Vibrational dynamics of carboxylic acid dimers in gas and dilute solution

Ultrafast mid-IR transient absorption spectroscopy has been used to study the vibrational dynamics of hydrogen-bonded cyclic dimers of trifluoroacetic acid and formic acid in both the gas and solution phases (0.05 M in CCl(4)). Ultrafast excitation of the broad O-H cyclic dimer band leads, in the gas phase, to large-scale structural changes of the dimer creating a species with a distinct free O-H stretching band on 20 ps and 200 ps timescales. These timescales are assigned to ring-opening and dissociation of the dimer, respectively. In the solution phase, no such structural rearrangement occurs and our results are consistent with previous studies. The gas phase dynamics are insensitive to both the specific excitation energy (over a span of 550 cm(-1)) and the chemical identity of the dimer.     

Observation of B(0)-->D(*-)tau(+)nu(tau) decay at Belle

We report an observation of the decay B{0}-->D{*-}tau{+}nu{tau} in a data sample containing 535x10{6} BB pairs collected with the Belle detector at the KEKB asymmetric-energy e{+}e{-} collider. We find a signal with a significance of 5.2sigma and measure the branching fraction B(B{0}-->D{*-}tau{+}nu{tau})=(2.02{-0.37}{+0.40}(stat)+/-0.37(syst))%. This is the first observation of an exclusive B decay with a b-->ctaunu{tau} transition.     

Sonolysis of chlorinated compounds in aqueous solution

To examine the reaction rates of sonochemical degradation of aqueous phase carbon tetrachloride, trichloroethylene and 1,2,3-trichloropropane at various temperatures, power intensities, and saturating gases, the batch tests were carried out. The degradations of chlorinated hydrocarbons were analyzed as pseudo first order reactions and their reaction rate constants were in the range of 10(-1)-10(-3)/min. The reaction was fast at the low temperature with higher power intensity. Also, the reaction went fast with the saturating gas with high specific heat ratio, high solubility and low thermal conductivity. The main mechanism of destruction of chemicals was believed the thermal combustion in the bubble.     

Reactivities of acridine compounds in hydride transfer reactions

Reactivities of acridine derivatives (10‐benzylacridinium ion, 1a ⁺, 10‐methylacridinium ion, 1b ⁺, and 10‐methyl‐9‐phenylacridinium ion, 1c ⁺) have been compared quantitatively for hydride transfer reactions with 1,3‐dimethyl‐2‐substituted phenylbenzimidazoline compounds, 2Ha–h . Reactions were monitored spectrophotometrically in a solvent consisting of four parts of 2‐propanol to one part of water by volume at 25 ± 0.1 °C. Reduction potentials have been estimated for acridine derivatives by assuming that the equilibrium constants for the reductions of 1a ⁺ –c ⁺ by 2Hb would be the same in aqueous solution and accepting ?361 mV as the reduction potential of the 1‐benzyl‐3‐carbamoylpyridinium ion. The resulting reduction potentials, E, are ?47 mV for 1a ⁺, ?79 mV for 1b ⁺, and ?86 mV for 1c ⁺. Each of acridine derivatives gives a linear Brønsted plot for hydride transfer reactions. The experimental slopes were compared with those obtained by Marcus theory. This comparison shows that the kinetic data are consistent with a one‐step mechanism involving no high‐energy intermediates. Copyright © 2007 John Wiley & Sons, Ltd.     

Photo‐crosslinkable hydrogel‐based 3D microfluidic culture device

We developed the photo‐crosslinkable hydrogel‐based 3D microfluidic device to culture neural stem cells (NSCs) and tumors. The photo‐crosslinkable gelatin methacrylate (GelMA) polymer was used as a physical barrier in the microfluidic device and collagen type I gel was employed to culture NSCs in a 3D manner. We demonstrated that the pore size was inversely proportional to concentrations of GelMA hydrogels, showing the pore sizes of 5 and 25 w/v% GelMA hydrogels were 34 and 4 μm, respectively. It also revealed that the morphology of pores in 5 w/v% GelMA hydrogels was elliptical shape, whereas we observed circular‐shaped pores in 25 w/v% GelMA hydrogels. To culture NSCs and tumors in the 3D microfluidic device, we investigated the molecular diffusion properties across GelMA hydrogels, indicating that 25 w/v% GelMA hydrogels inhibited the molecular diffusion for 6 days in the 3D microfluidic device. In contrast, the chemicals were diffused in 5 w/v% GelMA hydrogels. Finally, we cultured NSCs and tumors in the hydrogel‐based 3D microfluidic device, showing that 53–75% NSCs differentiated into neurons, while tumors were cultured in the collagen gels. Therefore, this photo‐crosslinkable hydrogel‐based 3D microfluidic culture device could be a potentially powerful tool for regenerative tissue engineering applications.     

A Si Photocathode Protected and Activated with a Ti and Ni Composite Film for Solar Hydrogen Production

An efficient, stable and scalable hybrid photoelectrode for visible‐light‐driven H₂ generation in an aqueous pH 9.2 electrolyte solution is reported. The photocathode consists of a p‐type Si substrate layered with a Ti and Ni‐containing composite film, which acts as both a protection and electrocatalyst layer on the Si substrate. The film is prepared by the simple drop casting of the molecular single‐source precursor, [{Ti₂(OEt)₉(NiCl)}₂] (TiNi_pre), onto the p‐Si surface at room temperature, followed by cathodic in situ activation to form the catalytically active TiNi film (TiNi_cat). The p‐Si|TiNi_cat photocathode exhibits prolonged hydrogen generation with a stable photocurrent of approximately ?5 mA cm^?2 at 0 V vs. RHE in an aqueous pH 9.2 borate solution for several hours, and serves as a benchmark non‐noble photocathode for solar H₂ evolution that operates efficiently under neutral–alkaline conditions.     

Fabrication and conduction mechanism evaluation of polyfluorene polymeric Schottky diode

A thin film of polyflourene polymer was sandwiched between a conductive polymer deposited on silver nanowire and metal electrode to form a multilayer polymer‐based diode device. The electrical properties of fabricated polymeric diode have been studied by current–voltage method. The current–voltage characteristics of the fabricated device exhibited non‐ideal, asymmetrical, and rectifying behavior. Ohmic current conduction mechanism was observed in the device at low voltage. At higher voltage values, the space‐charge‐limited current conduction mechanism was found to be dominated. The values of the Schottky barrier height, ideality factor, and saturation current density were extracted according to the standard thermionic emission model and discussed. The barrier height and ideality factor were calculated as 0.72 eV and 2.53, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Anion-induced switching of the helical orientation of a chiral indolocarbazole dimer

An indolocarbazole dimer, containing chiral urea appendages, that adopts a helically folded conformation by intramolecular hydrogen bonds as proven by ¹H NMR and circular dichroism (CD) spectroscopy has been prepared. Owing to the preferential formation of one helical conformer, strong CD signals appear in relatively non-polar solvents such as chloroform (CHCl₃) and dichloromethane (CH₂Cl₂) but the signal is negligible in dimethyl sulfoxide (DMSO). In addition, the optical rotation of the dimer is highly sensitive to the polarity of solvents. For example, the magnitude of the specific rotation ([α]_D) is ? 934° in CH₂Cl₂ and ? 657° in CHCl₃ but it is only ? 75° in DMSO. These observations suggest that the dimer folds to a helical structure by intramolecular hydrogen bonds in relatively non-polar solvents but exists in an unfolded extended conformation in polar solvents such as DMSO. The dimer strongly binds anions such as chloride, acetate and sulfate by multiple hydrogen bonds. In addition, anion binding leads to considerable CD spectral changes with the different pattern and degree of Cotton effects depending on the kind of anions. The dimer may be therefore utilised for the construction of an anion-responsive chiroptical sensor or switch.     

Size‐Controlled Construction of Magnetic Nanoparticle Clusters Using DNA‐Binding Zinc Finger Protein

Nanoparticle clusters (NPCs) have attracted significant interest owing to their unique characteristics arising from their collective individual properties. Nonetheless, the construction of NPCs in a structurally well‐defined and size‐controllable manner remains a challenge. Here we demonstrate a strategy to construct size‐controlled NPCs using the DNA‐binding zinc finger (ZnF) protein. Biotinylated ZnF was conjugated to DNA templates with different lengths, followed by incubation with neutravidin‐conjugated nanoparticles. The sequence specificity of ZnF and programmable DNA templates enabled a size‐controlled construction of NPCs, resulting in a homogeneous size distribution. We demonstrated the utility of magnetic NPCs by showing a three‐fold increase in the spin–spin relaxivity in MRI compared with Feridex. Furthermore, folate‐conjugated magnetic NPCs exhibited a specific targeting ability for HeLa cells. The present approach can be applicable to other nanoparticles, finding wide applications in many areas such as disease diagnosis, imaging, and delivery of drugs and genes.