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71.
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Dendrimer-encapsulated nanoparticles (DENs) containing averages of 55, 147, and 225 Pt atoms immobilized on glassy carbon electrodes served as the electroactive surface for the underpotential deposition (UPD) of a Cu monolayer. This results in formation of core@shell (Pt@Cu) DENs. Evidence for this conclusion comes from cyclic voltammetry, which shows that the Pt core DENs catalyze the hydrogen evolution reaction before Cu UPD, but that after Cu UPD this reaction is inhibited. Results obtained by in situ electrochemical X-ray absorption spectroscopy (XAS) confirm this finding. 相似文献
73.
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75.
Abate A Brenna E Costantini A Fuganti C Gatti FG Malpezzi L Serra S 《The Journal of organic chemistry》2006,71(14):5228-5240
Enantiomerically pure 1,3-diols 1-3 were obtained by a chemoenzymatic approach (lipase PS from Burkholderia cepacia). These diols were converted into useful chiral synthons, which could be considered homologues of glyceraldehyde and glyceric acid acetonides. Applications of these synthons to the de novo synthesis of sugars and preparation of conagenin carboxylic moiety were shown. Hydroxy ketone 4 was chosen as a model system for another synthetic evolution: it was obtained in enantiomerically pure form by enzymatic resolution and converted into chiral tetrahydropyranes, such as the stereoisomers of the commercial fragrance Gyrane. 相似文献
76.
We consider local smoothing of datasets where the design space is the d-dimensional (d≥1) torus and the response variable is real-valued. Our purpose is to extend least squares local polynomial fitting to this situation. We give both theoretical and empirical results. 相似文献
77.
It is shown that the Schwarzschild solution in general relativity, reconsidered adding to the vacuum a massless scalar field, is stable to perturbations from radiation fields of spin s = 0, ±1/2, ±1, ±2. 相似文献
78.
Brunella Cappello Clelia di Maio Maria Iervolino Agnese Miro 《Journal of inclusion phenomena and macrocyclic chemistry》2007,59(3-4):237-244
Investigation on the influence of hydroxypropyl methylcellulose (HPMC) on solubility and dissolution properties of celecoxib/hydroxypropyl-β-cyclodextrin
system was carried out, with the ultimate goal of enhancing the drug bioavailability. 1H-NMR and 13C-NMR spectroscopy were first performed to elucidate the type of interactions between celecoxib (CEL) and hydroxypropyl-β-cyclodextrin
(HP-β-CD). Then, solubility studies in the absence and in the presence of HPMC were carried out in aqueous solution. After
heating in autoclave of CEL/HP-β-CD/HPMC suspensions a synergistic increasing effect on the aqueous solubility of CEL was
observed. In fact, the presence of both HP-β-CD (0.05 M) and HPMC (0.25% w/v) gave rise to a 330-fold CEL solubility increase,
whereas the cyclodextrin alone provided a 34-fold increase. Gibbs free energy values calculated from phase solubility data
were all negative, indicating the spontaneous nature of CEL solubilization, and they decreased in the presence of HPMC, demonstrating
that the solubilization conditions became more favorable. CEL/HP-β-CD and CEL/HP-β-CD/HPMC solid systems (physical mixtures
and coevaporated products) were characterized by differential scanning calorimetry and infrared spectroscopy. Results suggested
that the coevaporation method yields a high degree of amorphous entities and indicated the formation of a CEL/HP-β-CD complex
in the coevaporated products. The positive effect of HPMC is particularly evident when looking at the CEL dissolution rate
from the binary and ternary solid systems. Specifically, the percent of CEL dissolved after 10 min. resulted 84.21% for ternary
coevaporated product and 50.18% for binary coevaporated product with respect to 13.10% for the drug alone. 相似文献
79.
Servili M Selvaggini R Esposto S Taticchi A Montedoro G Morozzi G 《Journal of chromatography. A》2004,1054(1-2):113-127
Hydrophilic phenols are the most abundant natural antioxidants of virgin olive oil (VOO), in which, however, tocopherols and carotenes are also present. The prevalent classes of hydrophilic phenols found in VOO are phenolic alcohols, phenolic acids, flavonoids, lignans and secoiridoids. Secoiridoids, that include aglycon derivatives of oleuropein, demethyloleuropein and ligstroside, that are present in olive fruit, are the most abundant phenolic antioxidants of VOO. The sensory and healthy proprieties of VOO hydrophilic phenols as well as the agronomic and technological parameters that affect their concentration in the oil are discussed in this paper. 相似文献
80.
The electrochemical determination of aqueous Hg(II) by anodic stripping voltammetry (ASV) at a solid gold electrode is described. The aim of this work is to optimise all factors that can influence this determination. Potential wave forms (linear sweep, differential pulse, square wave), potential scan parameters, deposition time, deposition potential and surface cleaning procedures were examined for their effect on the mercury peak shape and intensity. Five supporting electrolytes were tested. The best responses were obtained with square wave potential wave form and diluted HCl as supporting electrolyte. Electrochemical and mechanical surface cleaning, aimed at removing the amount of mercury deposited onto the gold surface, were necessary for obtaining a good performance of the electrode. Response linearity, repeatability, accuracy and detection limit were also evaluated. 相似文献