Photoluminescence enhancement of PEG-modified YAG:Ce3+ nanocrystal phosphor prepared by glycothermal method

Y3Al5O12:Ce3+ (YAG:Ce3+) nanocrystals were synthesized in 1,4-butylene glycol (BG) with and without poly(ethylene glycol) (PEG) by the glycothermal method. The internal quantum efficiency of the photoluminescence (PL) corresponding to the 5d --> 4f transition of Ce3+ in the YAG:Ce3+ nanocrystal increased from 21.3 to 37.9% by addition of PEG, while no appreciable change in the primary particle size, the crystallite size, and the lattice distortion was recognized by transmission electron microscopy and X-ray diffractometry. The thermogravimetry-differential thermal analysis, Fourier transform infrared absorption spectroscopy and 1H --> 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR) confirmed the preferential coordination of PEG to the YAG:Ce3+ nanocrystal. 27Al single-pulse excitation MAS NMR reveals that the ratio of the 4-fold coordination site to the 6-fold coordination site increased from 0.53 to 0.72 by addition of PEG. We conclude that the surface modification of the YAG:Ce3+ nanocrystal by PEG induces the surface passivation, the prevention of the oxidation of Ce3+ to Ce4+, the promotion of the incorporation of Ce3+ into YAG and the local structural rearrangement, resulting in the PL enhancement.     

Rhodium-catalyzed isomerization of alpha-arylpropargyl alcohols to indanones: involvement of an unexpected reaction cascade

A rhodium-catalyzed isomerization of alpha-arylpropargyl alcohols to indanones has been developed under mild conditions. Considering the ease of preparation of these propargyl alcohols (terminal alkynes + aromatic aldehydes), this method provides a new way of constructing indanones with high efficiency. By the mechanistic investigations using deuterium-labeled substrates, it has also been demonstrated that the reaction goes through an unexpected cascade, with a 1,4-hydrogen shift being the turnover-limiting step of the catalytic cycle.     

Dioxopyrrolines. LXII. Diels-Alder reaction of 1-Aryl-4- and 5-methoxycarbonyl-1H-pyrrole-2,3-diones with various 1,3-dienes

Two new dioxopyrrolines (1-aryl-4-methoxycarbonyl-1H-pyrrole-2,3-dione 6 and the 5-methoxycarbonyl isomer 8) behaved as good dienophiles to some kind of 1,3-dienes examined. In most cases, the products were explained by the reaction where the largest lobe of HOMO of dienes reacted to the larger LUMO of dienophiles in an expected cis-endo manner. However, in the reactions of 8 with alkylbutadienes, piperylene and isoprene, abnormality in the reaction was observed, which was well explained by taking account of steric factors.     

Rearrangement reaction of N-halo-s-[(1,2-benzisoxazol-3-yl)methyl]-sulfoximine to the corresponding α-halo sulfoximine

The first example of the rearrangement reaction of N-halosulfoximine to α-halo sulfoximine is described.     

Highly active, immobilized ruthenium catalysts for oxidation of alcohols to aldehydes and ketones. Preparation and use in both batch and flow systems

A novel, highly active immobilized ruthenium catalyst, which can be successfully used in oxidation of alcohols to aldehydes and ketones, has been developed. In contrast to most immobilized catalysts, the Ru catalyst has activity that is higher than that of the original non-immobilized catalyst. In a batch system, the Ru catalyst was recovered and reused several times without loss of activity. The catalyst was also applied to a flow system, in which excellent conversions and yields were demonstrated. No leaching of Ru was observed in both cases.     

Extraction equilibrium of palladium(II) with 2-methyl-8-quinolinol into supercritical carbon dioxide fluid

The present study is concerned with the extraction behavior and equilibrium of Pd(II) with 2-methyl-8-quinolinol (HMQ) into supercritical fluid CO(2) (SF-CO(2)). Pd(II)-HMQ complex extracted from a weakly acidic solution (pH 2-3) into SF-CO(2) was determined to be Pd(MQ)(2) on the basis of a slope analysis. The extraction constant K(ex,SF) (=[Pd(MQ)(2)](SF)[H(+)](2)[Cl(-)](4)[PdCl(4)(2-)](-1)[HMQ](-2)) was determined to be 10(4.3+/-0.2) at 8.5 MPa, 45 degrees C and I=0.4 M (H,Na)Cl (1 M=1 mol dm(-3)). The distribution behavior of HMQ between an aqueous and a SF-CO(2) phase was examined so as to discuss quantitatively the extraction equilibrium. The extraction constant (K(ex,Cy)) of Pd(II) with HMQ into cyclohexane with a similar polarity to SF-CO(2) was determined and the K(ex,SF) was compared with the K(ex,Cy). Pd(II) at the concentration range of 10(-5)-10(-4) M in the aqueous solution (pH<3) containing relatively high concentration of chloride ion was found to be extracted efficiently by the SF-CO(2) extraction.     

Kinetics of transient end-to-end contact of single-stranded DNAs

The formation of the pyrene (Py) dimer radical cation (Py(2)(*+)) was used to measure the kinetics of the intrastrand end-to-end contact rates of single-stranded DNAs (ssDNAs) in the 10 nanoseconds to the tens of microseconds time range. ssDNAs labeled with Py at both ends with the lengths of 3, 6, and 9 mer were synthesized, and the two-photon ionization method was employed to generate a Py(*+), which enables the measurements of the end-to-end contact rates from 10 ns. The formation rate of Py(2)(*+) depended on the length and the sequence of the ssDNAs, and about 1 order of magnitude faster rates were observed for the T-rich ssDNAs compared to those for the corresponding length of A-rich ssDNAs, showing that ssDNA made from adenines is much more rigid than that composed of thymidines. As for the T-rich ssDNAs, the formation of Py(2)(*+) attributed to the misfolded structures was also observed, which is consistent with the configurational diffusion model suggested by Ansari and co-workers.     

Self-oscillation of polymer chains induced by the Belousov-Zhabotinsky reaction under acid-free conditions

A novel self-oscillating polymer was prepared by utilizing the Belousov-Zhabotinsky (BZ) reaction. In this study, a sulfonic acid group was newly introduced as a pH-control site into the copolymer of N-isopropylacrylamide, and the ruthenium complex was introduced as a catalyst site. By introducing the pH-control site, we succeed in causing the soluble-insoluble self-oscillation of the polymer solution under acid-free conditions in which only two BZ substrates, malonic acid and sodium bromate, were present as added agents. The self-oscillating behavior was remarkably influenced by the temperature and polymer concentration, which reflects the intermolecular aggregative capacity of the polymer chains in the reduced state to change the lower critical solution temperature. This achievement of self-oscillation of polymer chains under acid-free conditions may lead to their practical use as novel biomimetic materials under biological conditions.     

Determination of p-chloronitrobenzene in plasma by reversed-phase high-performance liquid chromatography.

A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of p-chloronitrobenzene (p-CNB) in rat plasma. A plasma sample was deproteinized with methanol containing the internal standard (p-bromonitrobenzene). The resulting methanol eluate obtained after centrifugation was filtered and injected into a high-performance liquid chromatograph (50 microliters each). A column packed with 5 microns octadecylsilane (ODS) spherical particles was used with isocratic elution of methanol-water (45:55, v/v) at a flow-rate of 1.0 ml/min. The compounds were detected by ultraviolet absorbance at 280 nm. The retention times of p-CNB and the internal standard were 12.5 and 15.5 min, respectively, at a column oven temperature of 30 degrees C. The results were linear from 0.05 to 100 micrograms/ml (r = 0.999), and the detection limit was 0.01 microgram/ml. The relative error and the coefficient of variation on replicate assays were less than 7 and 10%, respectively, for all concentrations studied. The overall recoveries of p-CNB were between 97 and 105%. Plasma samples could be stored for up to one month at -20 degrees C.     

Self-assembling structures of long-chain phenyl glucoside influenced by the introduction of double bonds

Four long-chain phenyl glucoside amphiphiles possessing a saturated or unsaturated long alkyl chain group as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembling properties were investigated by EF-TEM, SEM, CD, FT-IR, and XRD. Compound 2 possessing one double bond in the lipophilic portion showed twisted helical fibers, which formed a bilayered structure with a 3.59 nm period, while compound 3 showed the helical ribbons and left-handed nanotubular structures with 150-200 nm inner diameters and ca. 20 nm of wall. Very interestingly, compound 4 possessing three double bonds showed a nanotubular structure with ca. 70 nm of inner diameter through a helical ribbon, which formed a loose bilayered structure with 4.62 nm. These results indicate that self-assembling properties strongly depend on the number of cis double bonds.