Mode change in the self-motion of a benzoquinone disk coupled with a NADPH system

The self-motion of a benzoquinone (BQ) disk on NADPH was investigated as the coupling of an autonomous motor and an enzyme reaction. In the absence of the enzyme reaction, features of motion changed depending on the concentration of NADPH, that is, continuous motion→ intermittent oscillatory motion→ no motion. When the reverse reaction from NADP(+) to NADPH was introduced into the system with the addition of an enzyme reaction, continuous motion changed to intermittent oscillatory motion with small amplitude. The mechanism of this mode change is discussed in relation to the surface tension as a driving force and the time course of UV spectra as a window to the progress of the reaction. Characteristic features of the mode change were qualitatively reproduced by a numerical calculation.     

Systematic study of protein detection mechanism of self-assembling 19F NMR/MRI nanoprobes toward rational design and improved sensitivity

(19)F NMR/MRI probe is expected to be a powerful tool for selective sensing of biologically active agents owing to its high sensitivity and no background signals in live bodies. We have recently reported a unique supramolecular strategy for specific protein detection using a protein ligand-tethered self-assembling (19)F probe. This method is based on a recognition-driven disassembly of the nanoprobes, which induced a clear turn-on signal of (19)F NMR/MRI. In the present study, we conducted a systematic investigation of the relationship between structure and properties of the probe to elucidate the mechanism of this turn-on (19)F NMR sensing in detail. Newly synthesized (19)F probes showed three distinct behaviors in response to the target protein: off/on, always-on, and always-off modes. We clearly demonstrated that these differences in protein response could be explained by differences in the stability of the probe aggregates and that "moderate stability" of the aggregates produced an ideal turn-on response in protein detection. We also successfully controlled the aggregate stability by changing the hydrophobicity/hydrophilicity balance of the probes. The detailed understanding of the detection mechanism allowed us to rationally design a turn-on (19)F NMR probe with improved sensitivity, giving a higher image intensity for the target protein in (19)F MRI.     

Medicinal foodstuffs. XXXI. Structures of new aromatic constituents and inhibitors of degranulation in RBL-2H3 cells from a Japanese folk medicine,the stem bark of Acer nikoense

Four new aromatic constituents, rhododendroketoside, (-)-sakuraresinoside, acernikol, and nikoenoside, were isolated from a Japanese folk medicine, the stem bark of Acer nikoense MAXIM. The structures of the new constituents were determined on the basis of chemical and physicochemical evidence. The principle cyclic diarylheptanoids were found to show inhibitory effects on the release of beta-hexosaminidase in RBL-2H3 cells.     

Synthesis of polymers by use of divalent metal salts of monohydroxyethyl phthalate: Metal-containing isocyanurate-type crosslinked polyurethanes

Divalent metal salts (I) of monohydroxyethyl phthalate have catalytic activity for polymerization of isocyanate groups. The synthesis of novel metal-containing isocyanurate-type crosslinked polyurethanes were investigated by the crosslinking reaction of I in DMF with diisocyanates or urethane prepolymers, that is, diisocyanate adducts of polyethylene glycol. 2,4-Toluene diisocyanate and diphenylmethane diisocyanate were used as diisocyanates, and DMF was the solvent. The crosslinking reactions were followed by determining the gelation time. Gelation time decreased with increasing temperature. The Ca salt was more effective than the Mg salt in the crosslinking reaction. The yields of resulting metal-containing three-dimensional polymers decreased with increasing metal content in the feed. The Ca salt was more easily introduced into the network polymers than the Mg salt was. Decomposition temperatures decreased on introducing metals into the network polymers. Some physical properties of the metal-containing network polymers are also discussed.     

Large Enhancement of the Single-Molecular Conductance of a Molecular Wire through a Radical Substituent

The single-molecular conductance between two π-conjugated wires with and without a radical substituent has been compared. Specifically, methyl- and iminonitroxide-substituted 4-(biphenyl-4-yl)pyridine wires bound onto a porphyrin template were subjected to scanning tunneling microscopy (STM) apparent-height measurement at the interface between highly oriented pyrolytic graphite (HOPG) and octan-1-oic acid. Statistical analysis of the STM images revealed that the radical-substituted wire has 3.2±1.7-fold higher conductance than the methyl-substituted reference. Although density functional theory (DFT) calculation suggests that only 17 % of the SOMO is distributed on the wire moiety, the effect was significant. This study presents the potential of radical substituents to achieve high conductivity in molecular wires.     

Skeletal Transformation Triggered by C−F Bond Activation after Photochemical Rearrangement of Fluorinated [7]Helicenes

Tri- and tetra-fluorinated [7]helicenes are photolabile and undergo a double fluorine atom transfer. Herein, we show that the transferred product further undergoes a skeletal transformation on silica gel. The transformation begins with activation of the allylic C−F bond on the silanol surface. Then, the resulting carbocation readily undergoes a regioselective nucleophilic aromatic substitution with water, depending on the position of the fluorine substituents. Hexafluoro-2-propanol also activated the allylic C−F bond and acted as a nucleophile. These findings support the generation of a highly reactive cationic electrophilic intermediate in the successive transformations involving fluorine atoms.     

Cycloaddition of oxetane and carbon dioxide catalyzed by tetraphenylstibonium iodide

Trimethylene carbonate was readily obtained in the reaction of oxetane and carbon dioxide in the presence of tetraphenylstibonium iodide.