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991.
992.
Catalán LE Marín KC Altamirano HC Fritis MC Chamy MC 《Molecules (Basel, Switzerland)》2007,12(12):2605-2620
A route for the degradation of the side chain of ent-labdane derivatives has been devised, giving the useful synthon 2beta,12-dihydroxy-13,14,15,16,17-pentanor-ent-labdane-8-one (8). The use of this compound in the preparation of terpenylquinone derivatives shall be reported elsewhere. In addition we have synthesized the compound 2beta,12-diacetoxy-8beta,17-epoxy-13,14,15,16-tetranor-ent-labdane (10), which upon catalytic epoxide ring opening in alkaline or acid media gave rise in all cases to the formation of tricyclicc ompounds. 相似文献
993.
Burguete MI García-España E López-Diago L Luis SV Miravet J Sroczynski D 《Organic & biomolecular chemistry》2007,5(12):1935-1944
Dioxapolyaza cyclophanes derived from resorcinol and different polyamine chains have been studied in aqueous solution as abiotic receptors for nucleotides. The presence of the additional ethyleneoxy subunits is reflected in a higher basicity and in a significant increase in the log K values for the interaction with nucleotides relative to that of related polyazacyclophanes. 相似文献
994.
995.
Hannon AC Di Martino D Santos LF Almeida RM 《The journal of physical chemistry. B》2007,111(13):3342-3354
Neutron diffraction data with high real-space resolution are reported for an extensive series of cesium germanate glasses with 2, 5, 10, 15, 18, 21, 25, and 30 mol % Cs(2)O, and also for pure GeO(2) in its vitreous, quartz, and rutile forms. The results for pure GeO(2) show that neutron diffraction can clearly identify an increase in the Ge-O coordination number above the tetrahedral value of four. The results for cesium germanate glasses give strong evidence that the Ge-O coordination number rises to a maximum of 4.36 +/- 0.03 for 18 mol % Cs(2)O and then declines. This behavior may be associated with the germanate anomaly in the thermophysical properties. A model is developed for the composition-dependence of the Ge-O coordination number, and according to this model the rise in the coordination number involves the formation of mostly GeO(5) units, rather than GeO(6) units. Our results also show that the low alkali anomaly is a longer range phenomenon, and is not associated with a preference for the formation of nonbridging oxygens for very low alkali oxide content. 相似文献
996.
Moreno-Osorio L Espinoza L Cuellar M Preite M 《Magnetic resonance in chemistry : MRC》2007,45(11):993-996
Two naturally occurring 11-nordrimanes were synthesized, and their (1)H and (13)C NMR spectra were unambiguously assigned in full for the first time. 相似文献
997.
998.
De Souza D de Toledo RA Galli A Salazar-Banda GR Silva MR Garbellini GS Mazo LH Avaca LA Machado SA 《Analytical and bioanalytical chemistry》2007,387(6):2245-2253
The use of a copper solid amalgam electrode (CuSAE) for the analytical determination of triazine herbicides (atrazine and
ametryne) instead of the conventional hanging mercury drop electrode (HMDE) is reported. The results obtained using electroanalytical
methods utilizing each of these electrodes were also compared with those provided by the HPLC technique. The results indicated
that the CuSAE electrode can be used to detect the herbicides studied, since the detection limits reached using the electrode
(3.06 μg L−1 and 3.78 μg L−1 for atrazine and ametryne, respectively) are lower than the maximum values permitted by CONAMA (Brazilian National Council
for the Environment) for wastewaters (50 μg L−1) and by the US EPA (Environmental Protection Agency of the United States) in natural water samples (10.00 μg L−1). An electroanalytical methodology employing CuSAE and square wave voltammetry (SWV) was successfully applied to the determination
of atrazine and ametryne in natural water samples, yielding good recoveries (70.30%–79.40%). This indicates that the CuSAE
provides a convenient substitute for the HMDE, particularly since the CuSAE minimizes the toxic waste residues produced by
the use of mercury in HDME-based analyses. 相似文献
999.
Roque J. Minari Georgina S. Stegmayer Luis M. Gugliotta Omar A. Chiotti Jorge R. Vega 《大分子反应工程》2007,1(3):405-412
This work investigates the industrial production of styrene‐butadiene rubber in a continuous reactor train, and proposes a soft sensor for online monitoring of several processes and polymer quality variables in each reactor. The soft sensor includes two independent artificial neural networks (ANN). The first ANN estimates monomer conversion, solid content, polymer production, average particle diameter, and average copolymer composition; the second ANN estimates average molecular weights and average branching degrees. The required ANN inputs are: (i) the reagent feed rates into the first reactor and (ii) the reaction heat rate in each reactor. The proposed ANN‐based soft sensor proved robust to several measurement errors, and is suitable for online estimation and closed‐loop control strategies.
1000.
A simple, sensitive, and specific biodiffusion assay for the antibacterial ceftazidime was developed using a strain of Staphylococcus epidermidis (ATCC 12228) as the test organism. Ceftazidime was measured in powder for injection at concentrations ranging from 100 to 400 microg/mL. The calibration graph for ceftazidime was linear (r2 = 1), and the method validation showed that it was precise (relative standard deviation = 0.415) and accurate. The results obtained by biodiffusion assay were statistically calculated by linear parallel model and by means of regression analysis and were verified using analysis of variance. It was concluded that the microbiological assay is satisfactory for in vitro quantification of the antibacterial activity of ceftazidime in pharmaceuticals. 相似文献