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21.
22.
Maurizio Lanfranchi Antonio Tiripicchio Giuliano Giuliano Mauro Ghedini 《Transition Metal Chemistry》1980,5(1):21-25
Summary The structure of [Ir(NCMe)3(NO)(PPh3)2][PF6]2 has been ] determined by x-ray methods. Crystals are orthorhombic, space groupPca 21 , witha = 21.753(14),b = 11.678(10),c = 18.474(12) Å and Z = 4. The structure has been solved from diffractometer data and refined by full-matrix leastsquares to R = 0.076 for 2776 observed reflections. The cation is a hexacoordinate and not a pentacoordinate species as expected. The extra acetonitrile molecule,trans to the nitrosyl ligand, is much more weakly bound to the metal atom [Ir-N 2.360(26) against 1.965(20) and 1.912(14) Å for the other two acetonitriles]. The nitrosyl is bent [Ir-N-O 111(1)° Å] and acts as the formally one-electron donor NO–. 相似文献
23.
Heilemann M Tinnefeld P Sanchez Mosteiro G Garcia Parajo M Van Hulst NF Sauer M 《Journal of the American Chemical Society》2004,126(21):6514-6515
We demonstrate the synthesis and spectroscopic characterization of an unidirectional photonic wire based on four highly efficient fluorescence energy-transfer steps (FRET) between five spectrally different chromophores covalently attached to double-stranded DNA. The DNA-based modular conception enables the introduction of various chromophores at well-defined positions and arbitrary interchromophore distances. While ensemble fluorescence measurements show overall FRET efficiencies between 15 and 30%, single-molecule spectroscopy performed on four spectrally separated detectors easily uncovers subpopulations that exhibit overall FRET efficiencies of up to approximately 90% across a distance of 13.6 nm and a spectral range of approximately 200 nm. Fluorescence trajectories of individual photonic wires show five different fluorescence intensity patterns which can be ascribed to successive photobleaching events. 相似文献
24.
C. Joly S. Goizet J. C. Schrotter J. Sanchez M. Escoubes 《Journal of membrane science》1997,130(1-2):63-74
The effect of introduction of silica particles prepared by the sol-gel technique on the gas transport properties of a polyimide film was studied. The sorption and permeation of N2, O2, CO2, H2 and CH4 were studied and correlated with morphological changes in the polymer structure. From sorption isotherms, we observed that the composite membrane presents higher solubility coefficients than the polyimide one. The solubility coefficient ratio between the composite and the polyimide is about 1.5–2.0. The isotherms were analyzed in terms of the dual mode sorption. The Henry's coefficient and the Langmuir's affinity and saturation constants were obtained allowing to calculate the Langmuir to Henry concentration ratios as function of the gas pressure. These ratios decrease until zero within a certain pressure range as long as the Langmuir's mode is acting and they are higher for the polyimide membrane when compared with the composite one. This study was completed with calorimetric measurements during the sorption. The gas interaction energy in kJ/mol decreases within the same pressure range as previously described. The measured energies are higher for the polyimide film when compared with the composite one because the polyimide membrane presents a stronger energetic effect caused by a higher Langmuir's contribution. From permeation studies at 3.155 Pa, the composite membrane showed higher permeability coefficients and permselectivities than the polyimide one. All these results were explained, taking into account the difference on the imidization degree of both membranes and the morphological changes which may be induced by the silica nodules in the organic/inorganic interphases. 相似文献
25.
Rudovsky J Hermann P Botta M Aime S Lukes I 《Chemical communications (Cambridge, England)》2005,(18):2390-2392
A marked increase of relaxivity has been observed upon rigidifying the internal frame of Gd-containing PAMAM dendrimers: the effect has been attained by either protonation of the dendrimer or by forming supramolecular adducts with cationic polyaminoacids. 相似文献
26.
Luis C. Mendes Andrea D. Tedesco Mauro S. Miranda Marcia R. Benzi Beatriz S. Chagas 《Polymer Testing》2005,24(8):963-968
In this third work, we evaluated the degree of conversion (DC) versus depth of dental filling composite named Prodigy Condensable™ using infrared spectroscopy. Confirming previous results, there was a gradual reduction of DC with increasing depth but the composite exhibited extreme values of DC, an upper value (45.9%) on the surface and a lower one (6.1%) at a depth of 5 mm. The composite presented the worst performance among materials studied. The composite formulation was 80% of inorganic fillers and BisfenolA/dimethacrylate (BisGMA) (18%)/triethyleneglycoldimethacrylate (TEGDMA) (2.0%) as monomers. As stated before, type/ratio/viscosity of monomers and type, amount, size and size distribution of fillers all together had an important role in the cure reaction contributing to the final performance of the composite. 相似文献
27.
Stefano Vecchio Alessia Catalani Vanessa Rossi Mauro Tomassetti 《Thermochimica Acta》2004,420(1-2):99-104
The thermal behaviour of acetanilide (Ac) and two of its analogues, namely the para-ethoxyacetanilide (p-Eto Ac) and the para-bromoacetanilide (p-Br Ac), which are used as analgesics in the pharmaceutical industry was studied with a simultaneous TG/DSC unit. The examined analgesics showed two endothermic DSC peaks due to melting and vaporization. By combining the experimental TG data with the corresponding reference vapour pressure data obtained with the Antoine equation the plot of P versus v was derived. From the slope of this equation the constant k-value was determined for Ac. Then, using the same k-value the vapour pressures of p-Eto Ac and p-Br Ac were determined in the same temperature range. The vaporization enthalpies for all the studied compounds were obtained from different methods and a very good agreement was found. Vaporization follows a zero-order kinetics. The activation energy of vaporization (Evap) was calculated from the dynamic TG experiments, using the Arrhenius equation. 相似文献
28.
Kujawa P Moraille P Sanchez J Badia A Winnik FM 《Journal of the American Chemical Society》2005,127(25):9224-9234
The layer-by-layer growth of multilayer assemblies of two polysaccharides, the polyanion hyaluronan (HA) and the polycation chitosan (CH), was investigated using atomic force microscopy (AFM) and surface plasmon resonance (SPR) spectroscopy, with primary emphasis on the effect of the polysaccharide molecular weights on the film thickness and surface morphology. The HA/CH multilayers exhibit an exponential increase of the optical film thickness with the number of deposited bilayers. We show that the multilayer thickness at a given stage depends on the size of both CH, the diffusing polyelectrolyte, and HA, the non-diffusing species. Assemblies (12 bilayers) of high molecular weight polysaccharides (HA, 360,000; CH, 160,000) were twice as thick (approximately 900 nm vs approximately 450 nm) as those obtained with low molecular weight polymers (HA, 30,000; CH, 31,000), as assessed by AFM scratch tests. The exponential growth rate is the same for the high and low molecular weight pairs; the larger film thicknesses observed by SPR and by AFM arising from an earlier onset of the steep exponential growth phase in the case of the high molecular weight pair. In all cases, isolated islets form during the deposition of the first CH layer onto the underlying HA. Upon further film growth, individual islets coalesce into larger vermiculate features. The transition from distinct islands to vermiculate structures depends on the molecular weights of the polysaccharides and the lower molecular weight construct presents larger worm-like surface domains than the high molecular weight pair. 相似文献
29.
Evelina Liarou Yisong Han Ana M. Sanchez Marc Walker David M. Haddleton 《Chemical science》2020,11(20):5257
Rapidly self-deoxygenating Cu-RDRP in aqueous media is investigated. The disproportionation of Cu(i)/Me6Tren in water towards Cu(ii) and highly reactive Cu(0) leads to O2-free reaction environments within the first seconds of the reaction, even when the reaction takes place in the open-air. By leveraging this significantly fast O2-reducing activity of the disproportionation reaction, a range of well-defined water-soluble polymers with narrow dispersity are attained in a few minutes or less. This methodology provides the ability to prepare block copolymers via sequential monomer addition with little evidence for chain termination over the lifetime of the polymerization and allows for the synthesis of star-shaped polymers with the use of multi-functional initiators. The mechanism of self-deoxygenation is elucidated with the use of various characterization tools, and the species that participate in the rapid oxygen consumption is identified and discussed in detail.The rapidly self-deoxygenating Cu-RDRP in aqueous media is investigated. 相似文献
30.
Maurizio Lenarda Renzo Ganzerla Adriana Lisini Mauro Graziani Tristano Boschi 《Transition Metal Chemistry》1981,6(4):199-203
Summary Platinum(0) and palladium(0) complexes of the type: P2M(R1R2C=CR3R4) (P=trisubstituted phosphine; R1, R2, R3 and R4 are different groups having electron acceptor or electron donor properties; M=Pt or Pd) with so called pushpull olefins, have been prepared and characterized. In some cases unusual patterns in the n.m.r. spectra of olefinic protons were observed. The spectra were analyzed by computer simulation and general rules for ABMX patterns for this type of complexes are given. 相似文献