Transparent poly(bisphenol A carbonate)-based nanocomposites with high refractive index nanoparticles

Transparent organic-inorganic nanocomposites were successfully synthesized from sulfonic acid-modified poly(bisphenol A carbonate) (SPC) and TiO₂ or ZrO₂ nanoparticles. The dispersibility of nanoparticles was significantly improved by both the surface treatment of nanoparticles with phosphoric acid 2-ethylhexyl esters (PAEH) and the introduction of a sulfonic acid moiety into the PC chain. It was found that in some cases, crystallization of the matrix caused a reduction in transparency. Efficient dispersion of nanoparticles and the absence of crystallization resulted in highly transparent nanocomposites with up to 42 wt% TiO₂ and 50 wt% ZrO₂ nanoparticles. The refractive indices of the nanocomposites based on SPC increased with the increasing amount of nanoparticles. Theoretical equation based on Maxwell-Garnett effective medium theory provided reasonably close estimation of the refractive indices to the experimentally observed values. The prepared nanocomposites had lower thermal stability than the host matrix polymers.     

Palladium-catalyzed C-H homocoupling of bromothiophene derivatives and synthetic application to well-defined oligothiophenes

Synthesis of oligothiophenes of well-defined structures that possess 2-8 thiophene units is performed with a new synthetic strategy involving C-H homocoupling of bromothiophenes and cross-coupling with organostannanes. Tolerance of the carbon-bromine bond to the palladium-catalyzed C-H homocoupling results in oligothiophenes bearing C-Br bonds at the terminal thiophene rings, which allow further transformation by the catalysis of a transition-metal complex.     

Biocleavable polyrotaxane-plasmid DNA polyplex for enhanced gene delivery

A biocleavable polyrotaxane, having a necklace-like structure consisting of many cationic alpha-cyclodextrins (alpha-CDs) and a disulfide-introduced poly(ethylene glycol) (PEG), was synthesized and examined as a nonviral gene carrier. The polyrotaxane formed a stable polyplex having positively charged surface even at low charge ratio. This is likely to be due to structural factors of the polyrotaxane, such as the mobile motion of alpha-CDs in the necklace-like structure. Rapid endosomal escape was observed 90 min after transfection. The positively charged surface and the good buffering capacity are advantageous to show the proton sponge effect. The pDNA decondensation occurred through disulfide cleavage of the polyrotaxane and subsequent supramolecular dissociation of the noncovalent linkages between alpha-CDs and PEG. Transfection of the DMAE-SS-PRX polyplex is independent of the amount of free polycation. Those properties played a key role for delivery of pDNA clusters to the nucleus. Therefore, the polyplex nature and the supramolecular dissociation of the polyrotaxane contributed to the enhanced gene delivery.     

Photo-sensitive self-motion of a BQ disk

The photo-sensitive self-motion of a benzoquinone (BQ) disk was investigated on a hydroquinone (HQ) aqueous solution. The mode-switching of self-motion, i.e., continuous → intermittent → no motion, was observed with an increase in the concentration of HQ. Upon irradiation with UV light (～254 nm), the critical concentrations of HQ that were associated with the three modes of motion shifted to lower values, and the average speed of motion decreased. We discuss the mechanism of the photo-sensitive self-motion in relation to the photochemical reaction from BQ to HQ and the driving force of the disk.     

Size-selected copper oxide nanoparticles synthesized by laser ablation

Size-tuned copper oxide nanoparticles with sizes of 9, 12, and 15 nm were fabricated by laser ablation and on-line size selection using a differential mobility analyzer at a gas pressure of 666 Pa. The dependence of the particle properties on the in situ annealing temperatures and selection sizes was investigated. The crystalline phases of the nanoparticles fabricated at temperatures below 973 K were assigned to monoclinic cupric oxide (CuO) which converted into cubic cuprous oxide (Cu₂O) when the annealing temperature was above 1,173 K. This indicates that the crystalline phases can be easily controlled by changing the annealing temperature. TEM images confirmed that well-crystallized and well-dispersed CuO and Cu₂O nanoparticles with narrow size distributions were obtained using this method. This fabrication process is useful and promising for the future investigation of the intrinsic size-dependent properties of CuO and Cu₂O.     

Highly efficient near-infrared-emitting lanthanide(III) complexes formed by heterogeneous self-assembly of Ag(I), Ln(III), and thiacalix[4]arene-p-tetrasulfonate in aqueous solution (Ln(III) = Nd(III), Yb(III))

Heterogeneous self-assembly of thiacalix[4]arene-p-tetrasulfonate (TCAS), Ag(I), and Ln(III) (= Nd(III), Yb(III)) in aqueous solutions conveniently afforded ternary complexes emitting Ln(III)-centered luminescence in the near-infrared (NIR) region. A solution-state study revealed that the Ag(I)-Nd(III)-TCAS system gave a complex Ag(I)(4)·Nd(III)·TCAS(2) in a wide pH range of 6-12. In contrast, the Ag(I)-Yb(III)-TCAS system gave Ag(I)(2)·Yb(III)(2)·TCAS(2) at a pH of around 6 and Ag(I)(2)·Yb(III)·TCAS(2) at a pH of approximately 9.5. The structures of the Yb(III) complexes were proposed based on comparison with known Ag(I)-Tb(III)-TCAS complexes that show the same self-assembly behavior. In Ag(I)(2)·Yb(III)(2)·TCAS(2), two TCAS ligands sandwiched a cyclic array of a Ag(I)-Ag(I)-Yb(III)-Yb(III) core. In Ag(I)(2)·Yb(III)·TCAS(2), Yb(III) was accommodated in an O(8) cube consisting of eight phenolate O(-) groups from two TCAS ligands linked by two S-Ag-S linkages. Crystallographic analysis of Ag(I)(4)·Nd(III)·TCAS(2) revealed that the structure was similar to Ag(I)(2)·Yb(III)·TCAS(2) but that it had four instead of two S-Ag-S linkages. The number of water molecules coordinating to Ln(III) (q) estimated on the basis of the luminescent lifetimes was as follows: Ag(I)(4)·Nd(III)·TCAS(2), 0; Ag(I)(2)·Yb(III)(2)·TCAS(2), 2.4; and Ag(I)(2)·Yb(III)·TCAS(2), 0. These findings were compatible with the solution-state structures. The luminescent quantum yield (Φ) for Ag(I)(4)·Nd(III)·TCAS(2) was 4.9 × 10(-4), which is the second largest value ever reported in H(2)O. These findings suggest that the O(8) cube is an ideal environment to circumvent deactivation via O-H oscillation of coordinating water. The Φ values for Ag(I)(2)·Yb(III)(2)·TCAS(2) and Ag(I)(2)·Yb(III)·TCAS(2) were found to be 3.8 × 10(-4) and 3.3 × 10(-3), respectively, reflecting the q value. Overall, these results indicate that the ternary systems have the potential for a noncovalent strategy via self-assembly of the multidentate ligand, Ln(III), and an auxiliary metal ion to obtain a highly efficient NIR-emissive Ln(III) complex that usually relies on elaborate covalent linkage of a chromophore and multidentate ligands to expel coordinating water.     

Can Thiacalixarene Surpass Calixarene?

Heteroatom-bridged calixarenes have been confined intothe unexplored frontier of the vast realm of the calixarene chemistry because of their syntheticdifficulty. Since we found facile one-step synthesis of thiacalix[4]arene, in which four methylenebridges of calix[4]arene are replaced by four sulfides, we have been engaged in the study on thisnew molecular platform regarding the improvements for the synthetic procedures, structuralanalyses, chemical modifications, and functional developments. In this review are describedthe results of our own study to demonstrate the potentials over the limits of the conventionalcalixarenes, putting emphasis on the indispensable role of the bridging sulfur. Highlighted examples are(1) enlargement of the calix skeleton to provide larger cavity, (2) ready oxidizability to sulfoxideand sulfone for providing new members of S bridged calixarenes, and (3) coordination to specificmetal ions controlled by the oxidation state of S. These indicate a hopeful future for thethiacalixarene platform in the forthcoming applications to functional molecular devices.     

Kinetic spectrophotometric determination of tetraphenylporphinecobalt(II) based on photochromism of immobilized norbornadiene

The cobalt(II) complex is detected spectrophotometrically by its catalysis of a photochromic isomerism of norbornadiene (NBD). NBD is immobilized on porous glass beads, and is isomerized to quadricyclane (QC) by UV irradiation. The beads are then immersed in a solution containing tetraphenylporphinecobalt(II) [TPPCo(II)], and the QC is converted back to NBD by a catalytic reaction with TPPCo(II). The rate constant, measured spectrophotometrically, is proportional to the concentration of TPPCo(II). The detection limit of TPPCo(II) is 60 μM for a reaction period of 1 h. This spectrophotometric detection can be applied repetitively without any supply of the chemical reagent, as NBD immobilized on the porous glass beads can be re-isomerized to QC by UV irradiation.     

Supramolecular hydrogel formation based on inclusion complexation between poly(ethylene glycol)-modified chitosan and alpha-cyclodextrin

Supramolecular hydrogels have been prepared on the basis of polymer inclusion complex (PIC) formation between poly(ethylene glycol) (PEG)-modified chitosans and alpha-cyclodextrin (alpha-CD). A series of PEG-modified chitosans were synthesized by coupling reactions between chitosan and monocarboxylated PEG using water-soluble carbodiimide (EDC) as coupling agent. With simple mixing, the resultant supramolecular assembly of the polymers and alpha-CD molecules led to hydrogel formation in aqueous media. The supramolecular structure of the PIC hydrogels was confirmed by differential scanning calorimetry (DSC), X-ray diffraction, and (13)C cross-polarized/magic-angle spinning (CP/MAS) NMR characterization. The PEG side-chains on the chitosan backbones were found to form inclusion complexes (ICs) with alpha-CD molecules, resulting in the formation of channel-type crystalline micro-domains. The IC domains play an important role in holding together hydrated chitosan chains as physical junctions. The gelation property was affected by several factors including the PEG content in the polymers, the solution concentration, the mixing ratio of host and guest molecules, temperature, pH, etc. All the hydrogels in acidic conditions exhibited thermo-reversible gel-sol transitions under appropriate conditions of mixing ratio and PEG content in the mixing process. The transitions were induced by supramolecular association and dissociation. These supramolecular hydrogels were found to have phase-separated structures that consist of hydrophobic crystalline PIC domains, which were formed by the host-guest interaction between alpha-CD and PEG, and hydrated chitosan matrices below the pK(a).The formation of inclusion complexes between alpha-cyclodextrin and PEG-modified chitosan leads to the formation of hydrogels that can undergo thermo-reversible supramolecular dissociation.