Influence of Ce addition on the catalytic behavior of alumina-supported Cu-Co catalysts in NO reduction with CO

Polyvinylidene difluoride (PVDF) is one of the most widely used piezoelectric materials in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS) due to its excellent properties. Its applications range from biological to electric devices, such as an artificial hip joint, a microgripper, and a force sensor. It is critical to understand friction, adhesion, and wear mechanisms of this material. In this study, effect of piezoelectricity and lubricant with electric field on tribological properties was investigated, using poled and unpoled PVDF. To understand the tribological properties at nano- and macroscales, scale effect was also studied using an AFM and a tribometer. Relevant mechanisms are discussed.     

Polymerization of ε-caprolactone initiated by stable salts. Initiation mechanism

The mechanism of initiation of ε-caprolactone polymerization by stable salts has been investigated. Gel permeation chromatography and ¹H-NMR spectroscopy were used for determining the compositions of the reaction mixtures and of the polymers. It was established that the initiation proceeds by addition of the initiator to the monomer.     

Controlled intracellular localization and enhanced antisense effect of oligonucleotides by chemical conjugation

Oligonucleotides can be covalently linked to peptides composed of any sequence of amino acids by solid phase fragment condensation. The peptides incorporated into the conjugates include nuclear localizing signals (NLS), nuclear export signals (NES), membrane fusion domain of some viral proteins and some designed peptides with amphipathic character. Evaluation of biological properties of DNA-peptide conjugates indicated that (a) the conjugates could bind to target RNA and dsDNA with increased affinity, (b) the conjugates were more resistant to cellular nuclease degradation, (c) the conjugate-RNA hybrids could activate RNase H as effectively as native oligonucleotides, (d) the conjugates with fusion peptides showed largely enhanced cellular uptake, (e) the conjugates with NLS could be predominantly delivered into the cell nucleus, (f) the conjugates with NES could be localized in the cytoplasm. As a result, antisense oligonucleotides conjugated with NLS could inhibit human telomerase in human leukemia cells much more strongly than phosphorothioate oligonucleotides.     

Enhancement of the photoluminescence of CdSe quantum dots during long-term UV-irradiation: privilege or fault in life science research?

The present study describes an impressive enhancement of the photoluminescence (PL) intensity of low-temperature synthesized CdSe nanocrystals (75 degrees C) during long-term UV-irradiation. The integrated PL-intensity of CdSe core and CdSe/ZnS core/shell nanocrystals, dispersed in chloroform, enhanced about 3 and 6 times, respectively, during 9 h exposure to UV-light, without any significant changes in the characteristic absorbance spectra and shifting of PL-spectra. After termination of the irradiation a comparatively slow photobleaching was detected with tau(1/2) = 6 h for CdSe core and tau(1/2) = 14 h for CdSe/ZnS core/shell nanocrystals. The most impressive was the effect of UV-irradiation on the photoluminescence of water-soluble CdSe nanocrystals. The integrated PL-intensity enhanced about 10 times during 11 h exposure to UV-light and the improved PL-intensity was preserved during 3 days after termination of the irradiation without any significant photobleaching. The results are discussed in the context of application of CdSe nanocrystals as novel fluorophores in life science experiments.     

Interaction of triphenylmethyl salts with vinyl ethers

The initiation of isobutyl, n-butyl, ethyl, and 2-chloroethyl vinyl ethers polymerization by trityl ion salts was investigated. The oligomers formed and the reaction mixtures were analyzed by GPC and ¹H-NMR spectroscopy. It is concluded that the initiation proceeds via two competing reactions. The addition of the initiator to the monomer is determined as usual by the electrophilicity of the former and the nucleophilicity of the latter. In order to realize initiation by hydride transfer it is necessary for the monomer to possess a hydrogen atom with hydride mobility and that the cation obtained is sufficiently stable. The relative part of these initiation reactions is determined.     

Transition from complete to partial wetting within membrane compartments

Wetting and dewetting phenomena are ubiquitous, but wetting transitions have been reported only in a few experimental systems. In this work, we present a wetting transition in a mesoscopic membrane compartment for the first time. A two-phase aqueous polymer solution was encapsulated in a giant vesicle (few tens of micrometers in size). The polymers used are poly(ethyleneglycol) (PEG) and dextran. By increasing the polymer concentration in the vesicle, the PEG-rich phase changed from complete wetting to partial wetting of the membrane.     

Synthesis of nylon‐6 triblock copolymers with bifunctional polymeric activators

ABA‐type copolymers were synthesized by the anionic polymerization of hexanelactam with the sodium salt of hexanelactam as an initiator and amino‐terminated polytetrahydrofuran telechelic functionalized with diisocyanates. Two types of diisocyanates, hexamethylene diisocyanate (1,6‐diisocyanatohexane) and isophorone diisocyanate (IF; 5‐isocyanato‐1‐isocyanatomethyl‐1,3,3‐trimethylcyclohexane), were used as precursors for polymeric activators (PACs). IF was used for the first time. It was proven that the PACs were incorporated as soft, flexible midblocks in the chains of hard nylon‐6 segments. The polymers were isolated and characterized with various spectroscopic techniques. The effects of the central PAC block (according to the type, molecular weight, and content) and the polymerization conditions on the kinetics, activation energies, molecular weights, and structures of the triblock copolymers were investigated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4154–4164, 2000     

Bis-macromonomers of 2-alkyl-2-oxazolines–synthesis and polymerization

Poly(2-alkyl-2-oxazoline)s having an acrylate group at both chain ends were synthesized by terminating living bifunctional poly(2-methyl-2-oxazoline) or poly(2-ethyl-2-oxazoline) with acrylic acid. These macromonomers have been polymerized to the corresponding polyoxazoline networks. Thermal as well as UV-initiated free radical polymerization were applied and the influence of the polymerization conditions and molecular weight of the prepolymer used on the properties of the networks were investigated. Both methods of polymerization produced high fractions of soluble material, probably due to the low concentration of the acrylate end groups.     

Nonradioactive telomerase activity assay by microchip electrophoresis: privileges to the classical gel electrophoresis assay

The present study accents on the privileges of microchip-based electrophoresis to the conventional gel electrophoresis in separation of telomerase repeat amplification protocol/polymerase chain reaction (PCR) ladder products obtained in telomerase-catalyzed reaction in cancer cells. We try to clarify the interpretation of the results obtained by both electrophoretic procedures and to avoid misinterpretation as a result of PCR-dependent artefacts.