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991.
Andre Rosowsky Katherine K. N. Chen Nickolas Papathanasopoulos Edward J. Modest 《Journal of heterocyclic chemistry》1972,9(2):263-273
Eighteen new 1,3-diamino-5,6-dihydrobenzo[f] quinazolines ( 6 , R. = alkyl, Cl, MeO) were synthesized via the condensation of appropriate 2-tetralones with cyanoguanidine under fusion conditions. Methods were developed for the preparation of a number of heretofore undescribed 2-tetralones as precursors. The final products can be viewed as conformationally rigid analogs of pyrimethamine ( 2 ), and are of interest as inhibitors of dihydrofolate reductase and as potential antimalarial and antitumor agents. 相似文献
992.
993.
Fang-Mo Chang Chen-Chia Huang Shin-Ming Shen Sun-I Chen 《Journal of Thermal Analysis and Calorimetry》1995,44(2):405-417
The effects of various burning rate catalysts on thermal decomposition of cured glycidyl azide polymer (GAP)-ammonium perchlorate (AP) propellants have been studied by means of thermal analysis and a modified vacuum stability test (MVST). Four types of iron-containing catalysts examined in this paper are catocene, ferrocenecarboxaldehyde (FCA), ferrocene, and ferric oxide. Results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) revealed that the catalysts play an important role in the decomposition of both AP and GAP. The peak decomposition temperature (T m) of DTA curves and onset decomposition temperature (T o) of TG patterns considerably shifted to a lower temperature as the concentration of catalysts increased in the propellants. The endothermic temperature of AP, however, is unaffected by the presence of burning rate catalysts in all cases. The activation energy of decomposition of the propellants in range of 80 to 120°C is determined, based on the MVST results. 相似文献
994.
疏水分配常数用于反相液相色谱保留值的预测 总被引:2,自引:0,他引:2
在反相液相色谱保留值基本方程log k_′=a+_cC_B的基础上,描述了采用疏水分配常数及氢键作用能来预测a、c参数的方法,并系统讨论了疏水分配常数对参数a、c的影响,借此对反相液相色谱宽浓度范围内的保留值进行了预测。 相似文献
995.
示波极谱法直接测定水中超痕量钨 总被引:2,自引:0,他引:2
本文对钨—溴邻苯三酚红极谱催化波进行了研究,发现体系中加入四乙基碘化铵后,极谱渡高明显增加,体系的稳定性显著提高,检出限达1.8×10~(-11)mol/L。确定了最佳条件,拟定了不经分离富集直接测定水中痕量钨的方法。此外还对极谱波性质进行了探讨,证明该极谱波为配合物吸附催化氢波,讨论了阳离子表面活性物质对催化氢波的作用机理。 相似文献
996.
在0.02mol/L NaHCO_3-0.05mol/L Na_2SO_4(pH9)介质中,对鸟嘌呤与Cu(Ⅰ)的配位作用进行了极谱研究,测定了鸟嘌呤与Cu(Ⅰ)配位的配体数(2)和该配合物的条件形成常数(β_1=1.80×10~(14),β_2=2.85×10~(18)),并对DcFord-Hume公式的适用性作了讨论. 相似文献
997.
A simple, sensitive and selective method has been developed for the determination of protein using resonance light scattering (RLS) technique. The method is based on the interaction of protein and arsenazo-DBC-Al(3+) in the pH range of 5.0-7.0, which causes a substantial enhancement of the resonance scattering signal of arsenazo-DBC-Al(3+) in the wavelength range of 300-550 nm with the maximum RLS platform at 405-420 nm. With this method, 2.50-50.00 mug ml(-1) of bovine serum albumin (BSA) and 2.50-60.00 mug ml(-1) of human serum albumin (HSA) can be determined, and the detection limits, calculated three times the standard deviation (S.D.) of six blank measurements, for BSA and HSA were 123.4 and 89.6 ng ml(-1), respectively. Moreover, the method is free from interference from many amino acids and metal ions. The method, with high sensitivity, selectivity and reproducibility, was satisfactorily applied to the determination of total protein in human serum samples. Mechanism studies indicated that arsenazo-DBC-Al(3+) could bind to BSA depending mainly on electrostatic forces, which results in enhanced RLS in the arsenazo-DBC-Al(3+)-protein system. 相似文献
998.
A new dihydroberberine alkaloid, 7,8‐dihydro‐8‐methoxyberberine ( 1 ), along with six known compounds including two dihydroberberine alkaloids, 7,8‐dihydro‐8‐hydroxyberberine ( 2 ) and oxyberberine ( 3 ) and four protoberberine alkaloids, berberine ( 4 ), palmatine ( 5 ), jatrorrhizine ( 6 ) and columbamine ( 7 ), were isolated from the stems of Mahonia japonica. These compounds were characterized and identified by physical and spectral evidence. 相似文献
999.
High-level expression of soluble human β-defensin-2 fused with green fluorescent protein in Escherichia coli cell-free system 总被引:2,自引:0,他引:2
Human β-defensin-2 (hBD2), a small cationic peptide, exhibits a broad range of antimicrobial activity and does not acquire
any microbial resistance. To produce this uneasily detectable, degradable, and toxic polypeptide efficiently, an alternative
approach based on the Escherichia coli cell-free biosynthesis system was proposed. The approach implies that a polypeptide of interest is synthesized as a fusion
protein linked to a green fluorescent protein (GFP) through a cleavable spacer. With batch-mode operation, a significant amount
of hBD2 fused with GFP (0.25 mg/mL) can be expressed in this cell-free system. The productivity of the fusion protein can
be improved up to 1.2 mg/mL by employing a continuous-exchange cell-free system. Furthermore, the GFP moiety provides directly
visible and quantitative monitoring of the polypeptide synthesis, and the product is soluble and stable. This work will be
helpful in allowing the rapid and visible expression of other similar defensins using an in vitro cell-free system. 相似文献
1000.
Heo YS Ryu JM Park SM Park JH Lee HC Hwang KY Kim J 《Experimental & molecular medicine》2002,34(3):211-223
Protein-tyrosine phosphatases (PTPs) constitute a family of receptor-like, and cytoplasmic enzymes, which catalyze the dephosphorylation of phosphotyrosine residues in a variety of receptors and signaling molecules. Together with protein tyrosine kinases (PTKs), PTPs are critically involved in regulating many cellular signaling processes. In this study, diverse compounds were screened for PTP inhibition and selectively screened for inhibitors with the end product inhibition properties. Among phosphate analogues and their derivatives for PTP inhibition, Keggin compounds phosphomolybdate (PM) and phosphotungstate (PT) strongly inhibited both PTP-1B and SHP-1, with K(i) values of 0.06-1.2 micromM in the presence of EDTA. Unlike the vanadium compounds, inhibition potencies of PM and PT were not significantly affected by EDTA. PM and PT were potent, competitive inhibitors for PTPs, but relatively poor inhibitors of Ser/Thr phosphatase. Interestingly, PM and PT did not inhibit alkaline phosphatase at all. The crystal structure of PTP-1B in complex with PM, at 2.0 A resolution, reveals that MoO(3), derived from PM by hydrolysis, binds at the active site. The molybdenium atom of the inhibitor is coordinated with six ligands: three oxo-ligands, two apical water molecules and a S atom of the catalytic cysteine residue. In support of the crystallographic finding, we observed that molybdenium oxides (MoO(3), MoO(2), and MoO(2)Cl(2)) inhibited PTP-1B with IC(50) in the range 5-15 micromM. 相似文献