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The binding properties of responsive amphiphilic molecular baskets, obtained by attaching four facially amphiphilic cholate groups to a tetraaminocalixarene scaffold, in polar and nonpolar solvent are presented. The water-soluble version of amphiphilic molecular baskets acts as a unimolecular micelle to solubilize hydrophobic molecules in aqueous solutions.

The enhanced folding of cholate oligomers in homogeneous solution through the inserction of flexible, 4-aminobutyroyl spacers in between the cholate repeat units which showed opposite effect when the oligomers were solubilized in aqueous solutions of sodium dodecyl sulfate (SDS) is reported. Folding is observed to favor both below and above the critical micelle concentration (CMC) of SDS and is enhanced by an increase in the chain length.

The studies related to the observed fluorescence resonance energy transfer (FRET) from the naphthyl to the dansyl in 2:1 hexane/ethyl acetate (EA) containing a few percent of methanol are reported. The results showed that the conformation of the oligocholates is strongly influenced by the 4-aminobutyroyl spacers.

The folding of the oligocholates within surfactant micelles, which is capable of controlling the conformation of the oligocholate, is studied. The results have shown that the oligocholate has preferred to fold within the small spherical sodium dodecyl sulfate (SDS) micelles but has unfolded when the preference for spherical over rodlike micelles is not strong enough to overcome the tendency for the oligocholate to unfold.

The article explains the mechanisms involved in the asymmetric organocatalytic direct aldol reactions of ketones with [alpha]-keto acids. The discussed interactions have been found to be extremely useful for the synthesis of 2-hydroxy-[gamma]-butyrolactones.

The performance of several density functionals are compared for the calculation of structures and energetics of protonated cyclic ethers, including epoxides. The results have shown that the newly developed DFT methods perform better that the B3LYP and the latest functional, M05-2X, has greatly improved performance for an unsymmetrical protonated epoxide.

A molecular basket that could reversibly switch between a micelle-like conformation in polar environments and a reversed-micelle-like conformation in nonpolar environment is reported. The molecular basket was obtained by linking four cholate units to a cone-shaped calix[4]arene scaffold through azobenzene spacers.

Amphiphilic molecular baskets were obtained by attaching facially amphiphilic cholate groups to a covalent scaffold (calix[4]arene or 1,3,5-2,4,6-hexasubstituted benzene). In a solvent mixture consisting of mostly a nonpolar solvent and a polar solvent, the hydrophilic faces of cholates turned inward to form a reversed-micelle-like conformer whose stability was strongly influenced by the number of the cholates and the topology of the scaffold.

Molecularly imprinted nanoparticles (MINPs) were prepared when surfactants with a tripropargylammonium headgroup and a methacrylate-functionalized hydrophobic tail were cross-linked in the micelle form on the surface and in the core in the presence of hydrophobic template molecules. With the surfactants containing an amide bond near the headgroup, the MINPs had a layer of hydrogen-bonding groups in the interior that strongly influenced their molecular recognition. Templates/guests with strong hydrogen-bonding groups in the midsection of the molecule benefited most, especially if the hydrophobe of the template could penetrate the amide layer to reach the hydrophobic core of the cross-linked micelles. The location and the orientation of the hydrophilic groups were also important, as they determined how the template interacted with the surfactant micelles and, ultimately, with the MINP receptors. [ABSTRACT FROM AUTHOR]

Oligocholate macracyclcs self-assemble into transmembrane nan op ores by the associative interactions of water molecules inside the amphiphilic macrocycles. Macrocycles functionalized with a terephthalic acid "side chain" displayed significantly higher transport activity for glucose across lipid bilayers than the corresponding methyl ester derivative. Changing the 1,4-substitution of the dicarboxylic acid to 1,3-substitution lowered the activity. Combining the hydrophobic interactions and the hydrogen-bond-based carboxylic acid dimerization was an effective strategy to tune the structure and activity of self-assembled nanopores in lipid membranes. [ABSTRACT FROM AUTHOR]

The aggregation of macrocyclic oligocholates with introverted hydrophilic groups and aromatic side chains was studied by fluorescence spectroscopy and liposome leakage assays. Comparison between the solution and the membrane phase afforded insight into the solvophobically driven aggregation. The macrocycles stacked over one another in lipid membranes to form transmembrane nanopores, driven by a strong tendency of the water molecules in the interior of the amphiphilic macrocycles to aggregate in a nonpolar environment. The aromatic side chains provided spectroscopic signatures for stacking, as well as additional driving force for the aggregation. Smaller, more rigid macrocycles stacked better than larger, more flexible ones because the cholate building blocks in the latter could rotate outward and diminish the conformation needed for the water-templated hydrophobic stacking. The acceptor--acceptor interactions among naphthalenediimide (NDI) groups were more effective than the pyrene--NDI donor--acceptor interactions in promoting the transmembrane pore formation of the oligocholate macrocycles. [ABSTRACT FROM AUTHOR]

The conformation of a cholate hexamer with a clicked tether in between two tricholate units and pyrene groups at the chain ends was studied by fluorescence spectroscopy. In contrast to the parent cholate hexamer that folded in all micelles investigated, the folding of the clicked hexamer was highly dependent on the type of surfactant used to solubilize the compound. The clicked oligocholate folded in the Brij 35 micelle, possibly due to the latter's small size and strong internal hydrophobicity. The oligocholate formed intermolecular aggregates in SDS solutions below the CMC of the surfactant The aggregates were dissociated by the SDS micelles but the individual oligocholate stayed unfolded. In Triton X-100 and sodium cholate solutions, the aggregated, unfolded, and folded oligocholates coexisted and gradual unfolding occurred with an increasing concentration of the surfactant The conformation of the clicked oligocholate was sensitive to the nonideal mixing of ionic/nonionic micelles and to the unconventional aggregation of sodium cholate. [ABSTRACT FROM AUTHOR]

In a recent article, Carlier et al. (J. Org. Chem. 2006, 71, 1592) examined the prediction of several DFT functionals and showed that the most popular density functional, B3LYP, and 15 others fail badly for the prediction of the structure of protonated 2-methyl-1,2-epoxypropane. In this note, we compare the performance of several recently developed density functionals for the calculation of structures and energetics of protonated cyclic ethers, including epoxides. We found that several of the newly developed DFT methods perform better than B3LYP or any of the other 17 functionals examined by Carlier. We conclude that a recently published functional, M05-2X, has greatly improved performance for an unsymmetrical protonated epoxide, and we recommend this functional for studies that involve protonated epoxides and protonated ethers. [ABSTRACT FROM AUTHOR]

Explores the preparation of a family of saturated beta-stabilized carbocations that are stable under ambient conditions in solution. Preparation of beta-silyl and beta-germyl carbocations; Distribution of positive charge between carbon and silicon or germanium; Hyperconjugation of the carbocations; Carbon resonance frequencies.

A variety of organocatalysts for the asymmetric direct aldol reactions of ketones with alpha-keto acids were designed on the basis of molecular recognition and prepared from proline and aminopyridines. The organic molecule 8e, derived from proline and 6-methyl-2-amino pyridine, was the best catalyst, affording excellent enantioselectivities (up to 98% ee) for the direct aldol reactions of acetone or 2-butanone with a wide range of alpha-keto acids and for the reactions of various acyclic aliphatic ketones with 3-(2-nitrophenyl)-2-oxopropanoic acid. The aldol adducts could be converted to 2-hydroxy-gamma-butyrolactones by reaction sequences of diastereoselective reduction and lactonization. Experimental and theoretical studies on the transition states revealed that the amide N-H and the pyridine N of the organocatalyst selectively form hydrogen bonds with the keto oxygen and the carboxylic acid hydroxy of the alpha-keto acid, respectively. These two hydrogen-bonding interactions are important for the reactivity and enantioselectivity of the direct asymmetric aldol condensation.