Solvent‐induced reversible color changes in block copolymer films and new locking method of structural colors

The well‐defined polystyrene‐block‐poly(4‐vinylpyridine) [PS‐block‐P4VP (SV1); lamellar morphology] and polyisoprene‐block‐poly(α‐methyl styrene) [PI‐block‐PMS (IMS1); PI spherical morphology] diblock copolymers were prepared by sequential anionic polymerization techniques. The segregated chains in the P4VP lamellar layers of the SV1 film (PS lamellae: 41 nm; P4VP lamellae: 51 nm) were crosslinked with 1,4‐dibromobutane. This crosslinked film was insoluble in organic solvents such as benzene and chloroform (CHCl₃) and exhibited various structural colors under the swollen state. The IMS1 film (body‐centered cubic lattice, diameter of PI spheres: 53 nm) was soaked in the mixture of CHCl₃/hexane (1 : 10, v/v). This solvent system resulted in the swelling of PI spherical domains. The transmitted and reflected light color through the swollen film changed to a deep blue. Such color changes were reversible upon swelling in solvent and evaporation of the solvent. Subsequently, photofunctional diethyldithiocarbamate (DC) groups were introduced into the PS block of the parent block copolymer IMS1 by means of polymer reactions. The locking of the cubic lattice was performed with living radical graft copolymerization from DC groups of swollen as‐cast film in methyl methacrylate (MMA) under UV irradiation. The locking of structural colors such as blue and green was also achieved, varying the content of poly(methyl methacrylate) (PMMA) grafted chains. Copyright © 2005 John Wiley & Sons, Ltd.     

Repetitive determination of ascorbic acid using iron(III)-1.10-phenanthroline-peroxodisulfate system in a circulatory flow injection method

Ascorbic acid (AA) could be determined in large quantities of a co-existing oxidant. The incorporation of an on-line reagent regeneration step based on redox reaction eliminates the baseline drift in the procedure. This makes it possible to adopt a circulatory flow injection method (cyclic FIA) and to determine AA repetitively. The method is based on the reduction of iron(III) to iron(II) by the analyte, the reaction of the produced iron(II) with 1,10-phenanthroline (phen) in a weak acidic medium to form a colored complex, and the subsequent oxidation reaction of iron(II) to iron(III) by the co-existing peroxodisulfate. A solution (50 ml) of 3.0×10⁻⁴ mol l⁻¹ ferric chloride, 9.0×10⁻⁴ mol l⁻¹ phen and 5.0×10⁻² mol l⁻¹ ammonium peroxodisulfate in acetate buffer (0.2 mol l⁻¹, pH 4.5) is continuously circulated at a constant flow rate of 1.0 ml min⁻¹. Into this stream, an aliquot (20 μl) of the sample solution containing AA is quickly injected by means of a six-way valve. The complex formed is monitored spectrophotometrically (at 510 nm) in the flow system. The stream then returns to the reservoir after passing through a time-delay coil (50 m). The iron(II)–(phen)₃ complex is oxidized to iron(III)–(phen)₃ complex by peroxodisulfate which exists excessively in the circulating reagent solution. The proposed method allows as many as 300 repetitive determinations of 15 mg l⁻¹ AA with only 50 ml reservoir solution. The contents of AA in commercial pharmaceutical products were analyzed to demonstrate the capability of the developed system.     

Syntheses of gramicidin s analogs containing D-Serine or a dehydroalanine residue,and asymmetric hydrogenation of the dehydroalanine

Gramicidin S (GS) analogs, (D-Ser(Bzl)^4,4′]-GS ($\text{17}$), [D-Ser^4,4′]-GS ($\text{18}$), and [L-Orn(Boc)^2,2′,D-Ser^4,4′]-GS ($\text{19}$) were synthesized and $\text{17}$ showed high antibacterial activity. One residue of D-Ser in $\text{19}$ was converted asymmetrically to D-Ala via α,β-dehydroalanine.     

Penicillin-cephalosporin conversion III. A Novel route to 3-chloromethyl-Δ3-cephems

Synthesis of 3-chloromethyl-Δ³-cephems $\text{3}$ from 4-arenesulfonylthioazetidin-2-ones $\text{1}$, derived from penicillins G and V, has been achieved by the electrolytic ene-type chlorination of $\text{1}$ in a CHC1₃-aqueous NaCl-H₂SO₄-(Pt electrodes) system and subsequent ring closure with NH₃ in DMF.     

Lissoclibadin 1, a novel trimeric sulfur-bridged dopamine derivative, from the tropical ascidian Lissoclinum cf. badium

A novel tribenzotetrathiepin alkaloid, named lissoclibadin 1 (1), has been isolated from the ascidian Lissoclinum sp. (cf. L. badium Monniot and Monniot, 1996). The gross structure was assigned on the basis of the spectral data, and one of two possible isomers was selected by the computational modeling study. Lissoclibadin 1 inhibited the growth of the marine bacterium Ruegeria atlantica (15.2 mm at 20 μg/disk).     

Modification of mono-dispersed silica colloid particles with polymer silane coupling agents

The reaction of monodispersed silica colloid with hydrophobic and hydrophilic polymer coupling agents in the presence of ammonia afforded dispersible polymer/SiO₂ composites into organic solvents without aggregation.     

Self-aggregation of synthetic zinc 31-hydroxy-131-oxo-17,18-cis-chlorin in a non-polar organic solvent

Zinc methyl 3¹-demethyl-17,18-cis-bacteriopheophorbide-d was prepared as a model of naturally occurring bacteriochlorophyll-d. From the absorption spectral analysis, the synthetic cis-chlorin self-aggregated in a non-polar organic solvent to give an oligomer possessing red-shifted and broadened peaks, compared to the non-aggregated form. The red-shifted values by self-aggregation were smaller than those observed in the corresponding trans-isomer, indicating that self-aggregates of the cis-isomer took on more disordered supramolecular structures than those of the trans-isomer.     

Synthesis of cross-linked core-shell polymer particles by free-radical dispersion copolymerization of 4-vinylpyridine with polystyrene macromonomers in nonaqueous media

Cross-linked core-shell polymer particles were synthesized by free-radical dispersion copolymerization of 4-vinylpyridine (4VP) and various kinds of cross-linking reagents with methacryloyl-terminated polystyrene (PS) macromonomers in nonaqueous media such as 1,4-dioxane and cyclohexane. Well-defined particles were obtained by copolymerization of 4VP with ethylene glycol dimethacrylate (EGDM) in a dioxane medium. The particle diameters (D(n)=40-990 nm) decreased drastically both with increasing the feed concentration ratio of macromonomer to 4VP, [PS-M]/[4VP], and with increasing molecular weight of PS-M macromonomers. The particle size distribution (D(w)/D(n)) was in the range 1.02-1.10. PS-M macromonomers acted not only as comonomers but also as stabilizers. The particle diameters obtained in dioxane were smaller than those obtained in cyclohexane. Thus, we observed a tendency to smaller particle size as the media became more soluble for PS-M macromonomer.     

Quantitative evaluation of weak nonbonded Se...F interactions and their remarkable nature as orbital interactions

To evaluate weak intramolecular nonbonded Se...F interactions recently characterized for a series of o-selenobenzyl fluoride derivatives (Iwaoka et al., Chem. Lett. 1998, 969-970), the temperature dependence of the nuclear spin coupling between Se and F (J(Se...F)) was investigated for 2-(fluoromethyl)phenylselenenyl cyanate (1a) and bis[2-(fluoromethyl)phenyl] diselenide (1e) in CD2Cl2 and CD3CN. A significant increase in the magnitude of J(Se...F) was observed for both 1a and 1e upon lowering temperature, whereas the values of J(Se...F) for the corresponding trifluoromethyl compounds slightly reduced or remained unchanged at low temperatures. Application of the rapid equilibrium model between two possible conformers revealed that conformer A with an intramolecular Se...F interaction is more stable in enthalpy (DeltaH) by 1.23 kcal/mol for 1a (in CD2Cl2) and by 0.85 and 0.83 kcal/mol for 1e (in CD2Cl2 and CD3CN, respectively) than conformer B, which does not have close Se...F contact. The negligible solvent effects for 1e suggested marginal electrostatic nature of the Se...F interactions. Instead, importance of the n(F) -->sigma*(Se-X) orbital interaction was suggested by quantum chemical (QC) calculations and the natural bond orbital (NBO) analysis.     

Diagonalization of theXXZ Hamiltonian by vertex operators

We diagonalize the anti-ferroelectricXXZ-Hamiltonian directly in the thermodynamic limit, where the model becomes invariant under the action of . Our method is based on the representation theory of quantum affine algebras, the related vertex operators and KZ equation, and thereby bypasses the usual process of starting from a finite lattice, taking the thermodynamic limit and filling the Dirac sea. From recent results on the algebraic structure of the corner transfer matrix of the model, we obtain the vacuum vector of the Hamiltonian. The rest of the eigenvectors are obtained by applying the vertex operators, which act as particle creation operators in the space of eigenvectors. We check the agreement of our results with those obtained using the Bethe Ansatz in a number of cases, and with others obtained in the scaling limit—thesu(2)-invariant Thirring model.Dedicated to Professors Huzihiro Araki and Noboru Nakanishi on the occasion of their sixtieth birthdays