Ultra-small-angle neutron scattering studies on phase separation of poly(vinyl alcohol) gels

Time-resolved light scattering measurements during the gelation process of a poly(vinyl alcohol) (PVA) solution in a mixture of dimethyl sulfoxide and water (H2O) have shown that a spinodal decomposition (SD) type phase separation takes place in the early stage of gelation. In this case the kinetics of SD is valid only before macroscopic gelation occurs because the growth rate is slowed down by gelation. Such SD type phase separation makes the solution opaque as it proceeds, and hence the structural change can no longer be followed by light scattering. To investigate the structure of the opaque PVA gel as well, we have employed an ultra-small-angle neutron scattering technique using a Bonse-Hart camera. These observations reveal that even after the macroscopic gelation the structure due to the microphase separation on a spatial scale of several &mgr;m continues to grow against the elasticity. This may be because at first the gel structure is too soft to suppress the growth of the microphase separation, but within 24 h after the quenching the growth terminates. On the basis of the results, we will discuss a possible mechanism of the microphase separation after gelation.     

Antimicrobial sesquiterpenoids from Laurus nobilis L

Activity-guided fractionations of leaf extracts from Laurus nobilis L. led to the isolation of a known sesquiterpene lactone, deacetyl laurenobiolide (1). Compound 1 showed antimicrobial activity against periopathic pathogens (Actinomyces viscosus, Porphyromonas gingivalis, Prevotella intermedia and Actinobacillus actinomycetemcomitans), opportunistic Gram-positive bacteria (Staphylococcus aureus and Streptococcus pyogenes) and fungi (Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus). Furthermore, acetylation and cyclisation of deacetyl laurenobiolide (1) yielded laurenobiolide (2) and a new compound, (5S,6R,7S,8S,10R)-6,8-dihydroxyeudesma-4(15),11(13)-dien-12-oic acid 12,8-lactone (3), respectively. Compounds 2 and 3 also showed antimicrobial activities. All compounds 1-3 demonstrated growth inhibitory effects with minimum inhibitory concentrations ranging from 31 to 1000?μg?mL(-1). This is the first report of compounds 1-3 showing antimicrobial activities.     

Fusion of phosphole and 1,1'-biacenaphthene: phosphorus(V)-containing extended π-systems with high electron affinity and electron mobility

A profusion of phospholes: Diacenaphtho[1,2-b:1',2'-d]phospholes, a new class of arene-fused phosphole π-systems, were synthesized and their structural and electrochemical properties studied. The P-sulfide derivative has a high electron-transporting ability (μ(E) =2.4×10(-3) cm(2) V(-1) s(-1)) in a vacuum-deposited film.     

Online transient isotachophoresis concentration by the pseudo-terminating electrolyte buffer for the separation of DNA-aptamer and its thrombin complex in poly(methyl methacrylate) microchip

Online automatic transient isotachophoresis concentration of DNA-aptamer and its thrombin complex by using one kind of pseudo-terminating electrolyte buffer in a cross-channel poly(methyl methacrylate) microchip is reported. Sample injection, transient concentration and separation were done continuously and controlled by a sequential voltage switching program, time-consuming steps and complicated chip design were not required. Peak resolution between DNA-aptamer and its thrombin complex was influenced by this novel pseudo-terminating electrolyte buffer, which was prepared by the addition of chemical component with slow mobility into the same buffer as leading electrolyte buffer. 1100-fold signal enhancement of thrombin complex was achieved by this transient isotachophoresis on a standard cross-form microchip. The concentration effect or standing time of transient isotachophoresis was proved to be influenced by the concentration of leading electrolyte ion and the concentration of pseudo-terminating electrolyte buffer ion (glycine). The transient concentration was followed by on-chip nondenaturing gel electrophoresis in methylcellulose solution for the size-based separation. The detection limit, taken as the lowest thrombin concentration at threefold S/N, was determined to be 0.5 amol in mass by this method.     

Search for B+-->D*+pi0 decay

We report on a search for the doubly Cabibbo suppressed decay B+-->D*+pi0, based on a data sample of 657x10(6) BB pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find no significant signal and set an upper limit of B(B+-->D*+pi0)<3.6x10(-6) at the 90% confidence level. This limit can be used to constrain the ratio between suppressed and favored B-->D*pi decay amplitudes, r<0.051, at the 90% confidence level.     

Measurement of time-dependent CP-violating parameters in B(0)-->K_(S)(0)K_(S)(0) decays

We report a measurement of the CP-violating parameters in B;{0}-->K_{S}{0}K_{S}{0} decays based on a data sample of 657x10{6} BB[over ] pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e;{+}e{-} collider. In this Letter, one neutral B meson is fully reconstructed in the B;{0}-->K_{S}{0}K_{S}{0} decay mode, and the flavor of the accompanying B meson is identified by its decay products. The CP-violating parameters are measured from the asymmetry in the distributions of the proper-time interval between the two B decays: S_K_{S}{0}K_{S}{0}}=-0.38_{-0.77}{+0.69}(stat)+/-0.09(syst) and A_{K_{S}{0}K_{S}{0}}=-0.38+/-0.38(stat)+/-0.05(syst).     

Ethene–propene copolymerization with the MgCl2-supported dichlorobis(4,4,4-trifluoro-1-phenyl- 1,3-butanedionato)titanium catalyst activated by an ordinary trialkylaluminum

The Ti(BFA)₂Cl₂/MgCl₂–Al(C₂H₅)₃ catalyst (BFA = 4,4,4-trifluoro-1-phenyl-1,3-butanedione) modified by DIPDMS (diisopropyldimethoxysilane), which had been proved to yield an extremely high isotactic polypropene in high selectivity, was tested for the copolymerization of ethene with propene. The analysis of resulting copolymers by CFC (cross fractionation chromatography) indicated the formation of a small quantity of ethene-rich copolymers as a byproduct, suggesting that the catalyst possesses not only Ti(III) species but a small portion of Ti(II) species. Whereas, the same catalyst without being modified by an external donor selectively yielded propene-rich random copolymers resulting from Ti(III) species in high yields. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2735–2740, 1998     

Amalgamation of ziegler-natta and metallocene catalysts

The MgCl₂ supported half titanocenes and Ti(4, 4, 4-trifluoro-1-phenyl-1, 3-butanedionato)₂Cl₂ catalysts were synthesized and applied to propene polymerization. Without supporting on MgCl₂, those complexes displayed almost no activity even using methylaluminoxane (MAO) as cocatalyst. When supported on MgCl₂, on the other hand, the resulting catalysts could be activated by ordinary alkylaluminums to yield polypropene in fairly high yields. The catalyst isospecificity was markedly improved by the addition of a suitable Lewis base.     

Robust Spirobifluorene Core Based Hole Transporters with High Mobility for Long-Life Green Phosphorescent Organic Light-Emitting Devices

Using a tailored high triplet energy hole transport layer (HTL) is a suitable way to improve the efficiency and extend the lifetime of organic light-emitting devices (OLEDs), which can use all molecular excitons of singlets and triplets. In this study, dibenzofuran (DBF)-end-capped and spirobifluorene (SBF) core-based HTLs referred as TDBFSBF1 and TDBFSBF2 were effectively developed. TDBFSBF1 exhibited a high glass transition temperature of 178 °C and triplet energy of 2.5 eV. Moreover, a high external quantum efficiency of 22.0 %, long operational lifetime at 50 % of the initial luminance of 89,000 h, and low driving voltage at 1000 cd m⁻² of 2.95 V were achieved in green phosphorescent OLEDs using TDBFSBF1 . Further, a high-hole mobility μ_h value of 1.9×10⁻³ cm² V⁻¹ s⁻¹ was recorded in TDBFSBF2 . A multiscale simulation successfully reproduced the experimental μ_h values and indicated that the reorganization energy was the primary factor in determining the mobility differences among these SBF core based HTLs.