Synthesis and properties of 2''-deoxy-8,2''-methylene-cycloadenosine

A method was developed to synthesize 2'-deoxy-8,2'-methylene-cycloadenosine (9) which was a new carbon-bridged cycloadenosine fixed in a high-antitorsional angle region. 3',5'-Di-O-acetyl-8-methanesulfonyl-2'-O-tosyladenosine (5) was cyclized with carbanions of malonic esters, followed by hydrolysis of the ester (7) and decarboxylation to afford 9. Compound 9 showed a positive CD band at 258 nm and was a substrate for adenosine deaminase with a K_m of 3.2 × 10^-4M and a V_max of 2% of that of adenosine.     

Long-range ordered magnet of a charge-transfer Ru2(4+)/TCNQ two-dimensional network compound

Two isostructural 2D assemblies composed of [Ru2(O2CCF3)4] and TCNQ or TCNQF4 in a 2:1 ratio were synthesized: [{Ru2(O2CCF3)4}2TCNQ].3(p-xylene) (1b) and [{Ru2(O2CCF3)4}2TCNQF4].3(p-xylene) (2). In 1b, the TCNQ moiety is assigned to be neutral because of no significant electron transfer from the Ru24+ units. Therefore, the magnetic property of 1b can be understood to be a paramagnetic nature of the isolated Ru24+ unit, while, a fully charge-transfer from the Ru2 units to the TCNQF4 molecules in 2 leads to charge delocalization spreading over the 2D network and allows a long-range magnetic order to occur. On the basis of an idea of the resonance scheme in charge-transfer D2A network systems, the first successful example of a charge-transferred magnet in the Ru2-TCNQ system was rationally designed by tuning redox between [Ru2]4+ and the TCNQ molecule changing from TCNQ to TCNQF4.     

Giant macrocycles composed of thiophene, acetylene, and ethylene building blocks

Fully conjugated giant macrocyclic oligothiophenes with 60pi, 90pi,120pi, 150pi, and 180pi frames (1, 2, 3, 4 and 5) have been designed, and their butyl-substituted derivatives (1a, 2a, 3a, 4a, and 5a) have been synthesized using modified Sonogashira and McMurry coupling reactions as key steps. The 60-180pi systems 1-5 are circular with 1.8-6 nm inner cavities and 3.3-7.5 nm outside molecular diameters. Compound 1a containing ten 3,4-dibutyl-2,5-thienylene, eight ethynylene, and two vinylene units has been converted into macrocyclic oligo(3,4-dibutyl-2,5-thienylene-ethynylene) 6a using bromination/dehydrobromination procedure. Giant macrocycles 1a-6a exhibit a red shift of their absorption spectra and a fairly strong fluorescence with a large Stokes shift as compared to a linear conjugated counterpart having five thiophene rings. Compounds 1a-6a exhibit multistep reversible redox behaviors with fairly low first oxidation potentials, reflecting their cyclic conjugation. Furthermore, chemical oxidation of 1a-6a with FeCl3 shows drastic changes of spectroscopic properties due to intramolecular and intermolecular pi-pi interactions. Doping of 1a-3a with iodine forms semiconductor due to its pi-donor properties and pi-pi stacking ability. X-ray analysis of 1a confirmed a round, planar structure with nanoscale inner cavity, and revealed host ability for alkanes and unique packing structure. Interestingly, 2a and 3a self-aggregate in the solid state to form "molecular wires," which are about 200 nm thick and more than 1 mm long. The internal structures of fibrous aggregates have been investigated by optical microscope, scanning electron microscopy, atomic force microscopy, and X-ray diffraction analyses.     

Fluorescent Diarylindoles by Palladium‐Catalyzed Direct and Decarboxylative Arylations of Carboxyindoles

Simple and brilliant : 1‐Substituted 1H‐indole‐2‐carboxylic acids efficiently undergo successive diarylation accompanied by C? H bond cleavage and decarboxylation upon treatment with aryl bromides in the presence of a palladium catalyst system to afford fluorescent 2,3‐diarylindoles. This facile synthetic method provides a highly efficient blue emitter with a quantum yield of 0.97 in the solid state (see scheme).

     

Mott-Anderson transition controlled by a magnetic field in pyrochlore molybdate

The pyrochlore molybdate Gd2MO2O7 locates near the phase boundary between the ferromagnetic-metallic and the spin-glass insulating state. This metal-insulator transition is governed on a large energy scale by the electron-correlation effect, while the geometrical frustration causes the random potential. The magnetic field can tune the randomness of the potential and control, under a suitable pressure, the continuous Mott-Anderson transition precisely. The critical exponent (mu = 1.04 +/- 0.1) of the Mott-Anderson transition has been determined for this ferromagnetic orbital-degenerate electron system.     

PHOTOELECTROCHEMICAL STUDY OF CHLOROPHYLL-a MULTILAYERS ON SnO2 ELECTRODE

Photoelectrochemical behaviour of Chl- a multilayers, built up on SnO₂ optically transparent electrode by means of the Langmuir technique, was investigated in an electrolyte solution with or without hydroquinone as a reducing agent. Quantum efficiencies of the anodic photocurrents in the presence of hydroquinone tended to decrease with increasing number of layers. In the electrolyte without hydroquinone, the cathodic photocurrents were observed in the presence of dissolved oxygen. A possibility of a reaction of water with the oxidized Chl- a is suggested.     

Typical fiber structure

Model fibers of polyethylene and nylon 6 were strained in the direction of the fiber axis and the internal deformation of the samples was studied by large-angle and small-angle x-ray diffraction. The compression of samples along the fiber axis was successfully carried out, and the results obtained by x-ray methods yielded more interesting information on the structure of the fibers than was obtained in extension. A model for the structure of the fiber was constructed on the basis of the results on compressed fibers. In this model, crystals are distributed in cylindrical symmetry around the fiber axis keeping a crystal axis tangential to circles in the section normal to the fiber axis. The characteristic crystal axis is the b axis in polyethylene and the a axis in nylon 6. The chain axis of the crystals varies in orientation with respect to the fiber axis. In compression of fibers with such a structure, the crystals rotate around the characteristic axis indicated above. In the case of nylon 6 fiber, only this simple rotation seems to occur, while additional changes occur in polyethylene fibers. However, the simple rotation predominates even in polyethylene fibers. This fiber structure is correlated with the structure of thin films of the materials. This similarity proves the existence of a common mechanism for the origin of the structure of fibers and films.     

Crystallization kinetics of biaxially stretched natural rubber

The isothermal crystallization of natural rubber was investigated under biaxial stretching. A marked planar orientation of crystals occurs in such a way that the (010) plane orients parallel to the film plane. The rate of crystallization increases with the biaxial stretching ratio, and the Avrami exponent n decreases. At the highest extension, n becomes less than unity. The equilibrium degree of crystallinity decreases with the stretching ratio. The crystallinity was less than 10% for the highest extension. The melting behavior is similar to that in uniaxial stretching.