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81.
Hesham A. Habib Beatriz Gil-Hernández Khalid Abu-Shandi Joaquín Sanchiz Christoph Janiak 《Polyhedron》2010
Hydrothermal synthesis with MCl2 (M = Fe, Cu, and Zn) and disodium 5-ammonium-1-hydroxypentylidene-1,1-bisphosphonate, (Na+)2[+H3N(CH2)4C(OH)(PO32−)(PO3H−)] (Na2HAC5OHP2) or sodium 3-ammonium-1-hydroxypropylidene-1,1-bisphosphonate hydrate, Na+[+H3N(CH2)2C(OH)(PO3H–)(PO3H–)]·H2O (NaH2PAM·H2O) the sodium salt of pamidronic acid, H3PAM) yielded the one-dimensional (1D) iron, molecular copper and two-dimensional (2D) zinc compounds 1D-{[Fe(μ3-η5-HAC5OHP2)]·H2O}, 1, [Cu(η2-H2AC5OHP2)2], 2, 2D-{[Zn2(μ5-η7-AC5OHP2)Cl], 3, and 2D-{[Zn(μ2-η3-H2PAM)2], 4, respectively. The bisphosphonate ligand bridges (μn) between 2–5 metal atoms and uses 2–7 oxygen donor atoms towards metal coordination (ηn). The zwitterionic nature of the now bis- or tetrakis-deprotonated ammonium–bisphosphonate is retained in the metal complexes. From the reaction of NiCl2 and Na2HAC5OHP2 the zwitterionic 5-ammonium-1-hydroxypentylidene-1-phosphonic acid, +H3N(CH2)4CH(OH)PO3H−, 5 was obtained as a product of the ligand P–C bond hydrolysis. Adjacent strands, molecules or layers in 1–4, respectively are organized through the Coulomb attraction between the positive ammonium group and the negative phosphonate groups, supported by hydrogen-bonding. Each protic H atom on the C–OH, NH3+ and –PO3H− group is involved in charge-assisted hydrogen-bonding. The ammonium-pentylidene groups act as hydrophobic separators between the hydrophilic units with the polar M{C(OH)(PO3)2} and {NH3} units. Bond valence sum calculations support the Fe(II) oxidation state in 1, which was experimentally determined from a quantitative polarographic Fe(II)/Fe(III) speciation analysis as well as a temperature variable magnetic study. 相似文献
82.
Beatriz Jurado-Sánchez Evaristo Ballesteros Mercedes Gallego 《Analytical and bioanalytical chemistry》2010,396(5):1929-1937
Humans are exposed to endogenous or exogenous formation of aromatic amines (AAs) and N-nitrosamines (NAms), which are considered to be potent carcinogens. The objective of this study was to monitor AAs and NAms
in human urine to obtain a way to assess exposure. However, while NAms can be directly detected in urine samples, AAs require
hydrolysis to convert their conjugates into free amines. A semiautomatic flow-base method is proposed for the simultaneous
determination of aliphatic and aromatic NAms, anilines and chloroanilines in human urine in one analytical run. Conjugated
AAs are released from urine by on-line microwave-assisted acid hydrolysis without degradation of NAms; all amines were then
preconcentrated using solid-phase extraction. Separation/determinations are carried out by gas chromatography and mass spectrometry
operating in selected ion monitoring mode. The method is fast (∼15 min for 25 mL of sample) and provides low limits of detection
(from 2 to 26 ng/L) with good precision (relative standard deviation within and between days less than 7%). Finally, the proposed
method was successfully applied to check AAs and NAms in the human urine of exposed and unexposed researchers. The kinetics
of amine excretion in the urine of the researchers exposed is calculated after termination of the exposure and shows half-life
times between 1.3 and 2.1 h, and that the dosage absorbed was eliminated within 6 h after exposure. 相似文献
83.
Eduardo A. Solano Espinoza Wilmer E. Vallejo Narváez 《Journal of mass spectrometry : JMS》2010,45(7):722-733
The potential energy profiles for the fragmentations that lead to [C5H5O]+ and [C4H6]+? ions from the molecular ions [C5H6O]+? of E‐2,4‐pentadienal were obtained from calculations at the UB3LYP/6‐311G + + (3df,3pd)//UB3LYP/6‐31G(d,p) level of theory. Kinetic barriers and harmonic frequencies obtained by the density functional method were then employed in Rice–Ramsperger–Kassel–Marcus calculations of individual rate coefficients for a large number of reaction steps. The pre‐equilibrium and rate‐controlling step approximations were applied to different regions of the complex potential energy surface, allowing the overall rate of decomposition to be calculated and discriminated between three rival pathways: C? H bond cleavage, decarbonylation and cyclization. These processes should have to compete for an equilibrated mixture of four conformers of the E‐2,4‐pentadienal ions. The direct dissociation, however, can only become important in the high‐energy regime. In contrast, loss of CO and cyclization are observable processes in the metastable kinetic window. The former involves a slow 1,2‐hydrogen shift from the carbonyl group that is immediately followed by the formation of an ion‐neutral complex which, in turn, decomposes rapidly to the s‐trans‐1,3‐butadiene ion [C4H6]+?. The predominating metastable channel is the second one, that is, a multi‐step ring closure which starts with a rate‐limiting cis—trans isomerization. This process yields a mixture of interconverting pyran ions that dissociates to the pyrylium ions [C5H5O]+. These results can be used to rationalize the CID mass spectrum of E‐2,4‐pentadienal in a low‐energy regime. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
84.
The carbamoylating agents carbamoyl azides and carbamoyl cyanides (aka cyanoformamides) react with hydroxylamine in different ways, leading in the first case to N-hydroxyureas and, in the case of carbamoyl cyanides, to carbamoyl amidoxime derivatives. The synthetic procedure developed for the latter type of compound, which represents an interesting precursor for heterocyclic structures, allowed the highly efficient preparation of a wide selection of examples. The Z configuration of the double bond in the amidoxime moiety was proposed on the basis of comparison between experimental and calculated (13)C and (15)N NMR chemical shift values for the isopropyl and benzyl derivatives. 相似文献
85.
Gerritsma R Lanyon BP Kirchmair G Zähringer F Hempel C Casanova J García-Ripoll JJ Solano E Blatt R Roos CF 《Physical review letters》2011,106(6):060503
We report on quantum simulations of relativistic scattering dynamics using trapped ions. The simulated state of a scattering particle is encoded in both the electronic and vibrational state of an ion, representing the discrete and continuous components of relativistic wave functions. Multiple laser fields and an auxiliary ion simulate the dynamics generated by the Dirac equation in the presence of a scattering potential. Measurement and reconstruction of the particle wave packet enables a frame-by-frame visualization of the scattering processes. By precisely engineering a range of external potentials we are able to simulate text book relativistic scattering experiments and study Klein tunneling in an analogue quantum simulator. We describe extensions to solve problems that are beyond current classical computing capabilities. 相似文献
86.
Casanova J Lamata L Egusquiza IL Gerritsma R Roos CF García-Ripoll JJ Solano E 《Physical review letters》2011,107(26):260501
We propose the quantum simulation of fermion and antifermion field modes interacting via a bosonic field mode, and present a possible implementation with two trapped ions. This quantum platform allows for the scalable add up of bosonic and fermionic modes, and represents an avenue towards quantum simulations of quantum field theories in perturbative and nonperturbative regimes. 相似文献
87.
Devika Kannan Ana Beatriz Lopes de Sousa Jabbour Charbel José Chiappetta Jabbour 《European Journal of Operational Research》2014
Due to an increased awareness and significant environmental pressures from various stakeholders, companies have begun to realize the significance of incorporating green practices into their daily activities. This paper proposes a framework using Fuzzy TOPSIS to select green suppliers for a Brazilian electronics company; our framework is built on the criteria of green supply chain management (GSCM) practices. An empirical analysis is made, and the data are collected from a set of 12 available suppliers. We use a fuzzy TOPSIS approach to rank the suppliers, and the results of the proposed framework are compared with the ranks obtained by both the geometric mean and the graded mean methods of fuzzy TOPSIS methodology. Then a Spearman rank correlation coefficient is used to find the statistical difference between the ranks obtained by the three methods. Finally, a sensitivity analysis has been performed to examine the influence of the preferences given by the decision makers for the chosen GSCM practices on the selection of green suppliers. Results indicate that the four dominant criteria are Commitment of senior management to GSCM; Product designs that reduce, reuse, recycle, or reclaim materials, components, or energy; Compliance with legal environmental requirements and auditing programs; and Product designs that avoid or reduce toxic or hazardous material use. 相似文献
88.
A useful application for copula functions is modeling the dynamics in the conditional moments of a time series. Using copulas, one can go beyond the traditional linear ARMA (p,q) modeling, which is solely based on the behavior of the autocorrelation function, and capture the entire dependence structure linking consecutive observations. This type of serial dependence is best represented by a canonical vine decomposition, and we illustrate this idea in the context of emerging stock markets, modeling linear and nonlinear temporal dependences of Brazilian series of realized volatilities. However, the analysis of intraday data collected from e‐markets poses some specific challenges. The large amount of real‐time information calls for heavy data manipulation, which may result in gross errors. Atypical points in high‐frequency intraday transaction prices may contaminate the series of daily realized volatilities, thus affecting classical statistical inference and leading to poor predictions. Therefore, in this paper, we propose to robustly estimate pair‐copula models using the weighted minimum distance and the weighted maximum likelihood estimates (WMLE). The excellent performance of these robust estimates for pair‐copula models are assessed through a comprehensive set of simulations, from which the WMLE emerged as the best option for members of the elliptical copula family. We evaluate and compare alternative volatility forecasts and show that the robustly estimated canonical vine‐based forecasts outperform the competitors. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
89.
Beatriz Zamora-Aviles 《Israel Journal of Mathematics》2014,202(1):105-115
We study the gap structure of the partial order of projections of the Calkin algebra of a complex, separable, infinite-dimensional Hilbert space. We prove the existence of an analytic Hausdorff gap in this partial order. As a consequence we obtain that under Todorcevic’s Axiom and MA the gap spectrum of P(C(H)) is strictly bigger than the gap spectrum of P(ω)/Fin. 相似文献
90.
Beatriz Margolis 《Numerical Functional Analysis & Optimization》2013,34(5-6):577-588
We develop a calculus structure in the Banach lattice introduced in a preceding paper, having in mind an approximation problem appearing in non-smooth optimization. We show that the essential results depend as much on the order structure as on the analytical one. 相似文献