Separation of polycyclic aromatic hydrocarbons by micellar electrokinetic chromatography with aqueous short-chain alcohol solvent

Micellar electrokinetic capillary chromatography (MEKC) with aqueous organic solvent has been developed to separate polycyclic aromatic hydrocarbons (PAHs). Methanol, ethanol or propanol as an organic modifier was added to sodium dodecyl sulfate (SDS) micellar solution in order to increase the solubility of very hydrophobic solutes in mobile phase. Both methanol and ethanol can be used as co-solvents for the separation of PAHs. Use of ethanol resulted in a shorter analysis time than use of methanol. The separations of some PAHs were unsatisfactory using propanol although the analysis time was much shorter than with ethanol. The influence of ethanol content, SDS concentration and temperature on the separations was studied. Benzene and nine polycyclic aromatic hydrocarbons were successfully separated using 50 mM SDS-20 mM phosphate-5 mM borate, containing 40% (v/v) ethanol at 35 degrees C. The relative standard deviation (R.S.D.) of t(R) ranged from 0.5 to 1.5% for six repeat injections.     

Control of mesoporous structure of aerogels derived from cresol-formaldehyde

Polycondensation of a cresol mixture (C(m)) with formaldehyde (F) in basic aqueous solutions leads to formation of highly cross-linked C(m)F aquagels that can be supercritically dried with carbon dioxide to form organic C(m)F aerogels. Aerogels synthesized with different catalyst contents and reactant concentrations are characterized by low-temperature nitrogen adsorption. The present experimental results suggest that the C(m)F aerogels are typical mesoporous materials and have almost no micropores in bulk. The microstructure of the organic C(m)F aerogels can be controlled and tailored effectively by varying synthesis conditions during the initial sol-gel process. C(m)F organic aerogels with specific surface area as high as 627 m(2)/g and corresponding pore volume 2.06 ml/g have been obtained with a dominant pore size of 30 nm. C(m)F organic aerogels with peaky pore size distributions concentrated at 11 nm have also been prepared.     

2型糖尿病患者血清钙镁与甲状腺激素含量变化及临床意义

为了监测 2型糖尿病人血清钙、镁和甲状腺激素含量 ,分析其临床意义及相关性 ,应用放射免疫分析法测定了 1 1 5例 2型糖尿病及 1 5 0例健康人血清甲状腺激素含量。同时用美国杜邦RXL自动生化仪测定了其血清钙、镁含量。结果表明 ,在 2型糖尿病伴有明显并发症者血镁、FT3水平明显降低 (P <0 0 5 ) ,钙镁两种元素与甲状腺激素水平无明显相关性。 2型糖尿病患者适当补镁对预防其并发症是有益的 ,测定FT3 等可作为判断 2型糖尿病严重程度和估计预后的参考指标。     

A NEW ONE-STEP REDUCTIVE N-ALKYLATION OF AMINO ACIDS AND THEIR ESTERS

The reductive alkylation of amine with carbonyl compounds usingsodium hydrogen telluride has been investigated in recent years.Application of this method to the synthesis of N-alkyl derivativesof biologically important amino acids and their esters is described.     

One-Pot Formation of Carbonates from the Reactions of Carbonyl Compounds with Samarium Diiodide and Methyl Chloroformate

Treatment of carbonyl compounds with SmI₂ and methyl chloroformate in the presence of molecular sieves provides the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry obtained by this procedure is different from that of conventional pinacolic couplings.     

Study of the Fluorescence System of Europium–Enoxacin and its Applications

 This paper is the study of the fluorescence enhancement of Eu³⁺-1-ethyl-6-fluoro-4-oxo-7-(1-piperazinyl)-1,8-naphthyridin-3-carbonic acid (enoxacin, EFLX) system by surfactants. It was found that sodium dodecylbenzenesulfonate (SDBS) exhibits great enhancement on the fluorescence of the Eu-EFLX system. The molar ratio is 1:2:1 for Eu:EFLX: SDBS. Under the optimum conditions, the fluorescence intensity is a linear function of europium in the range of 1.0 × 10⁻⁸ ∼ 5.0 × 10⁻⁶ mol/L, the detection limit is 1.0 × 10⁻⁹ mol/L. The application of the Eu-EFLX-SDBS system for the determination of trace europium in rare earth samples gave satisfactory results. Received October 19, 2000. Revision August 10, 2001.     

Resolution of the non-steady-state kinetics of the two-step mechanism for the Diels-Alder reaction between anthracene and tetracyanoethylene in acetonitrile

The Diels-Alder reaction between anthracene and tetracyanoethylene in acetonitrile does not reach a steady-state during the first half-life. The reaction follows the reversible consecutive second-order mechanism accompanied by the formation of a kinetically significant intermediate. The experimental observations consistent with this mechanism include extent of reaction-time profiles which deviate markedly from those expected for the irreversible second-order mechanism and initial pseudo first-order rate constants which differ significantly from those measured at longer times. It is concluded that the reaction intermediate giving rise to these deviations cannot be the charge-transfer (CT) complex, which is formed during the time of mixing, but rather a more intimate complex with a geometry favorable to the formation of the Diels-Alder adduct. The kinetics of the reaction were resolved into the microscopic rate constants for the individual steps. The rate constants, as shown in equation 1, at 293 K were observed to be 5.46 M(-)(1) s(-)(1) (k(f)), 14.8 s(-)(1) (k(b)), and 12.4 s(-)(1) (k(p)). Concentration profiles calculated under all conditions show that intermediate concentrations increase to maximum values early in the reaction and then continually decay during the first half-life. It is concluded that the charge-transfer complex may be an intermediate preceding the formation of the reactant complex, but due to its rapid formation and dissociation it is not detected by the kinetic measurements.