Application of 2-(3,5,6-trifluoro-2-hydroxy-4-methoxyphenyl)benzoxazole and -benzothiazole to fluorescent probes sensing pH and metal cations.

2-(3,5,6-Trifluoro-2-hydroxy-4-methoxyphenyl)benzoxazole (3) and benzothiazole analogue (4) are prepared by the two-step procedures from the corresponding 2-(pentafluorophenyl)benzazoles. Benzoxazole 3 is applicable to a fluorescent probe sensing magnesium cation, and 4 is suitable for sensing zinc cation. Both fluorophores 3 and 4 are sensitive to the pH change at pH 7-8, resulting in large fluorescence enhancement under basic conditions. Their high sensitivity to pH and selectivity in metal cations are ascribed to the high acidity of the fluorophenol moiety.     

Growth of LiNbO3 epitaxial films by oxygen radical-assisted laser molecular beam epitaxy

LiNbO₃ films were epitaxially grown on c-sapphire substrates using oxygen radical-assisted laser molecular beam epitaxy (MBE). X-ray diffraction-based structural analysis showed that the films were epitaxial. Triple-axis rocking curve measurements of the LiNbO₃ (0 0 0 6) reflection revealed that the film was highly c-oriented with an extremely narrow mosaic; the full width at half maximum of the LiNbO₃ (0 0 0 6) rocking curve was 0.0036°, comparable to the value of high-quality bulk crystals. The surface of the film was very smooth, with a surface roughness r.m.s. value, measured by atomic force microscope, of 0.4 nm for a film of thickness 15 nm. The chemical composition of the film measured by X-ray photoelectron spectroscopy (XPS) was stoichiometric within the accuracy of XPS measurement.     

Does the proton-transfer reaction take place in the ground state of phenol?(H2O)4 clusters?

In recent experimental studies of infrared (IR) spectra of hydrated phenol clusters, the Mikami and Ebata group at Tohoku University attributed apparently two very different spectra to PhOH(H₂O)₄. The first spectrum has a wide transparent region between 3500 and 3700 cm^-1, which they named a window region. The second spectrum has several absorption bands in this window region. Our previous study revealed that the first spectrum was assigned to the isomers which have a single-ring structure of a hydrogen-bonding network of OH's of phenol and waters. The experimentalists suggested that the second spectrum might be identified to a proton-transferred phenol(SINGLEBOND)water cluster. In the present article, the geometrical structures of proton-transferred hydrated phenol clusters were determined with the ab initio molecular orbital method and their IR spectra were calculated. The proton-transferred phenol(SINGLEBOND)water cluster is at a stable local minimum, but the energy is much higher than that of the most stable nontransferred cluster. The calculated IR spectrum has a still wider window region and is far different from the experimental spectrum of the second type. © 1996 John Wiley & Sons, Inc.     

Enhanced velocity of surfactant binding after the volume collapse of an oppositely charged gel

This paper is a kinetic study of the interaction between an ionic surfactant and an oppositely charged polymer gel. The volume collapse of the gel enhances substantially the velocity of surfactant uptake, despite the decreased free volume for diffusion. This indicates that the increased charge density of the polymer network accelerates the surfactant binding.     

Selective complete decomposition of poly(n‐hexylisocyanate) and its use in a new molecular design method

Poly(n‐hexylisocyanate) (PHIC‐NH) as a rod‐like polymer having a ? NH group at one end of the polymer chain was found to instantly (less than a few seconds) be completely decomposed by CH₃O^?Na⁺ in tetrahydrofuran/CH₃OH under a mild experimental condition ([CH₃O^?Na⁺] < 1 mol L^?1 at room temperature).The mechanism of the decomposition for the PHIC‐NH consists of two steps: the first is abstraction of the proton for PHIC‐NH by Na⁺ with a slow reaction rate, and the second is the consequent depolymerization of PHIC‐N^? based on the equilibrium polymerization with a rapid depolymerization rate. The decomposition rate constants (k_d) depend on M_w of PHIC‐NH, namely k_d ～ M_w^?1.0. The decomposition of the PHIC‐NR having an end‐capped ? NR group was completely depressed. Using an “all or nothing” mechanism for the decomposition, the (PHIC)_3.43 comb‐shaped polymer and polystyrene (PSt)‐graft‐(PHIC‐NH)_4.28 graft copolymer were, respectively, decomposed to produce (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 in a series with different numbers of PHIC‐NH combs and PHIC‐NH grafts by regulating the amount of CH₃O^?Na⁺ and the decomposition time. Molecular structure of (PHIC‐NH)_3.43–1.03 and PSt‐graft‐(PHIC‐NH)_4.28–0 was discussed from a viewpoint of PSt‐reduced chain dimension per molar mass. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Principal structure of submodular systems and Hitchcock-type independent flows

A recent paper of mine [1] contains an error, which is not critical to the main result but still may confuse the readers. I would like to apologize this sincerely and show how to flix it.     

Simple and highly sensitive determination of free fatty acids in human serum by high performance liquid chromatography with fluorescence detection.

A highly sensitive and simple reversed phase high performance liquid chromatographic (HPLC) method for the quantitative determination of free fatty acids in human serum is presented. The method is based on the direct derivatization of serum fatty acids with 6,7-dimethoxy-1-methyl-2(1H)-quinoxalinone-3-propionylcarboxylic acid hydrazide. The derivatization reaction proceeds in aqueous solution in the presence of pyridine and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide at 37 degrees C. The resulting derivatives are separated within 75 min on a reversed phase column (YMC Pack C8) with a gradient elution of aqueous acetonitrile and detected fluorimetrically. The detection limits are 2.5-5 fmol in a 10 microL injection volume. The sensitivity permits precise determination of free fatty acids in 5 microL serum. The method is simple and is without the conventional liquid-liquid extraction steps of serum fatty acids.     

Fabricating and aligning pi-conjugated polymer-functionalized DNA nanowires: atomic force microscopic and scanning near-field optical microscopic studies

We report a simple method to functionalize DNA with pi-conjugated polymer, forming highly aligned and integrated arrays of pi-conjugated polymer nanowires of a few nanometers diameter. pi-conjugated polymer, polyphenazasiline, having alkylammonium salts on the N atom (PPhenaz-TMA), synthesized in this study can be directly attached to DNA, which can be organized along stretched and aligned DNA molecules on surfaces as a template. Furthermore, PPhenaz-TMA/DNA nanowires were stretched and aligned on surfaces, even when PPhenaz-TMA/DNA complexes formed in solutions. The resulting PPhenaz-TMA/DNA nanowires could be easily converted to oxidized states or metallic nanowires by using adequate oxidant or metal salts. The direct visualization of PPhenaz-TMA/DNA nanowires and its structural changes have been studied by atomic force microscopy and scanning near-field optical microscopy.     

Strong fibers and films of microbial polyesters

Poly[(R)-3-hydroxybutyrate] (P(3HB)) and its copolymers are accumulated by a wide variety of microorganisms as intracellular carbon and energy material, and are extensively studied as biodegradable and biocompatible thermoplastics. However, these microbial polyesters have not been recognized as practical because of their stiffness and brittleness. Recently, by new drawing techniques, we succeeded in obtaining strong fibers and films from microbial polyesters, produced by both wild-type and recombinant bacteria. The improvement in mechanical properties of the fibers and films is due not only to the orientation of molecular chains, but also to the generation of a zigzag conformation and network structure, formed by fibrillar and lamellar crystals. The structure of strong fibers with a tensile strength over 1.0 GPa was analyzed by micro-beam X-ray diffraction with synchrotron radiation. The strong fibers and films were completely degraded in natural, river freshwater or by extracellular polyhydroxybutyrate depolymerases. In this feature article, the processing, mechanical properties, highly ordered structure and biodegradability of strong fibers and films produced from microbial polyesters are presented.