Synthesis of o,o′-dihydroxyazo compounds and their application to the determination of magnesium and calcium by flow injection analysis

Seven _o,o′-dihydroxyazo dyes were synthesized and examined as spectrophotometric reagents for magnesium and calcium. These reagents are highly sensitive for magnesium (? = 47 000) and calcium (? = 39 000 l mol^?1 cm^?1). Of the reagents synthesized, 2-(2-hydroxy-3,6-disulfo-1-naphthylazo)-5-(N,N-diethylamino)phenol was the best because of its ease of preparation and purification, and its stability in alkaline solution. This dye was applied in the determination of magnesium and calcium by flow injection analysis. The total concentration of magnesium (0.1–1.2 mg 1^?1) and calcium (0.4–4.0 mg 1^?1) was determined by masking iron(III), aluminium(III), copper(II), zinc(II), manganese(II) and cadmium(II) with 2,3-dimercapto-1-propanol (DMP) and triethanolamine (TEA). Magnesium was determined by masking calcium and the other metal ions with a ligand buffer containing barium(II)—EGTA, DMP and TEA. The amount of calcium was obtained as the difference between the two peak heights. Results for the determination of magnesium and calcium in potable water and serum are presented.     

Analysis of the conserved P9-G10.1 metal-binding motif in hammerhead ribozymes with an extra nucleotide inserted between A9 and G10.1 residues

Hammerhead ribozymes (Rz) have catalytically important tandem G:A pairs in the core region, and we recently demonstrated that the P9-G10.1 motif (a sheared-type G:A pair with a guanine residue on the 3' side of the adenine residue) with several flanking base pairs is sufficient for capture of divalent cations, such as Mg(2+) and Cd(2+) ions that are important to maintain full activities (Tanaka et al. J. Am. Chem. Soc. 2002, 124, 4595-4601; Tanaka et al. J. Am. Chem. Soc. 2004, 126, 744-752). We also found that mutant hammerhead ribozymes that have an additional G residue inserted between A9 and G10.1 residues (the metal-binding P9-G10.1 motif) have significant catalytic activities. In this study, we demonstrate that the hammerhead ribozymes are capable of maintaining the catalytically competent structure even when the tandem, sheared-type G:A pairs were perturbed by an insertion of an additional nucleotide, whereas the chirality of the phosphorothioate at the P9 position significantly influenced the enzymatic activity for both the natural and G-inserted ribozymes.     

Effect of temperature on the radiation-induced polymerization of ethylene in various media

The effects of temperature on the radiation-induced polymerization of ethylene in bulk and in the presence of ethyl alcohol, n-butyl alcohol, tert-butyl alcohol, cyclohexane, 2,2,4-trimethylpentane, and 2,2,5-trimethylhexane were studied. The changes of the amounts of polymerized monomer with the reaction temperature were different from each other in these reaction systems, especially in the range lower than 60–80°C. At temperatures lower than 60–80°C, as the reaction temperature increases, the amount of polymerized monomer decreased in bulk and in the presence of tert-butyl alcohol. The amount was almost constant in the presence of ethyl alcohol and 2,2,4-trimethylpentane, and it increased in the presence of n-butyl alcohol, cyclohexane, and 2,2,5-trimethylhexane. However, in the temperature range higher than 60–80°C, the amount of polymerized monomer increased with increasing temperature in every reaction system except for bulk polymerization. The molecular weight of polymer decreased with increasing temperature in every reaction system except at temperatures lower than 25°C. The molecular weight of polymer formed in bulk, in tert-butyl alcohol, and also in 2,2,4-trimethylpentane were relatively higher than that in other reaction systems. A bimodal molecular weight distribution was observed for the polymer formed in bulk and in tert-butyl alcohol at 40–60°C. These results are discussed in connection with the heterogeneity of the reaction system. The differences due to temperature in each reaction system are explained as due to the difference in affinity of the reaction system for the propagating chain and in the facility of chain transfer to the medium.     

Infrared reflection absorption spectroscopy of the sulfuric acid anion adsorbed on Pd(S)-[n(111) x (111)] electrodes

Adsorption of the sulfuric acid anion (HSO4- or SO42-) has been studied on Pd(S)-[n(111) x (111)] electrodes (n = 2, 3, 5, 9, 20, infinity) using in situ infrared reflection absorption spectroscopy (IRAS). A single band is observed around 1200 cm(-1) on all the electrodes. The band is assigned to the SO stretching vibration of the sulfuric acid anion adsorbed with three- or onefold geometry. This result differs from the case of Pt-stepped surfaces on which two IRAS bands are observed around 1200 and 1100 cm(-1). The maximum coverage of the sulfuric acid anion is enhanced with the increase of the terrace width. The surfaces with n more than 3 have similar IRAS band shifts (dv/dE). Pd-stepped surfaces, for which the terrace is wide enough for the anion adsorption, adsorb the anion on the terrace rather than the step.     

Characterization of alkoxy-derived iron silicate

Amorphous iron silicates, x Fe₂O₃ · (1 ? x) SiO₂ (0.1 ? x ? 0.4), were prepared by calcining alkoxy-derived gels obtained by the hydrolysis of metal alkoxide mixtures. Structural studies based on X-ray diffratometry. Mössbauer effect and infrared spectroscopy indicated that the materials were indeed amorphous up to 500°C in the composition range x ? 0.3 and that the structure is formed by SiOFe bonds. Crystallization took place on calcining the samples with the composition x ? 0.3 above 600°C. Fayalite deposited at 600°C and hematite and α-cristobalite deposited above 700°C. In the case of the composition x = 0.4 the product was amorphous up to 300°C and only hematite was detected above 400°C.     

Growth of high-purity ZnTe single crystals by the sublimation travelling heater method

A travelling heater method (THM) was developed to grow high-purity ZnTe from the vapor phase. This crystal growth method is called the “sublimation THM”. The temperature of the sublimation interface was set at 815°C and the temperature of the growth interface was varied from 785 to 800°C. The growth rate was 3 mm/day. Under these conditions, it was found that the growth process was mainly due to surface nucleation. Characteristics of the crystals were compared with those of solution-THM and vapor phase epitaxially grown crystals. The free-exciton line at 2.381 eV strongly appears and a doublet structure in neutral- acceptor bound exciton at 2.375 eV is clearly resolved with splitting energy of about 0.7 meV. We thus conclude that the THM from the vapor phase is suitable for preparing ZnTe single crystals which have excellent luminescent properties.     

Free-radical polymerization of vinyl esters using fluoroalcohols as solvents: Effect of monomer structure on stereochemistry

Free-radical polymerization of vinyl esters including vinyl propionate (VPr), vinyl isobutylate (ViBu), vinyl 2,2-dimethylbutylate (VDMB), vinyl 2,2-dimethylvalerate (VDMV), vinyl 2,2-bis(trifluoromethyl)propionate (VF6Pi), and vinyl benzoate (VBz) was carried out using fluoroalcohols as solvents, and the tacticity of the obtained polymers was determined by NMR analysis of the produced poly(vinyl alcohol) (PVA). The polymerization of VPr, ViBu, VDMB, and VDMV, which are bulkier than VAc, in fluoroalcohols afforded polymers rich in heterotacticity (up to mr = 61%) similar to that of vinyl pivalate (VPi) whereas VAc is known to give a syndiotactic polymer under the reaction conditions used here. The polymerization of VF6Pi, which is the bulkiest among the monomers used in this study, gave a polymer rich in syndiotacticity in bulk and in fluoroalcohols regardless of the structure of the solvents. On the other hand, the polymerization of VBz in fluoroalcohols gave polymers with a higher isotacticity (up to mm = 33%) than bulk polymerization. Thus the monomer structure strongly affected the stereochemistry of the free-radical polymerization of vinyl esters in fluoroalcohols. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2677–2683, 1999     

Synthesis and properties of poly(1‐naphthylacetylene) and poly(9‐anthrylacetylene)

Polymerizations of 1‐naphthylacetylene (1‐NA) and 9‐anthrylacetylene (9‐AA) by various transition metal catalysts were studied, and properties of the polymers were clarified. 1‐NA polymerized with WCl₆‐based catalysts to offer dark purple polymers in good yield. Especially, a binary catalyst composed of WCl₆ and Ph₃Bi gave a polymer with high molecular weight (M_w = 140×10³) and sufficient solubility in common solvents. The use of Mo and Rh catalysts, in contrast, resulted in the formation of insoluble red poly(1‐NA)s. 9‐AA gave insoluble polymers by both WCl₆‐ and MoCl₅‐based catalysts in moderate to good yields. Copolymerization of 9‐AA with 1‐NA by WCl₆–Ph₃Bi provided a soluble copolymer which exhibited the largest third‐order nonlinear optical susceptibilities (χ⁽³⁾(−3ω; ω, ω, ω) = 40×10⁻¹²) among all the substituted polyacetylenes synthesized so far. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 277–282, 1999     

Synthesis and characterization of a novel carbazole cyclic oligomer and main-chain polymer

The efficient synthesis of a novel cyclic carbazole tetramer and carbazole main-chain polymer via the Knoevenagel condensation has been developed. The carbazole cyclic tetramer could be obtained in a high yield by a one-stage Knoevenagel condensation of 3,6-diformyl-9-heptylcarbazole and 3,6-bis(cyanoacetoxymethyl)-9-heptylcarbazole in tetrahydrofuran (THF) without the use of the high-dilution principle. The corresponding carbazole main-chain polymer could also be obtained as a main product by a two-stage Knoevenagel polycondensation. Detailed structural characterization of this novel oligomer by spectroscopy and elemental analysis confirmed the cyclic structure. The corresponding main-chain polymer with large molecular weight was found to be amorphous by differential scanning calorimetry. Studies on the nonlinear optical and photorefractive properties of these materials are in progress. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2041–2047, 1997