Helical arrangement of a hydrogen‐bonded columnar liquid crystal induced by a centered triphenylene derivative bearing chiral side‐chains

A hydrogen‐bonded helical columnar liquid crystal was synthesized, in which the helical structure is induced by a centered triphenylene derivative bearing chiral side‐chains. The triphenylene derivative, 2,6,10‐tris(carboxymethoxy)‐3,7,11‐tris((S)‐(‐)‐2‐methyl‐1‐butanoxy)triphenylene ( TPC4(S) ), and a dendric amphiphile, 3,5‐bis‐(3,4‐bis‐dodecyloxy‐benzyloxy)‐N‐pyridine‐4‐yl‐benzamide ( DenC12 ), were mixed in a 1:3 ratio to obtain a complex, TPC4(S)‐DenC12 . Analyses by ¹H‐NMR spectroscopy, diffusion ordered spectroscopy (DOSY), CD spectroscopy, infrared (IR) spectroscopy, polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X‐ray diffractometry revealed that TPC4(S)‐DenC12 self‐assembles to form helical columnar stacks in solution and a helical columnar liquid crystal in bulk. The hydrogen bonding between TPC4(S) and DenC12 is essential for the helical columnar organization, and the preference for a one‐handed helical conformation is likely derived from the steric interaction between the chiral side‐chains and the dendric amphiphiles in the packing of the hydrogen‐bonded columnar assemblies. Copyright © 2008 John Wiley & Sons, Ltd.     

Novel method for obtaining homogeneous giant vesicles from a monodisperse water-in-oil emulsion prepared with a microfluidic device

A novel technique called the "lipid-coated ice droplet hydration method" is presented for the preparation of giant vesicles with a controlled size between 4 and 20 microm and entrapment yields for water-soluble molecules of up to about 30%. The method consists of three main steps. In the first step, a monodisperse water-in-oil emulsion with a predetermined average droplet diameter between 4 and 20 microm is prepared by microchannel emulsification, using sorbitan monooleate (Span 80) and stearylamine as emulsifiers and hexane as oil. In the second step, the water droplets of the emulsion are frozen and separated from the supernatant hexane solution by precipitation, followed by a removal of the supernatant and followed by the replacement of Span 80 by using a hexane solution containing egg yolk phosphatidylcholine, cholesterol, and stearylamine (5:5:1, molar ratio). This procedure is performed at -10 degrees C to keep the water droplets of the emulsion in a frozen state and thereby to avoid extensive water droplet coalescence. In the third step, hexane is evaporated at -4 to -7 degrees C and an external water phase is added to the remaining mixture of lipids and water droplets to form giant vesicles that have an average size in the range of that of the initial emulsion droplets (4-20 microm). The entrapment yield and the lamellarity of the vesicles obtained depend on the lipid/water droplet ratio and on the composition of the external water phase. At high lipid/water droplet ratio, the giant vesicles have a thicker membrane (indicating multilamellarity) and a higher entrapment yield than in the case of a low lipid/water droplet ratio. The highest entrapment yield ( approximately 35%) is obtained if the added external water phase contains preformed unilamellar egg phosphatidylcholine vesicles with an average diameter of 50 nm. The addition of these small vesicles minimizes the water droplet coalescence during the third step of the vesicle preparation, thereby decreasing the extent of release of water-soluble molecules originally present in the water droplets. The GVs prepared can be extruded through polycarbonate membranes to yield large unilamellar vesicles with about 100 nm diameter. This size reduction, however, leads to a decrease in the entrapment yield to about 12% due to solute leakage from the vesicles during the extrusion process.     

Silylmetalation of alkenes

Silylmetalation of alkenes is challenging due to the low reactivity of the substrates. In contrast, carbometalation of alkenes has been realized through several innovative methods, including activation of the reagent and the substrate. A similar approach could be applicable to silylmetalation of alkenes, and we have recently developed a bimetal activation method using zincate complexes for this purpose. Here, we describe how the silylzincation of alkenes was achieved. First, the strategies for carbometalation of alkenes will be summarized. Secondly, the history and development of silylzincation chemistry are briefly described. Then the details of our findings related to two types of silylzincation of alkenes, as well as recent progress in mechanistic studies, are discussed. The key point in the silylzincation of alkenes proved to be the bimetal activation of the substrate. One metal (copper or titanium) strongly coordinates and activates the alkene moiety, and the other metal (zinc) acts as the electron acceptor from the silyl group by way of the alkene moiety. This dual activation concept is expected to be applicable to other combinations of metals, as well as to new types of reactions.     

Very strong hydrogen bonds in a bent chain structure of fluorohydrogenate anions in liquid Cs(FH)2.3F

The structure of liquid Cs(FH)(2.3)F was revealed using a combination of high-energy x-ray and neutron diffraction measurements. We found that the strongest intermolecular H-F hydrogen bonds at an average distance of 1.36 A are accompanied by the formation of a high degree of bending of the oligomer chain in the melt, with [angle]FHF=150 degrees . A reverse Monte Carlo simulation showed that the average number of atoms per chain is 4.4. A detailed chain analysis of the atomic configuration revealed that (FH)(2)F(-) oligomer chains are the major entities in the liquid, and asymmetrical FHF(-) are formed owing to the strong H-F hydrogen bonds. The results suggest that an average of one or two HF molecules bond to each of the 11 fluorine atoms surrounding a cesium ion.     

Thermally Induced Intra‐Carboxyl Proton Shuttle in a Molecular Rack‐and‐Pinion Cascade Achieving Macroscopic Crystal Deformation

Proton transport via dynamic molecules is ubiquitous in chemistry and biology. However, its use as a switching mechanism for properties in functional molecular assemblies is far less common. In this study, we demonstrate how an intra‐carboxyl proton shuttle can be generated in a molecular assembly akin to a rack‐and‐pinion cascade via a thermally induced single‐crystal‐to‐single‐crystal phase transition. In a triply interpenetrated supramolecular organic framework (SOF), a 4,4′‐azopyridine (azpy) molecule connects to two biphenyl‐3,3′,5,5′‐tetracarboxylic acid (H₄BPTC) molecules to form a functional molecular system with switchable mechanical properties. A temperature change reversibly triggers a molecular movement akin to a rack‐and‐pinion cascade, which mainly involves 1) an intra‐carboxyl proton shuttle coupled with tilting of the azo molecules and azo pedal motion and 2) H₄BPTC translation. Moreover, both the molecular motions are collective, and being propagated across the entire framework, leading to a macroscopic crystal expansion and contraction.     

Palladium-catalyzed anti-hydrothiolation of 1-alkynylphosphines

[structure: see text]. Treatment of 1-alkynylphosphine with thiol in the presence of a catalytic amount of palladium acetate results in regio- and stereoselective anti-hydrothiolation, yielding the corresponding (Z)-1-phosphino-2-thio-1-alkene.     

Polyproline-rod approach to isolating protein targets of bioactive small molecules: isolation of a new target of indomethacin

Identification of protein targets of bioactive small molecules has been a technical hurdle of chemical genetics. Here we report a polyproline-rod approach to isolating protein targets of small molecules from cell lysates. The results indicate that insertion of a long, rigid polyproline helix between a small-molecule bait and a biotin tag boosts the capacity of affinity purification and thereby permits isolation of low-abundance or low-affinity proteins. In the course of the proof-of-concept experiments, we isolated glyoxalase 1 (GLO1) as a new target of indomethacin, a widely used antiinflammatory drug. Molecular biological experiments suggest that inhibition of GLO1 enzyme activity is related to the clinically recognized beneficial side effects of the indomethacin family of nonsteroidal antiinflammatory drugs.     

Hsp90 inhibitors disrupt mitochondrial homeostasis in cancer cells

Hsp90 is a cytosolic molecular chaperone whose paralog in mitochondria, TRAP1, protects cells from oxidative stress. The recent study in Cell by Kang et al. now identifies the molecular components of the proapoptotic network regulated by TRAP1, that includes Hsp90. Targeting Hsp90/TRAP1 inhibitors to mitochondria induces rapid tumor cell-specific apoptosis.