Synthesis, characterization, and OLED application of oligo(p-phenylene ethynylene)s with polyhedral oligomeric silsesquioxanes (POSS) as pendant groups

Two new classes of mono- and oligo(p-phenylene ethynylene)s grafted with polyhedral oligomeric silsesquioxanes (POSS) were synthesized via ‘click’ chemistry and palladium-catalyzed Sonogashira cross-coupling. These materials with cubic silsesquioxanes are very robust with excellent thermal stability in air (T_5%loss>330 °C) and exhibited T_g>80 °C. All the compounds showed high photoluminescence with a range of blue emission and quantum yield up to 80% in the solution. Extended π conjugation molecules of oligo-pPEs POSS maintain relatively high PL quantum efficiencies in the solid state, compared to mono-pPEs POSS. A preliminary report is made of some of the materials as multilayer OLED components with active dopants PVK and PBD.     

Intramolecular polar addition reactions of active methylene moieties to aryl-substituted alkenes via photoinduced electron transfer

The synthesis of cycloalkane derivatives with ring sizes of 5-7 was achieved in moderate yields by photoirradiation of aqueous acetonitrile solutions, containing compounds that consist of active methylene moieties tethered to aryl-substituted alkenes along with sodium hydroxide and 9-cyanophenanthrene. When the substrate contains ethyl cyanoacetate as an asymmetric active methylene moiety, the reaction proceeds in a highly diastereoselective manner.     

Hydrofluoroarylation of alkynes with fluoroarenes

A combination of Ni(cod)(2) and PCyp(3) is found to be an effective catalyst for chemoselective activation of the C-H bond of fluoroarenes over C-F bonds followed by insertion of alkynes to allow direct alkenylation of the electron-deficient arenes. The characteristics of the reactions are: a C-H bond ortho to a fluorine substituent is selectively activated; the reactivity of fluorobenzenes is roughly proportional to the number of fluorine atoms. The reaction conditions tolerate a broad range of both alkynes and fluoroarenes containing both electron-withdrawing and -donating groups, thus allowing efficient synthesis of a variety of substituted ethenes containing a fluoroaryl motif in high regio- and stereoselective manners. Mechanistic studies including both labeling experiments and stoichiometric reactions reveal that oxidative addition of C-H bonds in fluoroarenes to nickel(0) is kinetically highly facile whereas that of C-F bonds is thermodynamically favoured.     

Chemoenzymatic synthesis of (2S,3S,4S)-form, the physiologically active stereoisomer of dehydroxymethylepoxyquinomicin (DHMEQ), a potent inhibitor on NF-κB

A new route for (2S,3S,4S)-form, the physiologically active stereoisomer of dehydroxymethylepoxyquinomicin (DHMEQ), a potent NF-κB inhibitor, was established by chemoenzymatic approach. Elaboration on the asymmetric epoxidation of a p-benzoquinone monoketal with benzylcinchonidinium tert-butylhydroperoxide yielded an epoxyenone, in 79.8% ee and 57% yield in reproducible manner. By way of the transformation of this key intermediate to enantiomerically pure (2S,3S,4S)-DHMEQ, the contaminating undesired enantiomer could be effectively removed by applying Burkholderia cepacia lipase-catalyzed hydrolysis of diacylated precursor. The above integrated combination of chemical asymmetric synthesis and enzyme-catalyzed kinetic resolution enabled us to prepare active DHMEQ in a large-scale.     

Determination of vanillin and related flavor compounds in cocoa drink by capillary electrophoresis

In the first part of this study, the stability of five terpenes (alpha-pinene, limonene, camphor, citronellol, and carvacrol) under subcritical water conditions was investigated. The stability studies were carried out at four different temperatures (100, 150, 200, and 250 degrees C) with two different heating times (30 and 300 min). When water temperature was increased, the degradation of terpenes became more serious. Prolonged exposure time to each heating temperature also caused decreased terpene stability. The terpene recoveries were determined by conducting subcritical water extraction of sand spiked with terpenes. The recoveries are typically around 70 to 80% for extractions at 100 degrees C. Terpene recoveries were decreased with increasing water temperature due to poorer stability of terpenes. After the degradation and recovery studies, basil and oregano leaves were extracted using water at both 100 and 150 degrees C. The concentrations of each individual terpene in the water extract generally ranged from trace quantity to 65 microg terpene/g herb. However, the concentration of carvacrol in the oregano-water extract at 150 degrees C was found to be as high as 4270 microg carvacrol/g oregano.     

"Pocket dendrimers" as nanoscale receptors for bimolecular guest accommodation

A new series of dendrimer receptors was prepared by combining a (tetraphenylporphinato)zinc(II) core and benzyl ether type dendritic substituents. Since one direction of the (tetraphenylporphinato)zinc(II) was not substituted by a dendritic residue, the resulting unsymmetrical dendrimers have "pockets" available for access of external substrates. Molecular modeling, NMR measurements, and zinc-coordination experiments revealed that the third-generation dendrimer of this type exhibited characteristic inclusion of coordinative pyridine guests. When diamidopyridine moiety was introduced into the dendrimer pocket, a thymine derivative was bound through complementary hydrogen bonding. Two different kinds of substrates, pyridine and thymine derivatives, were simultaneously accommodated in the nanoscale pocket and bimolecular guest accommodation was realized with the designed dendrimer receptor.     

Low temperature properties of acetonitrile confined in MCM-41

The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C[triple bond]N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 A (C14), below which it is not frozen. In addition, phase changes between alpha-type and beta-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Deltagamma(l/alpha) = 22.4 mJ m(-2) for the liquid/pore surface (ps) and alpha-type/ps, and Deltagamma(alpha/beta) = 3.17 mJ m(-2) for alpha-type/ps and beta-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol(-1) compared to the bulk value of 12.7 kJ mol(-1). The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.     

Biooxidation of (+)-catechin and (-)-epicatechin into 3,4-dihydroxyflavan derivatives by the endophytic fungus Diaporthe sp. isolated from a tea plant

The microbial transformation of (+)-catechin (1) and (-)-epicatechin (2) by endophytic fungi isolated from a tea plant was investigated. It was found that the endophytic filamentous fungus Diaporthe sp. transformed them (1, 2) into the 3,4-cis-dihydroxyflavan derivatives, (+)-(2R,3S,4S)-3,4,5,7,3',4'-hexahydroxyflavan (3) and (-)-(2R,3R,4R)-3,4,5,7,3',4'-hexahydroxyflavan (7), respectively, whereas (-)-catechin (ent-1) and (+)-epicatechin (ent-2) with a 2S-phenyl group resisted the biooxidation.     

Synthesis and evaluation of 3-methyl-4-oxo-6-phenyl-4,5,6,7-tetrahydrobenzofuran-2-carboxylic acid ethyl ester derivatives as potent antitumor agents

For the construction of new combinatorial libraries, a lead compound was created by replacing the core structure of a hit compound discovered by screening for cytotoxic agents against a tumorigenic cell line. The newly designed compound maintained biological activity and allowed alternative library construction for antitumor drugs.     

Dichloro­oxo(quinoline‐8‐thiolato‐κ2N,S)(triphenyl­phosphine oxide‐κO)rhenium(V) acetone solvate

The complex mol­ecule in the title compound, [Re(C₉H₆NS)Cl₂O(C₁₈H₁₅OP)]·C₃H₆O, has distorted octa­hedral geometry. The Re=O bond occupies the position trans to the triphenyl­phosphine oxide O atom. The Re—Cl bond trans to the thiol­ate S atom is longer than that trans to the quinoline N atom, implying a stronger trans influence of the S atom. Intra‐ and inter­molecular π–π inter­actions are also observed between the π rings in the complex.