Search results for "Photometry"
showing 10 items of 797 documents
High-Performance TiO2 Nanoparticle/DOPA-Polymer Composites
2014
Many natural materials are complex composites whose mechanical properties are often outstanding considering the weak constituents from which they are assembled. Nacre, made of inorganic (CaCO 3 ) and organic constituents, is a textbook example because of its strength and toughness, which are related to its hierarchical structure and its well-defi ned organic–inorganic interface. Emulating the construction principles of nacre using simple inorganic materials and polymers is essential for understanding how chemical composition and structure determine biomaterial functions. A hard multilayered nanocomposite is assembled based on alternating layers of TiO 2 nanoparticles and a 3-hydroxytyramine…
Oral intake of cadmium, cobalt, copper, iron, lead, nickel, manganese and zinc in the university student's diet.
1993
A duplicate diet meal study was carried out with a group of university students living in a hostel, in order to estimate the intake of Zn, Cd, Co, Cu, Fe, Mn, Ni and Pb. Zn, Cu, Fe, Mn and Ni were determined by flame atomic absorption spectrophotometry and Cd, Co and Pb by graphite furnace atomic absorption spectrophotometry after a nitric acid wet digestion procedure. The estimated intake values from the contents of breakfast, lunch, dinner and drinks were compared with the values of the Provisional Tolerable Daily Intake (PTDI) in the case of Cd and Pb, Recommended Dietary Allowances (RDA) of Co, Fe and Zn and Estimated Safe and Adequate Dietetic Daily Intake (ESADDI) of Cu and Mn. Neithe…
Purification and spectroscopic studies on catechol oxidases from Lycopus europaeus and Populus nigra: evidence for a dinuclear copper center of type …
1999
We purified two catechol oxidases from Lycopus europaeus and Populus nigra which only catalyze the oxidation of catechols to quinones without hydroxylating tyrosine. The molecular mass of the Lycopus enzyme was determined to 39,800 Da and the mass of the Populus enzyme was determined to 56,050 Da. Both catechol oxidases are inhibited by thiourea, N-phenylthiourea, dithiocarbamate, and cyanide, but show different pH behavior using catechol as substrate. Atomic absorption spectrosopic analysis found 1.5 copper atoms per protein molecule. Using EPR spectroscopy we determined 1.8 Cu per molecule catechol oxidase. Furthermore, EPR spectroscopy demonstrated that catechol oxidase is a copper enzym…
Spectrophotometric investigation of the binding of vitamin E to water-containing reversed micelles.
2002
The distribution constants of vitamin E partitioned between apolar organic phase and water-containing reversed micelles of sodium bis (2-ethylhexyl) sulfosuccinate (AOT), didodecyldimethylammonium bromide (DDAB), soybean phosphatidylcholine (lecithin) and tetraethylene glycol monododecyl ether (C12E4) have been evaluated by a spectrophotometric method. The results suggest that in the presence of domains from apolar organic solvent to surfactant and to water, vitamin E is partitioned between the micellar palisade layer and the organic solvent and also that its binding strength to reversed micelles depends mainly by specific interactions between the head group of vitamin E and that of the sur…
Analytical methodologies for atomic spectrometric determination of metallic oxides in UV sunscreen creams.
2000
In this study, methodologies for determining titanium oxide, zinc oxide and iron oxide are proposed and assayed in commercial sunscreen products. The proposed methodology for TiO2, determination in sunscreens is based on a microwave-assisted treatment for digesting the organic components in a closed teflon reactor in presence of HNO3 and HCl. Titanium is determined by inductive coupled plasma emission spectrometry (ICP-AES). The proposed methodologies for measuring ZnO and Fe2O3 are based on a sample emulsification in water with a non ionic tensioactive and IBMK, followed by Zn and Fe determination by flame atomic absorption spectrometry (FAAS). The methodologies allow a precise and accurat…
Exposure to increased ambient ultraviolet B radiation has negative effects on growth, condition and immune function of juvenile Atlantic salmon (Salm…
2008
Atlantic salmon (Salmo salar) parr were exposed in two outdoor experiments, ranging in duration from 52 to 137 days, to spectral treatments: (1) natural sunlight (=present ambient UVB level), (2) solar radiation supplemented with enhanced UVB radiation from lamps simulating 20% or 8% stratospheric ozone loss or (3) UVB-depleted sunlight achieved by screening with Mylar-D film. The growth, condition and immune function of the salmon were quantified after treatments. Exposure to enhanced UVB radiation retarded growth, and decreased hematocrit value and plasma protein concentration. Further, enhanced UVB radiation affected plasma immunoglobulin concentration. The results demonstrate that juven…
Calcium-dependent conformational changes of membrane-bound Ebola fusion peptide drive vesicle fusion
2003
AbstractThe fusogenic subdomain of the Ebola virus envelope glycoprotein is an internal sequence located ca. 20 residues downstream the N-terminus of the glycoprotein transmembrane subunit. Partitioning of the Ebola fusion peptide into membranes containing phosphatidylinositol in the absence of Ca2+ stabilizes an α-helical conformation, and gives rise to vesicle efflux but not vesicle fusion. In the presence of millimolar Ca2+ the membrane-bound peptide adopts an extended β-structure, and induces inter-vesicle mixing of lipids. The peptide conformational polymorphism may be related to the flexibility of the virus–cell intermembrane fusogenic complex.
The lineshape of the electronic spectrum of the green fluorescent protein chromophore, part I: gas phase.
2014
The vibronic spectra of the green fluorescent protein chromophore analogues p-hydroxybenzylidene-2,3-dimethylimidazolinone (HBDI) and 3,5-tert-butyl-HBDI (35Bu) are similar in the vacuum, but very different in water or ethanol. To understand this difference, we have computed the vibrationally resolved solution spectra of these chromophores, using the polarizable continuum model (PCM) to account for solvent effects on the (harmonic) potential energy surfaces (PES). In agreement with experiment, we found that the vibrational progression increases with the polarity of the solvent, but we could neither reproduce the broadening, nor the large difference between the absorption spectra of HBDI and…
Determination of ascorbic acid in plasma and urine by high performance liquid chromatography with ultraviolet detection.
1999
Abstract A reliable simple reversed-phase liquid chromatographic method for the routine determination of ascorbic acid in plasma and urine with ultraviolet detection is described. This method enables the complete separation of the ascorbic acid peak from others with a recovery of above 95 % within 8 minutes. The method can be used for analysing multiple samples within a day. In addition, the storage conditions and stability of ascorbic acid in plasma and urine were investigated. Samples of plasma and urine can be stored on ice in darkness for at least 60 min without reduction of ascorbic acid concentration. Prepared samples can be stored in darkness at 4 °C for at least 120 min and in liqui…
Spectrophotometric determination of vitamin C using the copper(II)-nioxime-ascorbic acid system following stabilization in a propylene glycol medium
1989
Abstract A spectrophotometric method for the determination of Vitamin C is proposed. The procedure is based on formation and stabilization of the ternary complex Cu(II)-nioxime-ascorbic acid in 80% ( v v ) propylene glycol-water medium. The method has a high degree of tolerance for the determination of ascorbic acid in the presence of other active substances or excipients likely to be present along with vitamin C in pharmaceutical formulations. The suggested method has proved to be rapid and precise and has been successfully applied to different commercial pharmaceutical preparations of vitamin C. Precision, measured on the relative standard deviation, did not exceed 0.73%.