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81.
The synthesis of a new azacyclophane formed by two l-tyrosine units joined by two methylene bridges is presented. The structural and conformational characteristics are briefly discussed. Spectroscopic and theoretical data reveal a syn structure with two intramolecular hydrogen bonds. 相似文献
82.
Maria José González-álvarez José Vicente Carmen Ortiz Mellet José Maria García Fernández Francisco Mendicuti 《Journal of fluorescence》2009,19(6):975-988
The thermodynamics of the dimer formation of 2I,3I-O-(o-xylylene)-per-O-Me-γ-cyclodextrin (XmγCD) in aqueous solution was studied by fluorescence techniques, Molecular Mechanics and Molecular Dynamics. Lifetime averages
á t
ñ \left\langle \tau \right\rangle , obtained from fluorescence decay profiles upon excitation of the xylylene appended group, were used as the property sensitive
to the association process. The dimerization equilibrium constants (K
D) were obtained from non-linear regression analysis of the plots of
á t
ñ \left\langle \tau \right\rangle against [XmγCD] at several temperatures and they were compared with the values obtained for the counterparts Xmα- and XmβCDs. The van’t Hoff plot allows us to obtain the ΔH and ΔS showing that the dimerization process was also entropically disfavoured. Molecular Mechanics as well as Molecular Dynamics
calculations in the presence of water were also employed to study the conformational behaviour of isolated XmγCDs, the possible structure of the dimers formed and the driving forces involved in such association processes. Results indicate
that those conformations where Xy moiety does not block the cavity entrance are favoured. Dimers are preferably formed by
head-to-head CD approaching. However, the formation of stable head-to-tail is not dismissed. 相似文献
83.
E. Chávez P. Rodríguez A. Huerta M. E. Ortiz L. Barrón-Palos F. Favela D. Marín E. Moreno G. Murillo R. Policroniades A. Varela 《The European Physical Journal A - Hadrons and Nuclei》2009,42(2):179-184
Angular distributions were measured for neutron elastically scattered by natPb at 2.9, 3.0, 3.1, 3.2 and 3.4MeV at very forward angles. The mono-energetic neutron flux was produced at the tandem accelerator facility of the National Institute of Nuclear Research (ININ), Mexico, using the Associated Particle Technique (APT) in the D(d, n)3He reaction. Optical model predictions with best potential systematic show a fairly good agreement with our data, and also the need for a better understanding of the neutron scattering process at very small angles from the theoretical point of view. 相似文献
84.
Dr. Juan M. Ortiz‐Sánchez Dr. Ricard Gelabert Prof. Miquel Moreno Prof. José M. Lluch 《Chemphyschem》2010,11(17):3696-3703
A quantum electronic study of the effect of substituents on (2,2′‐bipyridyl)‐3,3′‐diol and (2,2′‐bipyridyl)‐3,3′‐diamine is presented. A large difference in the photochemical behavior between the original and the substituted selected systems is expected. For the sake of simplicity, the study is restricted to the symmetrically bi‐substituted compounds: fluorine, the more electronegative atom and thus a strong σ‐acceptor but also a weak π‐donor group, and NO2, a strong π‐acceptor substituent. Among the large set of compounds studied, two receive special attention: 5,5′‐dinitro‐(2,2′‐bipyridyl)‐3,3′‐diamine and 6,6′‐difluoro‐(2,2′‐bipyridyl)‐3,3′‐diol. While in the former case the nitro substitution transforms (2,2′‐bipyridyl)‐3,3′‐diamine, previously suggested to behave as a photomemory material, into a simple fluorescent species, the latter substitution turns (2,2′‐bipyridyl)‐3,3′‐diol into a fresh new candidate for a photomemory device. 相似文献
85.
Marina Sánchez Francisco J. Aranda José A. Teruel María J. Espuny Ana Marqués Ángeles Manresa Antonio Ortiz 《Journal of colloid and interface science》2010,341(2):240-247
Pseudomonas aeruginosa, when cultured under the appropriate conditions, secretes rhamnolipids to the external medium. These glycolipids constitute one of the most interesting classes of biosurfactants so far. A dirhamnolipid fraction was isolated and purified from the crude biosurfactant, and its action on model and biological membranes was studied. Dirhamnolipid induced leakage of internal contents, as measured by the release of carboxyfluorescein, in phosphatidylcholine unilamellar vesicles, at concentrations below its CMC. Membrane solubilization was not observed within this concentration range. The presence of inverted cone-shaped lipids in the membrane, namely lysophosphatidylcholine, accelerated leakage, whereas cone-shaped lipids, like phosphatidylethanolamine, decreased leakage rate. Increasing concentrations of cholesterol protected the membrane against dirhamnolipid-induced leakage, which was totally abolished by the presence of 50 mol% of the sterol. Dirhamnolipid caused hemolysis of human erythrocytes through a lytic mechanism, as shown by the similar rates of K+ and hemoglobin leakage, and by the absence of effect of osmotic protectants. Scanning electron microscopy showed that the addition of the biosurfactant changed the usual disc shape of erythrocytes into that of spheroechinocytes. The results are discussed within the frame of the biological actions of dirhamnolipid, and the possible future applications of this biosurfactant. 相似文献
86.
87.
M. Moreno-Maas Y. Arredondo R. Pleixats M. Teixid M. M. Raga C. Palacín J. M. Castell J. A. Ortiz 《Journal of heterocyclic chemistry》1992,29(6):1557-1560
Several new triazole antifungal agents derived from mercaptomethylisoxazoles of general structure 2(2,4-dihalogenophenyl)-3-((X-isoxazolyl)methylthio)-(1,2,4-triazol-1-yl)-2-propanol, as well as some selected sulfoxides and sulfones derived thereof, have been synthesized and tested for antifungal activity. Some of these compounds showed good activity against yeasts and dermatophytes. 相似文献
88.
Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
89.
Cristina Vázquez Graciela Custo Laura Dawidowski Darío Gómez Marina Villegas Martha Ortiz Mayumi Miyagusuku 《Analytical sciences》2005,21(7):763-767
Multielemental composition and morphology of particulate matter samples were examined to detect the presence of two potential responsible pollutant emitters at four sites impacted during a pollution episode in the City of Campana, Argentina. Coke and smoke black are the main constituents associated to the industrial plants that were considered, a priori, as responsible pollutant emitters. Wavelength dispersive X-ray fluorescence (WDXRF) was employed for the analysis of metals in samples coming from both, suspected sources and four sites. On the basis of multielemental composition profiles, a screening analysis was undertaken for exploring similarities among sources and sample sites adopting the average concentration profile of the crustal rock as soil surrogate. Particle morphology was studied by scanning electron microscopy (SEM) in source samples and in those environmental samples selected through the screening analysis. Two types of collected samples were analyzed: 1) those with composition profiles closer to the potential sources and 2) those closer to the cluster rock. This strategy was adequate to identify the responsible source of the contamination episode. 相似文献
90.
Andrea Braides Adrian J. Lew Michael Ortiz 《Archive for Rational Mechanics and Analysis》2006,180(2):151-182
A simple model of cleavage in brittle crystals consists of a layer of material containing N atomic planes separating in accordance with an interplanar potential under the action of an opening displacement δ prescribed on the boundary of the layer. The problem addressed in this work concerns the characterization of the constrained
minima of the energy EN of the layer as a function of δ as N becomes large. These minima determine the effective or macroscopic cohesive law of the crystal. The main results presented
in this communication are: (i) the computation of the Γ limit E0 of EN as N → ∞; (ii) the characterization of the minimum values of E0 as a function of the macroscopic opening displacement; (iii) a proof of uniform convergence of the minima of EN for the case of nearest-neighbor interactions; and (iv) a proof of uniform convergence of the derivatives of EN, or tractions, in the same case. The scaling on which the present Γ-convergence analysis is based has the effect of separating
the bulk and surface contributions to the energy. It differs crucially from other scalings employed in the past in that it
renders both contributions of the same order. 相似文献