Search results for "absorption spectroscopy"

Effect of Pre-Reduction on the Properties and the Catalytic Activity of Pd/Carbon Catalysts: A Comparison with Pd/Al2O3

2013

The effect of pre-reduction in solution with chemical reagents on the catalytic performance and catalyst properties of Pd/carbon catalysts was systematically investigated with a multitechnique approach. The results are critically discussed in comparison to those recently obtained on analogous Pd/alumina catalysts. It was proved that the Pd phase on the carbon surface is characterized by a high mobility, opposite to what occurs on alumina. As a result, the Pd particles on carbon aggregate together during pre-reduction, with a consequent decrease in available metal surface. Pd particles remain aggregated also in reaction conditions; the decreased Pd dispersion negatively affects the catalyst …

Dialysability of Calcium, Iron, and Zinc in Beans, Chick Peas, and Lentils

2002

Thermodynamic studies of iron(III) complex of some new dihydroxamic acids model of rhodotorulic acid

2018

Abstract The objective of this research is to elucidate the coordination chemistry and the structure of complexes formed with siderochelates organic ligands and the physico-chemical studies of iron(III) complexation. Three dihydroxamic acids synthesized ((LCyEt)2−, (LCyPr)2− and (LO)2−) mimicking a fungal siderophore, rhodotorulic acid. They were evaluated with iron(III) chelation by potentiometric and spectrophotometric titrations in 0.1 M KNO3. These measurements revealed the formation of dileptic and trileptic complexes in excess ligand conditions. The chemical model includes five species of [Fem(L)lHh](3m−2l+h)+ with general formula: [Fe(L)]+, [Fe(L)(OH)], [Fe(L)(OH)2]−, [Fe(L)2H] and […

Towards highly luminescent phenylene vinylene films

1996

Abstract Fluorescence and electronic absorption spectra, fluorescence decay curves and fluorescence quantum yields of a series of oligo (p-phenylene vinylenes) are investigated in solution, nanoaggregates and vapour-deposited or cast ultrathin films. The film constituting molecules are varied in chain length and modified by electron donating and withdrawing substituents and bulky alkyl spacers. PPP-MO calculations serve to rationalize the resulting spectral changes. In dilute solutions, fluorescence yields of the short oligomers with alkyl or oxyalkyl substituents approach the region of unity. The yields decrease with chain length, reaching a long-chain limit of ΦF=0.4–0.7. Introduction of …

Effects of metal–ligand coordination on the self-assembly behaviour of a crown ether functionalised perylenetetracarboxylic diimide

2012

A novel perylenetetracarboxylic diimide (PDI) derivative, N,N′-di(4′-benzo-15-crown-5-ether)-1,7-di(4-tert-butyl-phenoxy)perylene-3,4;9,10-tetracarboxylic diimide (CRPDI), has been synthesised and characterised. Dimerisation of CRPDI is induced by the presence of K+ in CHCl3 or spontaneously occurs in methanol, as revealed by absorption and emission spectroscopy. In particular, the formation of co-facial dimer in the presence of K+ proceeds in a three-stage process, as indicated by absorption spectroscopy. The belt- and rope-like nanostructures of CRPDI fabricated from methanol and CHCl3 solution in the presence of K+ are obtained by scanning electron microscopy. Furthermore, the conductivi…

Odd-even chain length-dependent order in pH-switchable self-assembled layers.

2004

The reversible self-assembly of a series of bipolar amphiphiles, alpha,omega-bis(3- or 4-amidinophenoxy)alkanes (chain length n = 5-12), on mercaptoalkanoic acid-functionalized gold surfaces (chain length n = 10, 11, 14, 15) has been studied by in-situ ellipsometry, IR reflection absorption spectroscopy (IRAS), and atomic force microscopy (AFM). The layer order, amphiphile orientation, and tendency to form bilayers depends on the position of the amidine substituent, the alkyl chain length of both the amidine amphiphile and the underlying acid self-assembled monolayer (SAM), and whether the amidine alkyl chain contained an even or odd number of methylene groups. Thus, para-substituted bisben…

Photochemical holes under pressure: Compressibility and volume fluctuations of a protein

1991

From the pressure induced frequency shift of photochemical holes burnt into mesomorphyrin substituted horseradish peroxidase, we determined the compressibility of the protein and the vacuum frequency of the chromophore. From the compressibility, an estimation of the volume fluctuations of the biomolecule is possible.

Microwave-assisted distillation of iodine for the indirect atomic absorption spectrometric determination of iodide in milk samples

2001

To complete these microwave distillation studies, a method for iodide determination in milk-type samples is proposed. The iodide contained in the sample is oxidized to iodine, which is distilled by means of microwave energy and reduced back to iodide. This iodide is combined with Hg(II) and 2,2′-dipyridyl to give an ion pair, which is selectively extracted into IBMK. Mercury is determined in the extract by ETAAS in order to determine iodide. The yield of the distillation process (100%) was evaluated using the Sandell–Kolthoff reaction. In addition, for the solvent extraction, no buffer was needed; 3/5 was the best phase ratio (organic/aqueous); 30 s was the shaking time and the extracts wer…

Metachromatic behavior of methylorange in the presence of ionenes

1994

The addition of different ionenes, polycations with defined structure and charge distances, to methylorange1 in very dilute solutions of water resulted in an observable shift of the absorption maxima from 464 nm to shorter wavelengths. The extent of this so-called metachromasy effect was found to be dependent on the nature of the hydrophobic unit of the polymer backbone. The comparison of UV/VIS spectra's of these solutions with the absorption of a film of a model substance — a dication with methylorange as counteranion — lead to the conclusion that ionenes undergo an exchange of the counteranions when added to a dilute solution of methylorange. Precipitation is slowed down, but the absorpt…

Complexation of phosphine ligands with peracetylated β-cyclodextrin in supercritical carbon dioxide: Effect of temperature and cosolvent on the equil…

2009

Abstract The interaction between peracetylated-β-cyclodextrin and tert-butyl and adamantyl functionalized triphenylphosphine derivatives was studied in supercritical carbon dioxide (scCO 2 ) based solvent media by UV–vis spectroscopy. The equilibrium constant for a 1:1 complexation reaction was obtained from titration spectra both in pure carbon dioxide and in the presence of methanol as a cosolvent in the temperature range 308–323 K to estimate the internal energy and entropy of the inclusion equilibrium. The values of the equilibrium constants were found significantly smaller than those obtained in aqueous solution with analogous phosphines and substantially independent of the nature of t…