Highly sensitive colour change system within slight differences in metal ion concentrations based on homo-binuclear complex formation equilibrium for visual threshold detection of trace metal ions

A new technique of expressing slight differences in metal ion concentrations by clear difference in colour was established for visual threshold detection of trace metal ions. The proposed method is based on rapid change of the mole fraction of the homo-binuclear complex (M₂L) about a ligand in a narrow range of the total metal ion concentration (M_T) in a small excess, in case the second metal ion is bound to the reagent molecule which can bind two metal ions. Theoretical simulations showed that the highly sensitive colour change within slight differences in metal ion concentrations would be realized under the following conditions: (i) both of the stepwise formation constants of complex species are sufficiently large; (ii) the stepwise formation constant of the 1:1 complex (ML) is larger than that of M₂L; and (iii) the absorption spectrum of M₂L is far apart from the other species in the visible region. Furthermore, the boundary of the colour region in M_T would be readily controlled by the total ligand concentration (L_T). Based on this theory, the proposed model was verified with the 3,3′-bis[bis(carboxymethyl)amino]methyl derivatives of sulphonephthalein dyes such as xylenol orange (XO), methylthymol blue (MTB), and methylxylenol blue (MXB), which can bind two metal ions at both ends of a π-electron conjugated system. The above-mentioned model was proved with the iron(III)-XO system at pH 2. In addition, MTB and MXB were suitable reagents for the visual threshold detection of trivalent metal ions such as iron(III), aluminium(III), gallium(III) and indium(III) ion in slightly acidic media. The proposed method has been applied successfully as a screening test for aluminium(III) ion in river water sampled at the downstream area of an old mine.     

A numerical model for thermal systems with helically-coiled tubes and its experimental verification

 A conjugate numerical model proposed by Nakayama et al. for the steady problem of cooling a fluid flowing through a coiled tube, has been successfully extended to investigate two distinctive thermal problems, namely, the transient cooling processes associated with a beer dispenser, and the transient processes of heat storage and recovery associated with a packed bed saturated with a molten salt. An axisymmetric numerical procedure is adopted for determining the velocity and temperature fields within the chilled water bath of the beer dispenser. A simplified one-dimensional heat transfer model is introduced for coupling the tube flow with the recirculating flow in the bath. A similar axisymmetric finite difference procedure is applied for the heat transfer analysis of the packed bed saturated with a molten salt. For the heat recovery process, a one-dimensional heat balance equation for the two-phase flow with a helically-coiled tube is introduced to update the wall surface temperatures, which are needed to calculate the temperature field in the saturated packed bed. The numerical results for both thermal systems associated with coiled tubes agree very well with the corresponding velocity and temperature data obtained from the experiments. Received on 28 August 2000 / Published online: 29 November 2001     

Studies on imidazole derivatives and related compounds. 2. Characterization of substituted derivatives of 4-carbamoylimidazolium-5-olate by ultraviolet absorption spectra

The representative mono- and dialkyl-substituted derivatives of 4-carbamoylimidazolium-5-olate (1) were synthesized unequivocally. On the basis of their spectral data for ultraviolet absorption spectra in acidic, basic and neutral solutions, we have found some spectral characteristics which make it facile to clarify the position of substituents.     

4- and 5-trifluoromethylimidazoles. Novel cyclization of trifluoroacetylated aldehyde dimethylhydrazones

Thermally induced cyclization reaction of trifluoroacetylated arylaldehyde dimethylhydrazones 1 in refluxing toluene afforded 1-methyl -4 -aryl -5 -trifluoromethylimidazoles 2 in good yields. In contrast thermal cyclization of 1 in the presence of silica gel gave regioisomeric 1-methyl -4 -trifluoromethyl -5 -aryl-imidazoles 5 as major products. These reactions could be extended to the syntheses of related several 1,4,5-trisubstituted imidazoles.     

Performance Characteristics of Power Build-Up Cavity for Raman Spectroscopic Measurement

Performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy based gas sensor were studied. The key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser. The optimum diameter determined by an appropriate distance between the cavity and diode laser was found to be comparable with the waveguide cross section of diode laser for the effective spatial filtering, where inevitable cavity coupling loss caused by slight spatial mode mismatching existed. A PBC with a finesse of ∼10300 achieved a stable TEM₀₀ mode in excess of intra-cavity power of 80 watts pumped by a 10 milliwatts diode laser. Simultaneously, the PBC wavelength is found to be passively locked effectively at 670 +/− 0.15 nm where the center of the gain region exists. A Raman spectrum of nitrogen measurement was demonstrated.     

Disilane- and siloxane-bridged biphenyl and bithiophene derivatives as electron-transporting materials in OLEDs

Optical, electrochemical, and electron-transporting properties of disilane- and siloxane-bridged biphenyl and bithiophene derivatives were investigated, in comparison with those of the monosilane-bridged analogues (siloles). The UV spectra and cyclic voltammograms indicated that elongation of the silicon bridge suppresses the π-conjugation, in accordance with the results of DFT calculations. The DFT calculations indicated also that the disilane-bridged biphenyl and siloxane-bridged bithiophene should have the low-lying HOMOs and LUMOs. The electron-transporting properties were evaluated by the performance of triple-layered OLEDs having vapor-deposited films of the Si-bridged compound, Alq₃, and TPD, as the electron-transport, emitter, and hole-transport, respectively. Of these, the device with a disilane-bridged biphenyl exhibited the high performance with the maximum current density of 590 mA/cm² at the applied electric field of 12 × 10⁷ V/m (applied bias voltage = 13 V) and the maximum luminance of 22 000 cd/m² at 13 × 10⁷ V/m.