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1.
M R Siro T L?vgren 《Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry》1978,32(6):447-451
An alpha-glucosidase was purified from baker's yeast. The molecular weight was approximately 44 000 daltons. SDS-disc gel electrophoresis suggested that the enzyme consisted of four subunits. The isoelectric point was at pH 5.4. The Km values for p-nitrophenyl alpha-D-glucopyranoside and maltose were 2.9 X 10(-4) and 2.5 X 10(-2) M, respectively. Binding of 2-(p-toluidino)naphthalene-6-sulfonate to the alpha-glucosidase was associated with a strong increase in fluorescence. The dissociation constant of the enzyme-TNS complex was 8 X 10(-5) M. The fluorescent probe did not interfere with the binding of glucose to the enzyme although the alpha-glucosidase was inhibited by high concentrations of TNS. The formation of an enzyme-glucose complex was indicated by an increase of fluorescence and by a shift in the wavelength for maximal emission which suggests that the binding process is associated with a change in conformation. The dissociation constant of the glucose--alpha-glucosidase complex KD = 0.57 X 10(-3) M, was calculated from the increase in fluorescence as a function of glucose concentration. 相似文献
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三种蒙药中微量元素含量与疗效相关性分析 总被引:2,自引:0,他引:2
用原子吸收分光光度计测定了蒙药扎木萨-4,阿拉坦-5,阿那日-5中多种微量元素及常量元素的含量。结果表明,这三种健胃消食蒙药中Mg、Fe、Mn、Zn均较高,呈一定相关性,而有害元素Pb、Cd很少,探讨了三种蒙药中微量元素与其疗效的关系。 相似文献
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V. P. Lezina N. A. Andronova L. D. Smirnov K. M. Dyumaev 《Chemistry of Heterocyclic Compounds》1971,7(11):1438-1440
The dependence of the chemical shifts of the ring protons on the pH of the medium for a number of 4-hydroxyquinoline derivatives was studied by means of PMR spectroscopy. The dipolar and uncharged hydroxy forms exist in equilibrium in aqueous solutions. The effect of intramolecular hydrogen bonding on the character of the dependence of the chemical shift on the pH of the medium in the case of 3-piperidinomethyl-4-hydroxyisoquinoline was investigated. The possibility of the separate protonation of the ring nitrogen and the side-chain nitrogen in 3-piperidinomethyl-4-hydroxyisoquinoline was established. The distribution of the -electron density in 4-hydroxyisoquinoline is in good agreement with its chemical behavior.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1546–1549, November, 1971 相似文献
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L. E. Kholodov T. A. Kovalenko M. K. Polievktov 《Chemistry of Heterocyclic Compounds》1975,11(8):909-914
The polarographic reduction of the sydnoneimmonium cation (I) was investigated in the case of 3--phenylisopropylsydnoneimine hydrochloride (sydnophen). The effect of the pH, alcohol concentration, ionic strength, and surface-active substances was studied, and the electrolysis was carried out at a controllable potential under various conditions. The cyclic voltampefograms were recorded. A mechanism for the reduction of I is proposed. Cleavage of the ring of I in the near-electrode space is observed in unbuffered media. The first direct proof of the existence of the unstable sydnoneimine base was obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1042–1048, August, 1975. 相似文献
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A series of triad type thermotropic polyesters based on phenylsulfonyl hydroquinone and α,ω-bis(4-carboxyphenoxy)alkane was prepared, and the effect of the thermal history on the phase transition and the liquid crystalline structure of the polyesters was studied. The phase transition was significantly affected by the thermal history. When annealed at various temperatures, multiple endotherms were observed for all polyesters in DSC thermograms. A phase stability concept was employed to explain the complicated phase transitions. The time evolution of the liquid crystalline structure was investigated by optical microscopy and transmitted light intensity measurement under crossed polars during annealing. The steady decrease in the density of disclinations with accompanying increase of transmitted light intensity was observed. Depending on the surface conditions of the liquid crystal polymer film, two markedly different domain growth patterns and different textures were found on isothermal annealing; the continuous wormlike texture and the discontinuous droplet texture. The structural relaxation of the deformed texture during annealing was also studied. When shear was applied, the characteristic banded texture was formed in all polyesters. 相似文献
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人胰岛素半合成方法的改进 总被引:1,自引:0,他引:1
本文对森原等人合成人胰岛素的方法进行了改进。用羧肽酶A和胰酶成功地实施了人胰岛素的半合成。精品的总收率为70%,高于1986年森原等报道的水平(50%)。 苏氨酸叔丁酯是半合成人胰岛素的主要原料之一。我们改进了它的合成方法。采用N端未加保护的苏氨酸一步法合成了 相似文献
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采用量子化学MM+和AM1方法计算聚甘油和脂肪酸多聚甘油酯的分子结构参数,然后用逐步线性回归方法建立脂肪酸多聚甘油酯HLB值的定量结构性质(QSPR)模型,所得的预测模型中包含四个参数(单位质量分子所含氧原子数Xo、生成热ΔfHm、电子能Ee和水合能Eh),预测值及外部检验的复相关系数(R2)和标准偏差(SD)分别为0.9553、0.73722和0.9678、6.34426。结果表明,量子化学方法计算简单,对脂肪酸多聚甘油酯结构的表征能力较强,所建QSPR模型具有能较好的预测能力和较强的稳健性,并在一定程度上阐明了脂肪酸多聚甘油酯分子结构与性能之间的关系。 相似文献
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A simple but effective frit formation technique was developed to stabilize the packing structure inside the microchannel of capillary electrochromatographic microchips, utilizing the electroless plating technique. A Ag(NH(3))(2)(+) solution was allowed to diffuse through the colloidal silica packing in the microchannel from the reservoir of the microchip for a limited amount of time, and then it was reduced by an excess amount of formaldehyde solution. A frit structure of ~70 μm in length was formed at the entrance of the microchannel without clogging when treated with 1mM Ag(NH(3))(2)(+) ion and formaldehyde for 30s and 150 s, respectively. The formation of the frit structure was confirmed by a scanning electron microscopy. The stability of the packing structure was tested rigorously and then confirmed by applying alternating electroosmotic flows back and forth with pulsed potential steps on both sides of the frit structure. The effect of the treatment on the electrochromatograms was evaluated after the microchips were repeatedly used and stored for a long period of time. The results indicated that the silver-cemented frit structure extended the lifetime of the fully packed CEC microchips distinctly. 相似文献
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Ali Naderi Per Tomas Larsson Jasna S. Stevanic Tom Lindström Johan Erlandsson 《Cellulose (London, England)》2017,24(3):1307-1317
The impact of the size of the charged group on the properties of alkoxylated NFC was studied by two chloroalkyl acid reagents. It was found that the employment of the larger 2-chloropropionic acid reagent leads to improved properties, e.g. higher fraction of nano-sized materials, and significantly better redispersion as compared to when the smaller monochloroacetic acid was employed. The differences in the impacts of the different reagents were hypothesized to be due to a more efficient disruption of the cohesion between the nanofibrils when a larger charged group was employed. 相似文献
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S. Liu X. Kong A. Xie Y. Shen J. Zhu C. Li Q. Zhang 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(12):2084-2089
The precipitation of three kinds of structures from gallbladder bile of a patient, fractal structure, regular crystal structure,
and small disperse granules, was observed in the same sample using Field Emission Gun-Scanning Electron Microscopy (FEG-SEM).
The results indicated that there was a transition from a linear equilibrium system to a nonlinear and nonequilibrium system,
which was discussed using the theory of entropy. The chemical compositions of these three different kinds of precipitates
were determined by energy dispersive X-ray spectroscopy (EDS). This experimental result revealed that Na and Cl played important
roles in the formation of the fractal and crystal structures. Besides, the Aggregation-Diffusion-Fractal (ADF) model was used
to explain the growth mechanism of the fractal.
The article is published in the original. 相似文献
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Construction of the Skeleton of Phthalascidin, Mechanism of the Formation of the Key Tricyclic Lactam Intermediate 总被引:1,自引:0,他引:1
Zhan Zhu LIU Ye WANG Shi Zhi CHEN* Institute of Materia Medica Chinese Academy of Medical Sciences& Peking Union Medical College Beijing 《中国化学快报》2002,13(8)
Phthalascidin is a structurally simplified version of Et-743, which is a potent anti-tumor marine natural product isolated from Ecteinascidia turbinata. Its antiproliferative activity is greater than that of the agents taxol, camptothecin, adriamycin, mitomycin C, cisplatin, bleomycin, and etoposide by 1-3 orders of magnitude. An elegant synthesis of Et-743 and phthalascidin has been reported by E. J. Corey and co-workers1,2. As part of our continuing program, we have also engaged in dev… 相似文献
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The transport of a drug to the cerebrospinal fluid directly from the nasal cavity: the relation to the lipophilicity of the drug. 总被引:5,自引:0,他引:5
T Sakane M Akizuki S Yamashita T Nadai M Hashida H Sezaki 《Chemical & pharmaceutical bulletin》1991,39(9):2456-2458
The objective of the present study was to clarify the relation between drug transport to the cerebrospinal fluid (CSF) from the nasal cavity and the lipophilicity of the drug using hydrophilic sulfonamides as model drugs. The nasal cavity of the rat was perfused in a single pass system and the concentrations of sulfonamides in plasma and CSF were measured. The drug concentrations in CSF and plasma after nasal perfusion were compared with those after intravenous (i.v.) administration. The drug concentrations in the CSF were remarkably high after nasal perfusion in comparison with those after i.v. administration, though the time course of the plasma concentration was not much different from that after i.v. administration. These results suggested the existence of a direct transport pathway of the sulfonamides from the nose to the CSF. In addition, the drug concentrations in the CSF increased with increasing the lipophilicity of the drugs (the partition coefficient (Pc) of the drugs between isoamyl alcohol and pH 7.4 phosphate buffer). A significant correlation was observed between the drug concentrations in CSF and Pc. In conclusion, the direct transport pathway of the sulfonamides from the nose to the CSF was confirmed and, with regard to drugs with comparatively low lipophilicity, the degree of the transport depended on its Pc. 相似文献
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Bour P 《The Journal of chemical physics》2004,121(16):7545-7548
For clusters of N-methylacetamide and water molecules the performance of the fixed-charged approximation was tested against continuum and explicit ab initio models. The dispersion of the vibrational frequencies when constant electrostatic potential was maintained at the solute atoms was compared to the distribution caused by geometry fluctuations. 相似文献
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V. I. Vasil’eva A. V. Zhil’tsova M. D. Malykhin V. I. Zabolotskii K. A. Lebedev R. Kh. Chermit M. V. Sharafan 《Russian Journal of Electrochemistry》2014,50(2):120-128
The size of the electroconvective instability region on the membrane-solution boundary at currents exceeding the limiting diffusion current was measured by laser interferometry. The influence of the chemical nature of the ionogenic groups of ion-exchange membranes on the development of electroconvective instability was studied. The thickness of the electroconvection region decreased as the catalytic activity of the ionogenic groups of commercial and pilot membrane samples with respect to the heterolytic water dissociation increased. The maximum size of the electroconvective instability region and the minimum currents at which it was recorded for the anion-exchange membranes under study were determined for the highly basic modified anion-exchange membrane MA-41M with an almost completely suppressed water dissociation function. A correlation was found between the size of the convective instability region and the characteristic points on the current-voltage curves. 相似文献