Polymerization and photoinitiation behavior in the light-cured dental composite resins

The polymerization behavior and photoinitiation process in the visible light-cured dental composite resins were studied using ESR and IR spectroscopies. The concentration of methacryl propagating radical corresponded to the transmittance of irradiated light. While the radical was stable and long-lived in the cured resin, its concentration quickly decreased in the oral cavity due to the ventilation of atmospheric oxygen accompanied by respiration. Camphorquinone radical in the presence of tertiary amine easily initiated the radical polymerization. A decrease in monomer consumption was explained by the inhibition effect of oxygen in the photoinitiation process. Post-curing by the residual radical proceeded effectively in the deeper part of the resin.     

Preparation of poly(1,4-phenylene)s by electro-oxidative polymerization

The effect of substituents on the electropolymerization of benzene derivatives and the redox properrties of the corresponding polymers were determined using Brown's substituent constants (σ⁺). Electron-donating groups lower the oxidation potential by which increase in the current efficiency was observed. However, stabilization of the produced cation radicals by the electron-donating groups resulted in a decrease in the polymerization efficiency. The appropriate values of σ⁺ for the efficient polymerization ranged near ?1.5.     

New Crystalline Lasers on the Base of Monoclinic KR(W04)2:Ln3+ Tungstates (R=Y and Ln)

Monoclinic KY(WO₄)₂:Pr₃₊, Tm₃₊:KY(WO₄)₂:Er₃₊, Yb₃₊ single crystals are grown by low-gradient Czochralski technique. Stimulated emission at 1.0223μm wavelength in the new lasing ¹D₂→³F₃ channel of Pr³⁺ ions in KY(WO₄)₂ at room temperature under Xe-flashlamp pumping is excited. Full sets of Stark-level energies for Pr₃₊ ions in KY(WO₄)2 and KGd(WO₄)₂ crystals at 77 K are determined. 4f²-4f² intensity-transitions for the KY(WO₄)₂:Pr³⁺ are analyzed preliminarily. All observed at present and earlier one-micron Pr³⁺-ion, induced transitions in the ¹D₂→³F₃ and ¹D₂→³F₄ channels are identified. In yttrium and gadolinium sensitized-tungstates a two-micron (³H₄→³H₆) low-threshold generation of Tm³⁺ ions at cryogenic temperatures is achieved.All authors cooperate with the Joint Open Laboratory for Laser Crystals and Precise Laser Systems at the Institute of Crystallography and Institute of Laser Physics, Russian Academy of Sciences.     

Transport properties of a lateral semiconductor quantum dot defined by a single connected metallic front-gate

We present studies on the electric transport in a lateral GaAs/AlGaAs quantum dot defined by a patterned single connected metallic front-gate. This gate design allows to easily couple a large number of quantum dots and therefore holds high potential in the design of new materials with tailor-made band structures based on quantum dot superlattices of controlled shape. Clear Coulomb diamond structures and well pronounced tunneling peaks observed in experiment indicate that single-electron control has been achieved. However, the dependence on electron density in the heterostructure embedding the dot, which is controlled by an additional back-gate, reveals that transport characteristics are strongly influenced supposedly by potential fluctuations in the dot and lead regions.     

Gold nanoparticle-templated assembly of oligothiophenes: preparation and film properties

Terthiophene-appended gold nanoparticles were prepared by the reduction of AuCl₄⁻(C₈H₁₇)₄N⁺ with NaBH₄ in the presence of bis[2,5-di(3-hexylthiophen-2-yl)thiophene-3-carboxyloxyhexanyl]disulfide. A hexagonal self-assembly of particles with gold core diameters (1.9±0.1 nm) was detected by high-angle annular dark-field scanning transmission electron microscopy. The electric conductivity of the iodine-doped film was 9.1×10⁻⁶ S cm⁻¹, which was ascribable to the terthiophene-based inter-ligand π-π interactions. The Au/terthiophene hybrid spin-coated film consisted of a highly three-dimensional assembled structure of terthiophenes, as inferred from grazing-incidence small-angle X-ray scattering, indicating that such monodispersed and small-sized gold nanoparticles can serve as a template for this organization. In this study, a gold nanoparticle-templated assembly of oligothiophenes has been fabricated for proposing a method to develop tailor-made organizations of π-conjugated oligomers.     

Quantitative determination of imatinib in human plasma with high-performance liquid chromatography and ultraviolet detection

A simple and sensitive high-performance liquid chromatography (HPLC) method was developed to quantitate imatinib in human plasma. Imatinib and the internal standard dasatinib were separated using a mobile phase of 0.5% KH(2)PO(4) (pH3.5)-acetonitrile-methanol (55:25:20, v/v/v) on a CAPCELL PAK C18 MG II column (250 mm × 4.6 mm) at a flow rate of 0.5 mL/min and measurement at UV 265 nm. Analysis required 100 μL of plasma and involved a solid phase extraction with an Oasis HLB cartridge, which gave recoveries of imatinib from 73% to 76%. The lower limit of quantification for imatinib was 10 ng/mL. The linear range of this assay was between 10 and 5000 ng/mL (regression line r(2) > 0.9992). Inter- and intra-day coefficients of variation were less than 11.9% and accuracies were within 8.3% over the linear range. The plasma concentrations of imatinib obtained by our present method were almost the same as those assayed by an LC-MS-MS method at the Toray Research Center, Inc. This method can be applied effectively to measure imatinib concentrations in clinical samples.     

Dimeric and trimeric tetrathiafulvalenes with strong intramolecular interactions in the oxidized states

New dimeric and trimeric TTF derivatives with methylenedithio spacers (1a,b, 2a, and 2b) have been synthesized. X-ray structure analysis revealed that TTF units of the dimer 1b adopted distorted face-to-face overlapping arrangement both in intra- and intermolecular stacking. Cyclic voltammetric study indicated that trimeric 2a was in favor of taking di- and tetracationic states, while the dimeric 1a was in favor of taking a monocation. The absorption spectroscopic study suggested an existence of the strong face-to-face interaction particularly in di-, tri-, and tetracationic state of the trimeric TTF derivatives.     

Nonlinear oscillations of fourth order quasilinear ordinary differential equations

We consider fourth order quasilinear ordinary differential equations. Firstly, we classify positive solutions into four types according to their asymptotic properties. Then we derive existence theorems of positive solutions belonging to each type. Using these results, we can obtain an oscillation criterion, which is our main objective. Moreover, applying such criteria for ordinary differential equations to binary elliptic systems, we establish nonexistence theorems for positive solutions.     

Significant substitution effects in dipolar and non-dipolar supercritical fluids

Vibrational Raman spectra of C=C stretching modes of ethylene derivates (cis-C(2)H(2)Cl(2), cis-stilbene, and trans-stilbene) were measured in supercritical fluids along an isotherm as functions of their densities. The substitution effect of the Raman shift is so significant that a difference among three solutes can be 20 times and is observed similarly in dipolar (CHF(3)) and non-dipolar (CO(2)) fluids. In particular, the shifts of trans-stilbene were enormously large among all systems for studies of vibrational spectroscopies of supercritical fluids and were equivalent to those of typical hydrogen-bonded fluids. Such large shifts arising from the significant attractive energy between solute and solvent molecules were attributed to a site-selective solvation around a phenyl group, which was driven by a dispersion force in the absence of steric hindrance. We found that the absence of steric hindrance causes the significant local density augmentation. To the best of our knowledge, Raman experiments and their theoretical analysis are the first ones quantifying how the difference of steric hindrance produces solvation structures in solution as well as supercritical solutions.     

Efficient synthesis of biazoles by aerobic oxidative homocoupling of azoles catalyzed by a copper(I)/2-pyridonate catalytic system

A highly efficient and convenient CuCl/2-pyridonate catalytic system for oxidative homocoupling of azoles affording a biazole product has been developed. With this system, a variety of biazoles have been effectively synthesized in good to excellent yields in the presence of a very small amount of copper catalyst (1.0 mol%). It was feasible to employ air as a green oxidant.