Chiral recognition in cucurbituril cavities

For the first time, achiral cucurbiturils (CBs) were endowed with significant enantiomeric and distereomeric discrimination by incorporating a strong chiral binder. Calorimetric, nuclear magnetic, light-scattering, and mass spectral studies revealed that (S)-2-methylbutylamine (as a strong binder) can be discriminated by two enantiomeric supramolecular hosts, composed of CB[6] and (R)- or (S)-2-methylpiperazine, with an unprecedented 95% enantioselectivity in aqueous NaCl solution. This is the highest enantioselectivity ever reported for a supramolecular system derived from an achiral host. Similarly, CB[7], with a larger cavity, exhibited diastereoselectivities up to 8 times higher for diastereomeric dipeptides, as demonstrated for L-Phe-L-Leu-NH3+ versus L-Phe-D-Leu-NH3+.     

Highly stable polymerizable vesicles in anionic surfactant/ammonium salt mixtures in the presence of cross-linking monomers for convenient preparation of hollow nanospheres

Spontaneous and stable vesicles are formed from vinylbenzyltrimethylammonium chloride (VBTAC) and sodium dodecyl sulfate (SDS) ranging in molar composition from 3:7 to 7:3 in the presence of 30 mol % divinylbenzene (DVB). Dynamic light scattering analysis and transmission electron microscope observations revealed that microparticles with diameters around 120 nm (30%) and 580 nm (70%) were formed. Trapping efficiency of the vesicles examined with D-(+)-glucose amounted to ca. 15%. These vesicles were capable of undergoing polymerization in the presence of water-soluble radical initiators such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride to fix the vesicular structure. Retention of the vesicle size and bimodal size distribution characteristics during the polymerization indicated that intravesicular polymerization prevailed over the intervesicular process. SDS was stably retained in the cross-linked vesicle and was not removed from the vesicle by exhaustive dialysis or ultrafiltration, due to the electrostatic interaction within the cross-linked polymeric framework produced from VBTAC and DVB. The resulting hollow nanospheres are readily redispersed in water without the aid of additional surfactants.     

Elucidation of stereospecificity of a selenium-containing hydrogenase from methanococcus vannielii — syntheses of (R)- and (S)-[4-2H1] 3,4-dihydro-7-hydroxy-1-hydroxyethylquinolinone

To elucidate the stereospecificity of the selenium-containing hydrogenase from Methanocuccus vannielii, (R) - and (S) - [4-²H₁-3,4-dihydro-7-hydroxy-1-hydroxyethylquinolinone were synthesized as authentic samples for comparison with the compound which was derived from the enzymic reaction product.     

A hexapeptide motif that electrostatically binds to the surface of titanium

A hexapeptide motif, RKLPDA, that recognizes the surface of titanium was identified from a peptide phage selection. Mutational analyses showed electrostatic interaction was a major factor in the binding, paving a new way to modify the surface of Ti with active biomolecules.     

On the locally univalent Bloch constant

We give a new lower bound of the locally univalent Bloch constant. Research supported in part by National Natural Science Foundation of China, #10231010, #10171047, and Grant-in-Aid for Scientific Research, Japan Society for the Promotion of Science (B), #1144048.     

Studies on microcapsules

Summary The permeability of polyphthalamide microcapsules to various electrolytes was studied. The permeability constants were found to be of the order of 10^–8 cm/sec and almost temperature-independent. The surprisingly low permeation rate was ascribed to the formation of a stable diffusion layer of the electrolytes in the interior of microcapsules. The insignificant temperature effect was interpreted as being due to the presence of adsorbed Tween 20 molecules on the microcapsule membrane.

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Zusammenfassung Es wurde die Durchlässigkeit von Polyphthalamidmikrokapseln für verschiedene Elektrolyten untersucht. Die Durchlässigkeitskonstanten liegen in der Größenordnung von 10^–8 cm/sec und sind von der Temperatur fast unabhängig. Die unerwartet niedrige Permeationsgeschwindigkeit wurde der Bildung einer stabilen Diffusionsschicht des Elektrolyten innerhalb der Mikrokapseln zugeschrieben. Der geringe Temperatureffekt wurde auf die Existenz der an die Mikrokapselmembranen adsorbierten Moleküle von Tween 20 zurückgeführt.