Search results for "Absorbance"
showing 10 items of 192 documents
Vis/NIR spectroelectrochemical analysis of poly-(Azure A) on ITO electrode
2006
Electrochromic behavior of poly-(Azure A) on indium–tin oxide electrode is analyzed in an aqueous potassium nitrate solution. The dependence of the absorbance on the applied potential during cyclic voltammograms proves very interesting at two selected characteristic wavelengths: at 925 nm, attributed to an intermediate species and another at 735 nm, attributed to the oxidized form of the polymer. Molar absorptivity coefficients for both species have been calculated from the relationship between current and the derivative of absorbance with respect to time. Voltammograms of formation of the intermediate are simulated from spectroelectrochemical results. Keywords: Poly-(Azure A), Spectroelect…
UDP-glucosyltransferase activity toward exogenous substrates in Drosophila melanogaster.
1991
To investigate the capacity of Drosophila extracts to glucosylate exogenous substrates we have developed a fast and sensitive method for the detection of UDP-glucosyltransferase activity using 4-nitrophenol, 1-naphthol, or 2-naphthol as substrates. High-performance liquid chromatography was used to separate and quantitate the reaction products, allowing detection of activities that produced as little as 1 pmol of 2-naphthol glucoside (fluorescence detection) or 16 pmol of 4-nitrophenol glucoside (absorbance detection). Optimal activity was found at 43 degrees C and alkaline pH. The affinity of the Drosophila enzyme was 250-fold higher for 1-naphthol or 2-naphthol (Km approximately 4 microM)…
Impact of high-fat diet on antioxidant status, vascular wall thickening and cardiac function in adult female LDLR<sup>–/–</sup> mice
2012
International audience; Background: Western diet, rich in saturated fatty acids and cholesterol, is associated with increased cardiovascular risk. We thus investigated in female mice the influence of this diet on plasma antioxidant status, vascular wall thickening and cardiac function. Methods and Results: Adult female C57BL/6J wild type (WT) and LDLR–/– mice were fed a normal diet (ND) or a high-fat diet (HFD) for 17 weeks. HFD induced an increase in plasma lipids and vitamin C (Vit C) levels in both groups but at a much higher level in LDLR–/– and a decrease in plasma ascorbyl free radical levels to Vit C ratio (an endogenous oxidative stress index) in LDLR–/–. We only found a slight decr…
Electrochromic absorbance changes in the chlorophyll-c-containing alga Pleurochloris meiringensis (Xanthophyceae)
1994
Flash-induced absorbance changes were measured in the Chl-c-containing alga Pleurochloris meiringensis (Xanthophyceae) between 430 and 570 nm. In addition to the bands originating from redox changes of cytochromes, three major positive and tow negative transient bands were observed both 0.7 and 20 ms after the exciting flash. These transient bands peaking at 520, 480 and 451 nm and 497 and 465 nm, respectively, could be assigned to an almost homogeneous shift of the absorbance bands with maxima at 506, 473 and 444 nm, respectively. The shape of the absorbance transients elicited from PS I or PS II was identical, and the two photosystems contributed nearly equally to the absorbance changes. …
Tansy fruit mediated greener synthesis of silver and gold nanoparticles
2010
Abstract In this paper we have reported the green synthesis of silver (AgNPs) and gold (AuNPs) nanoparticles by reduction of silver nitrate and chloroauric acid solutions, respectively, using fruit extract of Tanacetum vulgare ; commonly found plant in Finland. The process for the synthesis of AgNPs and AuNPs is rapid, novel and ecofriendly. Formation of the AgNPs and AuNPs were confirmed by surface plasmon spectra using UV–Vis spectrophotometer and absorbance peaks at 452 and 546 nm. Different tansy fruit extract concentration (TFE), silver and gold ion concentration, temperature and contact times were experimented in the synthesis of AgNPs and AuNPs. The properties of prepared nanoparticl…
Motional Resistance Evaluation of the Quartz Crystal Microbalance to Study the Formation of a Passive Layer in the Interfacial Region of a Copper|Dil…
2015
A hyphenated technique based on vis–NIR spectroscopy and electrochemical quartz crystal microbalance with motional resistance monitoring was employed to investigate the dissolution of copper in acid media. Changes in motional resistance, current, mass, and absorbance during copper dissolution allow the evolution of the interfacial region of copper|diluted sulfuric solution to be understood. In particular, motional resistance is presented in this work as a useful tool to observe the evolution of the passive layer at the interface. During the forced copper electrodissolution in sulfuric solution, SO4(2–) favors the formation of soluble [Cu(H2O)6]2+. On the contrary, OH– involves the formation…
Clean method for the simultaneous determination of propyphenazone and caffeine in pharmaceuticals by flow injection Fourier transform infrared spectr…
1997
A procedure is proposed for the simultaneous FTIR determination of propyphenazone (PFZ) and caffeine (CAF) in pharmaceuticals. The method involves the dissolution of the active principles in CHCl 3 , followed by filtration of sample solutions to remove the excipients. PFZ is then determined by absorbance measurements at 1595 cm - 1 , using a baseline established between 2000 and 890 cm - 1 , and CAF by using the first-derivative values at 1712 cm - 1 , using solutions of PFZ and CAF for external calibration. The method was applied in both the stopped-flow and flow-injection modes, providing precise and accurate results for the analysis of real samples. The incorporation of a distillation un…
Fourier transform infrared analysis of paint solvents
1991
Abstract The composition of solvent mixtures employed in the paint industry was determined by Fourier transform infrared spectrometry. A procedure based on the use of the ratio between the absorbance of characteristic bands of each component permits the ratio between two solvents in a binary mixture to be determined, independently of the thickness of the sample film. Typical mixtures of xylol with butan-1-ol and with butyl acetate (xylol=mixture of o-, m- and p-xylenes) were used as model systems to develop the proposed procedure and the accuracy was determined using synthetic formulations. Another possible application of the procedure is the characterization of azeotropic mixtures.
Artificial neural network for quantitative determination of total protein in yogurt by infrared spectrometry
2009
Abstract A method has been introduced for quantitative determination of protein content in yogurt samples based on the characteristic absorbance of protein in 1800–1500 cm− 1 spectral region by mid-FTIR spectroscopy and chemometrics. Successive Projection Algorithm (SPA) wavelength selection procedure, coupled with feed forward Back-Propagation Artificial Neural Network (BP-ANN) model was the benefited chemometric technique. Relative Error of Prediction (REP) in BP-ANN and SPA-BP-ANN methods for training set was 7.25 and 3.70 respectively. Considering the complexity of the sample, the ANN model was found to be reliable, while the proposed method is rapid and simple, without any sample prepa…
Organization of the pigment molecules in the chlorophyll a/c light-harvesting complex of Pleurochloris meiringensis (xanthophyceae). Characterization…
1997
Abstract By the aid of circular dichroism (CD), absorbance and fluorescence spectroscopy, we studied the molecular organization of the pigment molecules in cells, isolated chloroplasts and the chlorophyll a / c light-harvesting complex (LHC) associated with photosystem II of the chlorphyll c -containing alga, Pleurochloris meiringensis . In cells and chloroplasts, similarly to higher plant chloroplasts, a (+) 693 nm CD band accompanied by a tail outside the absorbance indicated a long-range chiral organization of the chlorophyll molecules. The LHCII of these algae exhibited an intense negative CD band at 679 nm. However, in contrast to the chlorophyll a / b LHCII of higher plants, where the…