiating a 30% DADMAC (by weight) homopolymer blend for 3 h showed the maximum reduction in the relative turbidity of the TiO₂ suspension as well as the largest fraction of larger particles flocculated. Received: 18 May 1999 Accepted in revised form: 1 June 1999     

毛细管电泳有效分离测定甜菊糖苷新方法的研究

本文采用100％二甲基甲酰胺（DMF）作为样品的溶剂,以Tris－硼砂作为分离甜菊糖苷的缓冲体系,探讨了进样量、柱温、电压、Tris-硼砂缓冲液浓度以及pH值等条件对甜菊糖苷分离结果的影响。通过优化各种分离条件,实现了毛细管电泳高效分离测定甜菊糖苷。     

Total Synthesis of Incarnatapeptins A and B

The first total synthesis of incarnatapeptins A and B, two novel marine natural products, was accomplished from readily available (S)-1-benzyloxycarbonylhexahydropyridazine-3-carboxylic acid. This route, whose longest linear sequence was 12 steps, provided the incarnatapeptins A and B in yields of 26.5 % and 19.7 %, respectively, and enabled the structure and stereochemistry of both natural products to be unambiguously confirmed. Highlights of our synthesis include the photoredox-mediated decarboxylative 1,4-addition reaction and a novel and practical N-acylation paradigm promoted by silver carbonate. The unusual facile atropisomerism of some linear peptidic intermediates was also observed by TLC analysis in the course of this work.     

On the effects of morphology and molecular composition on the electrical strength of polyethylene blends

The effects of morphology and molecular composition on the electrical strength of blends of linear and branched polyethylenes were investigated. A range of blend systems were considered, in which both the molecular mass of the linear polymer and the comonomer in the branched component were varied. All the blends contained 10% linear polyethylene and 90% branched polymer and, in each system, three crystallization procedures were employed to modify the morphology. Isothermal crystallization at 124 °C generally resulted in compact linear inclusions within a branched matrix; isothermal crystallization at 115 °C produced a space‐filling network of open, spherulitic structures; and quenching gave a banded spherulitic morphology. In these systems, the electrical strength, as measured by ramp testing, was dependent on the morphology of the material but was not influenced per se by significant changes in the molecular composition of the blend. The effect of crosslinking was also examined; the inclusion of a network did not, in itself, affect the breakdown strength or the morphology. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2309–2322, 2000