Catalytic one-pot synthesis of cyclic amidines by virtue of tandem reactions involving intramolecular hydroamination under mild conditions

A new synthetic methodology for the generation of cyclic amidines has been developed by the reaction of 1,n-aminoalkynes with electron-deficient azides using a ruthenium catalyst at ambient temperature. The reaction proceeds most likely via a tandem sequence of intramolecular hydroamination of aminoalkynes, cycloaddition of azides with the resulting enamines, and rearrangement of triazoline intermediates. It demonstrates, as the proof-of-principle, that an equilibria cascade sequence can be favorably driven by an irreversible step, thus enabling a facile one-pot synthetic route to deliver molecular complexity under unprecedented mild conditions without relying on the traditional linear approaches.     

A new photostable terrylene diimide dye for applications in single molecule studies and membrane labeling

A new terrylene diimide-based dye (WS-TDI) that is soluble in water has been synthesized, and its photophysical properties are characterized. WS-TDI forms nonfluorescing H-aggregates in water that show absorption bands being blue-shifted with respect to those of the fluorescing monomeric form. The ratio of monomeric WS-TDI to aggregated WS-TDI was determined to be 1 in 14 400 from fluorescence correlation spectroscopy (FCS) measurements, suggesting the presence of a large amount of soluble, nonfluorescent aggregates in water. The presence of a surfactant such as Pluronic P123 or CTAB leads to the disruption of the aggregates due to the formation of monomers in micelles. This is accompanied by a strong increase in fluorescence. A single molecule study of WS-TDI in polymeric films of PVA and PMMA reveals excellent photostability with respect to photobleaching, far above the photostability of other common water-soluble dyes, such as oxazine-1, sulforhodamine-B, and a water-soluble perylenediimide derivative. Furthermore, labeling of a single protein such as avidin is demonstrated by FCS and single molecule photostability measurements. The high tendency of WS-TDI to form nonfluorescent aggregates in water in connection with its high affinity to lipophilic environments is used for the fluorescence labeling of lipid membranes and membrane containing compartments such as artificial liposomes or endosomes in living HeLa cells. The superior fluorescence imaging quality of WS-TDI in such applications is demonstrated in comparison to other well-known membrane staining dyes such as Alexa647 conjugated with dextran and FM 4-64 lipophilic styryl dye.     

Conducting block copolymer for simple micro- to nanopatterns

To use conducting polymers as substitutes for metals and conventional semiconductors in device fabrication, a cost-effective process for the reproducible deposition of the conducting polymers is needed. In this letter, we report a simple solution casting method for the fabrication of micro- to nanopatterns using the conducting block copolymer, poly(thiophene-block-ethyleneoxide), which shows rectifying characteristics dependent on the pattern width.     

Self-assembly of a diblock copolymer on a patterned surface with low-energy electron beam

A pattern was generated by 500 eV electron beam irradiation on benzaldimine monolayer through a grid and subsequent hydrolysis of nonirradiated regions. While we tried to assemble a block copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), on the pattern, we observed that the polarity difference between the two different regions was not right for discriminating the wetting behavior of two blocks of the polymer. Among various modifications of the retrieved amine, it was found that tribromoacetaldehyde was suitable for this end. Surprisingly, treatment of the aldehyde gave a surface preferring the polystyrene block to poly(4-vinylpyridine) block, while the irradiated section favored the latter block. As a result, island morphology was observed on the tribromoacetaldimine region and hole morphology on the irradiated region when the film thickness was 1.3Lo. Contact angle data were consistent with the observed symmetric wetting on the former region and the asymmetric one on the latter.     

Synthesis and characterization of Ge2Sb2Te5 nanowires with memory switching effect

Ge2Sb2Te5 nanowires (NWs) were synthesized by vaporizing GeTe, Sb, and Te precursors assisted by metal catalysts. Current-voltage measurement of the Ge2Sb2Te5 NW device displays fast and reversible switching between two distinct resistive states, which is due to the crystalline-amorphous phase transition nature of these materials     

Reduction potential tuning of the blue copper center in Pseudomonas aeruginosa azurin by the axial methionine as probed by unnatural amino acids

The conserved axial ligand methionine 121 from Pseudomonas aeruginosa azurin (Az) has been replaced by isostructural unnatural amino acid analogues, oxomethionine (OxM), difluoromethionine (DFM), trifluoromethionine (TFM), selenomethionine (SeM), and norleucine (Nle) using expressed protein ligation. The replacements resulted in < 6 nm shifts in the S(Cys)-Cu charge transfer (CT) band in the electronic absorption spectra and < 8 gauss changes in the copper hyperfine coupling constants (AII) in the X-band electron paramagnetic resonance spectra, suggesting that isostructural replacement of Met resulted in minimal structural perturbation of the copper center. The slight blue shifts of the CT band follow the trend of stronger electronegativity of the ligands. This trend is supported by 19F NMR studies of the fluorinated methionine analogues. However, the order of AII differs, suggesting additional factors influencing AII. In contrast to the small changes in the UV-vis and EPR spectra, a large variation of > 227 mV in reduction potential was observed for the series of variants reported here. Additionally, a linear correlation was established between the reduction potentials and hydrophobicity of the variants. Extension of this analysis to other type 1 copper-containing proteins reveals a linear correlation between change in hydrophobicity and change in reduction potential, independent of the protein scaffold, experimental conditions, measurement techniques, and steric modifications. This analysis has also revealed for the first time high and low potential states for type 1 centers, and the difference may be attributable to destabilization of the protein fold by disruption of hydrophobic or hydrogen bonding interactions that stabilize the type 1 center.     

On determining a 1-tailed upper limit for future sample HorRat values

Two formulas were developed for use in computing 1-tailed upper limits for future HorRat values obtained from the collaborative study of materials. One formula is applicable when a future sample HorRat value H [formula: see text] is computed based on a known concentration (e.g., C = spike level and RSD(R) is the sample relative reproducibility standard deviation) and the other formula is applicable when the true concentration (C) is unknown and a future sample HorRat value [formula: see text] is computed using the sample mean (e.g., y, the collaborative study overall mean for an analyte). A Monte Carlo simulation procedure was developed using the Statistical Analysis System (SAS) software to assess the accuracy of the 2 developed formulas. Based on the degree of closeness between the simulated and calculated limits, the formulas for computing upper limits for future sample HorRat values will prove to be useful to Study Directors in determining worst case scenarios concerning a method's reproducibility precision relative to that predicted using the "Horwitz equation". We also define the current empirical HorRat limits as 1-tailed 100p% upper limits to assess the statistical consequence, in a probability sense, of their application as an analytical methods screening tool.     

Silylene-spaced diphenylanthracene derivatives as blue-emitting materials

A novel series of blue emitting silylene-spaced diphenylanthracene derivatives have been synthesized and characterized. The rhodium-catalyzed hydrosilylation of bis[4-(dimethylsilyl)phenyl]anthracene 3-4 yielded stable 9,10-disubstituted (E)-divinylsilylene-diphenylanthracene products 7-10 and salt elimination reaction of bis[4-(chlorodimethylsilyl)phenyl]anthracene 5-6 gave 9,10-disubstituted disilyldiphenylanthracene compounds 11-14. They are fluorescent in the blue region with good quantum efficiencies. The rhodium-catalyzed polyaddition including 2-tert-butyl-9,10-bis[4-(dimethylsilyl)phenyl]anthracene (4) afforded the nonconjugated copolymer 15.     

Synthesis and styrene polymerization properties of dinuclear half-titanocene complexes with xylene linkage

The new dinuclear half-sandwich complexes of titanium with xylene bridge, [Ti(η⁵-cyclopentadienyl)Cl₂L]₂[CH₂-C₆H₄-CH₂] (L = Cl (3), L = O-2,6-iPr₂C₆H₃ (4), L = N(SiMe₃)(2,6-Me₂C₆H₃) (5)), have been synthesized. The complexes 4 and 5 have been prepared by the reaction of the complex 3 with the corresponding lithium salts of aryloxy and anilide. Structure of these complexes has been characterized by ¹H and ¹³C NMR. The change of substituent from chloride, 3, to anilide, 5, at titanium resulted in chemical shift change of cyclopentadienyl protons from 6.92 and 6.79 to 6.13 and 5.95 ppm probably due to the positive electron density delivery from the anilide group. It was found that all three half-titanocenes were effective catalyst for the generation of SPS (syndiotactic polystyrene). Xylene bridged dinuclear catalyst (4) with aryloxy substituent exhibited very high activity (458 kg of SPS/(mol of [Ti])h), at 40 °C, whereas the analogous hexamethylene bridged dinuclear half-titanocene catalyst (7) showed a lower activity (80.7 kg of SPS/(mol of [Ti])h) under the same conditions. While the catalyst 3 was the most active catalyst among three complexes less than 40 °C the catalyst 5 exhibited the highest activity at 70 °C. Xylene linkage was suggested to be too stiff to permit any kind of intramolecular interaction between two active centers. Lack of steric disturbance due to the rigidity of the xylene bridge might give rise to the similar properties of dinuclear metallocene to the corresponding mononuclear metallocene to result in not only the facile coordination of monomer at the active center to lead high activity but also the easier β-H elimination comparing to the dinuclear catalysts with the flexible bridge to result in the formation of lower molecular weight polymer.