Synthèses dans la série des-indéno-fluorénes,VII. Le trioxo-5,12,13-dihydro-12,13-5H-bis-indéno[2.1-a; 2′.1′-g] fluoréne

Starting from 9-oxo-fluorene-1-carbaldehyde, the title compound, XII, a trioxoderivative of a new biangular diindenofluorene system, has been synthesized in 5 steps (overall yield 37,5%). The corresponding hydrocarbon could not be obtained by reduction of XII. Attempts to synthesize the isomer XX of the trioxoderivative XII are described.     

Determination of thiobarbituric acid adduct of malondialdehyde using on-line microdialysis coupled with high-performance liquid chromatography.

An on-line analytical system for the continuous monitoring of malondialdehyde (MDA) was developed. This method involves the use of microdialysis perfusion, on-line derivatization and on-line HPLC analysis. This method gave a linear response for MDA concentrations and HPLC peak areas in the range from 0.051 microM to 2.43 microM. The intra-day (RSD = 1.6-10.5%) and inter-day (RSD = 1.1-9.3%) precisions were acceptable. The average in vitro probe recovery of MDA standard was 18.4 +/- 1.0%. The detection limit was 0.03 microM, corresponding to 0.6 pmol for an injection volume of 20 microl. This method was used for in vitro peroxidation investigations, which provided evidence for elevated MDA levels following the incubation of metal ions to a linoleic acid solution.     

Isopropylation of naphthalene over modified-mordenite zeolites

Isopropylation of naphthalene with propylene was carried out over Ce-, Si-, La-, and Mg-modified mordenite zeolites. The reaction was performed in a 500 mL batch reactor at 300°C, 8 kg/cm², and naphthalene to catalyst weight ratio of 10:1, with excess propylene. It was attempted to eliminate the external acid sites of zeolites by these modifications. The results indicate that the CVD silanation and magnesium or cerium modification with Mg/Al or Ce/Al atomic ratios less than 0.5 can improve the 2,6-DIPN selectivity of mordenites. The improvement of catalyst performance is ascribed to the selective deactivation of acid sites on the external surface of HM zeolites.     

Preconcentration on hydrous magnesium oxide for neutron activation analysis

It was found that trace amount of various ions could be effectively adsorbed onto hydrous magnesium oxide from aqueous solution. Attempts were made to investigate the feasibility of using hydrous magnesium oxide as preconcentration agent for neutron activation analysis (NAA). The procedure was successfully applied for the measurements of trace amounts of elements in the surface water of a number of large rivers which play very important roles in the lives of local people. Some of them are polluted rather badly. In order to improve the living standards it is rather important to establish reliable analytical methods so that more effective surveillance may be enforced on pollution control problems. NAA is generally accepted as one of the most suitable methods for simultaneous and multielemental determination of trace amounts of elements. In this work polluted surface waters were investigated by NAA using Tsing Hua Open-pool Reactor (THOR).     

A simple regioselective synthesis of pyrimido[1,2-a]benzimidazoles

2-Aminobenzimidazoles were reacted with enaminones in acetic acid to give pyrimido[1,2-a]benzimidazoles. With a substituted enaminone only one regioisomer was obtained. Structural assignments based on nmr and uv spectroscopy are presented. Possible pathways leading to the products are discussed.     

Objective-derivative-free methods for constrained optimization

We propose feasible descent methods for constrained minimization that do not make explicit use of the derivative of the objective function. The methods iteratively sample the objective function value along a finite set of feasible search arcs and decrease the sampling stepsize if an improved objective function value is not sampled. The search arcs are obtained by projecting search direction rays onto the feasible set and the search directions are chosen such that a subset approximately generates the cone of first-order feasible variations at the current iterate. We show that these methods have desirable convergence properties under certain regularity assumptions on the constraints. In the case of linear constraints, the projections are redundant and the regularity assumptions hold automatically. Numerical experience with the methods in the linearly constrained case is reported. Received: November 12, 1999 / Accepted: April 6, 2001?Published online October 26, 2001     

Determination of the extraction constant of gold diethyldithiocarbamate dichloride by substoichiometric extraction

Radioactive gold(III) with radioactive palladium(II) as reference ion in a chloride medium was substoichiometrically extracted with zinc diethyldithiocarbamate in chloroform. A formula for calculation of the extraction constant of the gold(III) complex was derived, for which only the values of distribution ratios of gold and palladium between the two phases had to be measured experimentally. The extraction constant was found to be log K = 68.9 ± 0.4.     

SCF-Xα-SW calculation on the molecule N2 using theoretical αta

The first calculation of a molecule, N₂, by the SCF -Xα-SW method using the theoretically derived parameter α_ta is reported.     

On-line microdialysis sampling coupled with flame atomic absorption spectrometry for continuous in vivo monitoring of diffusible magnesium in the blood of living animals

A novel on-line microdialysis sampling coupled with flame atomic absorption spectrometry (FAAS) with an attractive application is reported. Microdialysates perfused through implanted microdialysis probes were directly introduced into the flame atomizer of a FAAS system using 0.2% HNO₃ as carrier solution at a nebulizer uptake flow rate of 6 ml min⁻¹. The interval for each determination was 90 s (60 s sampling time, 10 s read time and 20 s washing time). The analytical characteristics of the on-line microdialysis-FAAS system were validated as follows: linearity range, 0-300 mg l⁻¹; detection limit (3σ, n = 7), 0.53 mg l⁻¹; precision (R.S.D., n = 50), 4.1%. By comparing Mg levels in the blood of living rabbits with the results obtained from in vivo no net flux (NNF) method, the accuracy of the proposed on-line method was found to be good. The present method can be successfully applied to the in vivo monitoring of diffusible Mg in the blood of living rabbits after magnesium sulfate (MgSO₄) administration with a temporal resolution of 1.5 min.     

Effect of ionic sizes on the stability ratio of a dispersion of particles with a charge-regulated surface

The influence of the ionic sizes on the stability of a dispersion of particles, which have an amphoteric, charged-regulated surface, is discussed. A modified Poisson-Boltzmann equation, which takes into account the sizes of ionic species, is adopted to describe the electrical field. An extended DLVO theory, which takes into account the electrical, the van der Waals, and the hydration energies, is used to estimate the stability of a colloidal dispersion. The effects of the key parameters, including ionic strength, pH, and density of surface sites, on the behavior of problem under consideration are examined. The results obtained are qualitatively consistent with experimental findings in the literature.