Search results for " Spectroscopy"
showing 10 items of 6851 documents
Effect of Anions and Oxygen on the Kinetics of the Anodic Dissolution of Nickel
2006
An electrochemical impedance spectroscopy study on electrochemical dissolution and active/passive transition of polycrystalline nickel in acid media has been performed in sulfate and nitrate aqueous solutions. Oxygen favors the nickel electrodissolution in a nitrate aqueous acid medium, but the dissolution decreases in the sulfate medium due to nickel passivation. The anion and oxygen effect is analyzed from a model where Ni(I) species are stabilized on the Ni metal surface and all anions present in the solution compete in the neutralization of Ni(I) and Ni(II) and in the solubilization of Ni(II).
Conductimetric study of struvite crystallization in water as a function of pH
2017
Abstract The main objective of this work was to investigate the best pH for phosphorus removal from synthetic aqueous solutions using chemical precipitation of struvite, at constant temperature. The experimental approach, developed in the present study, consisted to precipitate struvite in synthetic wastewater containing PO 4 3− , NH 4 + and Mg 2+ ions in an equal molar ratio, using a stirred tank with continuous monitoring by conductimetry, at 25 °C. Different laboratory experiments were used to evaluate the effects of pH in the range of 8.5 till 11.8, on size, shape, and purity of the precipitated crystals. Struvite crystals were characterized by Infrared spectroscopy (FTIR), scanning ele…
Single Molecule Spectroscopy of Oriented Recombinant Trimeric Light Harvesting Complexes of Higher Plants
2002
The bleaching dynamics of reconstituted single light-harvesting chlorophyll a/b investigated. The complexes containing one histidine6 tag per monomeric subunit were immobilised predominantly in a defined orientation with their symmetry axis perpendicular to a Ni-ion-containing surface allowing for the first time the examination of single LHCIIb in an aqueous environment. Most complexes exhibit photobleaching in one step, indicating coupling between the monomeric subunits leading to an energy transfer between adjacent subunits. Differences in bleaching behaviour between these and previous observations with single LHCIIb are discussed.
Structural and Vibrational Study of a New Mixed Dipotassium Hydrogenselenate Dihydrogenphosphate K2(HSeO4)1.5 (H2PO4)0.5.
2006
Abstract Ongoing studies of the KHSeO4–KH2PO4 system, aimed at developing novel proton conducting solids, resulted in the new compound K2(HSeO4)1.5(H2PO4)0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals have been prepared by slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by X-ray single analysis (performed at room temperature), which revealed that K2(HSeO4)1.5(H2PO4)0.5 (KHSeP) crystallizes in space group P 1 ¯ with lattice parameters: a = 7.417(3) A, b = 7.668(2) A, c = 7.744(5) A, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. The compound has a unit cell volume 416.8(3) A3 and two formula unit…
Spectroscopic study of molecular associations between riboflavin and some (dihydro) β-carboline derivatives
1993
Abstract The spectrophotometric and thermodynamic properties of molecular complexes of riboflavin (RFN) with some dihydro β-carboline derivatives have been investigated by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The molecular associations have been examined by means of eletronic absorption spectra, since in each, a new charge transfer-like band has been located, and also by observing the variation of the fluorescence emission of RFN on the solutions. The formation constants for the molecular complexes were determined from absorption data, using the Forster—Hammick—Wardley method. The quenching phenomenon observed in RFN fluorescence is related…
29Si NMR and Small-Angle X-ray Scattering Studies of the Effect of Alkaline Ions (Li+, Na+, and K+) in Silico-Alkaline Sols
1999
Alkali−silica reactions (ASR) which occur in concrete can be simulated in laboratory by destabilization of silico-alkaline aqueous solutions by addition of calcium ions. The relevant features of the reaction depend on the nature of alkaline ions (Li+, Na+, or K+) and on the silica/alkaline ratios which fix the distribution of the molecular species in the precursor solution. 29Si NMR spectroscopy and small-angle X-ray scattering (SAXS) techniques were used to study the structure and size distribution of molecular and colloidal species in sols with different silica/alkaline molar ratio and several types of alkaline ions. Experimental SAXS curves were simulated using a simple structural model …
Conformational investigations of bis(α-aminoalkyl)phosphinic acids and studies of the stability of their complexes with Cu(II)
2008
Abstract Conformational investigations of a group of bis(α-aminoalkyl)phosphinic acids were performed by use of NMR spectroscopy and theoretical calculations. In the case of one of the studied compounds, substituted with aminobenzyl and amino(p-chlorobenzyl) moieties, a pH-dependent equilibrium between conformers, stabilized by intermolecular hydrogen bonds was observed. Potentiometric studies proved that these molecules formed stable complexes with copper(II) ions, where stoichiometry was 1:1 and 1:2 depending on pH of their aqueous solution.
Attenuated total reflectance infrared determination of sodium nitrilotriacetate in alkaline liquid detergents
2005
Abstract An attenuated total reflectance infrared (ATR–FTIR) method has been developed for the direct determination of the chelating agent sodium nitrilotriacetate (NTA) in high pH cleaning formulations. Aqueous samples and standards were placed directly on the diamond ATR cell without any pre-treatment and FTIR spectra were recorded between 4000 and 600 cm−1. Measurement conditions were evaluated. Results obtained for five different commercial formulations containing from 6.22 to 9.25% (w/w) of NTA were in good agreement with the manufacturer's declared content (differences between 3.2 and −3.7%). Recovery studies evidenced the accuracy of the developed method, having found values between …
N-Alkyl Ammonium Resorcinarene Chloride Receptors for Guest Binding in Aqueous Environment
2016
Host systems with guest binding ability in water and/or biological fluids are a current challenge in supramolecular host–guest chemistry. Here we present the first syntheses of water-soluble N-ethanol ammonium resorcinarene chlorides (NARCls) with terminal hydroxyl groups at the upper rim. The NARCls possess deep cavities and are shown to bind a variety of guest molecules such as linear and cyclic alkanes, linear halogenated alkanes, and aromatic fluorophores (naphthalene, p-(phenylazo)phenol) in water through hydrophobic interactions, as well as 1,4-dioxane (a water soluble guest) via hydrogen bonds. The receptors are monomeric in aqueous media and form 1:1 host–guest complexes with bindin…
Micro-Raman spectroscopy of pigments contained in different calcium carbonate polymorphs from freshwater cultured pearls
2008
The metastable calcium carbonate polymorph vaterite has recently been found to occur commonly in freshwater cultured pearls from Japan and China. Organic pigment molecules in these vaterite regions of freshwater cultured pearls were analysed by resonance and near-resonance micro-Raman spectroscopy, in single spectra and in mapping modes and are compared with their aragonitic counterparts. Four different excitation wavelengths (487.9, 514.5, 532.2 and 632.8 nm) were used, resulting in differential increase of resolution for the pigments. Although vaterite areas were always lightly coloured (light yellow, light brown or white), ten different pigments were identified and a single colour is for…