Synthesis and characterization of MCM-48 tubular membranes

MCM-48 membranes have been prepared on alumina supports of different pore sizes. A battery of characterization techniques has been used to study the physical properties and the quality of the membranes prepared. The highest quality membranes were prepared on supports with pore size of up to 60 nm. The MCM-48 membranes were tested in the separation of gas phase mixtures and a cyclohexane/O₂ selectivity higher than 270 was obtained. The selective separation of organic compounds from inert components is a result of the cooperative effects of capillary condensation in MCM-48 pores and of the specific interactions of the permeating compounds and the membrane material.     

Terbium-sensitized luminescence determination of levofloxacin in tablets and human urine and serum

A selective and sensitive luminescence method for the determination of levofloxacin is described. The method is based in the luminescence signal from a terbium(III)-levofloxacin complex, in a micellar solution of sodium dodecyl sulfate (SDS), using a chemical deoxygenation agent (Na2SO3). The method allows the determination of 8-600 ng mL-1 of levofloxacin in 10 mM SDS solution containing 0.04 M acetic acid-sodium acetate buffer (pH 6) and 7.5 mM Na2SO3 with lambda exc = 292 nm and lambda em = 546 nm. The luminescence method was applied to the determination of the levofloxacin in a Spanish commercialized pharmaceutical formulation Tavanic (Hoechst Marion Roussel). Good concordance was found between the nominal and experimental values (500 and 488 mg, respectively), with a relative standard deviation (RSD) of 0.6%. The proposed method was shown to be 100-fold more sensitive than the spectrophotometric method, and nearly 2-fold more sensitive than the fluorescence method. The method was also applied to levofloxacin determination in human serum (by external calibration method) and urine (by standard additions method), spiked at levels found after drug administration at normal clinical doses. Average recoveries found were 90.1 (RSD 1%) and 102 (RSD 1.9%), respectively.     

Compatibility mechanisms between EVA and complex impact heterophasic PP-EPx copolymers as a function of EP content

Compatibility mechanisms between EVA and complex heterophasic iPP-EPx copolymers have been studied as a function of EP content. Systematic studies were made in order to characterize the thermal, morphological and mechanical behavior, before and after blending a series of PP-EPx/EVA concentrations. Multiple melting, proportional to the EP content, was observed for the neat copolymers and an explanation was given for its evolution in terms of rejection-like secondary crystallization. After blending with EVA, the generation of a single T_g was taken as an indication of compatibility between both polymers. A morphological transition toward compatibility was first determined at 20 wt.% EVA which was in correlation with a morphological change from isolated spherical domains to interconnected voids. A second morphological transition from interconnected voids to fibrous crystals was observed above 40 wt.% EVA. This last transition marked the beginning of compatibility. Overall, the evolution of blends was explained in terms of the nature of the complex heterophasic copolymers. Tensile mechanical studies were also consistent with morphological changes. Increases in the x content in EPx and in EVA concentration worked in favor of impact resistance.     

Synthesis and reactivity of N-[α-acetoxy)-4-pyridylmethyl]-3,5-dimethylbenzamide

The synthesis of N-[(α-acetoxy)-4-pyridylmethyl]-3,5-dimethylbenzamide (4) and its reactivity are described. Since the acetoxy is a good leaving group, 4 gives S_N processes easily.     

Mathematical modeling of physico-chemical characteristics of cement-waste composites in radioactive waste management

An optimization of mortar (as matrix), improved with bentonite clay, used for immobilization of radionuclides⁶⁰Co,¹³⁷Cs,⁸⁵Sr and⁵⁴Mn, is presented. A relatively simple mathematical model is given, which permits minimization of leach rate and permeability and maximization of compressive strength. An optimal solution, based on experimental data, is given. These results will be used for a future Yugoslav radioactive waste storing center.     

Photophysics and redox behavior of chiral transition metal polymers

The absorption and emission spectra, excited-state lifetimes, quantum yields, and electrochemical measurements have been obtained for a new series of chiral complexes based on three different chiral 2,2':6',2' '-terpyridine ligands, (-)-ctpy, (-)-[ctpy-x-ctpy], and (-)-[ctpy-b-ctpy], with one, two, or multiple Ru metal centers. The room-temperature absorption and emission maxima of [[((-)-ctpy)Ru]-(-)-[ctpy-b-ctpy]-[Ru((-)-ctpy)]](PF(6))(4) and ((-)-[ctpy-b-ctpy])-[[Ru((-)-[ctpy-b-ctpy])](PF(6))(2)](n) were shifted to lower energies and also exhibited significantly longer luminescence lifetimes when compared to [Ru((-)-ctpy)(2)](PF(6))(2), [[((-)-ctpy)Ru]-(-)-[ctpy-x-ctpy]-[Ru((-)-ctpy)]](PF(6))(4), and ((-)-[ctpy-x-ctpy])-[[Ru((-)-[ctpy-x-ctpy])](PF(6))(2)](n). In terms of their electrochemical behavior, all of the complexes studied exhibited one Ru-centered and two ligand-centered redox waves and the [[((-)-ctpy)Ru]-(-)-[ctpy-x-ctpy]-[Ru((-)-ctpy)]](PF(6))(4), ((-)-[ctpy-x-ctpy])-[[Ru((-)-[ctpy-x-ctpy])](PF(6))(2)](n), and ((-)-[ctpy-b-ctpy])-[[Ru((-)-[ctpy-b-ctpy])](PF(6))(2)](n)() complexes were found to electrodeposit upon ligand-based reduction. The difference between the formal potentials of the Ru-centered and the first ligand-centered (least negative) waves corresponded linearly with the changes in the observed emission energies. The shifts in energy are discussed using a particle-in-a-box model, and the luminescence lifetimes are discussed in terms of the structure of the excited-state manifold.     

新型Zhuo酚酮类糖苷化合物的合成

根据Zhuo酮的结构特点，对Zhuo酚酮类化合物与半乳糖的Kenigs-Knorr反应进 行了研究。探索出一种具有较高立体选择性的合成方法，从而制得四种具有β－构 型的单一端基异构体的Zhuo酚酮半乳糖苷新化合物。生成的新化合物不但保持了原 有的生理活性，而且降低了毒性、提高了药效，为人工合成Zhuo酚酮类增添新化合 物的同时，也扩展了此类化合物的应用领域。应用元素分析、核磁共振、红外光谱 表征了它们的结构。     

Kinetics of the hydrogen electrode reactions of platinum in the NaHSO4 + KHSO4 eutectic melt

The kinetics of the hydrogen electrode reactions on Pt in the NaHSO₄ + KHSO₄ melt at ca. 185°C is studied. Under potentiodynamic conditions both the anodic and cathodic processes can be interpreted with the hydrogen electrode reaction mechanism already known. At potentials more negative than 0.1 V (vs. Ag/Ag⁺ (0.06 M)) the mechanism of the cathodic reaction changes because of a sulphide species formed on the electrode which is produced by a reduction of the melt components.