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431.
G. Alonzo N. Bertazzi G. Bombieri G. Bruno F. Nicolò 《Journal of chemical crystallography》1991,21(5):635-640
The compound has been characterized by X-ray crystal structure determination, Mössbauer and i.r. spectroscopy. It crystallizes in the monoclinic space groupP2
1
/c (No. 14) witha=24.228(4),b=8.335(2),c=23.975(4) Å,=117.83(3)° andZ=8. Least-squares refinement on 3749 observed reflections gave finalR=0.034 (R
w=0.037). The compound is constituted by [(C6H5)SbCl4OMe]– anions andphenH+cations. The coordination polyhedron about Sb is an octahedron (Sb-Cl 2.416(3), Sb-O 1.962(7) and Sb-C 2.138(9) Å). The whole structure is characterized by two short contacts (O(1)N(2) 2.76(1) O(2)N(4) 2.75(1) Å) involving the methoxy oxygens of the two independent anionic units [(C6H5)SbCl4OMe]– and two nitrogens of the two independent phenanthrolinium moieties. 相似文献
432.
A method based on microchip electrophoresis with electrochemical (EC) detection has been developed for the simultaneous determination of Yellow AB, Red 2G, Sunset Yellow, New Coccine, and Amaranth which are azo-dyes frequently added to foodstuffs. Factors affecting both separation and detection processes were examined and optimized, with best performance achieved by using a 10 mM phosphate buffer (pH 11) as BGE solution and applying a voltage of 2500 V both in the separation and in the electrokinetic injection (duration 4 s). Under these optimal conditions, the target dye analytes could be separated and detected within 300 s by applying a detection potential of -1.0 V (vs. Ag/AgCl) to the glassy carbon (GC) working electrode. The recorded peaks were characterized by a good repeatability (RSD=1.8-3.2%), high sensitivity, and a wide linear range. Detection limits of 3.8, 3.4, 3.6, 9.1, 15.1 microM were obtained for Yellow AB, Red 2G, Sunset Yellow, New Coccine, and Amaranth, respectively. Fast, sensitive, and selective response makes the new microchip protocol very attractive for the quantitative analysis of commercial soft drinks and candies. 相似文献
433.
Silvia A. Fuente Ricardo M. Ferullo Nicolás F. Domancich Norberto J. Castellani 《Surface science》2011,605(1-2):81-88
The adsorption of nitric oxide (NO) on Aun (n = 1–3) particles deposited on anionic (O2?) sites of MgO has been studied using the DFT (Density Functional Theory) approach. The regular O2? sites of MgO(100) and the sites in edge and corner topological defects with high symmetry of MgO were considered. The adhesion energy of Aun to MgO is larger for Au2 and Au3 due to higher polarization effects. On the other hand, the interaction strength of NO with supported Aun particles depends mainly on the electronic configuration (open or closed shell) of the particle; the Au particles with odd number of atoms show larger NO binding energies. A comparison was performed with the reactivity of free Aun particles. From this, it is possible to conclude that the support enhances the NO–Aun bonding strength for the monomer, weakens this interaction in the case of the dimer, and does not have an effect in the trimers. Besides, the NO–Aun bonding is essentially insensitive to the coordination of the anionic site where the Aun particle is linked. A large red-shift of the N–O stretching frequency was obtained, particularly for the Au particles with odd number of atoms, due to a negative charge transfer from Au to NO. 相似文献
434.
Castro AA Aucélio RQ Rey NA Miguel EM Farias PA 《Combinatorial chemistry & high throughput screening》2011,14(1):22-27
This paper describes a stripping method for the determination of nevirapine at the submicromolar concentration levels. The method is based on controlled adsorptive accumulation of nevirapine at thin-film mercury electrode, followed by a linear cyclic scan voltammetry measurement of the surface species. Optimal experimental conditions include a 2.0 x 10(-3) mol L(-1) NaOH solution (supporting electrolyte), an accumulation potential of -0.20 V, and a scan rate of 100 mV s(-1). The response of nevirapine is linear over the concentration range 0.01-0.14 ppm. For an accumulation time of 6 minutes, the detection limit was found to be 0.87 ppb (3.0 x 10(-9) mol L(-1)). More convenient methods to measure the nevirapine in presence of the efavirenz, acyclovir, didanosine, indinavir, nelfinavir, saquinavir, lamivudine, zidovudine and metals ions were also investigated. The utility of this method is demonstrated by the presence of nevirapine together with ATP or DNA. 相似文献
435.
Pulsed electric fields (PEFs), hashed modes of current consisting in the application of a constant current density during a fixed time (Ton) followed by a pause lapse (Toff), were recently demonstrated as an effective alternative for mineral fouling mitigation and process intensification during electrodialysis (ED) treatments. Recent ED studies have continuously reported a considerable mineral fouling formation on ion-exchange membranes, especially during the demineralization of solutions containing a high Mg/Ca ratio and a basified concentrate solution. The aim of this study was to evaluate the process performance under two different PEF conditions on a mineral solution containing a mineral mixture giving a high Mg(2+)/Ca(2+) ratio of 2/5. Two different pause-lapse durations (PEF ratio 1 (Ton/Toff 10s/10s); PEF ratio 0.3 (Ton/Toff 10s/33.3 s)) during consecutive ED treatments and their comparison with dc current were evaluated at a current density of 40 mA/cm(2). Our results showed that PEFs resulted in an intensification of ED process, enhancing the demineralization rates (DRs), reducing the system resistance (SR), and reducing the fouling and energy consumption (EC). PEF ratio 1 was the most optimal condition among the current regimes applied, leading to faster and higher demineralization rates due to a lower fouling and with low energy consumption during all consecutive runs. 相似文献
436.
The use of a mixed-valent ruthenium oxide/hexacyanoruthenate polymeric film electrochemically deposited onto glassy carbon electrodes is proposed here for the detection of biogenic amines and their amino acid precursors, following their separation by microchip capillary electrophoresis. The ability of this ruthenium coating to electrocatalyze the oxidation of aliphatic and heterocyclic amines, as well as their amino acid precursors, was checked by using ethanolamine, tryptamine and tryptophane as prototype compounds and adopting a 25 mM sulphuric acid as the electrolyte in the detection cell, where a constant potential of 1.05 V versus Ag/AgCl, 3 M KCl was applied to the modified working electrode. Optimization of parameters affecting both detection and separation steps led to satisfactory separations when performed by using a 20 mM phosphate running buffer (pH 2.5) and applying a high voltage of 2.5 kV both in the separation and in the electrokinetic injection (duration 4 s). The recorded peaks were characterized by good repeatability (RSD ≤ 3.6%), high sensitivity and a wide linear range. Detection limits of 23 μM (1.4 mg/L), 27 μM (4.3 mg/L) and 34 μM (6.8 mg/L) were inferred for ethanolamine, tryptamine and tryptophane, respectively. The approach proposed here was also applied for the analysis of some double malt dark beers spiked with a controlled amount of the analytes considered. 相似文献
437.
Ríos-Lombardía N Busto E Gotor-Fernández V Gotor V 《The Journal of organic chemistry》2011,76(14):5709-5718
A novel family of prochiral pentane-1,5-diamines has been efficiently synthesized, possessing stabilities significantly higher than those of corresponding propane-1,3-diamine analogues. Diamines have been later desymmetrized using Pseudomonas cepacia lipase as an efficient biocatalyst for the mono- but also stereoselective protection of one of their amino groups. Reaction parameters such as type and loading of enzyme, temperature, solvent, and acyl donor have been exhaustively analyzed, searching for optimal conditions for the production of interesting optically active nitrogenated compounds. Thus, acylation and alkoxycarbonylation processes have been compared in terms of conversion and enantiomeric excess values. The best results were found in the reaction of prochiral diamines with ethyl methoxyacetate as acyl donor and 1,4-dioxane as solvent, yielding (S)-monoamides in 33-59% isolated yield and 54-99% ee, depending on the aromatic pattern substitution. 相似文献
438.
Mathematical Programming - Tailored Mixed-Integer Optimal Control policies for real-world applications usually have to avoid very short successive changes of the active integer control. Minimum... 相似文献
439.
440.
Flávio Vinicius Crizóstomo Kock Dr. Attila Forgács Nicol Guidolin Rachele Stefania Dr. Adrienn Vágner Dr. Eliana Gianolio Prof. Silvio Aime Dr. Zsolt Baranyai 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(5):1849-1859
Herein, the synthesis and an extensive characterization of two novel Gd(AAZTA) (AAZTA=6-amino-6-methylperhydro-1,4-diazepine tetra acetic acid) derivatives functionalized with short (C2 and C4) n-alkyl acid functions are reported. The carboxylate functionality is the site for further conjugations for the design of more specific contrast agents (CAs). Interestingly, it has been found that the synthesized complexes display enhanced properties for use as MRI contrast agents on their own. The stability constants determined by using potentiometric titration and UV/Vis spectrophotometry were slightly higher than the one reported for the parent Gd(AAZTA) complex. This observation might be accounted for by the larger sigma-electron donation of the acyl substituents with respect to the one provided by the methyl group in the parent complex. As far as concerns the kinetic stability, transmetallation experiments with endogenous ions (e.g. Cu2+) implied that the Gd3+ ions present in these Gd(AAZTA) derivatives show somewhat smaller susceptibility to chemical exchange towards these ions at 25 °C, close to the physiological condition. The 1H NMR spectra of the complexes with EuIII and YbIII displayed a set of signals consistent with half the number of methylene protons present on each ligand. The number of resonances was invariant over a large range of temperatures, suggesting the occurrence of a fast interconversion between structural isomers. The relaxivity values (298 K, 20 MHz) were consistent with q=2 being equal to 8.8 mm −1 s−1 for the C2 derivative and 9.4 mm −1 s−1 for the C4 one, that is, sensibly larger than the one reported for Gd(AAZTA) (7.1 mm −1 s−1). Variable-temperature (VT)-T2 17O NMR measurements showed, for both complexes, the presence of two populations of coordinated water molecules, one in fast and one in slow exchange with the bulk water. As the high-resolution 1H NMR spectra of the analogs with EuIII and YbIII did not show the occurrence of distinct isomers (as frequently observed in other macrocyclic lanthanide(III)-containing complexes), we surmised the presence of two fast-interconverting isomers in solution. The analysis of the 17O NMR VT-T2 profiles versus temperature allowed their relative molar fraction to be established as 35 % for the isomer with the fast exchanging water and 65 % for the isomer with the water molecules in slower exchange. Finally, 1H NMRD profiles over an extended range of applied magnetic field strengths have been satisfactory fitted on the basis of the occurrence of the two interconverting species. 相似文献