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21.
Molecular Diversity - 相似文献
22.
D. Oyola Lozano L. E. Zamora G. A. Perez Alcazar Y. A. Rojas H. Bustos J. M. Greneche 《Hyperfine Interactions》2005,161(1-4):203-209
In this work we report the magnetic and structural properties obtained by Mössbauer spectrometry, Vibrating Sample Magnetometer and X-ray diffraction of milled powders with initial composition Nd2(Fe100 ? x Nb x )14B with x = 0 and x = 4. The mixtures were ball milled for different times up to 240 h. Structural and microstructural parameters were derived from high statistics X-ray patterns and discussed as a function of milling time. The Mössbauer spectra of the samples were fitted by means of a sextet and an hyperfine field distribution, associated to a pure iron phase (α-Fe) and a disordered iron-based phase, respectively. The α-Fe grain size decreases from 50 nm for 6 h up to 5 nm for 240 h milling time. The Vibrating Sample Magnetometer results allow to conclude that these samples behave as soft ferromagnets. 相似文献
23.
Direct On‐Surface Patterning of a Crystalline Laminar Covalent Organic Framework Synthesized at Room Temperature 下载免费PDF全文
Alejandro de la Peña Ruigómez David Rodríguez‐San‐Miguel Dr. Kyriakos C. Stylianou Dr. Massimiliano Cavallini Dr. Denis Gentili Dr. Fabiola Liscio Prof. Silvia Milita Dr. Otello Maria Roscioni Dr. Maria Luisa Ruiz‐González Carlos Carbonell Prof. Daniel Maspoch Dr. Rubén Mas‐Ballesté Dr. José Luis Segura Dr. Félix Zamora 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10666-10670
We report herein an efficient, fast, and simple synthesis of an imine‐based covalent organic framework (COF) at room temperature (hereafter, RT‐COF‐1 ). RT‐COF‐1 shows a layered hexagonal structure exhibiting channels, is robust, and is porous to N2 and CO2. The room‐temperature synthesis has enabled us to fabricate and position low‐cost micro‐ and submicropatterns of RT‐COF‐1 on several surfaces, including solid SiO2 substrates and flexible acetate paper, by using lithographically controlled wetting and conventional ink‐jet printing. 相似文献
24.
Micelle‐Triggered β‐Hairpin to α‐Helix Transition in a 14‐Residue Peptide from a Choline‐Binding Repeat of the Pneumococcal Autolysin LytA 下载免费PDF全文
Héctor Zamora‐Carreras Dr. Beatriz Maestro Dr. Erik Strandberg Prof. Anne S. Ulrich Dr. Jesús M. Sanz Dr. M. Ángeles Jiménez 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8076-8089
Choline‐binding modules (CBMs) have a ββ‐solenoid structure composed of choline‐binding repeats (CBR), which consist of a β‐hairpin followed by a short linker. To find minimal peptides that are able to maintain the CBR native structure and to evaluate their remaining choline‐binding ability, we have analysed the third β‐hairpin of the CBM from the pneumococcal LytA autolysin. Circular dichroism and NMR data reveal that this peptide forms a highly stable native‐like β‐hairpin both in aqueous solution and in the presence of trifluoroethanol, but, strikingly, the peptide structure is a stable amphipathic α‐helix in both zwitterionic (dodecylphosphocholine) and anionic (sodium dodecylsulfate) detergent micelles, as well as in small unilamellar vesicles. This β‐hairpin to α‐helix conversion is reversible. Given that the β‐hairpin and α‐helix differ greatly in the distribution of hydrophobic and hydrophilic side chains, we propose that the amphipathicity is a requirement for a peptide structure to interact and to be stable in micelles or lipid vesicles. To our knowledge, this “chameleonic” behaviour is the only described case of a micelle‐induced structural transition between two ordered peptide structures. 相似文献
25.
26.
A quantitative analytical imaging approach for determining the nickel content of metallic meteorites is proposed. The approach uses a digital image of a series of standard solutions of the nickel-dimethylglyoxime coloured chelate and a meteorite sample solution subjected to the same treatment as the nickel standards for quantitation. The image is processed with suitable software to assign a colour-dependent numerical value (analytical signal) to each standard. Such a value is directly proportional to the analyte concentration, which facilitates construction of a calibration graph where the value for the unknown sample can be interpolated to calculate the nickel content of the meteorite. The results thus obtained were validated by comparison with the official, ISO-endorsed spectrophotometric method for nickel.The proposed method is fairly simple and inexpensive; in fact, it uses a commercially available digital camera as measuring instrument and the images it provides are processed with highly user-friendly public domain software (specifically, ImageJ, developed by the National Institutes of Health and freely available for download on the Internet).In a scenario dominated by increasingly sophisticated and expensive equipment, the proposed method provides a cost-effective alternative based on simple, robust hardware that is affordable and can be readily accessed worldwide. This can be especially advantageous for countries were available resources for analytical equipment investments are scant. The proposed method is essentially an adaptation of classical chemical analysis to current, straightforward, robust, cost-effective instrumentation. 相似文献
27.
Megger N Welte L Zamora F Müller J 《Dalton transactions (Cambridge, England : 2003)》2011,40(8):1802-1807
The incorporation of an artificial 5-methyl-2,2'-bipyridine nucleoside at the 5' terminus of an otherwise self-complementary oligonucleotide sequence opens up the opportunity of metal-mediated aggregation of DNA double helices triggered by the addition of the respective metal ions. Interestingly, two-dimensional aggregates (DNA monolayers) are formed in the presence of nickel(ii), whereas copper(ii) leads to the formation of three-dimensional disc-shaped structures. With iron(ii), a coexistence of both types of aggregates had been observed previously. Models are proposed in which these observations are explained based on geometrical considerations. The artificial nucleoside itself represents a rare example for a C(1)-symmetric chiral derivative of 2,2'-bipyridine, enabling the formation of four isomeric octahedral complexes. 相似文献
28.
Robert Hakl Pedro J. Torres Manuel Zamora 《Nonlinear Analysis: Theory, Methods & Applications》2011,74(18):7078-7093
In this paper, we continue the study of the periodic problem for the second-order equation u′′+f(u)u′+g(u)=h(t,u), where h is a Carathéodory function and f,g are continuous functions on (0,+∞) which may have singularities at zero. Both attractive and repulsive singularities are considered. The method relies on a novel technique of construction of lower and upper functions. As an application, we obtain new sufficient conditions for the existence of periodic solutions to the Rayleigh–Plesset equation. 相似文献
29.
Francisca Zamora Khalid Hakkou Abdelilah Alla Manuel Rivas Isaac Roff Manuel Mancera Sebastin Muoz‐Guerra Juan A. Galbis 《Journal of polymer science. Part A, Polymer chemistry》2005,43(19):4570-4577
The synthesis and characterization of a new series of aromatic polyesters based on D‐mannitol and galactitol are described. These polyesters were obtained by polycondensation reaction of the terephthaloyl chloride or isophthaloyl chloride and 2,3,4,5‐tetra‐O‐methyl‐D‐mannitol or 2,3,4,5‐tetra‐O‐methyl‐galactitol in o‐dichlorobenzene. All the new polyesters were characterized by elemental analyses, GPC, IR, and NMR. They were soluble in chloroform, but insoluble in water and other polar oxygenated solvents. They showed a notable hygroscopicity, lower for those containing isophthalic units. DSC and X‐ray diffraction studies showed that D‐mannitol‐based polyesters were stiffer and less crystalline than those derived from galactitol, which presented a noticeably lower thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4570–4577, 2005 相似文献
30.
M. Salazar Ligia E. Zamora G. A. Prez Alcazar J. A. Plascak W. R. Aguirre 《Physica B: Condensed Matter》2002,320(1-4):236-238
In this work we present a theoretical study of the magnetic behavior of disordered Fe–Al alloys on the basis of a simple-diluted quantum Heisenberg spin model with the assumption that the exchange interaction J depends on the Al concentration q. We calculated the critical temperature and exponents through the mean field renormalization group method. An acceptable fit to the experimental phase diagram for Al concentration in the range 0.30q0.45 is obtained. 相似文献