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131.
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
132.
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
133.
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
134.
The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium
was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair,
lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization
rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization
with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid
chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to
reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results
showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent
with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the
cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence
of ferrous ion was also necessary together with the lactate and sulfate substrates. 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.
Cristina Rota Lino Liverani Franco Spelta Giuseppe Mascellani Aldo Tomasi Anna Iannone 《Research on Chemical Intermediates》2006,32(1):73-81
The use of low-molecular-weight heparins (LMWHs) has become common, since compared to unfractionated heparin (UFH), they have
a much longer plasma half-life and lower incidence of side effects. LMWHs are derived from the depolymerization of UFH, obtained
either chemically, physically or enzymatically. We employed electron spin resonance (ESR) spectroscopy to study the depolymerization
of UFH by copper in the presence of hydrogen peroxide. A stable nitroxide radical was detected. This could be generated by
the hydroxyl radical attack either to the N-SO−3 group or to free amino groups present in the UFH preparation. 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