Ion-exclusion chromatography of aliphatic car☐ylic acids on a cation-exchange resin by elution with polyvinyl alcohol

Ion-exclusion chromatography of aliphatic car☐ylic acids of different acidity (pK_a) and hydrophobicity was investigated on a polystyrene-divinylbenzene (PS-DVB) based strongly acidic cation-exchange resin in the H⁺ form and conductivity detection by elution with polyvinyl alcohol (PVA). When water was used as an eluent, the resolution of the car☐ylic acids was very low and the peak accompanied a fronting depending on their hydrophobicities. Therefore, to improve the peak shape and the peak resolution, aqueous eluents containing PVAs (degrees of polymerization, n=500, 1500and2000) with many OH groups were tested for the ion-exclusion chromatographic separation of the car☐ylic acids. When aqueous eluents containing PVA were used, the fronting was decreased dramatically by the effect of increased hydrophilicity of the PS-DVB cation-exchange resin surface due to adsorption of OH group in PVA. The high resolution ion-exclusion chromatographic separation without the fronting and highly sensitive conductimetric detection of the car☐ylic acids was accomplished successfully by elution with a 0.2% PVA (n=1500)-10% methanol-water.     

Fluorescent polymer particles incorporating pyrene derivatives

Fluorescent polymer particles incorporating pyrene and alkynylpyrenes were prepared by miniemulsion polymerization of styrene. The pyrenes were simply dissolved in styrene monomer and then added to the reaction mixture in a vessel, followed by ultrasonication and the polymerization. The pyrenes were incorporated in the polystyrene particles and gave monomer fluorescence emission. The fluorescent particles incorporating the alkynylpyrenes, which have high fluorescence quantum yield and short fluorescence lifetime, showed the same fluorescence emission intensity under air and nitrogen. The fluorescence of the alkynylpyrenes in the polymer particles will not be quenched by molecular dioxygen in contrast to that in organic solvents. Incorporation of fluorophore into polymer particles will protect the fluorophore from its undesirable interaction with oxygen, affording the particles highly fluorescent even under air. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1470–1475, 2008     

Palladium-catalyzed allylic alkylation of optically active α-alkenyl-α-acyloxytrialkylsilane

Pd-catalyzed inter- and intramolecular allylic alkylations of optically active α-alkenyl-α-acyloxysilanes are described. The reactions proceeded in a regio- and stereoselective manner to give the corresponding (E)-vinylsilanes in which the ee of the starting material was completely transferred to the product.     

Copolymerization of 3‐buten‐1‐ol and propylene with an isospecific zirconocene/methylaluminoxane catalyst

The copolymerization of propylene and 3‐buten‐1‐ol protected with alkylaluminum [trimethylaluminum (TMA) or triisobutylaluminum] was conducted with an isospecific zirconocene catalyst [rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride], combined with methylaluminoxane as a cocatalyst, in the presence of additional TMA or H₂ as the chain‐transfer reagent if necessary. The results indicated that end‐hydroxylated polypropylene was obtained in the presence of the chain‐transfer reagents because of the formation of dormant species after the insertion of the 3‐buten‐1‐ol‐based monomer followed by chain‐transfer reactions. The selectivity of the chain‐transfer reactions was influenced by the alkylaluminum protecting the comonomer and the catalyst structure. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5600–5607, 2004     

Determination of hydroxyl radical photoproduction rates in natural waters.

The photochemical formation rates of hydroxyl radicals (OH radicals) in river water and seawater were determined by a simple, rapid and sensitive benzene probe method, in which phenol formed by the reaction between benzene and photochemically-generated OH radicals was analyzed by on-line preconcentration HPLC. The OH radical formation rates from well-known OH radical sources, such as nitrate, nitrite and hydrogen peroxide, were in good agreement with those reported previously. River water samples containing high concentrations of nitrate and nitrite were found to show high OH radical formation rates. Ten to 80% of the OH radical formation in river water and seawater was due to the photolysis of nitrate and nitrite, but OH radical formation from hydrogen peroxide was negligible. The OH radical formation from unknown sources other than nitrate, nitrite and hydrogen peroxide was strongly correlated to the amount of fluorescent matter.     

Group Delay of a Coupled-Defect Waveguide in a Photonic Crystal

The group-delay characteristics of the light transmitting in a coupled defect waveguide (CDW) in a one-dimensional (1D) photonic crystal were experimentally investigated. Because of its simplicity, a 1D structure is suitable for scientific research as well as device application. The transmission spectrum agrees well with the calculated result by a characteristic matrix method. Group-delay measurement using the phase-shift method revealed the characteristic dispersion features and small group velocity of the CDW. This experimental investigation suggests that such unique features of the CDW promise the possibility of various applications such as a dispersion compensator.     

Electric field effects on absorption and fluorescence spectra of trimethylsilyl- and trimethylsilylethynyl-substituted compounds of pyrene in a PMMA film

External electric field effects on absorption and fluorescence spectra of 1,3,6,8-tetrakis(trimethylsilyl)pyrene and 1,3,6,8-tetrakis(trimethylsilylethynyl)pyrene (TMSPy and TMS(E)Py, respectively) have been examined in a poly(methyl methacrylate) (PMMA) film at various concentrations at various temperatures. TMS(E)Py preferentially forms an aggregate in a PMMA film, as the concentration increases, indicating that the acetylenic groups enhance the pi-pi interactions between pyrene molecules. The change in molecular polarizability following excitation has been determined both for the monomer and for the aggregate, based on the electroabsorption spectra. The change in molecular polarizability following emission has also been determined in both compounds, based on the electrofluorescence spectra. TMSPy exhibits two excimer fluorescence emissions at high concentrations which are ascribed to the partially overlapping excimer and the sandwich-type excimer, respectively, besides the monomer fluorescence emitted from the locally excited state. The sandwich-type excimer fluorescence as well as monomer fluorescence is quenched by an electric field, whereas the fluorescence of the partially overlapping excimer is enhanced by an electric field. Excimer fluorescence of TMS(E)Py, which arises from the sandwich-type excimer, is quenched by an electric field at any temperature. Only one species of the partially overlapping excimer is confirmed in TMSPy, while no partially overlapping excimer is confirmed in TMS(E)Py.     

The role of CH/pi interaction in the stabilization of less-soluble diastereomeric salt crystals

Enantiopure 2-naphthylglycolic acid (NGA) and cis-1-aminobenz[f]indan-2-ol (ABI) were rationally designed as new resolving agents on the model of mandelic acid (MA) and cis-1-aminoindan-2-ol (AI), respectively. As expected, NGA and ABI showed superior chiral recognition ability to racemates, compared with MA and AI. In order to clarify any factors governing the chiral recognition abilities of NGA and ABI, the crystal structures of their less- and more-soluble diastereomeric salts were determined by X-ray crystallographic analyses and revealed that CH/pi interactions play an intrinsic role in chiral recognitions. A theoretical investigation was also performed with the periodic ab initio method by using the X-ray crystal structures of the less-soluble salt crystals with AI and ABI to find the unique properties of CH/pi interaction in the crystalline state, which largely contributed to the stabilization of the crystals.     

Charge-transfer controlled exchange interaction in radical-triplet encounter pairs as studied by FT-EPR spectroscopy

The exchange interaction, J, producing quartet and doublet energy separation in radical-triplet excited molecule encounter pairs, was investigated in solution by measuring chemically induced dynamic electron polarization (CIDEP) created through the radical-triplet pair mechanism. A time-resolved FT-EPR method was utilized to measure CIDEP of galvinoxyl radical by recording FID signals and an absolute magnitude of CIDEP, P(n), was determined for each radical-triplet system by detailed analysis of the time evolution curves of CIDEP. A transient FT-EPR signal phase remarkably depends on the triplet molecule. The signal phase is related to the sign of J value, which is responsible for the radical-triplet pair interaction. Most of galvinoxyl-triplet systems showed normal negative sign. An unusual positive sign was found in some systems characterized by a small energy gap, DeltaG, between the radical-triplet pair and intermolecular charge transfer (CT) states. A theoretical calculation of J value for radical-triplet encounter pairs was carried out by considering exchange integral and intermolecular CT interaction. According to the calculated J value and the diffusion theory for CIDEP magnitude, experimental Pn values were theoretically reproduced as a function of DeltaG. The present results confirm our previously reported CT model explaining the complicated nature of the sign of J value in the galvinoxyl-triplet encounter pairs. According to the proposed model for CT effect on J value and CIDEP results, nature of J value in radical-triplet pairs is discussed.