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131.
Torquato Mussini Maurizio Cicognini Paolo Longhi Sandra Rondinini Arthur K. Covington 《Analytica chimica acta》1984
Standard pH(S) values for 0.05 mol kg?1 potassium hydrogenphthalate (KHpH) reference buffer solutions in 10, 30 and 50% (w/w) 1,4-dioxane/water solvent mixtures within the temperature range 288.15–318.15 K are determined from e.m.f. measurements of the cell without transference Pt|H2|KHPh + KCl|AgCl|Ag|Pt. The consistency of the results is analysed by a recently described method of multilinear regression of the quantity p(aHγCl) as a function of both solution composition and temperature. The standard pH(S) determined can be reproduced to within ±0.01 by the equation pH(S) - 4.004 + 3.309w + 0.408z + 1.037w3 - 14.95zw2 + 27.1zw3, where w is the weight fraction of dioxane in the solvent mixture,z = (T –θ)/θ, and θ - 298.15 K. Values of the first ionization constant of phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid) in the above solvent mixtures are also determined from e.m.f. measurements of the cell without transference Pt|H2|H2Ph + KHPh + KCl|AgCl|Ag|Pt. 相似文献
132.
The electrophilic iodocyclization reaction of (Z)- and (E)-5-n-alkylsubstituted 4-alken-1-ols followed by base-induced hydrodeiodination reaction stereoselectively gave, respectively, (Z)- and (E)-alkylidentetrahydrofurans in high yield. Completely different outcomes were observed with (Z)- and (E)-6,6-dimethylhept-4-en-1-ol: their iodocyclization furnished, respectively, threo- and erythro-2-(1-iodo-2,2-dimetylpropyl)tetrahydrofuran with high stereoselectivity. The threo isomer gave clean formation of 6-tert-butyl-3,4-dihydro-2H-pyran by base-induced ring expansion, while erythro isomer underwent a base-induced ring contraction to 1-cyclopropyl-3,3-dimethylbutan-1-one. Moreover, (Z)- and (E)-5-cyclopropylpent-4-en-1-ol underwent a 6-endo-iodocyclization to threo- and erythro-2-cyclopropyl-3-iodotetrahydro-2H-pyran, respectively, that under the same basic treatment, gave two isomeric 6-cyclopropyldihydro-2H-pyrans in a stereoselective fashion. 相似文献
133.
The third-rank electric hypershieldings at the nuclei of four small molecules have been evaluated at the Hartree-Fock level of theory in the Hellmann-Feynman approximation. The nuclear electric hypershieldings are closely related to molecular vibrational absorption intensities and a generalization of the atomic polar tensors (expanded in powers of the electric field strength) is proposed to rationalize these intensities. It is shown that the sum rules for rototranslational invariance and the constraints imposed by the virial theorem provide useful criteria for basis-set completeness and for near Hartree-Fock quality of nuclear shieldings and hypershieldings evaluated in the Hellmann-Feynman approximation. Twelve basis sets of different size and quality have been employed for the water molecule in an extended numerical test on the practicality of the proposed scheme. The best results are obtained with the R12 and R12+ basis sets, designed for the calculation of electronic energies by the explicitly correlated R12 method. The R12 basis set is subsequently used to investigate three other molecules, CO, N2, and NH3, verifying that the R12 basis consistently performs very well. 相似文献
134.
Air quality in Province of Trieste was studied in terms of PM10 trends. Observed correlations between PM10 and atmospheric pollutants produced by combustion are in evidence. Nitrogen oxides and PM10 are critical parameters for air quality in Province of Trieste. Wind speed has a diluting action higher than rain for all pollutants. 相似文献
135.
Bruno P Caselli M de Gennaro G De Rienzo M Ielpo P Manigrassi D 《Annali di chimica》2002,92(9):815-824
In this paper an application of new procedures for atmospheric particulate analysis is illustrated. PM10, PAHs (benzo[a]anthracene (BaA), benzo[b]fluoranthene (BbF), benzo[j]fluoranthene (BjF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1, 2, 3-cd]pyrene (Ip), dibenzo[a, h]anthracene (DbA)) and heavy metals (Cu, Ni, Zn, Co, Mn, Cd, Fe and Pb) were investigated. PM10 determination was performed by gravimetric method, PAHs were measured by GC-MS, and heavy metals by HPIC. An air quality monitoring campaign on the territory of Bari municipality has been organised, and its results are shown. 相似文献
136.
Fábio C. Sampaio Paolo Torre Flávia M. Lopes Passos Célia Alencar de Moraes Patrizia Perego Attilio Converti 《Applied biochemistry and biotechnology》2007,136(2):165-181
To obtain in-depth information on the overall metabolic behavior of the new good xylitol producer Debaryomyces hansenii UFV-170, batch bioconversions were carried out using semisynthetic media with compositions simulating those of typical acidic
hemicellulose hydrolysates of sugarcane bagasse. For this purpose, we used media containing glucose (4.3–6.5 g/L), xylose
(60.1–92.1 g/L), or arabinose (5.9–9.2 g/L), or binary or ternary mixtures of them in either the presence or absence of typical
inhibitors of acidic hydrolysates, such as furfural (1.0–5.0 g/L), hydroxymethylfurfural (0.01–0.30 g/L), acetic acid (0.5–3.0
g/L), and vanillin (0.5–3.0 g/L). D. hansenii exhibited a good tolerance to high sugar concentrations as well as to the presence of inhibiting compounds in the fermentation
media. It was able to produce xylitol only from xylose, arabitol from arabinose, and no glucitol from glucose. Arabinose metabolization
was incomplete, while ethanol was mainly produced from glucose and, to a lesser less extent, from xylose and arabinose. The
results suggest potential application of this strain in xyloseto-xylitol bioconversion from complex xylose media from lignocellulosic
materials. 相似文献
137.
A new high-performance liquid chromatographic/electrospray ionization tandem mass spectrometric (HPLC/ESI-MS/MS) method was developed for the simultaneous quantification of 5-fluorouracil (5FU), methotrexate (MTX) and cyclophosphamide (CP) in environmental samples. These compounds, commonly used in the treatment of cancer, are recognized as genotoxic. In order to estimate the occupational exposure of hospital personnel handling these drugs, wipe samples were taken from the working surfaces and directly analyzed (with trophosphamide as internal standard) using a reversed-phase capillary column and MS/MS detection. This is the first HPLC/MS/MS method for the simultaneous determination of 5FU, MTX and CP. The present method offers high sensitivity, with detection limits of 1.1 microg l(-1) for MTX and CP and 33.3 microg l(-1) for 5FU, avoiding any sample preconcentration procedure. Rapidity, specificity, high accuracy (mean values between 92.4 and 99.9%) and precision (mean RSD values between 3.4 and 12.1%) make the method suitable for the routine determination of these three antineoplastic drugs. 相似文献
138.
The electroanalytical method described for the simultaneous determination of concentration, the number of electrons involved in the redox process and diffusion coefficient is based on evaluation of the ratios between the currents recorded for the analyte and for an easily standardized reference species dissolved in the same medium. Three different electroanalytical techniques are used in which the currents exhibit, for two techniques at least, different dependences on both the diffusion coefficient and electron number. The approach is applicable to diffusion-controlled processes, regardless of the degree of reversibility involved. Reliability tests with electroactive organic compounds dissolved in dimethyl sulphoxide show that both accuracy and precision are within 10% depending on the chosen combination of techniques. 相似文献
139.
The use of high-performance ion chromatography (HPIC) for the determination of N-nitrosoglyphosate [N-nitroso-N-(phosphonomethyl)glycine] is reported. NMR, spectrophotometric and electroanalytical measurements showed that two conformers of N-nitrosoglyphosate in slow equilibrium are always present. Separation of these conformers is achieved by using appropriate chromatographic conditions. The conductimetric detection of N-nitrosoglyphosate and glyphosate and application to the determination of traces of N-nitrosoglyphosate in complex matrices are also reported. 相似文献
140.
2-Mercapthoethanol undergoes carbonylation in pyridine solution in the presence of oxygen and of [Ni(CO)3Pyl as a catalyst to give cyclic O, S-ethylelnethiorcarbonate. The isolation of thiolatonickel compound [Ni(SCH2CH2OH)2] by the oxidation of a solution containing [Ni(CO)3Py] and 2-mercaptoethanol, and its reaction with carbon monoxide to give the cyclic thiocarbonate and [Ni(CO)3Py] prove that the reaction proceeds in at least two steps. 相似文献