SYNTHESIS OF MESOPOROUS POLY(STYRENE-co-MALEIC ANHYDRIDE)/SILICA HYBRID MATERIALS VIA A NONSURFACTANT-TEMPLATED SOL-GEL PROCESS*

Mesoporous poly (styrene-co-maleic anhydride)/silica hybrid materials have been prepared. The synthesis wasachieved by the HCl-catalyzed sol-gel reactions of tetraethyl orthosilicate (TEOS) and styrene-maleic anhydride copolymerin the presence of 3-aminopropyl triethoxysilane (APTES) as a coupling agent and citric acid as a nonsurfactant template orpore-forming agent, followed by ethanol extraction. Characterization results from nitrogen sorption isotherms and powder X-ray diffraction indicate that polymer-modified mesoporous materials with large specific surface areas (e.g. 900 m~2/g) andpore volumes (e.g. 0.6 cm~3/g) could be prepared. As the citric acid concentration is increased, the specific surface areas, porevolumes and pore diameters of the hybrid materials increase.     

Analysis of dielectric observations of KCl-charged poly(methyl methacrylate) microcapsules using a two-component model consisting of KCl-permeable and KCl-impermeable capsules

Dielectric measurements were carried out on aqueous suspensions of poly(methyl methacrylate) microcapsules charged with KCl solutions to examine the KCl permeability of the microcapsules. The specimens exhibited three kinds of dielectric relaxation. Two kinds of dielectric relaxation were observed immediately after washing the specimens with distilled water. These overlapped each other when the specimen was left standing in the measuring cell for a long time. Their relaxation frequencies were affected by the KCl concentration of the suspending medium in which the specimen was kept before washing. Another relaxation was observed distinctly when the spepcimens were washed thoroughly with distilled water. Its relaxation frequency was affected by the KCl concentration of the charged solution. These results were explained by assuming that the specimens were mixtures of KCl-permeable and KCl-impermeable capsules. The theoretical analysis procedure was devised in the light of dielectric theory of interfacial polarization to estimate the parameters which characterize the structure of the specimens.     

MORPHOLOGIES AND GAS SEPARATION PROPERTIES OF MELT-SPUN ASYMMETRIC POLY(4-METHYL-1-PENTENE)HOLLOW FIBER MEMBRANES*

Poly(4-methyl-1-pentene) (PMP) hollow fiber membranes were prepared by the melt-spun and cold-stretch(MSCS) method. Scanning electronic microscopy (SEM) was used to characterize the section and surface structures of themembranes with special asymmetric structure. The preliminary results of gas permeation measurements indicated that the resultant hollow fiber membranes have the potential ability for oxygen/nitrogen separation.     

A Biokinetic Model to Describe Consequences of Inhibition/Stimulation in DNA-Proofreading and -Repair,Part 2. Calibration of the Model

Summary.  A biokinetic model has been developed to describe the mathematical consequences of inhibition, respectively stimulation of proofreading. According to data reported in the literature, a first approximative calibration of the model has been carried out in an attempt to make it both: practically applicable and comparable with experimental data and clinical facts. The model is open for further improvements and adjustable according to results of further researches via the parameters chosen. In a first test of the model it is shown that it does well reflect the results described in the literature upon proof-reading-inhibition and its consequences, i.e., the reduction of replication-fidelity (→ exponential increase of malignant cells with time). As a further result it is shown that the model also does well describe in its kinetic approach opposite effects as, e.g., a reduction of wrong genetic information by classical cancer-therapies like chemotherapy and surgergy. The system is orientated towards known biochemical relations and chemical similarities together with a discussion of the potential chance which offer special combinations of chemically identifyable substances (like nucleotides’ precursors or effector-molecules contained in low-molecular-human-placenta-extracts as an alternative to umbilical cords’-blood/cells) as stimulators of the enzymatic proof-reading- and -repair-machinery. E-mail: Haschke.H@isovolta.com Received January 20, 2002; accepted (revised) June 26, 2002     

On-line sorption preconcentration of metals based on mixed micelle cloud point extraction prior to their determination with micellar chemiluminescence: Application to the determination of chromium at ng l levels

The on-line incorporation of cloud point extraction (CPE) to flow injection analysis (FIA) is modified to extract and preconcentrate metal species rapidly, avoiding the formation of hydrophobic complexes, using a mixed micellar medium. Coupling the procedure with chemiluminescence (CL) detection based on the catalytic activity of metal species on the luminol-hydrogen peroxide reaction and enhancing the signal with the presence of a micellar carrier containing bromide ions produces a powerful tool for the preconcentration and determination of metal species at ng l⁻¹ levels. As an analytical demonstration ultratrace concentrations of chromium were conveniently detected and quantified in samples with a complex matrix such as seawater and wastewater. The figures of merit for the determination of chromium were: 0.9-1.6% R.S.D. (n=5) with detection and quantification limits 0.5 and 2.0 ng l⁻¹, respectively. The calibration graph was rectilinear from 2 to 200 ng l⁻¹ (r=0.9996, n=6). Several other metal ions were determined in ideal situations, with analogous results.     

Electroreduction of cerium ions on silver electrode in halide melts at 973 K

The mechanism of electroreduction of cerium ions in equimolar KCl-NaCl melt is explored at 973 K. The effect of the anionic composition of the melt on the electroreduction of cerium ions is studied. It is shown that the electrodeposition of metal cerium from halide melts on a silver electrode is the primary electrochemical process that occurs at potentials more positive than those corresponding to the supporting-electrolyte decomposition. The electroreduction of chloride complexes of cerium on a silver electrode in the melt in both steady-and non-steady-state polarization modes at rates below V ≤ 0.5 V/s is limited by the diffusion delivery; at higher polarization rates, the charge-transfer stage predominates.     

网胰藻Hydroclathrus clathratus的化学成分研究

报道从中国南海网胰藻Hydroclathrus clathratus中分离得到3个单体化合物,经过MS,IR,1HNMR,13CNMR(DEPT),HMQC和HMBC等波谱技术鉴定为:(6R,7aS)-6-羟基-4,4,7a-三甲基-2,4,5,6,7,7a-六氢苯并呋喃-2-酮(1),1-(2-脱氧-β-D-呋喃核糖)-5-甲基-1,2,3,4-四氢嘧啶-2,4-二酮(2),尿嘧啶(3),并通过X射线单晶衍射实验确定化合物1的立体结构,其中化合物1是首次从自然界中分离得到.     

LB膜诱导Ba(NO3)2晶体取向生长

In this work, Ba(NO₃)₂ crystals with single crystal face were induced by using the the method of bio-mimetic mineralization and double LB films of behenic acid (BA) as the template. The crystals were characterized by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The crystals were observed in regular square shape with uniform size about 5～8 μm by SEM, and they were found by XRD to grow along the (111) plane. From these experiments, we can conclude that the good selection of the (111) crystal face of Ba(NO₃)₂ is due to the electrostatic interactions , the match between this crystal face and the definite lattice structure of the LB films.     

Carbon-bromine cleavage by dimethyl sulfoxide: the key step of C(5) functionalization of push-pull 2-alkylidene-4-oxothiazolidine vinyl bromides

Push-pull 2-alkylidene-4-oxothiazolidine vinyl bromides undergo efficient C(5) functionalization through DMSO-assisted carbon-bromine cleavage, followed by a bromine transfer-substitution (or elimination) sequence. A mechanism for this novel transformation is proposed.