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431.
M Lanchas D Vallejo-Sánchez G Beobide O Castillo AT Aguayo A Luque P Román 《Chemical communications (Cambridge, England)》2012,48(79):9930-9932
The direct acid-base reaction between ZnO/CoO/Co(OH)(2) and imidazolic ligands under moderate heating (100-160 °C), in a closed vessel, leads to the generation of the corresponding zinc/cobalt-imidazolates in a high yield (87-97%) in which network topology is controlled by the addition of small amounts of structure directing agents. Moreover, the fine tuning of the thermal process at the synthetic stage permits us to increase the crystal size, and even to grow X-ray quality single crystals. 相似文献
432.
433.
Absorption and fluorescence properties of methylene blue (MB), a well-known singlet molecular oxygen photosensitizer, and its mixtures with pheophorbide-a (Pheo) sorbed on microgranular cellulose are studied, with emphasis on radiative and nonradiative energy transfer from Pheo to MB. Although pure MB builds up dimeric species on cellulose even at 2 x 10(-8) mol g(-1), addition of 2.05 x 10(-7) mol g(-1) Pheo largely inhibits aggregation up to nearly 10(-6) mol g(-1) MB. At the same time, the absorption spectrum of monomeric MB in the presence of Pheo differs from the spectrum in pure cellulose. Both effects reveal a strong influence of Pheo on the medium properties. A model relying entirely on experimental data is developed, through which energy transfer efficiencies can be calculated for thin and thick layers of dye-loaded cellulose. At the largest concentration of MB assuring no dye aggregation, nonradiative energy transfer efficiencies reach a maximum value of nearly 40%. This value is quite high, taking into account the low fluorescence quantum yield of Pheo, Phi = 0.21, and results from the existence of high local concentrations of the acceptor within the supporting material. These results show that large energy transfer rates can exist in a system devoid of any special molecular organization. 相似文献
434.
Simó C Pérez P Neusüss C Pelzing M San Román J Gallardo A Cifuentes A 《Electrophoresis》2006,27(11):2250-2258
Analytical characterization of dimethacrylate-tyrosine-lysine-tyrosine (DMTLT, a new biodegradable acrylic cross-linker synthesized at our laboratory) is carried out using CE-MS. DMTLT is a pseudopeptide composed by tyrosine-lysine-tyrosine amino acids linked through urea bonds with two methacrylic groups, one at each end of the molecule, making this compound an excellent cross-linker for polymerization reactions and for obtaining new biodegradable materials. A new CE-MS method is developed for the characterization of DMTLT and its products of degradation after basic hydrolysis. In order to carry out an exhaustive examination of such degradation products methods based on CE coupled to IT and TOF-MS are employed. Based on CE-IT-MS results and the elemental composition of the degradation products obtained by CE-TOF-MS, conclusions on the mechanism and kinetic of hydrolysis of DMTLT are obtained confirming both the usefulness of CE-MS to characterize new biomaterials and the applicability of DMTLT for preparing new biodegradable polymers. These results are corroborated through the CE-MS detection of the identified products of degradation in a dimethyl acrylamide polymer cross-linked with DMTLT. 相似文献
435.
Beobide G Castillo O Luque A García-Couceiro U García-Terán JP Román P 《Inorganic chemistry》2006,45(14):5367-5382
The synthesis, crystal structure, and magnetic behavior of nine transition-metal complexes based on pyrazine-2,5-dicarboxylato (pz25dc) and pyrazine-2,3-dicarboxylato (pz23dc) ligands are reported. The pz25dc ligand displays a bis-bidentate coordination mode, with the carboxylate groups almost coplanar with the pyrazine ring, to afford polymeric 1-D chains [Mn(1), Fe(2), Zn(3), and Cu(4 and 5)] and discrete dimeric entities [Mn(6)] when the 1,10-phenanthroline (phen) blocking ligand is used to avoid further polymerization. The nonplanar pz23dc ligand chelates to a unique copper center, while it bridges another one or two metal centers via the remaining carboxylate group, leading to 1-D polymeric chains (7), ladder chains (8), and sheets (9). The crystal packing of the metal-organic frameworks of compounds 4-9 generates voids which are occupied by assembled water molecules. The different water cluster patterns (tapes, four-membered discrete rings, and chains for compounds 6, 8, and 9, respectively) and their role in the cohesiveness of supramolecular architectures are analyzed. Thermogravimetric and variable-temperature X-ray powder diffraction studies have revealed the occurrence of reversible dehydration processes in compounds 6, 8, and 9. Furthermore, the magnetic behavior of these compounds has been studied in order to analyze the capability of the pyrazine ring to transmit magnetic interactions. 相似文献
436.
Multivariate curve resolution-alternating least squares (MCR-ALS) is applied to solve coelution problems in liquid chromatograpy with diode array detection (DAD) and mass spectrometry (MS). Fusion of DAD and MS detector signals improved results versus those obtained using only one of the two detector signals. Application of wavelet transform to MS data before its fusion with DAD data, further help to facilitate the resolution and quantitation of the coeluted compounds under study, besides a decrease of time of analysis. Mixtures of biocide compounds in standard mixtures and in environmental samples (sediment and wastewater samples) were analyzed with estimated quantitation errors below 12%. 相似文献
437.
Rom Harré 《Foundations of Chemistry》2009,11(2):93-103
The traditional ontology within which chemistry has developed involved various versions of a general substance/attribute scheme.
Recently this has been challenged by two versions of Dynamism. One version is derived from the writings of A. N. Whitehead
and the other from several sources, including G. Leibniz and I. Kant. Both involve the idea of flux of actual occasions. Unlike
the former scheme, the latter involves a foundation of causal powers and the energetics of field theory. The situation has
been made more interesting because of the revival of trope theory, based on an ontology of particularized attributes. This
notion is claimed to resolve philosophical problems about the nature of universals and of substances through the introduction
of spatial and temporal sequences of tropes. While trope theory seems, at first sight, to work as an attractive alternative
to substance/attribute close inspection shows that it is beset with difficulties that are more problematic that the dynamist
ontology based on casual powers, dispositions and affordances.
相似文献
Rom HarréEmail: |
438.
Werner Grogger Ferdinand Hofer Bernd Kraus Irmgard Rom Werner Sitte Peter Warbichler 《Mikrochimica acta》2000,133(1-4):125-129
Energy-filtering transmission electron microscopy (EFTEM) is more and more becoming an important nanoanalytical technique
in both materials science and biology. The main advantage of the method lies in the possibility to obtain two-dimensional
chemical information from large specimen areas as well as from features on a nanometer scale. Due to its excellent lateral
resolution it is perfectly suited for the investigation of nanometer sized features (e.g. interfaces).
In this paper we will show how EFTEM can be used to characterize the interface between a Pt layer and a NiO crystal as part
of a coulometric titration cell. In addition to elemental distribution maps electron energy-loss spectra (EELS) across the
interface (EELS linescans) have been acquired to obtain quantitative compositional profiles. By employing these methods the
following interfacial layers could be identified, all of which containing Pt, Ni and O in different proportions: 13 nm Pt-rich,
32 nm Ni-rich and 29 nm Pt-rich. The origin of these is discussed in terms of displacement reactions. 相似文献
439.
We derive the width of the Higgs boson into vector bosons. General formulas are derived both for the on–shell decay as well for the off–shell decays, and , where . For the off-shell decays the width of the decaying vector boson is properly included. The formulas are valid both for the
Standard Model as well as for arbitrary extensions. As an example we study in detail the gauge-invariant effective Lagrangian
models where we can have sizable enhancements over the Standard Model that could be observed at LEP.
Received: 31 July 1998 / Revised version: 23 September 1998 / Published online: 6 November 1998 相似文献