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排序方式: 共有284条查询结果,搜索用时 31 毫秒
271.
Leandro M. de Carvalho Carine Viana Ana Paula L. Moreira Paulo C. do Nascimento Denise Bohrer Monique J. Motta Géssica D. da Silveira 《Journal of Solid State Electrochemistry》2013,17(6):1601-1608
Herein, we present a new method based on separation by ion-pair chromatography with pulsed amperometric detection for evaluating various diuretics, including hydrochlorothiazide, chlorthalidone, furosemide, and amiloride, which are adulterants in herbal-based pharmaceutical formulations. The amperometric detection cycle (time?=?2 s) was performed at a gold electrode by applying a detection potential (E1) of +800 mV for 0.4 s and an oxidation potential (E2) of +1,000 mV for 0.40 s, followed by a reduction potential (E3) of ?200 mV for 1.20 s. The mobile phase for separating the diuretics was composed of 5 mmol L?1 phosphate buffer and 0.3 mmol L?1 sodium dodecyl sulfate in 50 % (v/v) methanol (pH 4.5). This method enabled the quantification of the drugs at low concentrations (i.e., 0.08 mg/capsule for hydrochlorothiazide, 0.01 mg/capsule for chlorthalidone, and 0.007 mg/capsule for furosemide). Twenty-six herbal formulations were analyzed, and eight samples (30.8 %) were found to contain diuretics that were added to the final composition (declared or not). 相似文献
272.
Antonio Evidente Alessio Cimmino Maurizio Vurro Charles L. Cantrell Andrea Motta 《Tetrahedron》2008,64(8):1612-1619
Phyllosticta cirsii, a fungal pathogen isolated from Cirsium arvense and proposed as biocontrol agent of this noxious perennial weed, produces in liquid cultures different phytotoxic metabolites with potential herbicidal activity. Four new oxazatricycloalkenones, named phyllostictines A-D, were isolated and characterized using essentially spectroscopic and chemical methods. Tested by leaf-puncture assay on the fungal host plant phyllostictine A proved to be highly toxic. The phytotoxicity decreases when both the dimension and the conformational freedom of the macrocyclic ring change, as in phyllostictines B and D, and it is totally lost when also the functionalization of the same ring is modified, as in phyllostictine C. Beside its phytotoxic properties, phyllostictine A has no antifungal activity, an interesting antibiotic activity only against Gram+ bacteria, and a noticeable zootoxic activity when tested at high concentrations. The integrity of the oxazatricycloalkenone system appears to be an important feature to preserve these activities. 相似文献
273.
Chao Cai Kang Liu Long Zhang Fangbiao Li Yao Tan Pengcheng Li Yanqiu Wang Maoyu Wang Zhenxing Feng Debora Motta Meira Wenqiang Qu Andrei Stefancu Wenzhang Li Hongmei Li Junwei Fu Hui Wang Dengsong Zhang Emiliano Cortés Min Liu 《Angewandte Chemie (International ed. in English)》2023,62(26):e202300873
The slow water dissociation process in alkaline electrolyte severely limits the kinetics of HER. The orientation of H2O is well known to affect the dissociation process, but H2O orientation is hard to control because of its random distribution. Herein, an atomically asymmetric local electric field was designed by IrRu dizygotic single-atom sites (IrRu DSACs) to tune the H2O adsorption configuration and orientation, thus optimizing its dissociation process. The electric field intensity of IrRu DSACs is over 4.00×1010 N/C. The ab initio molecular dynamics simulations combined with in situ Raman spectroscopy analysis on the adsorption behavior of H2O show that the M−H bond length (M=active site) is shortened at the interface due to the strong local electric field gradient and the optimized water orientation promotes the dissociation process of interfacial water. This work provides a new way to explore the role of single atomic sites in alkaline hydrogen evolution reaction. 相似文献
274.
Otaciro R. Nascimento Claudio J. Magon Jose Fernando Lima Jose Pedro Donoso Eglantina Benavente Jaime Paez Vladimir Lavayen Maria Angelica Santa Ana Guillermo Gonzalez 《Journal of Sol-Gel Science and Technology》2008,45(2):195-204
In this work we report results from continuous-wave (CW) and pulsed electron paramagnetic resonance (EPR) and proton nuclear
magnetic resonance (NMR) studies of the vanadium pentoxide xerogel V2O5:nH2O (n ≈ 1.6). The low temperature CW-EPR spectrum shows hyperfine structure due to coupling of unpaired V4+ electron with the vanadium nucleus. The analysis of the spin Hamiltonian parameters suggests that the V4+ ions are located in tetragonally distorted octahedral sites. The transition temperature from the rigid-lattice low-temperature
regime to the high temperature liquid-like regime was determined from the analysis of the temperature dependence of the hyperfine
splitting and the V4+ motional correlation time. The Electron Spin Echo Envelope Modulation (ESEEM) data shows the signals resulting from the interaction
of 1H nuclei with V4+ ions. The modulation effect was observed only for field values in the center of the EPR absorption spectrum corresponding
to the single crystals orientated perpendicular to the magnetic field direction. At least three protons are identified in
the xerogel by our magnetic resonance experiments: (I) the OH groups in the equatorial plane, (ii) the bound water molecules
in the axial V=O bond and (iii) the free mobile water molecules between the oxide layers. Proton NMR lineshapes and spin-lattice
relaxation times were measured in the temperature range between 150 K and 323 K. Our analysis indicates that only a fraction
of the xerogel protons contribute to the measured conductivity. 相似文献
275.
Servoli E Maniglio D Aguilar MR Motta A San Roman J Belfiore LA Migliaresi C 《Macromolecular bioscience》2008,8(12):1126-1134
Surface properties have a significant influence on the performance of biomedical devices. The influence of surface chemistry on the amount and distribution of adsorbed proteins has been evaluated by a combination of atomic force microscopy (AFM) and surface plasmon resonance (SPR). Adsorption of albumin, fibrinogen, and fibronectin was analyzed under static and dynamic conditions, employing self-assembled monolayers (SAMs) as model surfaces. AFM was performed in tapping mode with antibody-modified tips. Phase-contrast images showed protein distribution on SAMs and phase-shift entity provided information on protein conformation. SPR analysis revealed substrate-specific dynamics in each system investigated. When multi-protein solutions and diluted human plasma interacted with SAMs, SPR data suggested that surface chemistry governs the equilibrium composition of the protein layer. 相似文献
276.
L Lendinara C Accorsi C Agostini G Angelini F Baruffaldi M Fini M Motta G Giavaresi 《Magnetic resonance imaging》2001,19(5):745-753
Detailed analysis of proton spin-spin and spin-lattice relaxation behaviors of the bone marrow in the presence of trabecular bone network was performed at low-resolution (B(0) = 0.496T) on rat vertebrae specimens deprived of spinal cord. Two groups of samples, from young and old healthy animals, were investigated before cellular necrosis had started. BMD measurements were carried out to quantify the expected age-related modifications of the trabecular bone network. 1H-MR measurements were also performed on the same samples, deprived of marrow and saturated with water, in order to control the validity of a possible interpretation of the marrow 1H-MR characteristics, in terms of marrow components, and to investigate the possible employment of these samples to study the trabecular bone network properties. We pointed out that: 1) a bimodal distribution of T(2i) and T(1i) values (distinguishing "fast" and "slow" relaxations) describes satisfactorily all the 1H-MR experimental decays; 2) age-related modifications of the trabecular bone network are marked by correlate variations of the BMD value and of the proton spin-spin relaxation rates in water saturated samples; 3) age-related modifications of marrow are underlined by variations of the average value of the "fast" T(2i) and of the "slow" T(1i) relaxation time distributions, which could be attributed to the marrow components different from the fat granules of the adipose cells.Our results suggest that studies in vitro on bone tissue, by 1H-MR techniques at low-resolution, may contribute to a better bone function characterization and, therefore, to a better clinical utilization of MRI techniques. 相似文献
277.
Yue W Lv A Gao J Jiang W Hao L Li C Li Y Polander LE Barlow S Hu W Di Motta S Negri F Marder SR Wang Z 《Journal of the American Chemical Society》2012,134(13):5770-5773
Hybrid rylene arrays have been prepared via a combination of Stille coupling and C-H transformation. The ability to extend the π system along the equatorial axis of rylenes not only leads to broadened light absorption but also increases the electron affinity, which can facilitate electron injection and transport with ambient stability. 相似文献
278.
Catarina Motta de Moura Jaqueline Motta de Moura Jaqueline Pozzada dos Santos Roberta da Costa Kosinski Guilherme Luiz Dotto Luiz Antonio de Almeida Pinto 《Macromolecular Symposia》2012,319(1):240-245
Summary: Chitosan biofilms were prepared with and without plasticizer (glycerol and sorbitol). The physical and mechanical properties of chitosan biofilms with and without plasticizer were evaluated. Chitosan was obtained from shrimp wastes and characterized. The film forming solution (FFS) was obtained through chitosan dissolution and drying. The solution had its pH adjusted to 6.0 and oven dried (40 °C, 24 h) with forced air circulation. Chitosan biofilms without plasticizer showed a tensile strength about 36% higher than biofilms produced with plasticizer. On the other hand, biofilms with plasticizer presented superior values of elongation. The permeability of the water vapor and color presented significant difference (p < 0.05) between all biofilms. Chitosan/plasticizer biofilms showed higher values of water vapor permeability in relation to chitosan biofilms without plasticizer. 相似文献
279.
Tsukamoto Y Santa T Yoshida H Miyano H Fukushima T Hirayama K Imai K Funatsu T 《Biomedical chromatography : BMC》2006,20(10):1049-1055
The combined use of a so-called internal standard and the isotope-labeled derivatization reagent for the quantification of analytes for liquid chromatography-mass spectrometry (LC/MS) was further studied. The sample solution (containing the analytes and an internal standard) was derivatized with the light form of the derivatization reagent, 7-(N,N-dimethylaminosulfonyl)-4-(aminoethyl)piperazino-2,1,3-benzoxadiazole (DBD-PZ-NH(2)) or 7-(N,N-dimethylaminosulfonyl)-4-piperazino-2,1,3-benzoxadiazole (DBD-PZ). A standard solution of the analytes (containing an internal standard) was derivatized with the isotope (d(6))-labeled derivatization reagent, DBD-PZ-NH(2) (D) or DBD-PZ (D), and served as the isotope-labeled internal standards. The peak heights of the targeted analytes derivatives in the sample solution were corrected using those of the internal standard and the heavy form derivatives of the standards, and the calibration curves were constructed. The curve bending of the calibration curves caused by the ion suppression at the ion source was suppressed and the linear dynamic ranges of the calibration curves were expanded. The derivatives of DBD-PZ-NH(2) were about 10 times more sensitively detected than those of DBD-PZ derivatives and, therefore, DBD-PZ-NH(2) might be suitable for sensitive detection. 相似文献
280.
Ciapina EM Melo WC Santa Anna LM Santos AS Freire DM Pereira N 《Applied biochemistry and biotechnology》2006,131(1-3):880-886
The production of biosurfactant by Rhodococcus erythropolis during the growth on glycerol was investigated. The process was carried out at 28 degrees C in a 1.5-L bioreactor using glycerol as carbon source. The bioprocess was monitored through measurements of biosurfactant concentration and glycerol consumption. After 51 h of cultivation, 1.7 g/L of biosurfactant, surface, and interfacial tensions values (with n-hexadecane) of 43 and 15 mN/m, respectively, 67% of Emulsifying Index (E (24)), and 94% of oil removal were obtained. The use of glycerol rather than what happens with hydrophobic carbon source allowed the release of the biosurfactant, originally associated to the cell wall. 相似文献