排序方式: 共有25条查询结果,搜索用时 171 毫秒
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Bekzat ABDIKADYR Alp KILI Onur ALEV Serkan BÜYÜKK
SE Zafer Ziya
ZTÜRK 《Turkish Journal of Chemistry》2021,45(2):295
Pristine and WO3 decorated TiO2 nanorods (NRs) were synthesised to investigate n-n-type heterojunction gas sensing properties. TiO2 NRs were fabricated via hydrothermal method on fluorine-doped tin oxide coated glass (FTO) substrates. Then, tungsten was sputtered on the TiO2 NRs and thermally oxidised to obtain WO3 nanoparticles. The heterostructure was characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. Fabricated sensor devices were exposed to VOCs such as toluene, xylene, acetone and ethanol, and humidity at different operation temperatures. Experimental results demonstrated that the heterostructure has better sensor response toward ethanol at 200 °C. Enhanced sensing properties are attributed to the heterojunction formation by decorating TiO2 NRs with WO3. 相似文献
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In this study, methanol extracts (MEs) and essential oil (EO) of Angelica purpurascens (Avé-Lall.) Gill obtained from different parts (root, stem, leaf, and seed) were evaluated in terms of antioxidant activity, total phenolics, compositions of phenolic compound, and essential oil with the methods of 2,2-azino-bis(3ethylbenzo-thiazoline-6-sulfonic acid (ABTS•+), 2,2-diphenyl-1-picrylhydrazil (DPPH•) radical scavenging activities, and ferric reducing/antioxidant power (FRAP), the Folin–Ciocalteu, liquid chromatography−tandem mass spectrometry (LC−MS/MS), and gas chromatography-mass spectrometry (GC−MS), respectively. The root extract of A. purpurascens exhibited the highest ABTS•+, DPPH•, and FRAP activities (IC50: 0.05 ± 0.0001 mg/mL, IC50: 0.06 ± 0.002 mg/mL, 821.04 ± 15.96 µM TEAC (Trolox equivalent antioxidant capacity), respectively). Moreover, EO of A. purpurascens root displayed DPPH• scavenging activity (IC50: 2.95 ± 0.084 mg/mL). The root extract had the highest total phenolic content (438.75 ± 16.39 GAE (gallic acid equivalent), µg/mL)). Twenty compounds were identified by LC−MS/MS. The most abundant phenolics were ferulic acid (244.39 ± 15.64 μg/g extract), benzoic acid (138.18 ± 8.84 μg/g extract), oleuropein (78.04 ± 4.99 μg/g extract), and rutin (31.21 ± 2.00 μg/g extract) in seed, stem, root, and leaf extracts, respectively. According to the GC−MS analysis, the major components were determined as α-bisabolol (22.93%), cubebol (14.39%), α-pinene (11.63%), and α-limonene (9.41%) among 29 compounds. Consequently, the MEs and EO of A. purpurascens can be used as a natural antioxidant source. 相似文献
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Chatterjee A Jurgenson CT Schroeder FC Ealick SE Begley TP 《Journal of the American Chemical Society》2006,128(22):7158-7159
The biosynthesis of thiamin pyrophosphate in eukaryotes is different from the prokaryotic biosynthesis and is poorly understood to date. Only one thiazole biosynthetic gene has been identified (Thi4 in Saccharomyces cerevisiae). Here we report the identification and characterization of a Thi4-bound metabolite that consists of the ADP adduct of 5-(2-hydroxyethyl)-4-methylthiazole-2-carboxylic acid. The unexpected structure of this compound yields the first insights into the mechanism of thiamin thiazole biosynthesis in eukaryotes. 相似文献
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Steven E. Ealick Dick Van Der Helm K. Ramalingam George X. Thyvelikakath K. D. Berlin 《Journal of heterocyclic chemistry》1977,14(3):387-390
The structure of 1,4-rlihydro[1 ]benzothiopyrano[4,3-c ]pyrazole 5,5-dioxide was determined by single crystal x-ray diffraction. The molecule crystallizes in space group P21/c with a = 13.4378(6), b = 5.5938(3), c = 12.9837(6)Å, and β = 103.831°. The final R value is 0.083. Surprisingly, the tautomer with N(2)-H exists in the crystal with the pyrazole ring being planar. The entire system is not planar as the benzene ring is rotated about C(9a) and C(9b) with respect to the pyrazole ring. In the crystal structure the pyrazole exists as hydrogen-bonded dimers with two molecules related by a center of symmetry. 相似文献
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Hazra AB Han Y Chatterjee A Zhang Y Lai RY Ealick SE Begley TP 《Journal of the American Chemical Society》2011,133(24):9311-9319
In many bacteria tenI is found clustered with genes involved in thiamin thiazole biosynthesis. However, while TenI shows high sequence similarity with thiamin phosphate synthase, the purified protein has no thiamin phosphate synthase activity, and the role of this enzyme in thiamin biosynthesis remains unknown. In this contribution, we identify the function of TenI as a thiazole tautomerase, describe the structure of the enzyme complexed with its reaction product, identify the substrates phosphate and histidine 122 as the acid/base residues involved in catalysis, and propose a mechanism for the reaction. The identification of the function of TenI completes the identification of all of the enzymes needed for thiamin biosynthesis by the major bacterial pathway. 相似文献
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Chatterjee A Jurgenson CT Schroeder FC Ealick SE Begley TP 《Journal of the American Chemical Society》2007,129(10):2914-2922
Thiazole synthase catalyzes the formation of the thiazole moiety of thiamin pyrophosphate. The enzyme from Saccharomyces cerevisiae (THI4) copurifies with a set of strongly bound adenylated metabolites. One of them has been characterized as the ADP adduct of 5-(2-hydroxyethyl)-4-methylthiazole-2-carboxylic acid. Attempts toward yielding active wild-type THI4 by releasing protein-bound metabolites have failed so far. Here, we describe the identification and characterization of two partially active mutants (C204A and H200N) of THI4. Both mutants catalyzed the release of the nicotinamide moiety from NAD to produce ADP-ribose, which was further converted to ADP-ribulose. In the presence of glycine, both the mutants catalyzed the formation of an advanced intermediate. The intermediate was trapped with ortho-phenylenediamine, yielding a stable quinoxaline derivative, which was characterized by NMR spectroscopy and ESI-MS. These observations confirm NAD as the substrate for THI4 and elucidate the early steps of this unique biosynthesis of the thiazole moiety of thiamin in eukaryotes. 相似文献
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Designer gene therapy using an Escherichia coli purine nucleoside phosphorylase/prodrug system 总被引:1,自引:0,他引:1
Bennett EM Anand R Allan PW Hassan AE Hong JS Levasseur DN McPherson DT Parker WB Secrist JA Sorscher EJ Townes TM Waud WR Ealick SE 《Chemistry & biology》2003,10(12):1173-1181
Activation of prodrugs by Escherichia coli purine nucleoside phosphorylase (PNP) provides a method for selectively killing tumor cells expressing a transfected PNP gene. This gene therapy approach requires matching a prodrug and a known enzymatic activity present only in tumor cells. The specificity of the method relies on avoiding prodrug cleavage by enzymes already present in the host cells or the intestinal flora. Using crystallographic and computer modeling methods as guides, we have redesigned E. coli PNP to cleave new prodrug substrates more efficiently than does the wild-type enzyme. In particular, the M64V PNP mutant cleaves 9-(6-deoxy-alpha-L-talofuranosyl)-6-methylpurine with a kcat/Km over 100 times greater than for native E. coli PNP. In a xenograft tumor experiment, this compound caused regression of tumors expressing the M64V PNP gene. 相似文献
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G. D. Macdonell K. D. Berlin S. E. Ealick Dick van der Helm 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):187-197
Abstract Intramolecular acylation involving three ω-carboxyalkylphosphonium salts 1a-c has been achieved in the presence of 115% polyphosphoric acid (PPA) to yield the heretofore unknown 2,3,4,5-tetrahydro-5-oxo-2,2-diphenyl-1H-2-benzo-phosphepinium salts 2a-c. The open-chain precursors were easily prepared by quaternization of the corresponding tertiary arylmethyl-substituted phosphines with 3-chloropropanoic acid. Cyclization of the carboxy-substituted salts was accomplished at 200°C with PPA in modest yields (37–64%). A mechanism reminiscent of a classic electrophilic acylation process was tentatively proposed. An x-ray crystallographic analysis of a single crystal of 2a showed the phosphepin ring to exist in a twisted-chair conformation. 相似文献