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排序方式: 共有655条查询结果,搜索用时 15 毫秒
81.
James Mitchell Naveena Yanamala Yi Lei Tan Eric E. Gardner Kalyan C. Tirupula Fernanda Balem Mordechai Sheves Daniel Nietlispach Judith Klein‐Seetharaman 《Photochemistry and photobiology》2019,95(3):787-802
The chlorophyll‐derivative chlorin e6 (Ce6) identified in the retinas of deep‐sea ocean fish is proposed to play a functional role in red bioluminescence detection. Fluorescence and 1H NMR spectroscopy studies with the bovine dim‐light photoreceptor, rhodopsin, indicate that Ce6 weakly binds to it with μm affinity. Absorbance spectra prove that red light sensitivity enhancement is not brought about by a shift in the absorbance maximum of rhodopsin. 19F NMR experiments with samples where 19F labels are either placed at the cytoplasmic binding site or incorporated as fluorinated retinal indicate that the cytoplasmic domain is highly perturbed by binding, while little to no changes are detected near the retinal. Binding of Ce6 also inhibits G‐protein activation. Chemical shift changes in 1H‐15N NMR spectroscopy of 15N‐Trp labeled bovine rhodopsin reveal that Ce6 binding perturbs the entire structure. These results provide experimental evidence that Ce6 is an allosteric modulator of rhodopsin. 相似文献
82.
Roly J. Armstrong Wasim M. Akhtar Tom A. Young Fernanda Duarte Timothy J. Donohoe 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(36):12688-12692
Hydrogen borrowing catalysis serves as a powerful alternative to enolate alkylation, enabling the direct coupling of ketones with unactivated alcohols. However, to date, methods that enable control over the absolute stereochemical outcome of such a process have remained elusive. Here we report a catalytic asymmetric method for the synthesis of enantioenriched cyclohexanes from 1,5‐diols via hydrogen borrowing catalysis. This reaction is mediated by the addition of a chiral iridium(I) complex, which is able to impart high levels of enantioselectivity upon the process. A series of enantioenriched cyclohexanes have been prepared and the mode of enantioinduction has been probed by a combination of experimental and DFT studies. 相似文献
83.
dos Reis Lima Fernanda Maria Silva Saimon Moraes da Silva Freires André Goulart Marília Oliveira Fonseca Damos Flavio Santos de Cassia Silva Luz Rita 《Journal of Solid State Electrochemistry》2019,23(3):725-734
Journal of Solid State Electrochemistry - This paper reports the development of a photoelectrochemical platform based on indium tin oxide (ITO) electrode modified with carboxyl-functionalized... 相似文献
84.
Fernanda das Neves Costa Ricardo Moreira Borges Gilda Guimares Leito Gerold Jerz 《Journal of separation science》2019,42(8):1528-1541
Salicornia species have just been introduced to the European market as a vegetable named ‘samphire’, ‘green asparagus’, or ‘sea asparagus’. Due to its increasing attention, and associated value, minor compounds of Salicornia gaudichaudiana Moq were investigated. The use of countercurrent chromatography and mass spectrometry enabled the search for known, as well as potentially novel natural products. Their identification was achieved based on molecular weights and mass‐spectrometric fragmentation data. Low detection limits enabled the visualization of all compounds with their identification in almost real time close to the preparative countercurrent chromatography experiment. A list of known natural products from Salicornia genus guided the identification process of compounds occurring in Salicornia gaudichaudiana Moq by tandem mass spectrometry fragment comparison. The natural product classes were divided into four groups: chlorogenic acid derivatives; flavonoid derivatives; pentacyclic triterpenoid saponins; and other compounds. 相似文献
85.
Silicon is an important element for plants at their structure and physiology and plays an important role in bone mineralization and soft tissue development in human beings. Furthermore, its determination is being requested more frequently due to nutritional requirements. However, the methods found in the literature to determine silicon in this type of samples require a sample preparation step, which makes them time-consuming and provides high uncertainties. In this paper, a method for the determination of silicon in plants by wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry has been developed. Horsetail (Equisetum arvense L.) and nettle leaf (Urtica dioica) have been used as a source of silicon due to its medical use. Sample preparation involved calcining the sample at 700°C and preparing fused beads from the calcined sample. Calibration standards for WD-XRF measurement were prepared by mixing certified reference materials and chemical products to reproduce the samples matrix. The linear range for silicon concentration ranges from 6 to 55 wt% SiO2. The validation of the method was performed measuring a reference material (NCS DC73349 Bush branches and leaves) and comparing the results obtained by WD-XRF with those obtained by an independent method by atomic absorption spectrometry. The developed methodology is rapid and accurate, provides low uncertainties, and is environmentally friendly, as it does require the use of less hazardous reagents. 相似文献
86.
Danilo Antonio Giarola Paulo Rogério Catarini da Silva Alexandre Urbano Fernanda Midori de Oliveira César Ricardo Texeira Tarley Luiz Henrique Dall’Antonia 《Journal of Solid State Electrochemistry》2014,18(2):497-504
Nickel hydroxide films were electrosynthesized in the presence of different diluted surfactant solutions by galvanostatic electroprecipitation. Lamellar α-Ni(OH)2 films are obtained using cationic surfactant cetyltrimethylammonium bromide (CTAB), anionic surfactant sodium dodecyl sulfate (SDS), and also neutral surfactant Tween® 80. The films were structurally and morphologically characterized by X-ray diffraction, thermal gravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy, and electrochemically by cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The results evidenced that SDS remains intercalated between the lamellae of α-Ni(OH)2. Albeit the presence of CTAB and Tween® 80, it was noticed in FTIR spectra that the surfactants did not intercalate. The morphology was affected by the presence of different surfactants. All studied surfactants displaced the oxidation potential (E O) of Ni2+/Ni3+ process to less positive values. Also, the presence of surfactants improved the electrode charge efficiency and the charge response for the same number of moles of nickel ions deposited. The ratio of the charge and frequency change is 4.4 times bigger for films deposited with SDS when compared with pure α-Ni(OH)2 films. 相似文献
87.
Karina Basso Santiago Gilce Maria Piana Bruno José Conti Eliza de Oliveira Cardoso Bruna Fernanda Murbach Teles Andrade Mirella Rossitto Zanutto 《Natural product research》2018,32(12):1441-1445
Propolis is a bee product with several biological properties. This study aimed at investigating a propolis-containing mouthwash, its organoleptic properties, microbial contamination and its antibacterial action in vitro. This mouthwash was assessed in vivo to control dental plaque in humans. The presence of microorganisms was analyzed and the minimum inhibitory concentration against Streptococcus mutans was determined. A comparative study was done in vivo using propolis, chlorhexidine, and propolis plus chlorhexidine in lower concentrations for 14 days. Dental plaque was analyzed by the Patient Hygiene Performance (PHP) index. The odontological product was yellow, cloudy, free of microbial contamination, and exerted an inhibitory action in vitro. Individuals who used a propolis-containing mouthwash for 14 consecutive days in combination or not to chlorhexidine showed a similar PHP index to chlorhexidine alone. The product exerted an antibacterial action in vitro and in vivo, exhibiting a positive action in the control of dental plaque. 相似文献
88.
Fernanda Moreira Tatiane de Andrade Maranhão Almir Spinelli 《Journal of Solid State Electrochemistry》2018,22(5):1303-1313
A carbon paste electrode (CPE) modified with Fe3O4 nanoparticles (Fe3O4 NP) and the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (IL BMI.PF6) was employed for the electroanalytical determination of estrone (E1) by square-wave voltammetry (SWV). At the modified electrode, cyclic voltammograms of E1 in B–R buffer (pH 12.0) showed an adsorption-controlled irreversible oxidation peak at around +0.365 V. The anodic current increased by a factor of five times and the peak potential shifted 65 mV to less positive values compared with the unmodified CPE. Under optimized conditions, the calibration curve obtained showed two linear ranges: from 4.0 to 9.0 μmol L?1 and from 9.0 to 100.0 μmol L?1. The limits of detection (LOD) and quantification (LOQ) attained were 0.47 and 4.0 μmol L?1, respectively. The proposed modified electrode was applied to the determination of E1 in pork meat samples. Data provided by the proposed modified electrode were compared with data obtained by UV–vis spectroscopy. The outstanding performance of the electrochemical device indicates that Fe3O4 NP and the IL BMI.PF6 are promising materials for the preparation of chemically modified electrodes for the determination of E1. 相似文献
89.
Monteiro MJ Bazito FF Siqueira LJ Ribeiro MC Torresi RM 《The journal of physical chemistry. B》2008,112(7):2102-2109
Lithium salt solutions of Li(CF3SO2)2N, LiTFSI, in a room-temperature ionic liquid (RTIL), 1-butyl-2,3-dimethyl-imidazolium cation, BMMI, and the (CF3SO2)2N(-), bis(trifluoromethanesulfonyl)imide anion, [BMMI][TFSI], were prepared in different concentrations. Thermal properties, density, viscosity, ionic conductivity, and self-diffusion coefficients were determined at different temperatures for pure [BMMI][TFSI] and the lithium solutions. Raman spectroscopy measurements and computer simulations were also carried out in order to understand the microscopic origin of the observed changes in transport coefficients. Slopes of Walden plots for conductivity and fluidity, and the ratio between the actual conductivity and the Nernst-Einstein estimate for conductivity, decrease with increasing LiTFSI content. All of these studies indicated the formation of aggregates of different chemical nature, as it is corroborated by the Raman spectra. In addition, molecular dynamics (MD) simulations showed that the coordination of Li+ by oxygen atoms of TFSI anions changes with Li+ concentration producing a remarkable change of the RTIL structure with a concomitant reduction of diffusion coefficients of all species in the solutions. 相似文献
90.
MSPD procedure for determining buprofezin,tetradifon, vinclozolin,and bifenthrin residues in propolis by gas chromatography–mass spectrometry 总被引:1,自引:0,他引:1
dos Santos TF Aquino A Dórea HS Navickiene S 《Analytical and bioanalytical chemistry》2008,390(5):1425-1430
A simple and effective extraction method based on matrix solid-phase dispersion (MSPD) was developed to determine bifenthrin,
buprofezin, tetradifon, and vinclozolin in propolis using gas chromatography–mass spectrometry in selected ion monitoring
mode (GC–MS, SIM). Different method conditions were evaluated, for example type of solid phase (C18, alumina, silica, and Florisil), the amount of solid phase and eluent (n-hexane, dichloromethane, dichloromethane–n-hexane (8:2 and 1:1, v/v) and dichloromethane–ethyl acetate (9:1, 8:2 and 7:3, v/v)). The best results were obtained using 0.5 g propolis, 1.0 g silica as dispersant sorbent, 1.0 g Florisil as clean-up sorbent,
and dichloromethane–ethyl acetate (9:1, v/v) as eluting solvent. The method was validated by analysis of propolis samples fortified at different concentration levels
(0.25 to 1.0 mg kg−1). Average recoveries (four replicates) ranged from 67% to 175% with relative standard deviation between 5.6% and 12.1%. Detection
and quantification limits ranged from 0.05 to 0.10 mg kg−1 and 0.15 to 0.25 mg kg−1 propolis, respectively. 相似文献