Dawson型磷钨酸催化合成乳酸月桂醇酯

用Dawson型磷钨酸催化合成乳酸月桂醇酯。实验结果表明:Dawson型磷钨酸有较高的催化活性,反应时间短,酯收率高,工艺简单。最佳工艺条件为:醇/酸摩尔比为1.5:1,催化剂用量为0.3%,带水剂甲苯体积(mL)与反应物质量(g)之比为0.4:1~0.5:1,反应温度为115~140℃,反应时间30~50min。在此条件下,酯收率可超过93% 。     

示差脉冲伏安法测定乳酸脱氢酶活性及纳米微粒生物毒性检测新方法研究

采用示差脉冲伏安法，在乳酸脱氢酶(LDH)酶促体系“丙酮酸盐 + NADH +H⁺ (?) 乳酸盐 + NAD⁺”中，通过检测NAD⁺还原峰电流的变化，测定了不同条件下(不同酶用量、缓冲液pH值以及温度)LDH的活性、酶促体系的米氏常数K_m^NADH以及最大反应速率v_max。并且在最佳实验条件下，通过检测LDH活性的改变，实验考察了3种纳米物质(ZnS，TiO₂(R)和TiO₂(A))对乳酸脱氢酶酶促体系的影响。     

Additive telluromolybdates. Structure and catalysis in oxidation

Additive telluromolybdates, MoO₃·2TeO₂ and M^IIO·TeO₂·MoO₃ (M^IITeMoO₆; M^II = Co, Mn, Zn), converted ethyl lactate selectively to pyruvate in a vaporphase fixedbed flow system at 250–300 °C. A synergy in activity was observed for binary TeO₂–MoO₃, and crystalline Te₂MoO₇ was suggested as the active species. The Rietveld analysis of powder XRD patterns of ternary CoTeMoO₆ revealed the layer structure quite different from that of the reference Te₂MoO₇, but tellurium was again located adjacent to molybdenum linked through lattice oxygen.     

Fibre optic fluorometric enzyme sensors for hydrogen peroxide and lactate,based on horseradish peroxidase and lactate oxidase

An optical biosensor for the determination of hydrogen peroxide based on immobilized horseradish peroxidase is described. The fluorescence of the dimeric product of the enzyme catalysed oxidation of homovanillic acid is utilized to determine the concentration of H₂O₂. The membrane-bound enzyme is attached to a bifurcated fibre bundle permitting excitation and detection of the fluorescence by a fluorometer. The response of the sensor is linear from 1 to 130 M hydrogen peroxide; the coefficient of variation is 3%. The sensor is stable for more than 10 weeks. The operating pH for maximal sensor response is 8.15. This allows the sensor to be used in combination with oxidase reactions producing hydrogen peroxide, as is demonstrated with a co-immobilized lactate oxidase-horseradish peroxidase optode for the determination of L-lactate. The fluorescence intensity of this sensor depends linearly on the concentration of lactate between 3 and 200 M and a throughput of 10 samples per hour is possible. The precision is in the same range as that of the monoenzyme optode. The lifetime of the bienzyme sensor for lactate is considerably shorter than that of the peroxidase sensor; it is limited by the stability of the immobilized lactate oxidase enzyme. The sensor has been applied to the determination of lactate in control serum.     

间接原子吸收法测定乳酸环丙沙星

研究了在弱酸性介质中，乳酸环丙沙星与雷氏盐定量生成缔合物的反应条件，以及通过原子吸收法测定沉淀中Cr的含量而间接测定乳酸环丙沙星含量的分析方法。线性范围在5－40mg/L，相对标准偏差为2．5％，回收率在98％－101％之间。     

介体型乳酸脱氢酶生物传感器的研制及应用

本报道了能对丙酮酸产生良好响应的电流型乳酸脱氢酶生物传感器。该传感器以耐尔兰Ａ修饰浸石墨电极为基体电极，将酶直接固化在蚕丝蛋白膜上。在ＰＨ７．４的ＮａＨ２ＰＯ４－ＮａＯＨ介质中，当２．４×１０＾－４ｍｏｌ／Ｌ的辅酶Ｉ（ＮＡＤＨ）存在下，该传感器的响应电流与丙酮酸浓度在３．２×１０＾－５ｍｏｌ／Ｌ范围内有良好的线性关系。响应时间为６０ｓ．本讨论了影响传感器响应的各种因素，用此传感器测定了人血清中     

Preparation and partial characterization of a soluble site-to-site directed enzyme complex composed of alcohol dehydrogenase and lactate dehydrogenase

A soluble, bifunctional enzyme complex has been prepared by crosslinking lactate dehydrogenase and alcohol dehydrogenase with glutaraldehyde. The crosslinking was performed on a solid phase while the active sites of alcohol dehydrogenase and lactate dehydrogenase were held adjacent to one another with the aid of a bis-NAD analog. Subsequently, the enzyme complex was released from the solid phase. The soluble enzyme complex was then purified by using NAD-Sepharose as an affinity adsorbent. Based on gel filtration experiments, the complex was estimated to consist of one of each dehydrogenase. By using a third enzyme, lipoamide dehydrogenase, which competes with lactate dehydrogenase for NADH produced by alcohol dehydrogenase, the effect of site-to-site orientation was studied. It was found that about 83% of the NADH produced by alcohol dehydrogenase was oxidized by site-to-site oriented lactate dehydrogenase compared to a figure of only about 61% obtained in an identical system of separate enzymes. This indicates that given two alternative routes, the preference for the one to lactate dehydrogenase over the one to lipoamide dehydrogenase is enhanced when lactate dehydrogenase and alcohol dehydrogenase are site-to-site oriented.     

Isobaric vapor–liquid equilibria for the quaternary reactive system: Ethanol + water + ethyl lactate + lactic acid at 101.33 kPa

Isobaric vapor–liquid equilibrium (VLE) data of the reactive quaternary system ethanol (1) + water (2) + ethyl lactate (3) + lactic acid (4) have been determined experimentally. Additionally, the reaction equilibrium constant was calculated for each VLE experimental data. The experimental VLE data were correlated using the UNIQUAC equation to describe the chemical and phase equilibria simultaneously. For some of the non-reactive binary systems, UNIQUAC binary interaction parameters were obtained from the literature. The rest of the binary UNIQUAC parameters were obtained by correlating the experimental quaternary VLE data obtained in this work. A maximum pressure azeotrope at high water concentration for the binary reactive system ethyl lactate + water has been calculated.     

用胆甾型苯并—15—冠—5气相色谱固定相分离乳酸和乳酸乙酯光学异构体

胆甾型苯并－１５－冠－５（简称ＣＨ－Ｂ－１５－Ｃ－５）在不同温度范围内的相态不同，在同一温 度范围内因处理方式不同而物性亦相去甚远，用其作成的ＧＣ固定相兼具气固色谱（ＧＳＣ）、 普通气液色谱（ＧＬＣ）和冠醚液晶气液色谱（ＣＬ－ＧＬＣ）多种功能。用该固定相在不同条件下对 乳酸和乳酸乙酯光学异构体混合物的分高效果进行了比较研究，并探讨了手性拆分机理。     

Growth inhibition in animal cell culture

Eight independent cell lines accumulated ammonia in culture to concentrations between 1.3 and 2.9 mM. The growth inhibition of such concentrations of ammonium chloride when added to culture medium was variable. The cell lines tested could be divided into 3 groups depending on their growth response to 2 mM added NH4Cl. In the first group (293, HDF, Vero, and PQXB1/2) little (less than 14%) or no growth inhibition occurred. In the second group (McCoy and MDCK) a reduction in final cell yield of 50-60% was observed. The third group (HeLa and BHK) was most sensitive to the effects of NH4Cl with growth inhibition (greater than 75%) compared to controls. The growth inhibitory effect of added lactate up to 20 mM was negligible (less than 10%) for 3 cell lines, although one cell line (PQXB1/2) showed greater sensitivity. The interactive effects of ammonia and lactate were determined in a matrix experiment. At lactate (greater than 12 mM) and ammonia (1-4 mM), the growth inhibitory effects of the two components were synergistic. However, at low concentrations of lactate (less than 12 mM) the toxic effect of ammonia was reduced. A proposed mechanism for the sparing effect of lactate on ammonia toxicity is discussed. This may have importance in developing strategies for the optimal growth of ammonia-sensitive cell lines.