Control of self-aggregation of fullerenes by connection with calix[4]arene: solvent- and guest-effects to particle size

A new molecular design of fullerene derivatives exhibiting trigger-responsive self-aggregation in organic solvents has been established. Calix[4]arene was covalently connected with fullerene in order to apply host-guest interaction to the aggregation control. The self-assembly behaviour was studied in organic solvents by UV-vis absorption spectroscopy, dynamic light scattering and transmission electron microscopy. Results show that the bisfullerene formed self-aggregations with a low polydispersity index due to the fullerenes' tendency to aggregate in polar organic solvents. Furthermore, the aggregate sizes can be changed readily by solvent composition and the addition of guest cations. Especially, disaggregation of the bisfullerene was induced by addition of LiClO4 or NaClO4.     

Direct synthesis of bipyrroles using phenyliodine bis(trifluoroacetate) with bromotrimethylsilane

[reaction: see text] The hypervalent iodine(III) reagent, phenyliodine bis(trifluoroacetate) (PIFA), mediates the unprecedented, oxidative coupling reaction of pyrroles to give alpha-linked bipyrroles selectively in the presence of bromotrimethylsilane. This straightforward synthesis could provide 2,3'-bipyrrole by the choice of a N-substituent of pyrrole. Mechanistic consideration of the present reaction is also described.     

Highly regioselective propanoylation of dihydroxybenzenes mediated by Candida antarctica lipase B in organic solvents

Candida antarctica lipase B (CAL-B) was found to be a highly active biocatalyst for the direct acylation of the phenolic hydroxyls of substituted hydroquinones and resorcinols with vinyl propanoate as an acyl donor. The acylation reactions took place generally in a very regioselective manner. Especially in the case of 4-substituted resorcinols, the hydroxyl remote from the substituent was regiospecifically acylated to afford only the 1-O-propanoylated resorcinols.     

Secondary alcohols act as better nucleophiles than primary alcohols in the lipase-catalyzed regioselective deacylation of dihydroxybenzenes acylated at both phenolic hydroxyls

Candida antarctica lipase B (CAL-B) was found to be highly regioselective as well as active in the deacylation of resorcinols and hydroquinones acylated at both phenolic hydroxyls. Contrary to expectation, secondary alcohols acted as better nucleophiles than primary alcohols in these enzymatic deacylations.     

Characteristic properties of film prepared from poly(L‐lactide)‐grafted dextran of a relatively high sugar unit content as a degradable biomaterial

To develop novel biomedical soft materials with degradability, amphiphilic poly(L ‐lactide)‐grafted dextrans (Dex‐g‐PLLAs) of relatively high sugar unit contents were synthesized with the trimethylsilyl protection method. The characteristic properties of solution‐cast films prepared from the obtained Dex‐g‐PLLAs were investigated. The water absorption and degradation rate of the Dex‐g‐PLLA films increased with increasing sugar unit content. The morphology of the bulk phase and top surface of the Dex‐g‐PLLA films was evaluated with transmission electron microscopy and atomic force microscopy, respectively. The bulk phase of the Dex‐g‐PLLA films with a sugar unit content of 16–25 wt % was found by transmission electron microscopy to form a lamellar type of phase‐separated structure composed of approximately 80–100‐nm‐wide nanodomains because of their amphiphilic and branched structures. The hydrophobic top surface for a Dex‐g‐PLLA film with a sugar unit content of 25 wt % covered with PLLA segments was confirmed by atomic force microscopy phase images to be easily converted to a wettable top surface covered with hydrophilic dextran aggregates showing an 8–10‐nm‐wide honeycomb pattern by means of annealing in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6402–6409, 2006     

Preparation of Au-TiO2 Hybrid Nano Particles in Silicate Film Made by Sol-Gel Method

TiO₂ nano particles with photo catalytic property were mixed with silica alkoxides solution with HAuCl₄/4H₂O. STS02 (purchased from Ishihara Sangyo Kaisha, Ltd.) was used as TiO₂ nano particles. The average size of TiO₂ nano particles was 7 nm in diameter. The gel film coated on glass substrate was heated and then HAuCl₄/4H₂O was thermally reduced at 390 degree. The coated silica gel film doped with HAuCl₄/4H₂O and TiO₂ nano particles was turned into light blue from colorless gel film after heat treatment. The optical absorption spectrum showed the absorption peak of the film heated at 390 degree shifted to at about 650 nm compare to SiO₂ film doped with Au nano particles without TiO₂ nano particles that had absorption peak at 542 nm. On the other hand, the film formed from coating solution incorporated TiAA (titanium tetraisopropoxide chelated by acetyl acetone) as TiO₂ source instead of TiO₂ nano particles had absorption peak at 550 nm. That means there was no effect on formation of Au nano particles when TiAA was incorporated. The average size of the particles was found to be about 23 nm in diameter by TEM observation. Furthermore EDX (Energy Dispersive X-ray Fluorescence Spectrometer) analysis of nano particles in the film indicated that Au-TiO₂ nano hybrid particles were formed. Simulation results also supported that the size in diameter of Au nano particles had little influence on the absorption coefficient of the silica film doped with Au nano particles.     

Acid–Base‐Responsive Intense Charge‐Transfer Emission in Donor–Acceptor‐Conjugated Fluorophores

Herein we report on the synthesis and acid‐responsive emission properties of donor–acceptor (D–A) molecules that contain a thienothiophene unit. 2‐Arylthieno[3,2‐b]thiophenes were conjugated with an N‐methylbenzimidazole unit to form acid‐responsive D–A‐type fluorophores. The D–A‐conjugated fluorophores showed intense intramolecular charge‐transfer (ICT) emission in response to acid. The effect of the substitution on their photophysical properties as well as their solvent‐dependence indicated non‐twisting ICT emission in protonated D–A molecules. The quinoidal character of 2‐arylthienothiophene as a donor part is discussed, as it is assumed that it contributes to suppression of the molecular twisting in the excited state, therefore decreasing the nonradiative rate constant, thereby resulting in the intense ICT emission. Acid–base‐sensitive triple‐color emission was also achieved by the introduction of a base‐responsive phenol group in the donor part.     

Maximal Thurston-Bennequin numbers of alternating links

We show that the upper bound of the maximal Thurston-Bennequin number for an oriented alternating link given by the Kauffman polynomial is sharp. As an application, we confirm a question of Ferrand. We also give a formula of the maximal Thurston-Bennequin number for all two-bridge links. Finally, we introduce knot concordance invariants derived from the Thurston-Bennequin number and the Maslov number of a Legendrian knot.