Fluorometric sensing of alkali metal and alkaline earth metal cations by novel photosensitive monoazacryptand derivatives in aqueous micellar solutions

Novel monoazacryptand-type fluorescent chemosensors, (derived from an 18-crown-6) and (derived from a 15-crown-5) both with a pyrene ring as their photoresponsive moiety, were synthesized. Their fluorescence properties for alkali metal and alkaline earth metal cations in water were then examined. The detection of metal cations was accomplished by a change in the fluorescence intensity of the host compounds, based on a photoinduced electron transfer (PET) mechanism. In aqueous solution, showed little fluorescence upon the addition of Ba2+ because of the very weak complexation with Ba2+, but the presence of micelles of polyoxyethylene(10) isooctylphenyl ether (Triton X-100) enabled to show highly sensitive and selective Ba2+ detection among alkali metal and alkaline earth metal cations. With respect to the selective fluorescent detection of important metal cations (Na+, K+, Mg2+, Ca2+) relevant to living organisms, was found to detect K+ with high selectivity in aqueous micellar solutions of polyoxyethylene(20) sorbitan monostearate (Tween-60). The selectivity for metal cations was mainly dependent on the goodness of fit of the host cavity and the metal cation size. In the presence of anionic surfactants, detected alkaline earth metal cations more effectively than alkali metal cations.     

Study on interaction between Tb(III) and poly(N-isopropylacrylamide)-g-poly(N-isopropylacrylamide-co-styrene) core-shell nanoparticles

Based on the synthesis of poly(N-isopropylacrylamide-co-styrene) P(NIPAM-co-St) and poly(N-isopropylacrylamide) (PNIPAM) grafted P(NIPAM-co-St) core-shell nanoparticle, a new kind of thermoresponsive and fluorescent complex of Tb(III) and PNIPAM-g-P(NIPAM-co-St) (PNNS) was successfully prepared. The PNNS-Tb(III) complex was characterized with the different techniques. It was found that when PNNS with the core-shell structure interact with Tb(III), Tb(III) mainly bonded to O of the carbonyl groups of PNNS, forming the novel PNNS-Tb(III) complex. After forming the complex, the emission fluorescence intensity of Tb(III) in the complex is significantly enhanced. Especially, the maximum emission intensity of the PNNS-Tb(III) complex at 545 nm is enhanced about 223 times comparing to that of the pure Tb(III) because the effective intramolecular energy transfer from PNNS to Tb(III). The intramolecular energy transfer efficiency from PNNS to Tb(III) reaches 50%. The fluorescence intensity is related the weight ratio of Tb(III) and PNNS in the PNNS-Tb(III) complex. When the weight ratio of Tb(III) and the PNNS is 12 wt%, the enhancement of the emission fluorescence intensity at 545 nm is highest. This novel fluorescence characterization of the PNNS-Tb(III) complex may be useful in the fluorescence systems and the biomedical field.     

Functional monomers and polymers. XXXXVI. A copolymerization study of methacryloyl-type monomers containing nucleic acid bases in chloroform solution

Behavior of the free radical copolymerization of N-β-methacryloyloxyethyl derivatives of adenine with that of thymine was studied in chloroform solution, taking account of the specific base-base interaction of these monomers. Hydrogen bonding interaction between such monomers was observed by NMR spectroscopy. The acceleration of copolymerization was found to be greater either at lower monomer concentration or at lower polymerization temperature. When N-β-methacryloyloxyethylcarbazole was used as a comonomer, the rate of copolymerization showed a similar trend as in the case of usual free radical copolymerizations. From r₁ and r₂ values obtained, the copolymerization was found to be alternating, particularly in the case of copolymerization between monomers having complementary nucleic acid bases. The results suggest that the hydrogen bonding interaction between adenine and thymine plays a role in the propagation step.     

Fixation of Atmospheric Nitrogen: Synthesis of Heterocycles with Atmospheric Nitrogen as the Nitrogen Source

Dry air is the source of molecular nitrogen for reactions with TiL₄, Li, and TMSCl (L = Cl, OiPr; TMS = trimethylsilyl). The nitrogen–titanium complexes thus prepared can be used to synthesize indoles, pyrroles, and lactams from carbonyl compounds. Applying this method to 1 provides access to 2 , the key compound in the synthesis of (±)-lycopodine.     

Synthesis of platinum colloids sterically stabilized by poly(N-vinylformamide) or poly(N-vinylalkylamide) and their stability towards salt

Colloidal dispersions of nanometer-sized platinum colloids were prepared by ethanol reduction of PtCl₆ ²⁻ in the presence of poly(N-vinylformamide) (PNVF), poly(N-vinylacetamide) (PNVA) or poly(N-vinylisobutyramide) (PNVIBA) and analyzed by UV-vis spectroscopy and transmission electron microscopy. The dispersion stability of each colloid to the presence of added KCl was determined by a stirring and centrifugation procedure. The platinum colloid stabilized by PNVF (PNVF-Pt) was the most stable and its critical flocculation concentration was not observed up to the highest electrolyte concentration employed (4.0 M). The stability of the platinum colloids stabilized by poly(N-isopropylacrylamide) (PNIPAAm) and poly(vinylpyrrolidone) (PVP) was also examined. The sequence of polymer-stabilized platinum colloids in increasing order of dispersion stability was found to be PNIPAAm-Pt < PNVIBA-Pt < PVP-Pt < PNVA-Pt < PNVF-Pt. Received: 25 August 1998 Accepted in revised form: 14 January 1999     

Modulation Frequency Characteristics of Erbium-Doped Fiber Amplifier

The modulation frequency characteristics of an erbium-doped fiber amplifier are analyzed theoretically and experimentally for various values of modulation frequency. The theoretical predictions by the approximate equations in the low and high frequency modulation and that by the Runge-Kutta method for all modulation frequencies are in good agreement with the experimental results. In the low frequency modulation, the population inversion is depleted because of the saturation effect due to the instantaneous power of the incident light, and a distorted output is obtained without phase delay. In the high frequency modulation, the linear amplification is obtained with the gain depletion determined by the time averaged power of the incident signal. In the intermediate frequency modulation, the highly distorted output is obtained with phase delay.     

Loading and release of charged dyes using ultrathin hydrogels

The anionic dyes methyl orange (MO) and allura red (AR) were used as model drugs to assess the loading and release by layer-by-layer assembled ultrathin hydrogels prepared via the amide formation of poly(acrylic acid-co-N-isopropylacrylamide) with AAc contents of 5, 10, and 15 mol % plus poly(vinylamine hydrochloride). The amount of MO loaded was potentially controlled by changing the dye concentrations, film thickness, and AAc content of the copolymers. The release of AR was controlled by the NaCl concentration and pH. We conclude that the polymeric matrices of ultrathin hydrogels have great potential for the loading and release of charged drugs.     

Direct observation of rectified motion of vortices in a niobium superconductor

Using Lorentz microscopy to directly image vortices, we investigate vortex motion control and rectification in a niobium superconductor. We directly observe a net motion of vortices along microfabricated channels with a spatially asymmetric potential, even though the vortices were driven by an oscillatory field. By observing the individual motion of vortices, we clarify elementary processes involved in this rectification. To further demonstrate the ability to control the motion of vortices, we created a tiny vortex "racetrack" to monitor the motion of vortices in a closed circuit channel.     

Funktionelle Monomere und Polymere. 31. Mitt. Zur Stereoregularit?t von Vinylnolvmeren, die Nukleinsliure-Basen enthalten

Ohne Zusammenfassung     

Observation of structures of chain vortices inside anisotropic high- Tc superconductors

In order to elucidate the formation mechanism of unconventional arrangements of vortices in high- Tc superconducting thin films at an inclined magnetic field to the layer plane, we investigated the structures of vortex lines inside the films by Lorentz microscopy using our 1-MV field-emission electron microscope. Our observation results concluded that vortex lines are tilted to form linear chains in YBaCu3O(7,8). Vortex lines in the chain-lattice state in Bi2Sr2CaCu2O(8+delta), on the other hand, are all perpendicular to the layer plane, and therefore only vortices lined up along Josephson vortices form chains.