Browsing by Subject "Absorption"

Now showing 1 - 3 of 3
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    Investigating comproportionation in multielectron transfers via UV–visible spectroelectrochemistry: the electroreduction of anthraquinone-2-sulfonate in aqueous media
    (ACS Publications, 2022-08-22) Romay García, Luis; González Sánchez, Joaquín; Molina Gómez, Ángela; Laborda Ochando, Eduardo; Química Física; Facultad de Química
    UV–vis spectroelectrochemistry is assessed as a tool for the diagnosis and quantitative in situ investigation of the incidence of comproportionation in multielectron transfer processes. Thus, the sensitivity of the limiting current chronoabsorptometric signals related to the different redox states to the comproportionation kinetics is studied theoretically for different working modes (normal and parallel light beam arrangements) and mass transport regimes (from semi-infinite to thin layer diffusion). The theoretical results are applied to the spectroelectrochemical study of the two-electron reduction of the anthraquinone-2-sulfonate in alkaline aqueous solution, tuning the thermodynamic favorability of the comproportionation reaction through the electrolyte cation. The quantitative analysis of the experimental results reveals the occurrence of comproportionation in the three media examined, showing different kinetics depending on the cationic species in solution.
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    Synthesis and Photophysical Properties of Cyclometallated Pt(II) 1,2-Benzenedithiolate Complexes and Heterometallic Derivatives Obtained from the Addition of [Au(PCy3)]+ Units
    (American Chemical Society, 2012-04-13) Juliá Hernández, Fabio; Jones, Peter G.; González Herrero, Pablo; Química Inorgánica
    The cyclometalated compounds [Pt(C^N)(HC^N)Cl] [HC^N = 2-phenylpyridine (Hppy; 1a), 1-(4-tert-butylphenyl)isoquinoline (Htbpiq; 1b)] react with 1,2-benzenedithiol, t-BuOK, and Bu4NCl in a 1:1:2:1 molar ratio in CH2Cl2/MeOH to give the complexes Bu4N[Pt(C^N)(bdt)] [bdt = 1,2-benzenedithiolate; C^N = ppy (Bu4N2a), tbpiq (Bu4N2b)]. In the absence of Bu4NCl, the same reactions afford solutions of K2a and K2b, which react with [AuCl(PCy3)] to give the neutral heterometallic derivatives [Pt(C^N)(bdt){Au(PCy3)}] [C^N = ppy (3a), tbpiq (3b)]. The cationic derivatives [Pt(C^N)(bdt){Au(PCy3)}2]ClO4 [C^N = ppy (4a), tbpiq (4b)] are obtained by reacting 3a and 3b with acetone solutions of [Au(OClO3)(PCy3)]. The crystal structures of 3b and 4b reveal the formation of short Pt···Au metallophilic contacts in the range 2.929–3.149 Å. Complexes 3b, 4a, and 4b undergo dynamic processes in solution that involve the migration of the [Au(PCy3)]+ units between the S atoms of the dithiolate. Complexes Bu4N2a and 2b display a moderately solvatochromic band in their electronic absorption spectra that can be ascribed to a transition of mixed ML′CT/LL′CT character (M= metal; L = bdt; L′ = C^N; CT = charge transfer), while their emissions are assignable to transitions of the same orbital parentage but from triplet excited states. The successive addition of [Au(PCy3)]+ units to the anions 2a and 2b results in an increase in the absorption and emission energies attributable to lower highest occupied molecular orbital energies. Additionally, the characteristics of the absorption and emission spectra of the heterometallic derivatives indicate a gradual loss of LL′CT character in the involved electronic transitions, with a concomitant increase of the L′C and ML′CT contributions.
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    The nature and implication of intestinal endocrine cell changes in coeliac disease
    (Murcia : F. Hernández, 1998) El-Salhy, M.
    Coeliac disease is associated with intestinal lesion. This lesion causes architectural derangement of the mucosa in the form of villus atrophy, increased crypt length and increased volume of the lamina propria. Several changes in the intestinal endocrine cells have been reported over the years, e.g. the number of secretin cells and increased numbers of GIP, CCKIgastrin, motilin, and serotonin cells. There is no consensus about the nature of the changes in somatostatin-cells. It has been postulated that the changes in the endocrine cells are a selective process to meet the new demands exerted by the dramatic decrease in intestinal absorptive area. It has been speculated further that the changes in the endocrine cells would cause an incomplete digestion of the ingested food and its rapid elimination from the intestine. These changes may be responsible for the diarrhoea and steatorrhoea that occur in patients with coeliac disease.