Recyclable self-assembly-supported catalytic system for orthoalkylation

[reaction: see text] A new recyclable supported catalyst system for orthoalkylation was devised using a self-assembly consisting of the barbiturate and 2,4,6-triaminopyrimidine H-bonding motifs. At high temperature, the system is completely homogeneous so as to give an efficient catalytic activity, while it is heterogenized at room temperature to form an insoluble solid phase for the easy recovery of the catalyst after the reaction.     

Comparison of activities of homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) for synthesis of syndiotactic polystyrene by UV/visible spectroscopic study

The catalytic activities in syndiospecific polymerization of styrene in hydrocarbon using homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) were investigated through UV/visible spectroscopic analysis. A strong UV absorption band of CpTiCl₃, itself, incipiently appeared at λ_max = 400 nm in toluene, followed by a bathochromic shift with its remarkable decrease by the addition of MAO. The absorption band intensity at λ_max = 400 nm arising from delocalization of π-electrons on the cyclopentadienyl ring decreased by methylation in the presence of MAO with regard to the mechanism for production of an active center (“cation-like”), for example, the change of the ionic nature. The intensity decrease at λ_max = 400 nm was suppressed over 2000 of the [Al]/[Ti] ratio. In the case of Ti(OC₄H₉)₄ having a σ-ligand, new and broad UV absorption bands were developed at λ_max = 340 nm and 410 nm in the presence of MAO in contrast with the CpTiCl₃/MAO system. Comparison between the relative absorption intensities at λ_max = 340 nm and 410 nm led to the determination of a maximum catalytic activity of Ti(OC₄H₉)₄ in the presence of MAO related to the polymerization yield. The maximum polymerization yield was observed with regard to the relative maximum value of the absorption intensity at λ_max = 410 nm with the [Al]/[Ti] ratio (500). From observation for polymorphism of the final products via differential scanning calorimetric analysis (DSC), the thermally unstable β-form seemed to be produced by the CpTiCl₃/MAO system independent of the MAO concentration, the Ti(OC₄H₉)₄/MAO system produced a thermally stable α-form in the low MAO concentration (up to 100 of the [Al]/[Ti] ratio), and a mixture of α- and/or β-forms over 200 of the [Al]/[Ti] ratio under our experimental conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1733–1741, 1998     

High Performance Polyimide with High Internal Free Volume Elements

This paper reports a new polyimide design with high internal free volume elements for fast mass transport simultaneously with high selectivity. Here, we show that the polymer design using a three‐dimensional rigid molecular structure having internal void space can lead to the formation of high fractional free volume with proper cavity size to separate small gas molecules with high selectivities as high permeabilities. These findings could strongly impact emerging gas separation applications using polymeric membranes such as natural gas purification and biogas purification to get clean energy resources.

     

Controlling side-chain density of electron donating polymers for improving their packing structure and photovoltaic performance

A simple and efficient approach of controlling the side-chain density in the electron donating polymers has been demonstrated to tune their 3-D packing structure and HOMO level, which increases the hole mobility and V(oc) values, thus improving the solar cell performance.     

Induction-driven stabilization of the anion-π interaction in electron-rich aromatics as the key to fluoride inclusion in imidazolium-cage receptors

Intermolecular interactions that involve aromatic rings are key processes in both chemical and biological recognition. It is common knowledge that the existence of anion-π interactions between anions and electron-deficient (π-acidic) aromatics indicates that electron-rich (π-basic) aromatics are expected to be repulsive to anions due to their electron-donating character. Here we report the first concrete theoretical and experimental evidence of the anion-π interaction between electron-rich alkylbenzene rings and a fluoride ion in CH(3)CN. The cyclophane cavity bridged with three naphthoimidazolium groups selectively complexes a fluoride ion by means of a combination of anion-π interactions and (C-H)(+)···F(-)-type ionic hydrogen bonds. (1)H NMR, (19)F NMR, and fluorescence spectra of 1 and 2 with fluoride ions are examined to show that only 2 can host a fluoride ion in the cavity between two alkylbenzene rings to form a sandwich complex. In addition, the cage compounds can serve as highly selective and ratiometric fluorescent sensors for a fluoride ion. With the addition of 1 equiv of F(-), a strongly increased fluorescence emission centered at 385 nm appears at the expense of the fluorescence emission of 2 centered at 474 nm. Finally, isothermal titration calorimetry (ITC) experiments were performed to obtain the binding constants of the compounds 1 and 2 with F(-) as well as Gibbs free energy. The 2-F(-) complex is more stable than the 1-F(-) complex by 1.87 kcal mol(-1), which is attributable to the stronger anion-π interaction between F(-) and triethylbenzene.     

Aspirin-induced Bcl-2 translocation and its phosphorylation in the nucleus trigger apoptosis in breast cancer cells

Here, we report that B-cell lymphoma 2 (Bcl-2) is a novel target molecule of aspirin in breast cancer cells. Aspirin influenced the formation of a complex by Bcl-2 and FKBP38 and induced the nuclear translocation of Bcl-2 and its phosphorylation. These events inhibited cancer cell proliferation and subsequently enhanced MCF-7 breast cancer cell apoptosis. Bcl-2 knockdown using small interfering RNA (siRNA) delayed apoptotic cell death, which correlated with increased proliferation following aspirin exposure. In contrast, Bcl-2 overexpression enhanced the onset of aspirin-induced apoptosis, which was also associated with a significant increase in Bcl-2 phosphorylation in the nucleus. Therefore, this study may provide novel insight into the molecular mechanism of aspirin, particularly its anticancer effects in Bcl-2- and estrogen receptor-positive breast cancer cells.     

TCE and PCE decomposition by a combination of gamma-rays, ozone and titanium dioxide

Gamma-ray treatment in the presence of ozone (O₃) and titanium dioxide (TiO₂) showed an efficient removal of trichloroethylene (TCE) and perchloroethylene (PCE). Without gamma-irradiation, TCE and PCE were not sufficiently decomposed to comply with the water quality limit of groundwater. However, near 100% of TCE and PCE were removed at a dose of 300 Gy in the presence of O₃ and TiO₂, where TiO₂ showed an explicit enhancement of decomposition. Cytotoxicity test using Chinese hamster V79 cells showed no toxicity of the TCE and PCE decomposition products.     

Characteristics of excited-state intermediates of TiO2–Y-Zeolite and MCM41 encapsulating photosensitive molecules: design of new photocatalysts

Some photosensitive molecules, such as p-N,N′-dimethylaminobenzoic acid (DMABA), Nile Red, heteropolytungstic acid (H₃PW₁₂O₄₀, HPA) and metalloporphyrins, have been entrapped onto nano-scale pores or channels of TiO₂-modified Y-Zeolite (TiO₂-Y-Zeolite) and MCM41 (TiO₂-MCM41) and their excited-state intermediates have been characterized in terms of the excited-state dynamics by using laser spectroscopic techniques. Through these studies, it has been found that the photo-induced electrons are generated from the intramolecular charge transfer (ICT) state of DMABA, Nile Red or metalloporphyrin (MnTPP(Cl)), followed by transferring to the TiO₂-Y-Zeolite or TiO₂-MCM41 more efficiently as compared to the bulk TiO₂, NaY-Zeolite or MCM41. The efficient photoinduced interfacial electron transfer causes the rapid formation of radicals of those photosensitive molecules (a few tens ps). It has been also found that these photophysical properties can be applied to develop the new photocatalyst as observed by the efficient photocatalytic activities of the DMABA or Nile Red-entrapped TiO₂-Y-Zeolites for the photoreduction of an azo-dye such as Methyl Orange in water. On the other hand, in case of HPA-entrapped TiO₂-Y-zeolite, the electron generated from the excited-state TiO₂ is transferred to HPA, followed by formation of the reduction product, heteropoly blue (HPB) which is also generated by UV irradiation of HPA. This electron transfer is analogous to the Z-scheme mechanism of plant photosynthetic systems showing two photon reactions. Because of this photoelectron transfer mechanism, the HPA-entrapped TiO₂-Y-zeolite has demonstrated the synergistic enhancement of the photocatalytic decomposition of Methyl Orange and hydrogen generation from photolysis of water.     

High-Throughput Analysis of Sofalcone in Human Plasma by Use of Automated 96-Well Protein Precipitation and LC-MS-MS

A sensitive and selective method for the determination of sofalcone in human plasma was established by use of protein precipitation and liquid chromatography-tandem mass spectrometry. Plasma samples were transferred into 96-well plate using an automated sample handling system and spiked with 10 L of 2 g mL^–1 internal standard solution (d₃-sofalcone). 0.5 mL of acetonitrile was added to the 96-well plate and the plasma samples were then vortexed for 30 sec. After centrifugation, the supernatant was transferred into another 96-well plate and completely evaporated at 40 °C under a stream of nitrogen. The dry residue was reconstituted with mobile phase. All sample transfer and protein precipitation was automated through the application of both the PerkinElmer MultiPROBE II HT and TOMTEC Quadra 96 workstation. The limit of quantitation of sofalcone was 2 ng mL^–1 using a sample volume of 0.2 mL for the analysis. The reproducibility of the method was evaluated by analyzing five samples at nine quality control (QC) levels over the nominal concentration range from 2 ng mL^–1 to 1000 ng mL^–1. Validation of the method showed that the assay has good precision and accuracy. Sofalcone and internal standard produced a protonated precursor ion ([M+H]⁺) at m/z 451 and 454, and both gave a corresponding product ion at m/z 315. The high sample throughput of the method has been successfully applied to a pharmacokinetic study of sofalcone in human plasma.