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861.
A simple and highly selective electrochemical method was developed for the single or simultaneous determination of paracetamol (N-acetyl-p-aminophenol, acetaminophen) and caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) in aqueous media (acetate buffer, pH 4.5) on a boron-doped diamond (BDD) electrode using square wave voltammetry (SWV) or differential pulse voltammetry (DPV). Using DPV with the cathodically pre-treated BDD electrode, a separation of about 550 mV between the peak oxidation potentials of paracetamol and caffeine present in binary mixtures was obtained. The calibration curves for the simultaneous determination of paracetamol and caffeine showed an excellent linear response, ranging from 5.0 × 10−7 mol L−1 to 8.3 × 10−5 mol L−1 for both compounds. The detection limits for the simultaneous determination of paracetamol and caffeine were 4.9 × 10−7 mol L−1 and 3.5 × 10−8 mol L−1, respectively. The proposed method was successfully applied in the simultaneous determination of paracetamol and caffeine in several pharmaceutical formulations (tablets), with results similar to those obtained using a high-performance liquid chromatography method (at 95% confidence level). 相似文献
862.
Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method 总被引:1,自引:0,他引:1
Claudineia R. Silva Cleone D. C. Conceição Viviane G. Bonifácio Orlando Fatibello Filho Marcos F. S. Teixeira 《Journal of Solid State Electrochemistry》2009,13(5):665-669
A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as
an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater.
The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on
analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l−1 COD with detection limit of 20.3 mg l−1 COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The
results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate)
COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end
products do not contain toxic metals. 相似文献
863.
Viviane G. Bonifácio Orlando Fatibello Filho Luiz H. Marcolino-Júnior 《Central European Journal of Chemistry》2013,11(11):1830-1836
In this work, a flow-injection spectrophotometric method for dipyrone determination in pharmaceutical formulations was developed. Dipyrone sample solutions were injected into a carrier stream of deionized water and the reaction was carried out in a solid-phase reactor (12 cm, 2.0 mm i.d.) packed with Cu3(PO4)2(s) entrapped in a matrix of polyester resin. The Cu(II) ions were released from the solid phase reactor by the formation of Cu(II)-(dipyrone)n complex. When the complex is released, it reacts with 0.02% m/v alizarin red S in deionized water to produce a Cu(VABO3)3 complex whose absorbance was monitored at 540 nm. The calibration graph was linear over the range 5.0×10?5–4.0×10?4 mol L?1 with a detection limit of 2.0×10?5 mol L?1 and relative standard deviation for 10 successive determinations of 1.5% (2.0×10?4 mol L?1 dipyrone solution). The calculated sample throughput was 60 h?1. The column was stable for at least 8 h of continuous use (500 injections) at 25°C. Pharmaceutical formulations were analyzed and the results from an official procedure measurement were compared with those from the proposed FIA method in order to validate the latter method. 相似文献
864.
The nucleophilic reactivity of a representative series of anions has been measured in [hmim][ClO4] 3i, [hm2im][ClO4] 3′i, and [hmim][PF6] 3l ILs in the reaction with n-alkyl methanesulfonates and compared with that found in common molecular solvents (MeOH, DMSO, PhCl). The reactivity is found to depend on both the imidazolium cation-anion interaction and the specific solvation by water present in the IL, the water playing the main effect, in particular with hydrophilic anions. Removal of the largest quantity of water remarkably increases the ion pair reactivity in the IL up to rate constant value k comparable with those obtained in DMSO and in low polarity media (PhCl). 相似文献
865.
Santos SG Santana JV Maia FF Lemos V Freire VN Caetano EW Cavada BS Albuquerque EL 《The journal of physical chemistry. B》2008,112(45):14267-14272
Adsorption of ascorbic acid (AsA) on C60 is investigated using classical molecular mechanics and density functional theory (DFT). Classical annealing was performed to explore the space of molecular configurations of ascorbic acid adsorbed on C60, searching for optimal geometries. From the structure with the smallest total energy, 10 initial configurations were prepared by applying rotations of 90 degrees about three orthogonal axes. Each one of these configurations was optimized using DFT (for both LDA and GGA exchange-correlation functionals), and an estimate of their total and adsorption energies was found. Different configurations have minimal adsorption energies (defined here as the total energy of the adsorbate minus the total energy of the separate molecules) from -0.54 to -0.10 eV, with distinct optimal distances between the AsA and C60 centers of mass. According to a Hirshfeld population analysis, AsA is, in general, an acceptor of electrons from C60. Our results demonstrate the feasibility of noncovalent functionalization of C60 with AsA and provide minimal energy values for the several different configurations investigated. These results should be considered in reactions as a possible way to prevent against the oxidative damage and toxicity of C60. The beneficial effects of using AsA-C60 includes its action when administered together with levodopa, against the neurotoxicity generated by levodopa isolated, which opens new strategies for the Parkinson's disease treatment. 相似文献
866.
Amanda P. Neves Kelly C.B. Maia Maria D. Vargas Lorenzo C. Visentin Annelise Casellato Miguel A. Novak Antônio S. Mangrich 《Polyhedron》2010
A novel versatile tridentate 3-(aminomethyl)naphthoquinone proligand, 3-[N-(2-pyridylmethyl)aminobenzyl]-2-hydroxy-1,4-naphthoquinone (HL), was obtained from the Mannich reaction of 2-hydroxy-1,4-naphthoquinone (Lawsone) with 2-aminomethylpyridine (amp) and benzaldehyde. The reactions of HL with CuCl2·2H2O yielded two novel dinuclear copper(II) complexes, [Cu(L)(H2O)(μ-Cl)Cu(L)Cl] (1b), [CuCl(L)(μ-Cl)Cu(amp)Cl] (2) and a polymeric compound, [Cu(L)Cl)]n (1a), whose relative yields were sensitive to temperature, reagents concentration and presence of base. The crystalline structures of 1b and 2 were determined by X-ray diffraction studies. The two copper atoms in complex 1b are connected by a single chloro bridge with a Cu?Cu separation of 4.1342(8) Å and Cu(1)–Cl(1)–Cu(2) angle of 109.31(4)°. In complex 2 the two copper atoms are held together by a chloro and a naphthalen-2-olate bridges [Cu(1)–Cl(2)–Cu(2) and Cu(1)–O(1)–Cu(2) angles being 83.31(3) and 109.70(9)°, respectively, and the Cu?Cu separation, 3.3476(9) Å]. As expected, variable-temperature magnetic susceptibility measurements of complex 1b showed weak antiferromagnetic intramolecular coupling between the copper(II) centers, with J = −5.7 cm−1, and evidenced for complex 2 strong antiferromagnetic coupling, with J ∼ −120 cm−1. Furthermore, the magnetic behaviour of compound 1a suggested an infinite 1D coordination polymeric structure in which the copper(II) centers are connected by Cl–Cu–Cl bridges. Solution data (UV–Vis spectroscopy and cyclic voltammetry) indicated structural changes of 2 and 1a in CH3CN, and evidenced conversion of polymer 1a into dimer 1b. 相似文献
867.
This paper reports a simple and reliable HPLC method to evaluate the influence of two currently available photostabilizers on cosmetic formulations containing combined UV-filters and vitamins A and E. Vitamins and UV-filters, widely encountered in products of daily use have to be routinely evaluated since photoinstability can lead to reductions in their efficacy and safety. UV-irradiated formulation samples were submitted to a procedure that included a reliable, precise and specific HPLC method employing a C18 column and detection at 325 and 235 nm. Methanol, isopropanol and water were the mobile phases in gradient elution. The method precision was between 0.28 and 5.07. The photostabilizers studied [diethylhexyl 2,6-naphthalate (DEHN) and benzotriazolyl dodecyl p-cresol (BTDC)], influenced the stability of octyl methoxycinnamate (OMC) associated with vitamins A and E. BTDC was considered the best photostabilizer to vitamins and OMC when the UV-filters were combined with both vitamins A and E. 相似文献
868.
The Cl‐atom‐initiated oxidation of two esters, ethyl formate [HC(O)OCH2CH3] and ethyl acetate [CH3C(O)OCH2CH3], has been studied at pressures close to 1 atm as a function of temperature (249–325 K) and O2 partial pressure (50–700 Torr), using an environmental chamber technique. In both cases, Cl‐atom attack at the CH2 group is most important, leading in part to the formation of radicals of the type RC(O)OCH(O?)CH3 [R = H, CH3]. The atmospheric fate of these radicals involves competition between reaction with O2 to produce an anhydride compound, RC(O)OC(O)CH3, and the so‐called α‐ester rearrangement that produces an organic acid, RC(O)OH, and an acetyl radical, CH3C(O). For both species studied, the α‐ester rearrangement is found to dominate in air at 1 atm and 298 K. Barriers to the rearrangement of 7.7 ± 1.5 and 8.4 ± 1.5 kcal/mole are estimated for CH3C(O)OCH(O?)CH3 and HC(O)OCH(O?)CH3, respectively, leading to increased occurrence of the O2 reaction at reduced temperature. The data are combined with those obtained from similar studies of other simple esters to provide a correlation between the rate of occurrence of the α‐ester rearrangement and the structure of the reacting radical. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 397–413, 2010 相似文献
869.
Exploitation of symmetry in periodic Self-Consistent-Field ab initio calculations: application to large three-dimensional compounds 总被引:1,自引:0,他引:1
Marco De La Pierre Roberto Orlando Matteo Ferrabone Claudio M. Zicovich-Wilson Roberto Dovesi 《中国科学:化学(英文版)》2014,57(10):1418-1426
Symmetry can dramatically reduce the computational cost (running time and memory allocation) of Self-Consistent-Field ab initio calculations for crystalline systems. Crucial for running time is use of symmetry in the evaluation of one- and two-electron integrals, diagonalization of the Fock matrix at selected points in reciprocal space, reconstruction of the density matrix. As regards memory allocation, full square matrices (overlap, Fock and density) in the Atomic Orbital (AO) basis are avoided and a direct transformation from the packed AO to the SACO (Symmetry Adapted Crystalline Orbital) basis is performed, so that the largest matrix to be handled has the size of the largest sub-block in the latter basis. We here illustrate the effectiveness of this scheme, following recent advancements in the CRYSTAL code, concerning memory allocation and direct basis set transformation. Quantitative examples are given for large unit cell systems, such as zeolites (all-silica faujasite and silicalite MFI) and garnets (pyrope). It is shown that the full SCF of 3D systems containing up to 576 atoms and 11136 Atomic Orbitals in the cell can be run with a hybrid functional on a single core PC with 500 MB RAM in about 8 h. 相似文献
870.
Tabanca N Bernier UR Tsikolia M Becnel JJ Sampson B Werle C Demirci B Başer KH Blythe EK Pounders C Wedge DE 《Natural product communications》2010,5(9):1409-1415
Natural plant extracts often contain compounds that are useful in pest management applications. The essential oil of Eupatorium capillifolium (dog-fennel) was investigated for antifungal and insecticidal activities. Essential oil obtained by hydrodistillation of aerial parts was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC/MS). The major components were determined to be thymol methyl ether (=methyl thymol) (36.3%), 2,5-dimethoxy-p-cymene (20.8%) and myrcene (15.7%). Antifungal activity of the essential oil was weak against the plant pathogens Colletotrichum acutatum, C. fragariae, and C. gloeosporioides in direct bioautography assay. The E. capillifolium oil showed promising repellent activity against the yellow fever mosquito Aedes aegypti, whereas the oil exhibited moderate activity against the mosquito's first instar larvae in a high throughput bioassay. Topical applications of the oil showed no activity against the blood-feeding female adults of A. aegypti. Eupatorium capillifolium essential oil showed a linear dose response between adult lace bug (Stephanitis pyrioides) mortality and increasing oil concentration in an adulticidal activity bioassay. The dog-fennel oil was more potent than the conventional insecticide malathion. In conclusion, these combined results showed Eupatorium capillifolium oil is a promising novel source of a biological insecticide with multiple modes of action. 相似文献