Polymer-aided stereodivergent synthesis (PASS): a new concept for the discrete preparation of optical antipodes

[structure: see text]. A new concept for the discrete preparation of optical antipodes is reported. The approach makes use of a cyclization/cleavage procedure that has been applied to polymer-supported quasi-meso compound 1, containing a polymeric leaving group and a regular leaving group. Two-directional cyclization leads to the formation and separation of quasi-enantiomers 2 and 3 simultaneously, with one being immobilized and one free in solution. Treatment of 2 and 3 with appropriate nucleophiles gives discrete enantiomers 4 and 5.     

Stretching a heteropolymer

We study the elastic properties of single heteropolymers. By means of exact enumeration of conformations, Monte Carlo (MC) simulation, and variational principles, we calculate equilibrium force-extension curves of heterocopolymers for specific arrangements of the monomer types along the sequence. At a given extension z, the time averaged measured force is the weighted sum of restoring forces for various configurations. Using variational principles, we calculate force-extension (f-z) curves of heteropolymers with fixed extensions z. These results are compared with f-z curves obtained from MC simulations and exact enumeration of all conformations. Typical random sequences manifest several piecewise unfoldings of blocks of various size, which are overlapping due to thermal fluctuations. The shape of the elastic response of a heteropolymer reflects the disorder in the primary block structure and the binding energies of these blocks.     

Multiple micellar morphologies from tri‐ and tetrablock copoly(2‐oxazoline)s in binary water–ethanol mixtures

We report on the micellization behavior of tri‐ and tetrablock copoly(2‐oxazoline)s in water–ethanol mixtures. The copolymers are based on different combinations of 2‐methyl‐, 2‐ethyl‐, 2‐phenyl‐, and 2‐nonyl‐2‐oxazoline. The solvophilic/solvophobic balance of these copolymers can be tuned thanks to the solubility dependence of the poly(2‐phenyl‐2‐oxazoline) block on the solvent composition. Characterization of the obtained micelles by dynamic light scattering and transmission electron microscopy revealed that their size and morphology depend on the solvophobic content of the copolymers and on the block order. Spherical micelles are always obtained when poly(2‐nonyl‐2‐oxazoline) is the only solvophobic block. When the solvophobic fraction consists of both the poly(2‐phenyl‐2‐oxazoline) and poly(2‐nonyl‐2‐oxazoline) blocks, spherical and cylindrical micelles as well as vesicles have been observed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3095–3102, 2010     

Temperature dependence of the electrical conductivity of imidazolium ionic liquids

The electrical conductivities of 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and of 1-hexyl-3-methylimidazolium ionic liquids with different anions were determined in the temperature range between 123 and 393 K on the basis of dielectric measurements in the frequency range from 1 to 10(7) Hz. Most of the ionic liquids form a glass and the conductivity values obey the Vogel-Fulcher-Tammann equation. The glass transition temperatures are increasing with increasing length of the alkyl chain. The fragility is weakly dependent on the alkyl chain length but is highly sensitive to the structure of the anion.     

Crystal structure of 2-{(R)-1-hydroxy-1-[(2S)-1-tritylaziridin-2-yl] methyl}acrylate and spectroscopic properties of the (R,S) and (S,S) stereoisomers

The crystal and molecular structure of 2-{(R)-1-Hydroxy-1-[(2S)-1-tritylaziridin-2-y1] methy1}acrylate is described. Crystal data: C₂₆H₂₅NO₃, orthorhombic, space group P2₁2₁2₁, a = 9.6954(5), b = 13.1458(5), c = 16.7885(7) Å, V = 2139.8(2) ų, Z = 4. The (R,S) diastereomer shows an intramolecular hydrogen bonding N···H—O under formation of a five-membered ring with N···O distance of 2.664 Å. IR, ¹H NMR and ¹³C NMR data are discussed. The ¹H NMR of the (R,S) diastereomer shows a singlet- whereas the (S,S) diastereomer exhibits a doublet-pattern for the hydroxyl proton.     

Photoinitiated polymerization of vinyl monomers by benzophenone t-butyl peresters

Benzophenone peresters undergo efficient photodecomposition when irradiated at 366 nm. This article reports peresters derived from benzophenone p,p′-dicarboxylic acid 1 which may produce radicals at two different centers in the same molecule. These peresters represent a unique new example of an efficient photoinitiator for acrylate and styrene polymerization.      

Task-specific ionic liquid for solubilizing metal oxides

Protonated betaine bis(trifluoromethylsulfonyl)imide is an ionic liquid with the ability to dissolve large quantities of metal oxides. This metal-solubilizing power is selective. Soluble are oxides of the trivalent rare earths, uranium(VI) oxide, zinc(II) oxide, cadmium(II) oxide, mercury(II) oxide, nickel(II) oxide, copper(II) oxide, palladium(II) oxide, lead(II) oxide, manganese(II) oxide, and silver(I) oxide. Insoluble or very poorly soluble are iron(III), manganese(IV), and cobalt oxides, as well as aluminum oxide and silicon dioxide. The metals can be stripped from the ionic liquid by treatment of the ionic liquid with an acidic aqueous solution. After transfer of the metal ions to the aqueous phase, the ionic liquid can be recycled for reuse. Betainium bis(trifluoromethylsulfonyl)imide forms one phase with water at high temperatures, whereas phase separation occurs below 55.5 degrees C (temperature switch behavior). The mixtures of the ionic liquid with water also show a pH-dependent phase behavior: two phases occur at low pH, whereas one phase is present under neutral or alkaline conditions. The structures, the energetics, and the charge distribution of the betaine cation and the bis(trifluoromethylsulfonyl)imide anion, as well as the cation-anion pairs, were studied by density functional theory calculations.