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321.
Summary The chelating behaviour of the system has been examined and compared in metal complexes of three different organic molecules in relation to the different geometry of the ligand and to the nature of the metal and of the counter-ion. Bond distances and angles, planarities, and vibrational bands of the system are discussed and correlated. 相似文献
322.
We prove several theorems that lend support to Greene's criterion for the existence or not of invariant circles in twist maps. In particular, we show that some of the implications of the criterion are correct when the Aubry-Mather sets are smooth invariant circles or uniformly hyperbolic. We also suggest a simple modification that can work in the case that the Aubry-Mather sets have nonzero Lyapunov exponents. The latter is based on a closing lemma for sets with nonzero Lyapunov exponents, which may have several other applications. 相似文献
323.
Paolo Crotti Gabriele Renzi Graziella Roselli Sandra Giuli Maria Rosaria Romano 《Tetrahedron》2007,63(25):5501-5509
The regioselectivity of the addition reaction of MeOH both in the condensed phase (MeOH/H2SO4) and in the gas-phase (MeOH/D3+) was examined in a series of activated aziridines. The results indicate that gas-phase operating conditions are particularly favorable for the occurrence of D+-mediated chelated bidentate species, which influence the regioselectivity of the opening process. In the condensed phase, the chelating MeOH/LiClO4 protocol turned out to be decidedly less effective for regioselectivity and also in determining the composition of the reaction mixture. 相似文献
324.
[reaction: see text] N-Mesyl aziridine 7alpha, a new activated vinyl aziridine derived from d-glucal, has been synthesized by cyclization of trans-N,O-dimesylate 6 with t-BuOK in anhydrous benzene. The reaction of 7alpha with alcohols, phenol, and monosaccharides (O-nucleophiles) leads to the corresponding 4-N-(mesylamino)-2,3-unsaturated-O-glycosides and disaccharides through a completely regioselective 1,4-addition process that proceeds with high or complete alpha-stereoselectivity. 相似文献
325.
Riccardo Pratesi Laura Ronchi Giovanna Cecchei Giuseppe Sbrana Maria Grazia Migliorini Corrado Vecchi Gianpaolo Donzelli 《Photochemistry and photobiology》1984,40(1):77-83
Abstract The Kubelka–Munk theory of radiation transfer is applied to determine the influence of skin optical losses on the efficiency of phototherapy of jaundice. Using a multi-layer model of the skin the photon absorption rate of bilirubin molecules is calculated for spectrally Gaussian light sources and fluorescent lamps used in phototherapy. Light absorption and scattering processes in the skin layers shift the optimum value of the peak excitation wavelength from λ= 453 nm (absorption maximum of bilirubin in vitro ) to λ= 480 nm. This suggests the clinical investigation of narrow-spectrum lamps emitting in the blue-green region of the spectrum. 相似文献
326.
Bacchi A Carcelli M Pelizzi C Pelizzi G Pelagatti P Rogolino D Tegoni M Viappiani C 《Inorganic chemistry》2003,42(19):5871-5879
Two novel photoactivatable Ca(2+) compounds were synthesized to achieve a fast concentration jump of calcium ions in solution; this is of paramount importance for investigating the physiological cellular response. The light-sensitive ligands 4-(2-nitrophenyl)-3,6-dioxaoctane dioic acid (H2L1) and 4-(4,5-dimethoxy-2-nitrophenyl)-3,6-dioxaoctane dioic acid (H2L2) were generated by multistep syntheses, and the corresponding calcium complexes, Ca1 and Ca2, were isolated and characterized. The solution equilibria of H2L1 and H2L2 with Ca2+ were investigated; for both ligands, the formation of a 1:2 Ca2+/ligand species is detected and the complete characterization is presented. The crystal structures of Ca1 and Ca2 were determined. In Ca1 the solid state assembly is attained by a polymeric association of [(CaL1(H2O))2(mu-OH2)] dimeric units. Each calcium ion coordinates four oxygen atoms of one ligand (two ethereal, one carboxylic, and one bridging carboxylic oxygen atom), one water molecule, one bridging water molecule, and a carboxylate group of the other ligand within the dimer. The octacoordination of the metal is completed by an interaction with the adjacent dimeric unit. The crystal structure of the complex Ca2 does not show a polymeric nature, but it is a centrosymmetric dimer. The coordination number of the metal ion is still 8:4 oxygen atoms of the ligand; 3 water molecules; 1 bridging carboxylate group. A preliminary study of the photochemical features of the complexes Ca1 and Ca2 is reported: photoexcitation by a nanosecond pulsed UV laser induces the cleavage of the ligand. This drastically reduces the affinity of the ligand toward Ca2+, which is then released in solution. 相似文献
327.
328.
Didier Gigmes Anouk Gaudel‐Siri SylvainR.A. Marque Denis Bertin Paul Tordo Paola Astolfi Lucedio Greci Corrado Rizzoli 《Helvetica chimica acta》2006,89(10):2312-2326
A series of stable 2,2‐disubstituted 3‐(phenylimino)indol‐1‐oxyls, the alkoxyamines 3 , were prepared, characterized, and tested as possible candidates in controlled radical polymerization (CRP). The sturctures of 3d and 10 were additionally solved by X‐ray diffraction. The lability of the N? O(C) and (N)O? C bonds of compounds 3 were compared, and the possibility of N? O vs. O? C bond cleavage was evaluated by thermal degradation, ESR spin trapping, MS experiments, and DFT calculations. Alkoxyamines with a primary‐ or secondary‐alkyl group bound to the O‐atom of the nitroxide function (hexyl and i‐Pr) mainly underwent (undesired) N? O bond homolysis. When the O‐alkyl radical was a tertiary or a benzyl group (crotonyl or styryl), O? C bond cleavage occurred as the main process, thus suggesting a possible use of these compounds in CRP processes. 相似文献
329.
Monti D Venanzi M Mancini G Natale CD Paolesse R 《Chemical communications (Cambridge, England)》2005,(19):2471-2473
The mode of aggregation of amphiphilised porphyrin derivatives bearing a chiral functionality is strongly affected by solvent composition; this results in the tuning of the supramolecular chirality of the porphyrin aggregates. 相似文献
330.