Aqueous Titanate Sols from Ti Alkoxide-α-Hydroxycarboxylic Acid System and Preparation of Titania Films from the Sols

Aqueous titanate sols were prepared by reactions of titanium tetraisopropoxide (TIP) with -hydroxycarboxylic acids in water. IR and Raman spectra, and elemental analyses of the precipitates obtained from the sols revealed that the carboxylates were chelated to titanium but the Ti species were polymerized to form a cluster that had a colloidal nature. Spin-coating of titania (TiO₂) thin films from these sols was also examined. Interestingly, it was found that (004) preferentially oriented anatase films with refractive index of 2.54 were obtained from TIP-lactic acid-NH₃ (1:1:1, molar ratio) aqueous sol. This crystallographic orientation was characteristic of the TIP-lactic acid-NH₃ (1:1:1) system, and was not affected by the kinds of substrates used and the heating rate of the film. TEM observation indicated that small anatase grains had already formed at 200°C. Therefore, the crystallographic orientation might depend strongly on the structure of the chemical species of the precursor solutions.     

Asymmetric sequential Michael reaction: Synthesis of optically active bicyclo[2.2.2]octane derivatives

The sequential Michael reaction of (S)-4,5-di-O-isopropylidenepent-2- enoate and with lithium enolate afforded diastereo- and enantioselectively bicyclo[2.2.2]octane and (or ), respectively. The adducts were efficiently converted into both enantiomeric keto aldehydes (−)- and (+)- .     

Preparation of porous clay minerals with organic-inorganic hybrid pillars using solvent-extraction route

A microporous clay mineral with organic-inorganic hybrid pillars was synthesized using a hydrochloric acid (HCl)/ethanol extraction method after intercalation of tetraethoxysilane (TEOS) or TEOS/methyltriethoxysilane (MTS) into the cetyltrimetylammonium ion (CTA)-exchanged vermiculite. The products retained their layered structure, due to the formation of stable pillars by the polymerization of hydrolyzed TEOS and MTS during the HCl/ethanol treatment. The BET surface areas, which increased to above 500 m2g(-1) with an increase in the HCl concentration up to 0.4 moldm(-3), are nearly equal to that of the calcined product obtained by the conventional method. However, the pore sizes of HCl/ethanol-treated materials were narrower than those of the calcined product, owing to the formation of the polysiloxane networks in the gallery. A water adsorption study showed that the product treated with a TEOS/MTS mixture had a hydrophobic surface as a result of the successful incorporation of methyl groups at the surface of the pillars. This novel method is advantageous for the synthesis of organophilic pillared clays with different kinds of organic materials in the interlayers.     

(2,7-Disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) as bidentate organoaluminum Lewis acids: elucidation and synthetic Utility of the double electrophilic activation phenomenon

A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction. The structure of the bidentate Lewis acid 2 was unambiguously determined by single-crystal X-ray diffraction analysis of 2g possessing a bulky 3,5-di-tert-butylphenyl substituent, revealing the rigid dimeric assembly in the solid state. The double electrophilic activation of carbonyl substrate by 2a has been supported by low-temperature 13C NMR analysis as well as theoretical study using the Gaussian 98 program. Moreover, unique stereoselectivity has been observed in the 2a-promoted Mukaiyama Michael addition, and highly chemoselective functionalization of carbonyl compounds in the presence of their acetal counterparts has been realized using 2a. Finally, the effectiveness of 2a for the activation of ether functionality has been demonstrated in the Claisen rearrangement of allyl vinyl ethers.     

Separation and simultaneous determination of cobalt, nickel and copper with 2-(4-methyl-2-quinolylazo)-5-diethylaminophenol by reversed-phase high-performance liquid chromatography

Performance of six quinolylazo compounds was studied as a pre-column derivatizing reagent for the separation of metal ions in the reversed-phase high-performance liquid chromatography. 2-(4-Methyl-2-quinolylazo)-5-diethylaminophenol (QADP) was suited for the determination of Co, Ni and Cu in the presence of a large amount of Fe. The detection limits under the optimized conditions [stationary phase: L-column ODS; mobile phase: acetone-water (62:38, v/v) containing 0.01 M NH(4)SCN and 0.01 M 2-morpholinoethanesulfonic acid-NaOH (pH 6); injection volume: 10 mul] were 0.24 ng for Co, 0.22 for Ni and 0.53 for Cu. This method was successfully applied to the determination of these metal ions in a standard steel sample.     

Synthesis, structure and thermal stability of fully hydrophobic porphyrin-DNA conjugates

The DNAs modified with tetraphenyl porphyrin at the center of 13mer oligonucleotide were synthesized using phosphoramidite chemistry and automated DNA synthesis. When the porphyrin modified oligonucleotide was annealed with its complementary strand, they formed a standard B-form duplex. The porphyrin moiety intercalated in the duplex, and moderately lowered the thermal stability.     

On-line measurement of intramolecular carbon isotope distribution of acetic acid by continuous-flow isotope ratio mass spectrometry

Molecular and intramolecular carbon isotope measurements of acetic acid present in natural environments have been performed by off-line procedures. The off-line method is complicated and time-consuming and requires micromolar to millimolar amounts of sample. This limits geochemical isotopic studies, especially at the intramolecular level, on acetic acid present in natural samples. Here, we examine an on-line measurement of intramolecular carbon isotope distribution of acetic acid using continuous-flow isotope ratio mass spectrometry (CF-IRMS) coupled with an on-line pyrolysis system. This is achieved by measurement of the respective carbon isotope ratios of CH4 and CO2 produced by on-line pyrolysis of acetic acid. Results for authentic standards of pure acetic acid demonstrated the practicality of this on-line method, although the carbon isotope ratio of the methyl group could not be determined directly. The precision of the carbon isotope measurements was 0.4 per thousand (1sigma). The carbon isotope distribution determined by the on-line method was identical to that determined by the conventional off-line method within analytical error. The advantages of the on-line method compared with the conventional off-line method are that it is less laborious, requires less analytical time (less than one hour per sample) and, most importantly, uses smaller sample sizes (ca. 10 nanomole). An application of this on-line method to natural geochemical samples will provide an insight into the geochemical cycle of acetic acid.     

Efficient regioselective aldol condensation of methyl ketones promoted by organoaluminum compounds,and its application to muscone synthesis

Regioselective aldol condensation of 2-octanone and 2-butanone at the methyl side proceeded in high yields using a system of dialkylaluminum phenoxide/tertiary amine. The intramolecular aldol condensation of 2,15-hexadecanedione was carried out by the same system, especially di-i-butylaluminum phenoxide/pyridine, to give dehydromuscone in 65% yield. Its hydrogenation afforded muscone (3-methylcyclopentadecanone).     

Metal-complex assemblies constructed from the flexible hinge-like ligand H2bhnq: structural versatility and dynamic behavior in the solid state

Novel metal-complex assemblies constructed from the flexible hinge-like ligand H(2)bhnq (H(2)bhnq=2,2'-bi(3-hydroxy-1,4-naphthoquinone)) have been synthesized. The X-ray crystal structures of these compounds reveal that four types of architectures are accessible by variation of the metal ions. In copper(II) compounds 1-3, the chelating bhnq(2-) ions bridge copper(II) centers to form one-dimensional zigzag chains. The chains of 1-3 are arranged by hydrogen-bonding interactions and stacking interactions to produce porous structures. Cobalt(II) and zinc(II) compounds 4 and 5 form one-dimensional helical chains. In 4 and 5, the crystal packing induces spontaneous resolution of the helical chains with chiral cavities formed perpendicular to the helices. Nickel(II) compounds 6 and 7 form cyclic tetramers. The fourth architecture, a dimer (compound 8), is obtained by the reaction of zinc(II) and bhnq(2-) in MeOH. In these compounds, changes of the dihedral angles and the metal-coordination mode of the bhnq(2-) ion induce the structural versatility. The assemblies of the zigzag chains of the copper(II) compounds exhibit reversible vapochromic behavior. UV/Vis, powder X-ray diffraction, EPR, and adsorption isotherm measurements indicate that this vapochromic behavior is based on the hinge-like flexibility of the bhnq(2-) ion.     

Mass spectral fragmentations of 6-aryl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-Oxides

The mass spectral fragmentation of 4-, 5-, and 4,8-disubstituted derivatives of 6-aryl-5,6,7,8-tetrahydro-4H-1,3,2,6-dioxathiazocine 2-oxides is reported.