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991.
Rino A. Michelin Paolo Sgarbossa Alessandro Scarso Giorgio Strukul 《Coordination chemistry reviews》2010,254(5-6):646-660
The Baeyer–Villiger oxidation of ketones to the corresponding esters or lactones is a valuable transformation that has been upgraded several times over the last century, from the original use of monopersulfuric acid as oxidant to more atom efficient and environmentally friendly oxidants such as hydrogen peroxide. The latter requires activation with organometallic complexes to explicate its oxidizing power. The catalytic version of the reaction can be achieved with several transition metal catalysts, but major differences are present among the various catalysts proposed in terms of scope of the reaction. In particular, most of the catalytic systems are active towards four-membered ring ketones leading to the corresponding substituted γ-butyro-lactones. PtII complexes characterized by the employment of chelating diphosphines turned out to be the most efficient in catalyzing the BV oxidation of a wider range of substrates, in particular cyclohexanones are suitable substrates and acyclic ketones can be converted into the corresponding esters, albeit with low turnover. As long as organometallic catalyzed BV reaction is concerned, PtII catalysts show the most versatile activity and selectivity. Such peculiar features are the result of the unique electronic properties of such metal combined with an easily tailored soft Lewis acid character modulated by the proper choice of the ancillary ligands. The enantioselective version of the reaction benefits from these properties and the compatibility of PtII species with water enabled the development of asymmetric catalytic BV reactions in water aided by the presence of micelles as dynamic self-assembled environments. 相似文献
992.
Lin K Lebedev OI Van Tendeloo G Jacobs PA Pescarmona PP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(45):13509-13518
Porous titanosilicate beads with a diameter of 0.5-1.5 mm (TiSil-HPB-60) were synthesized from a preformed titanosilicate solution with a porous anion-exchange resin as template. The bead format of this material enables its straightforward separation from the reaction mixture in its application as a liquid-phase heterogeneous catalyst. The material displays hierarchical porosity (micro/mesopores) and incipient TS-1 structure building units. The titanium species are predominantly located in tetrahedral framework positions. TiSil-HPB-60 is a highly active catalyst for the epoxidation of cyclohexene with t-butyl hydroperoxide (TBHP) and aqueous H(2)O(2). With both oxidants, TiSil-HPB-60 gave higher epoxide yields than Ti-MCM-41 and TS-1. The improved catalytic performance of TiSil-HPB-60 is mainly ascribed to the large mesopores favoring the diffusion of reagents and products to and from the titanium active sites. The epoxide yield and selectivity could be further improved by silylation of the titanosilicate beads. Importantly, TiSil-HPB-60 is a stable catalyst immune to titanium leaching, and can be easily recovered and reused in successive catalytic cycles without significant loss of activity. Moreover, TiSil-HPB-60 is active and selective in the epoxidation of a wide range of bulky alkenes. 相似文献
993.
Leszek Zalewski Dr. Michael Wykes Sergio Brovelli Dr. Massimo Bonini Dr. Thomas Breiner Dr. Marcel Kastler Dr. Florian Dötz Dr. David Beljonne Dr. Harry L. Anderson Prof. Franco Cacialli Prof. Paolo Samorì Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(13):3933-3941
A dithiophene rotaxane 1 ?β‐CD and its shape‐persistent corresponding dumbbell 1 were synthesized and fully characterized. 2D NOESY experiments, supported by molecular dynamics calculations, revealed a very mobile macrocycle (β‐CD). Steady‐state and time‐resolved photoluminescence experiments in solution were employed to elucidate the excited‐state dynamics for both systems and to explore the effect of cyclodextrin encapsulation. The photoluminescence (PL) spectrum of 1 ?β‐CD was found to be blueshifted with respect to the dumbbell 1 (2.81 and 2.78 eV, respectively). Additionally, in contrast to previous observations, neither PL spectra nor the decay kinetics of both threaded and unthreaded systems showed changes upon increasing the concentration or changing the polarity of the solutions, thereby providing evidence for a lack of tendency toward aggregation of the unthreaded backbone. 相似文献
994.
Ilya Kuselman Francesca Pennecchi Cathy Burns Aleš Fajgelj Paolo de Zorzi 《Accreditation and quality assurance》2010,15(5):283-288
A metrological background for investigating out-of-specification (OOS) test results of chemical composition is discussed.
When an OOS test result is identified, it is important to determine its root causes and to avoid reoccurrence of such results.
An investigation of the root causes based on metrological concepts would be beneficial. It includes (1) assessment of validation
data of the measurement process, (2) evaluation of the measurement uncertainty contributions, and (3) assessment of metrological
traceability chains critical for measurement parameters and environmental conditions influencing the test results. The questions,
how can the validation data be applied for this investigation, and how can measurement uncertainty contributions and/or metrological
traceability chains change a probability of OOS test results, are analyzed. 相似文献
995.
Paolo Cardillo Lucia Gigante Angelo Lunghi Paolo Zanirato 《Journal of Thermal Analysis and Calorimetry》2010,100(1):191-198
The thermal decomposition (TD) of 2-azidophenylmethanol (1), 2-azidobenzenecarbaldehyde (2), 1-(2-azidophenyl)-1-ethanone (3), (2-azidophenyl)(phenyl)methanone (4) and 1-azido-2-nitrobenzene (5) was analysed by DSC, TG and C80 calorimetric techniques under both oxidative and non-oxidative conditions. The TD of these
azides in solution is well known to give the corresponding benzoxazoles, generally in good yields, with the exception of azide
1. When both the outcomes from the solid phase and in ‘solution phase’ TD reactions combined with the results from EI-MS experiments
were considered, sufficient information was available to estimate the azides intrinsic molecular reactivity (MIR). 相似文献
996.
997.
Alessandro Chiolerio Paolo Allia Edvige Celasco Paola Martino Federico Spizzo Federica Celegato 《Journal of magnetism and magnetic materials》2010,322(9-12):1409-1412
Patterned soft magnetic materials are eligible for use in magnetic random access memories. A hexagonal-lattice pattern of circular antidots was produced by optical lithography in a Co film. In order to test the effect of geometry on the local magnetisation configuration of such a structure, we performed room-temperature angle-resolved magnetisation measurements aimed to check the pinning of domain walls by the pattern's lattice. Magnetoresistance (MR) room-temperature measurements were performed at various angles between the magnetic field direction and the macroscopic electrical current vector, to clarify whether and how the local current density configuration affects the MR response. We found that the magnetoresistance is of anisotropic type (AMR) and has a local origin. Furthermore, the largely unsaturating behaviour of MR at high fields may be explained only by considering that tiny portions of the pattern constitute highly frustrated regions and align their magnetisation at rather high fields. A simplified model based on a local anisotropy term is shown to account for the experimental results for both M and MR. 相似文献
998.
We study purely nonlocal Hamiltonian structures for systems of hydrodynamic type. In the case of a semi-Hamiltonian system, we show that such structures are related to quadratic expansions of the diagonal metrics naturally associated with the system. 相似文献
999.
Massimo Peruffo Pablo Contreras-Carballada Paolo Bertoncello Ren M. Williams Luisa De Cola Patrick R. Unwin 《Electrochemistry communications》2009,11(10):1885-1887
A method for assembling Pt nanoparticles (5 nm diameter) on indium tin oxide (ITO) and highly oriented pyrolytic graphite (HOPG) electrodes, via the potential-assisted deposition of pre-formed perthiolated-β-cyclodextrin-capped Pt nanoparticles is described. Cyclic voltammetry allowed control over the surface coverage of monodisperse Pt nanoparticles in a simple fashion, as evidenced by the voltammetric response and atomic force microscopy of the resulting electrode surface. The Pt nanoparticle arrays formed in this way were electrocatalytically active towards proton reduction-hydrogen evolution. The methodology described thus opens up a new approach for the deposition of metal nanoparticles with controlled surface density for the investigation of electrocatalytic processes. 相似文献
1000.
Angela Chambery Antimo Di Maro Carmen Sanges Valeria Severino Maura Tarantino Annalisa Lamberti Augusto Parente Paolo Arcari 《Analytical and bioanalytical chemistry》2009,395(7):2281-2291
Diagnostic techniques applied to the field of cultural heritage represent a very important aspect of scientific investigation.
Recently, proteomic approaches based on mass spectrometry coupled with traditional spectroscopic methods have been used for
painting analysis, generating promising results for binder’s protein identification. In the present work, an improved procedure
based on LC-ESI/Q-q-TOF tandem mass spectrometry for the identification of protein binders has been developed for the molecular
characterization of samples from an early-twentieth-century mural painting from the St. Dimitar Cathedral in Vidin, Bulgaria.
The proteomic investigation has led to the identification of both egg white and egg yolk proteins, according to traditional
old recipes for tempera paintings. In addition, beyond the egg components, the presence of caseins was also revealed, thus
suggesting the use of milk as binding medium, fixative or stabilising agent. Furthermore, for the first time, the capability
to discriminate the milk origin on the basis of alpha casein proteotypic peptides is reported, that are diagnostic for a given
species, thus opening interesting perspectives in art and archaeological fields. 相似文献