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71.
Boglio C Lenoble G Duhayon C Hasenknopf B Thouvenot R Zhang C Howell RC Burton-Pye BP Francesconi LC Lacôte E Thorimbert S Malacria M Afonso C Tabet JC 《Inorganic chemistry》2006,45(3):1389-1398
The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands. 相似文献
72.
The Lewis acid mediated reaction of acyclic vinyl allenes and imines, yielding tetrahydropyridines has been carried out. Only one cycloadduct was observed in each case, and thus, the reaction progressed in all cases with total regio-, face- and endo/exo selectivities. The cycloadducts were transformed into polysubstituted pyridines, including bipyridines, by catalytic transfer hydrogenation using cyclohexene as hydrogen donor in good yield. The reaction was extended to the aromatization of the bicyclic cycloadducts prepared in previous works from the reaction of semicyclic vinyl allenes and imines, yielding tetrahydropyridines. 相似文献
73.
J.A. Chaos J. Gonzalo C.N. Afonso J. Perrière M.T. García-González 《Applied Physics A: Materials Science & Processing》2001,72(6):705-710
Laser ablation of single-crystal LiNbO3 in a gas environment is used to grow films on (100) Si substrates heated to 650 °C. The film composition and crystallinity
are studied as a function of the nature (reactive, O2, or inert, Ar) and pressure of the gas environment applied during deposition and cooling-down processes, the laser energy
density and the target–substrate distance. Experimental results show that a gas pressure close to 1 mbar is required to produce
stoichiometric films in either O2 or Ar. The modification of the laser energy density and the target–substrate distance allows us to improve the crystallinity
of the films that become textured along the (006) direction. The influence of the experimental parameters on the film properties
is discussed in the frame of the formation of a blast wave, that leads to the focusing of the expanding Li species and thus,
to the increase of the Li content in the films.
Received: 8 February 2001 / Accepted: 9 February 2001 / Published online: 3 May 2001 相似文献
74.
Ana P. X. Mariano Ana L. C. C. Ramos Afonso H. de Oliveira Júnior Yesenia M. García Ana C. C. F. F. de Paula Mauro R. Silva Rodinei Augusti Raquel L. B. de Araújo Júlio O. F. Melo 《Molecules (Basel, Switzerland)》2022,27(3)
Eugenia klotzschiana O. Berg is a native species to the Cerrado biome with significant nutritional value. However, its volatile organic compounds (VOCs) chemical profile is not reported in the scientific literature. VOCs are low molecular weight chemical compounds capable of conferring aroma to fruit, constituting quality markers, and participating in the maintenance and preservation of fruit species. This work studied and determined the best conditions for extraction and analysis of VOCs from the pulp of Eugenia klotzschiana O. Berg fruit and identified and characterized its aroma. Headspace solid-phase microextraction (HS-SPME) was employed using different fiber sorbents: DVB/CAR/PDMS, PDMS/DVB, and PA. Gas chromatography and mass spectrometry (GC-MS) were employed to separate, detect, and identify VOCs. Variables of time and temperature of extraction and sample weight distinctly influenced the extraction of volatiles for each fiber. PDMS/DVB was the most efficient, followed by PA and CAR/PDMS/DVB. Thirty-eight compounds that comprise the aroma were identified among sesquiterpenes (56.4%) and monoterpenes (30.8%), such as α-fenchene, guaiol, globulol, α-muurolene, γ-himachalene, α-pinene, γ-elemene, and patchoulene. 相似文献
75.
Noncovalent complexes of DNA and Hoechst 33258 were investigated by ESI-FT/ICR MS in various activation modes (collision-induced dissociation (CID), sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiphoton dissociation (IRMPD) and electron detachment dissociation (EDD)). The binding selectivity of Hoechst 33258 was confirmed by the comparative study of its noncovalent association with different DNA sequences. The CID spectra of [ds + HO - 5H](5-) obtained with a linear hexapole ion trap resulted in unzipping of the strands. This outcome is a clue to the drug-binding mode, shading light on the localization of the binding sites of Hoechst 33258 to the DNA sequence. The IRMPD and SORI-CID experiments mainly gave DNA backbone cleavages and internal fragment ions. From this result, information on the localization of the binding sites of Hoechst 33258 in the DNA sequence was obtained. No sodium cationization was observed on the DNA sequence ions although they were present on fragmentation of the duplex, indicating that the backbone cleavages were generated from the single strand associated with the Hoechst 33258 where the number of alkali cation is restricted. Under electron detachment (ED) conditions, multiple EDs were achieved for the [ds + HO - 5H](5-) ion without any significant dissociation. The presence of drug appears to enhance the stability of the multiply charged system. It was proposed that the studied noncovalent complex involved the formation of zwitterions and consequently strong salt-bridge interactions between DNA and drug. 相似文献
76.
Dr. Bhavana Gupta Mariana C. Afonso Dr. Lin Zhang Dr. Cedric Ayela Patrick Garrigue Dr. Bertrand Goudeau Prof. Alexander Kuhn 《Chemphyschem》2019,20(7):941-945
Combining the actuation of conducting polymers with additional functionalities is an interesting fundamental scientific challenge and increases their application potential. Herein we demonstrate the possibility of direct integration of a miniaturized light emitting diode (LED) in a polypyrrole (PPy) matrix in order to achieve simultaneous wireless actuation and light emission. A light emitting diode is used as a part of an electroactive surface on which electrochemical polymerization allows direct incorporation of the electronic device into the polymer. The resulting free-standing polymer/LED hybrid can be addressed by bipolar electrochemistry to trigger simultaneously oxidation and reduction reactions at its opposite extremities, leading to a controlled deformation and an electron flow through the integrated LED. Such a dual response in the form of actuation and light emission opens up interesting perspectives in the field of microrobotics. 相似文献
77.
78.
J. Gonzalo R. Gómez San Román J. Perrière C.N. Afonso R. Pérez Casero 《Applied Physics A: Materials Science & Processing》1998,66(5):487-491
2 , Ar) in a broad pressure range (10-7–1 mbar) are correlated to the plasma expansion dynamics. It is found that the deposited films present an excess of Ba in
the intermediate pressure range (10-2<P<10-1 mbar) and a peaked distribution of Ba to Ti atoms ratio, that is not related to either the substrate temperature or the nature
of the gas environment. The results are discussed in terms of the dependence of the plume length (LP) on the gas pressure and the existence of scattering processes for distances (d) from the target lower than LP and the diffusion of the ejected species for LP<d.
Received: 7 November 1997/Accepted: 8 November 1997 相似文献
79.
Nuno M.T LourençoCarlos A.M Afonso 《Tetrahedron》2003,59(6):789-794
The use of the room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate as an efficient catalyst and solvent for several representative nucleophilic substitution reactions under aqueous-RTIL phase transfer conditions was explored. Recycling and reuse of the reaction medium was demonstrated for the azide formation. 相似文献
80.
Adel M. S. de Oliveira Humberto Abdalla Luis Afonso Bermudez 《International Journal of Infrared and Millimeter Waves》1992,13(1):43-53
This paper presents a CAD for analysis and synthesis of Unilateral Fin-Lines with Taper design, FINAS. For analysis, the system uses empirical formula. On the other hand, for synthesis is applied an iterative method based on Newton-Raphson Algorithm. At the Tapered Fin-Line conception the system presents three kinds of tapers. In spite of the use of empirical formula, comparisons with Spectral Domain Method revealed excellent results. 相似文献