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501.
Credi A Dumas S Silvi S Venturi M Arduini A Pochini A Secchi A 《The Journal of organic chemistry》2004,69(18):5881-5887
A calix[6]arene wheel, whose cavity has been extended and rigidified by N-phenylureido groups on the upper rim, forms pseudorotaxane species with molecular axles containing the viologen (4,4'-bipyridinium) unit in CH(2)Cl(2) solution. In these conditions, the self-assembly process is very efficient, with associated DeltaG degrees values of around -8 kcal mol(-1). The counteranions of the bipyridinium-based threads play indeed an important role in the formation of the complex. The use of either tosylate or hexafluorophosphate salts of the guests affects both the stability of the complexes and the rate of the threading process. Such effects have been interpreted in terms of ion-pair recognition, suggesting that coordination of the counteranions of the viologen thread by the ureido groups of the calixarene wheel is crucial for the breaking of tight ion pairs prior to threading. The rate constants of the threading/dethreading reactions coupled with the redox processes of the viologen unit of the axle have been obtained by means of cyclic voltammetry. The pseudorotaxane species undergo fast dethreading (submicrosecond time scale) on electrochemical reduction of the guest. The heterogeneous electron-transfer kinetics for the reduction of the viologen unit is slowed upon encapsulation into the calixarene cavity. 相似文献
502.
The triacylglycerols of some vegetable oil samples were determined using isocratic HPLC with refractive index (RI) detection, gradient solvent HPLC with evaporative light scattering detection (ELSD), capillary GC and theoretical calculations from FAME analysis in order to establish the suitability of these techniques. The response factors and the repeatability were investigated. Generally, the HPLC-RI detection technique can be used without application of response factors. HPLC-ELSD yields inaccurate results for low concentrations. Calculations assuming a 1,3-random 2-random distribution of fatty acids gave good results for olive oil and acceptable results for sunflower oil. The GC analysis requires the use of response factors. 相似文献
503.
Beltrán HI Esquivel R Lozada-Cassou M Dominguez-Aguilar MA Sosa-Sánchez A Sosa-Sánchez JL Höpfl H Barba V Luna-García R Farfán N Zamudio-Rivera LS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2705-2715
Thermal and microwave reactions between [PcSn(IV)Cl2] (1) and the potassium salts of eight fatty acids (2 a-h) led to cis-[(RCO2)2Sn(IV)Pc] compounds (3 a-h) in yields ranging from 54 to 90 %. Compounds 3 a-h were fully characterized by elemental analysis, spectroscopy (IR, UV/Vis, multinuclear NMR), and seven X-ray diffraction structures, whereby two different allotropes were observed in two cases. The two carboxylates in 3 have a cis anisobidentate binding mode, octacoordination of the tin atoms with square-antiprismatic geometry, and pi-electron-rich nanocap shapes. On account of the latter characteristics, 3 a-h compounds have anticorrosion properties. LPR and Tafel electrochemical methods were used to characterize the behavior of these derivatives in naturally aerated sour brine, which is a common environment in petroleum production and refinery operations. The measurement of the corrosion rate of carbon steel AISI 1018 in the presence of 3 a-h (500 ppm) gave efficiencies of 61-87 % for the inhibitor performance. Of the different derivatives examined, compounds 3 e and 3 h were the most effective corrosion inhibitor prototypes. 相似文献
504.
Voltammetric response of diclofenac-molecularly imprinted film modified carbon electrodes 总被引:1,自引:0,他引:1
Blanco-López MC Lobo-Castañón MJ Miranda-Ordieres AJ Tuñón-Blanco P 《Analytical and bioanalytical chemistry》2003,377(2):257-261
A voltammetric sensor for the determination of diclofenac was developed, based on the molecular recognition of the analyte by molecularly imprinted methacrylate-ethyleneglycol dimethacrylate co-polymers. Pre-polymerisation solutions were deposited onto the surface of a glassy carbon electrode and a polymer film was obtained after spin coating control of thickness and in situ thermal polymerisation. After the template extraction from the resultant film, re-binding of diclofenac is performed from acetonitrile solutions containing the analyte. The amount of bonded diclofenac was then evaluated by differential pulse voltammetry in different electrolytes. The best results were obtained in 0.025 M citrate solution pH 6 containing 10% of acetonitrile. This medium favours the release of diclofenac from the polymer binding sites. In this way, the voltammetric transduction of the molecular recognition event is achieved. Voltammetric selectivity measurements revealed negligible interferences from diclofenac family of anti-inflammatory drugs, such as niflumic or meclofenamic acids. 相似文献
505.
Jos R. Espinosa Marisol Galvn Arturo S. Quiones Jorge L. Ayala Vernica vila Sergio M. Durn 《Molecules (Basel, Switzerland)》2021,26(11)
In this work, a low-cost and rapid electrochemical resistive DNA biosensor based on the current relaxation method is described. A DNA probe, complementary to the specific human papillomavirus type 16 (HPV-16) sequence, was immobilized onto a screen-printed gold electrode. DNA hybridization was detected by applying a potential step of 30 mV to the system, composed of an external capacitor and the modified electrode DNA/gold, for 750 µs and then relaxed back to the OCP, at which point the voltage and current discharging curves are registered for 25 ms. From the discharging curves, the potential and current relaxation were evaluated, and by using Ohm’s law, the charge transfer resistance through the DNA-modified electrode was calculated. The presence of a complementary sequence was detected by the change in resistance when the ssDNA is transformed in dsDNA due to the hybridization event. The target DNA concentration was detected in the range of 5 to 20 nM. The results showed a good fit to the regression equation , and a detection limit of 2.39 nM was obtained. As the sensing approach uses a direct current, the electronic architecture of the biosensor is simple and allows for the separation of faradic and nonfaradaic contributions. The simple electrochemical resistive biosensor reported here is a good candidate for the point-of-care diagnosis of HPV at a low cost and in a short detection time. 相似文献
506.
Cristina Aller Jesús Castro Paulo Prez‐Lourido Elena Labisbal Jos Arturo García‐Vzquez 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(3):m155-m157
In the title compound, [CuCl(C7H7O3S)(C12H8N2)(H2O)], the central Cu atom is coordinated by a water molecule, a chloride ion, an O‐monodentate p‐toluenesulfonate anion and an N,N′‐bidentate 1,10‐phenanthroline ligand. The copper environment is best described as a slightly distorted square pyramid, with bond distances Cu—Cl 2.2282 (9) Å, Cu—OW 1.984 (3) Å, and Cu—N 2.006 (3) and 2.028 (3) Å; the apical Cu—O distance is 2.281 (2) Å. In the supramolecular structure, π–π‐stacking stabilization is observed, and classical and non‐classical hydrogen bonds also play an important role. 相似文献
507.
PierLuigi Zanonato Plinio Di Bernardo Arturo Bismondo Linfeng Rao Gregory R. Choppin 《Journal of solution chemistry》2001,30(1):1-18
Complexation of neodymium (III) with acetate in 2.2 mol-kg-1 NaClO4 solution was studied at elevated temperatures (45 and 70°C) by potentiometry, calorimetry, and optical spectroscopy. The formation constants of the consecutive complexes, Nd(OOCCH3),2+ Nd(OOCCH3)
2
+
, and Nd(OOCCH3)3, and the molar enthalpies of complexation at these temperatures were determined. The stability of the three complexes increases with increased temperatures, because of increased positive entropy change at higher temperatures, which exceeds the increased values of the positive (endothermic) enthalpy. The molar heat capacity changes of complexation Cp,m(MLj) (J-K-1-mol-1) for Nd(OOCCH3)
j
(3-j)+
in the temperature range from 25 to 70°C were calculated to be: 102 ± 13 (j = 1); 122 ± 19 (j = 2); and 239 ± 27 (j = 3). The effect of temperature on the complexation is discussed in terms of the electrostatic model. 相似文献
508.
Rao L Garnov AY Jiang J Di Bernardo P Zanonato P Bismondo A 《Inorganic chemistry》2003,42(11):3685-3692
The complexation of uranium(VI) and samarium(III) with oxydiacetate (ODA) in 1.05 mol kg(-1) NaClO(4) is studied at variable temperatures (25-70 degrees C). Three U(VI)/ODA complexes (UO(2)L, UO(2)L(2)(2-), and UO(2)HL(2)(-)) and three Sm(III)/ODA complexes (SmL(j)((3-2)(j)+) with j = 1, 2, 3) are identified in this temperature range. The formation constants and the molar enthalpies of complexation are determined by potentiometry and calorimetry. The complexation of uranium(VI) and samarium(III) with oxydiacetate becomes more endothermic at higher temperatures. However, the complexes become stronger due to increasingly more positive entropy of complexation at higher temperatures that exceeds the increase in the enthalpy of complexation. The values of the heat capacity of complexation (Delta C(p) degrees in J K(-1) mol(-1)) are 95 +/- 6, 297 +/- 14, and 162 +/- 19 for UO(2)L, UO(2)L(2)(2-), and UO(2)HL(2)(-), and 142 +/- 6, 198 +/- 14, and 157 +/- 19 for SmL(+), SmL(2)(-), and SmL(3)(3-), respectively. The thermodynamic parameters, in conjunction with the structural information from spectroscopy, help to identify the coordination modes in the uranium oxydiacetate complexes. The effect of temperature on the thermodynamics of the complexation is discussed in terms of the electrostatic model and the change in the solvent structure. 相似文献
509.
Mayya Korochkina Alessandro Casnati Arturo Arduini Rocco Ungaro Vladimir Kataev Vladimir Alfonsov 《Tetrahedron》2005,61(23):5457-5463
Novel calix[4]arene derivatives functionalized with two or four isosteviol units at the upper rim and a new calix[6]arene having six isosteviol moieties at the lower rim have been synthesized. The structures of these compounds have been confirmed by NMR and mass spectrometry data. All 1H and 13C NMR chemical shifts of isosteviol were fully assigned by extensive NMR spectroscopic methods, and used to clarify the structures and conformations of isosteviol-calixarene conjugates. 相似文献
510.
Lucas Blanes Maria F. Mora Claudimir L. do Lago Arturo Ayon Carlos D. García 《Electroanalysis》2007,19(23):2451-2456
In this work, the development of a packed immobilized enzyme reactor (IMER) and its integration to a capillary electrophoresis microchip is described. The present microchip design differs from others, in the fact that the same design could be used with or without the particles and, just by changing the material used to pack the IMER, different analytes can be detected. The applied procedure involves the separation of the target analyte by capillary electrophoresis (CE), which is then coupled to a post‐column IMER that produces H2O2. The H2O2 produced is finally detected downstream at the surface of a working electrode. Glucose was detected above 100 μM by packing particles modified with glucose oxidase at the end of the separation channel. The analytical performance of the microchip‐CE has been demonstrated by performing the separation and detection of glucose and noradrenaline. Additions of fructose showed no effect on either the peak position or the peak magnitude of glucose. The microchip‐CE‐IMER was also used to quantify glucose in carbonated beverages with good agreement with other reports. 相似文献