共查询到19条相似文献，搜索用时 140 毫秒
1.
利用基于Box-Behnken设计的响应面优化了影响β-衣康酸单甲酯合成的3个关键因素:反应温度、反应时间和底物摩尔比.获得催化合成的最佳条件为:反应温度:58.98℃,时间:0.5 s,底物摩尔比:3.71,收率为99.2％.通过气相色谱和熔点测定的方法对产品进行了初步的鉴定. 相似文献
2.
对铑催化的1,6-烯炔环异构化反应进行了研究，这类反应具有较广的底物适应范围，在转化过程中，卤素发生了分子内转移。这类反应提供了一条新的立体选择性合成具有α-氯烯基结构的丁内酯、丁内酰胺、四氢呋喃、吡喃以及五元碳环等分子的方法。发展了两种不同的催化剂体系，即阳离子催化剂体系和中性催化剂体系。阳离子催化剂体系仅能催化顺式烯炔底物的环异构化，相反中性催化剂体系不但能催化顺反烯炔底物的环异构化，而且具有更广的底物适应范围。利用各种烯炔异构体，通过合适的控制实验对反应机理进行了研究。提出了涉及π-烯丙基铑中间体的可能机理，并且利用该机理对一些反应现象进行了解释。最后利用Suzuki偶联反应对产物进行了衍生。 相似文献
3.
研究了细胞内存在的分子伴侣、蛋白质聚集和大分子拥挤环境对蛋白质折叠的影响.首先,发现分子伴侣GroEL与底物蛋白的结合有"半位"和"全位"两种模式,它是由底物蛋白的分子形状、分子大小以及与GroEL的相互作用性质决定的.接着,发现两种不同的蛋白质一起复性时相互不干扰,提示细胞内蛋白质折叠可能不受其他蛋白聚集的影响;后又发现α-乳清蛋白的前熔球态不仅是分子伴侣也是蛋白质聚集体的作用对象.最后,研究大分子拥挤环境对蛋白质折叠热力学和动力学的影响,揭示了这种影响的复杂性和多样性. 相似文献
4.
枇杷果肉制成丙酮粉,经硫酸铵分级沉淀、透析,DEAE-纤维素柱层析、ACA_(34)柱层析和FPLC分离等方法,分离和纯化得到多酚氧化酶的两个同工酶(酶A和酶B).酶B由一个或几个分子量为42×10~3D的亚基组成.酶的动力学研究表明:酶A、酶B的K_m(多巴胺为底物)均为2.40×10~(-3)mol/L,以邻苯二酚为底物时,酶A和酶B的K_m分别为0.163×10~(-3)mol/L和1.54×10~(-3)mol/L.酶底物特异性表明,酶B是邻位二酚酶,不能作用于单酚和间位二酚. 相似文献
5.
自1978年 Koros 和 Orban 首先报导以苯酚和苯胺及其衍生物为底物的非催化反应振荡现象以来,人们普遍认为可用 OKN 机理或修正的 OKN 机理来解释此类以有机物为底物的反应振荡行为.但我们在详细考察了苯胺-溴酸钾-硫酸体系的反应振荡现象(反应物浓度、反应温度对振荡诱导期、周期、寿命和振荡周期次数随时间的变化规律)以及对振荡时间参数动力学作了分析后,发现无催化剂时,振荡存在浓度“分界”和温度“分界”点,而在有催化剂时,“分界”现象消失.这些独特的行为是很难用 OKN 机理作出合理解释的. 相似文献
6.
本文用能量共振转移催化理论讨论了酶催化作用机理,提出了当酶活化中心部位某残基基团和底物(或大分子底物某残基)的光谱重叠及它们的轨道对称时,酶对底物的催化效率和专一性最好的观点。文中就几种酶的催化作用机理进行了探讨。 相似文献
7.
研究了细胞内存在的分子伴侣、蛋白质聚集和大分子拥挤环境对蛋白质折叠的影响.首先,发现分子伴侣GroEL与底物蛋白的结合有 半位 "和 全位"两种模式,它是由底物蛋白的分子形状、分子大小以及与GroEL的相互作用性质决定的.接着,发现两种不同的蛋白质一起复性时相互不干扰,提示细胞内蛋白质折叠可能不受其他蛋白聚集的影响;后又发现α 乳清蛋白的前熔球态不仅是分子伴侣也是蛋白质聚集体的作用对象.最后,研究大分子拥挤环境对蛋白质折叠热力学和动力学的影响,揭示了这种影响的复杂性和多样性. 相似文献
8.
羧基修饰的石墨烯氧化物（GO—COOH）表现出内源性类过氧化物酶的活性,在H2O2存在下可催化过氧化物酶底物3,3．5．5-四甲基联苯胺反应产生蓝色反应物。基于这一反应我们提出了一种用于探测葡萄糖的简单、廉价、 相似文献
9.
10.
本文基于酶底物法与多管发酵法测定同一水样3种菌群的结果,菌落总数、粪大肠菌群分别采用3种分析方法进行准确性分析,得出2组样本相对偏差在允许范围内、t检验无统计学意义上的显著性差异、相关性为高度相关,说明酶底物法用于检测水样中的菌落总数、粪大肠菌群准确性较高,可以作为评价水质微生物污染的标准方法;受检测水样耐热大肠菌群含量较低、检测手段精度等因素制约,导致酶底物法检测耐热大肠菌群准确性分析工作未能开展。 相似文献
11.
Hydrogels—natural or synthetic polymer networks that swell in water—can be made mechanically, chemically and electrically compatible with living tissues. There has been intense research and development of hydrogels for medical applications since the invention of hydrogel contact lenses in 1960. More recently, functional hydrogel coatings with controlled thickness and tough adhesion have been achieved on various substrates. Hydrogel-coated substrates combine the advantages of hydrogels, such as lubricity, biocompatibility and anti-biofouling properties, with the advantages of substrates, such as stiffness, toughness and strength. In this review, we focus on three aspects of functional hydrogel coatings: (i) applications and functions enabled by hydrogel coatings, (ii) methods of coating various substrates with different functional hydrogels with tough adhesion, and (iii) tests to evaluate the adhesion between functional hydrogel coatings and substrates. Conclusions and outlook are given at the end of this review. 相似文献
12.
Jagannath G. Satav Surendra S. Katyare 《Indian journal of clinical biochemistry : IJCB》2004,19(2):23-31
The reports in the literature on effects of diabetes on mitochondrial energy-linked functions are conflicting. Hence we carried
out systematic studies to evaluate the effects at the early and the late stages of the disease using STZ-diabetic rat as a
model. At the end of one week, after induction of diabetes, respiration rates with glutamate and succinate as the substrates
increased; respiration rates with other substrates e.g. β-hydroxybutyrate, pyruvate + malate and ascorbate + TMPD were not
affected despite substantial decrease in the β-hydroxybutyrate dehydrogenase activity and cytochrome b and c+c1 contents. Insulin treatment brought about increase in the cytochrome contents beyond control values. The ATPase activity
was generally low in the diabetic animals and was not restored by insulin treatment.
At the end of one month, the respiratory activities with all the substrates were generally low. Insulin treatment either restored
or stimulated the respiration rates beyond control values. The content of cytochromes was differentially affected in the diabetic
animals, but insulin treatment caused significant increase beyond control levels. The pattern for ATPase activity was similar
to the early effects.
At both the stages i.e. early and late stages of diabetes the mitochondria were tightly coupled. The ADP/O ratios were in
normal expected ranges and the respiratory control ratios were comparable with the control groups. Insulin treatment resulted
in apparent restoration of respiratory activity. However, the effects on the cytochromes and dehydrogenases activities were
differential. Taken together the two observations would suggest that the mitochondria were not re-instated to normality despite
apparent restoration of respiratory function. 相似文献
13.
The effective migration of amoeboid cells requires a fine regulation of cell-substratum adhesion. These entwined processes have been shown to be regulated by a host of biophysical and biochemical cues. Here, we reveal the pivotal role played by calcium-based mechanosensation in the active regulation of adhesion resulting in a high migratory adaptability. Using mechanotactically driven Dictyostelium discoideum amoebae, we uncover the existence of optimal mechanosensitive conditions—corresponding to specific levels of extracellular calcium—for persistent directional migration over physicochemically different substrates. When these optimal mechanosensitive conditions are met, noticeable enhancement in cell migration directionality and speed is achieved, yet with significant differences among the different substrates. In the same narrow range of calcium concentrations that yields optimal cellular mechanosensory activity, we uncovered an absolute minimum in cell-substratum adhesion activity, for all considered substrates, with differences in adhesion strength among them amplified. The blocking of the mechanosensitive ion channels with gadolinium—i.e., the inhibition of the primary mechanosensory apparatus—hampers the active reduction in substrate adhesion, thereby leading to the same undifferentiated and drastically reduced directed migratory response. The adaptive behavioral responses of Dictyostelium cells sensitive to substrates with varying physicochemical properties suggest the possibility of novel surface analyses based on the mechanobiological ability of mechanosensitive and guidable cells to probe substrates at the nanometer-to-micrometer level. 相似文献
14.
Jacob C. K. Leung Rhodri W. Taylor-Kamall Arthur J. Hilliker Pouya Rezai 《Biomicrofluidics》2015,9(3)
Drosophila melanogaster (fruit fly) is a model organism and its behaviours including oviposition (egg-laying) on agar substrates have been widely used for assessment of a variety of biological processes in flies. Physical and chemical properties of the substrate are the dominant factors affecting Drosophila''s oviposition, but they have not been investigated precisely and parametrically with the existing manual approaches. As a result, many behavioral questions about Drosophila oviposition, such as the combined effects of the aforementioned substrate properties (e.g., exposure area, sugar content, and stiffness) on oviposition and viability, and their threshold values, are yet to be answered. In this paper, we have devised a simple, easily implementable, and novel methodology that allows for modification of physical and chemical composition of agar substrates in order to quantitatively study survival and oviposition of adult fruit flies in an accurate and repeatable manner. Agar substrates have been modified by surface patterning using single and hexagonally arrayed through-hole polydimethylsiloxane (PDMS) membranes with various diameters and interspacing, as well as by substrate stiffness and sugar content modification via alteration of chemical components. While pure PDMS substrates showed a significant lethal effect on flies, a 0.5 mm diameter through-hole access to agar was found to abruptly increase the survival of adult flies to more than 93%. Flies avoided ovipositing on pure PDMS and on top of substrates with 0.5 mm diameter agar exposure areas. At a hole diameter of 2 mm (i.e., 0.25% exposure area) or larger, eggs were observed to be laid predominately inside the through-holes and along the edges of the PDMS-agar interface, showing a trending increase in site selection with 4 mm (i.e., 1% exposure area threshold) demonstrating natural oviposition rates similar to pure agar. The surface-modified agar-PDMS hybrid devices and the threshold values reported for the substrate physical and chemical conditions affecting oviposition are novel; therefore, we advocate their use for future in-depth studies of oviposition behaviour in Drosophila melanogaster with accuracy and repeatability. The technique is also useful for development of novel assays for learning and decision-making studies as well as miniaturized devices for self-assembly of eggs and embryonic developmental investigations. 相似文献
15.
The reproducibility of microwave integrated circuits can be improved by employing substrates which are anisotropic. A method is presented which facilitates the computation of the characteristics of distributed integrated microwave circuits of finite conductor thickness on anisotropic and inhomogeneous substrates. The method is variational and it relies on a quasi-static approach which assumes that the charge distribution on each side of the conductor can be represented by a spatially dependent set of exponential functions. 相似文献
16.
R. Senthil Kumar T. N. Pattabiraman 《Indian journal of clinical biochemistry : IJCB》1996,11(2):152-157
A chymotrypsin-like enzyme was purified from rat plasma, involving ammonium sulfate fractionation and chromatographgy on CM-sephadex and red sepharose. The purified enzyme effectively hydrolysed the ester substrates for chymotrypsin (N-acetyl L-tyrosine ethyl ester and N-acetyl L-tryptophan ethyl ester). The Km values for the two substrates were 2.2×10?3M and 9.0×10?3M respectively. The hydrolytic activity of the enzyme was inhibited by phenylmethyl sulfonyl fluoride and tosylphenylalanine chloromethylketone, suggesting the presence of serine and histidine at the active centre. The enzyme exhibited anionic nature and possessed a high molecular weight (MW 71,000) as observed by gel exclusion chromatography on Sephadex G-200. The enzyme was stable upon exposure to pH 7.0–9.0, but was inactivated upon heat treatment at 60°C for 5 min. 相似文献
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18.
M. M. Khanolkar A. V. Sirsat S. S. Walvekar M. S. Bhansali L. J. Desouza 《Indian journal of clinical biochemistry : IJCB》1997,12(1):67-70
Serum beta-glucuronidase activity was estimated by our modified method using two substrates phenolphthalein glucuronide and
p-nitrophenyl glucoronide in 49 healthy subjects and 94 patients with gastrointestinal tract (GIT) carcinoma. The correlation
coefficient using the two substrates was found to be r=0.8383. The method of Gabor Szasz was modified wherein the incubation
time was decreased from 5 hours to 2 hours and the incubation temperature was increased from 25°C to 37°C. The increase in
beta-glucuronidase activity in GIT carcinoma appears to be a good biochemical marker in patients with such type of carcinomas,
a finding not reported in literature to-date.
The modified quantitative method used for estimation of beta-glucuronidase is reliable, accurate, simple and rapid. 相似文献