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751.
Ballester L Gil AM Gutiérrez A Perpiñán MF Azcondo MT Sánchez AE Coronado E Gómez-García CJ 《Inorganic chemistry》2000,39(13):2837-2842
New derivatives of formula [M(dieneN4)](TCNQ)3, M = Ni or Cu and dieneN4 = cis- or trans-hexamethyltetraazacyclotetradecadiene, have been obtained. The TCNQ units show electronic delocalization and formation of 1D stacks, with no direct interactions with the metal cations. The stack is not uniform and can be seen as formed by trimeric dianions (TCNQ)3(2-). The electronic delocalization favors the conductivity in these materials, which behave as good semiconductors. The crystal structures of the trans derivatives have been solved: [Ni(transdieneN4)](TCNQ)3, triclinic, P-1, a = 8.809(2) A, b = 10.896(2) A, c = 13.727(2) A, alpha = 103.04(1) degrees, beta = 101.23(2) degrees, gamma = 109.37(2) degrees, Z = 1; [Cu(trans-dieneN4)](TCNQ)3: triclinic, P-1, a = 7.872(1) A, b = 9.840(1) A, c = 14.819(1) A, alpha = 92.32(1) degrees, beta = 95.05(1) degrees, gamma = 95.66(1) degrees, Z = 1. 相似文献
752.
The iodide-catalysed reaction between cerium(IV) and arsenic(III) has been studied using a modular stopped-flow system. The features of both the stopped-flow and conventional kinetic methods have been compared by using the same instrument. The stopped-flow method has a wider linear range and is faster than the conventional kinetic method and has been applied satisfactorily to the photometric determination of iodide in pharmaceutical preparations, table salt and cow's milk. The results obtained show that the stopped-flow method is simple, inexpensive and rapid and requires no sophisticated equipment. In addition, its high sampling rate makes it particularly suitable for the routine determination of iodide. 相似文献
753.
J.F Fernández-SánchezA Segura-Carretero C Cruces-BlancoA Fernández-Gutiérrez 《Analytica chimica acta》2002,462(2):217-224
This paper presents two easy and selective methods for determining the active principles nafronyl (NFL) and naproxen (NAP), using a flow-through fluorescence optosensor based on the on-line immobilization on a nonionic-exchanger (Silica Gel, Davisil™ and Amberlite XAD 7, respectively) solid support. The determination was performed in 5×10−3 M HAc/NaAc buffer solution at pH 5 for NFL and 15×10−3 M glycine/HCl buffer solution at pH 2.5 for NAP at a working temperature of 20 °C. The fluorescence intensities were measured at λex/em=294/336 nm and λex/em=332/354 nm for NFL and NAP, respectively. The response time for these optosensors were practically instant, obtaining a linear concentration range between 0 and 700.0 ng ml−1 with a detection limit of 20.8 ng ml−1, an analytical sensitivity of 10.1 ng ml−1 and a standard deviation of 1.27% at a 500 ng ml−1 concentration level for NFL and a linear concentration range between 0 and 200.0 ng ml−1 with the detection limit of 13.3 ng ml−1, an analytical sensitivity of 6.0 ng ml−1 and a standard deviation of 3.52% at a 100 ng ml−1 concentration level for NAP. The proposed methods were satisfactorily applied to real samples (three commercial formulations and urine samples). The effects of the possible interferences were evaluated in all cases. 相似文献
754.
A Mg,Al layered double hydroxide (LDH) with [Cr(C(2)O(4))(3)](3)(-) anions in the interlayer has been synthesized following two different routes: reconstruction from a mildly calcined Mg,Al-carbonate LDH, and anion exchange from a Mg,Al-nitrate LDH. The solids prepared have been characterized by elemental chemical analysis, powder X-ray diffraction, FT-IR and UV-vis/DR (diffuse reflectance) spectroscopies, thermal methods, nitrogen adsorption at -196 degrees C, and FT-IR monitoring of pyridine adsorption. The results obtained indicate that the most appropriate method is anion exchange, leading to a well crystallized LDH with an interlayer spacing of 10 A. Due to the high pH value (>8) of the solution in the reconstruction method, however, a polyphasic system is obtained, where, in addition to a phase with the LDH structure, amorphous magnesium oxalate and chromium oxohydroxides are also formed due to hydrolysis of the complex. The interlayer complex is stable up to 200 degrees C, but the layered structure is stable up to 330 degrees C, probably because of the presence of interlayer oxalate anions formed during decomposition of the complex. Calcination leads to oxidation of Cr(3+) ions to the six-valent state, which reverts to Cr(3+) when the calcination temperature is further increased. 相似文献
755.
VíctorManuel Gutirrez‐García Gloria Reyes‐Rangel Omar Muoz‐Muiz Eusebio Juaristi 《Helvetica chimica acta》2002,85(12):4189-4199
Inexpensive acryloyl chloride was converted in 91% overall yield to two derivatives of β‐alanine, (R,R,R)‐ 6 and (R,R,S)‐ 6 , containing two chiral auxiliaries. C‐Alkylation of (R,R,R)‐ and (R,R,S)‐ 6 via a dianion derivative, was performed by direct metallation with 2.2 equiv. of lithium hexamethyldisilazane (LHMDS) in THF at ?78°. C‐Alkylation of (R,R,S)‐ 6 ‐Li2 (‘matched' pair of chiral auxiliaries) afforded the mono‐alkylated products 8 – 11 in 29–96% yield and 54–95% stereoselectivity. Employment of LiCl as an additive generally increased stereoselectivities, whereas the effect of HMPA as a cosolvent was erratic. Chemical correlation of the major diastereoisomer from the alkylation reactions with (S)‐α‐alkyl‐β‐alanine ( 12 – 15 ) showed that addition of the electrophile preferentially takes place on the enolate's Si‐face. This conclusion is also supported by molecular‐modeling studies (ab initio HF/3‐21G), which indicate that the lowest‐energy conformation for (R,R,S)‐ 6 ‐Li2 presents the more sterically hindered Re‐face of the enolate. The theoretical studies also predict a determining role for N? Li? O chelation in (R,R,S)‐ 6 ‐Li2, giving rise to an interesting ‘ion‐triplet' configuration for the dilithium dianion. 相似文献
756.
We address the dynamic lot size problem assuming time-varying storage capacities. The planning horizon is divided into T periods and stockouts are not allowed. Moreover, for each period, we consider a setup cost, a holding unit cost and a production/ordering unit cost, which can vary through the planning horizon. Although this model can be solved using O(T3) algorithms already introduced in the specialized literature, we show that under this cost structure an optimal solution can be obtained in O(T log T) time. In addition, we show that when production/ordering unit costs are assumed to be constant (i.e., the Wagner–Whitin case), there exists an optimal plan satisfying the Zero Inventory Ordering (ZIO) property. 相似文献
757.
The analysis of a kernel involving the product of three Bessel functions motivates the introduction of the translation operator and the convolution associated to the Hankel–Kontorovich–Lebedev tranformation, first in a classical framework, and then in certain spaces of generalized functions. The main properties of this convolution are investigated, the more important operational rules are obtained and some applications are shown. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
758.
José Sandoval Cortés Silvia Gutiérrez Granados Alejandro Alatorre Ordaz Jorge A. López Jiménez Sophie Griveau Fethi Bedioui 《Electroanalysis》2007,19(1):61-64
Peroxynitrite, ONOO? also so‐called PON, is a very powerful oxidant and cytotoxic agent produced in biological systems by the recombination of nitric oxide and superoxide anion radical. Most of the techniques for assaying PON (chemiluminescence, fluorescence, UV‐visible spectroscopy, immunochemistry and EPR ) use indirect methods relying on measurements of secondary species. We report in this study the calibration of a chemically modified Pt ultramicroelectrode by electropolymerized manganese tetraaminophthalocyanine film (MnTAPc) for the determination of PON in aqueous solution. The obtained result allows showing for the first time a real‐time calibration curve of the amperometric determination of stable PON in aqueous solution. The sensitivity of the sensor is 14.6 nA mM?1 and its detection limit is 5 μM. 相似文献
759.
S. Amat S. Busquier J.M. Gutirrez M.A. Hernndez 《Journal of Computational and Applied Mathematics》2008,220(1-2):17-21
In [A. Melman, Geometry and convergence of Euler's and Halley's methods, SIAM Rev. 39(4) (1997) 728–735] the geometry and global convergence of Euler's and Halley's methods was studied. Now we complete Melman's paper by considering other classical third-order method: Chebyshev's method. By using the geometric interpretation of this method a global convergence theorem is performed. A comparison of the different hypothesis of convergence is also presented. 相似文献
760.
V. García-Cuello J. C. Moreno-Pirajan L. Giraldo-Gutiérrez K. Sapag G. Zgrablich 《Journal of Thermal Analysis and Calorimetry》2009,97(2):705-709
This work shows the results obtained to determine the noise in the baseline of a specially designed Tian Calvet-Type adsorption
microcalorimeter. The results show that noise levels vary from 0.5 to 10 μV, which were evaluated varying the electrical work
and the micro calorimeter surrounding temperature. Relationships can be seen between the variables employed in the observation
of stability, temperature, potency levels and generated noise. 相似文献