Yu-Fei Ao

Self-Assembly and Disassembly of Vesicles as Controlled by Anion-π Interactions.

Anion-π interactions have been widely studied as new noncovalent driving forces in supramolecular chemistry. However, self-assembly induced by anion-π interactions is still largely unexplored. Herein we report the formation of supramolecular amphiphiles through anion-π interactions, and the subsequent formation of self-assembled vesicles in water. With the π receptor 1 as the host and anionic amphiphiles, such as sodium dodecylsulfate (SDS), sodium laurate (SLA), and sodium methyl dodecylphosphonate (SDP), as guests, the sequential formation of host-guest supramolecular amphiphiles and self-assembled vesicles was demonstrated by SEM, TEM, DLS, and XRD techniques. The intrinsic anion-π interactions between 1 and the anionic amphiphiles were confirmed by crystal diffraction, HRMS analysis, and DFT calculations. Furthermore, the controlled disassembly of the vesicles was promoted by competing anions, such as NO3 (-) , Cl(-) , and Br(-) , or by changing the pH value of the medium.

Chiral Phosphoric Acid Catalyzed Asymmetric Ugi Reaction by Dynamic Kinetic Resolution of the Primary Multicomponent Adduct

Reaction of isonitriles with 3-(arylamino)isobenzofuran-1(3H)-ones in the presence of a catalytic amount of an octahydro (R)-binol-derived chiral phosphoric acid afforded 3-oxo-2-arylisoindoline-1-carboxamides in high yields with good to high enantioselectivities. An enantioselective Ugi four-center three-component reaction of 2-formylbenzoic acids, anilines, and isonitriles was subsequently developed for the synthesis of the same heterocycle. Mechanistic studies indicate that the enantioselectivity results from the dynamic kinetic resolution of the primary Ugi adduct, rather than from the C-C bond-forming process. The resulting heterocycle products are of significant medicinal importance.

Anionic Head Containing Oxacalix[2]arene[2]triazines: Synthesis and Anion−π-Directed Self-Assembly in Solution and Solid State

A series of oxacalix[2]arene[2]triazines bearing one anionic head such as carboxylate, sulfonate, sulfate, and phosphate were synthesized. With the anionic head and complementary V-shape electron-deficient cavity, these macrocycles can serve as dual building units, and their anion-π directed self-assembly was investigated. The formation of oligomeric aggregates in solution was revealed by nuclear magnetic resonance, dynamic light scattering, and mass spectroscopy. Crystal structures further confirmed chainlike assembly formation directed by anion-π interactions.

Biotransformations of Racemic 2,3-Allenenitriles in Biphasic Systems: Synthesis and Transformations of Enantioenriched Axially Chiral 2,3-Allenoic Acids and Their Derivatives

Catalyzed by Rhodococcus erythropolis AJ270 whole cells in an aqueous phosphate buffer-n-hexane biphasic system, racemic axially chiral 2,3-allenenitriles underwent hydrolysis to afford enantioenriched (aR)-2,3-allenamides and (aS)-2,3-allenoic acids with ees up to >99.5%. Overall biotransformations proceeded through the nitrile hydratase-catalyzed efficient but nonselective hydration of nitriles followed by the amide hydrolysis catalyzed by the substrate-dependent enantioselective amidase. The application of the method has been demonstrated by the transformations of the resulting allene products into highly functionalized heterocyclic compounds with axial chirality of reactants being entirely transferred into or expressed as point chirality of products.

Molecular Barrel by a Hooping Strategy: Synthesis, Structure, and Selective CO2 Adsorption Facilitated by Lone Pair−π Interactions

A sophisticated molecular barrel 5 was efficiently constructed by hooping a 63-membered loop around a D3h-symmetric, shape-persistent bis(tetraoxacalix[2]arene[2]triazine) core. The hooping strategy involved 3-fold ring-closing metathesis (RCM) reactions of six branched olefin arms which were preanchored on the inner core. Through hooping, the loop tightens the cage structure and significantly enhances its stability toward nucleophilic decomposition. The X-ray crystal structure showed the molecular barrel bears three enclosed fan-shaped cavities as divided by the triazine rings and each of the cavities can hold a solvent CHCl3 or CH2Cl2 molecule. With the intrinsic porosity, the amorphous solids of 5 exhibit considerable CO2 uptake with an exceptionally large isosteric enthalpy. Lone pair (lp)-π interactions between the electron-deficient triazine rings and CO2 could contribute to the strong adsorption as supported by IR studies and DFT modeling.

Multiresponsive Vesicles Composed of Amphiphilic Azacalix[4]pyridine Derivatives

Biomimicry of multiresponsive recognition of cell membrane with artificial membranes is challengeable. In this work, we designed azacalix[4]pyridine-based amphiphilic molecules 1 and 2. The self-assembly behaviors of 1 and 2 were investigated in aqueous medium. As demonstrated by DLS, SEM, TEM, and LSCM measurements, 1 formed stable vesicles (size 322 nm) in a mixture of THF/water, whereas 2 produced giant vesicles with decreased stability (size 928 nm). The vesicles composed of 1, with surface being engineered with the cavities of azacalix[4]pyridines, showed selective responses to a variety of guests including zinc ion, hydroquinone, and proton as monitored by DLS.

Synthesis of Quaternary-Carbon-Containing and Functionalized Enantiopure Pentanecarboxylic Acids from Biocatalytic Desymmetrization of meso-Cyclopentane-1,3-Dicarboxamides

Catalyzed by Rhodococcus erythropolis AJ270, a nitrile hydratase-amidase containing microbial whole-cell catalyst under mild conditions, enantioselective desymmetrizations of meso-cyclopentane-1,3-dicarbonitriles and cyclopentane-1,3-dicarboxamides were studied. Although the nitrile hydratase was found to exhibit high enzymatic activity, but low 1R enantioselectivity toward dinitriles, a number of 2,2-unsymmetrically substituted meso-cyclopentane-1,3-dicarboxamide substrates were converted by the 1S enantioselective amidase into quaternary carbon-bearing enantiopure (1S,2R,3R)-3-carbamoylcyclopentanecarboxylic acids in yields up to 94 %. The application of the method was demonstrated by convenient and practical transformations of the resulting (1S,2R,3R)-2-allyl-3-carbamoylcyclopentanecarboxylic acid derivatives into functionalized cyclopentane-fused δ-lactam and δ-lactone compounds.

Synthesis of carboxylate head-containing self-complementary building units and their anion-π directed self-assembly

Abstract Self-complementary building units of carboxylate head-containing oxacalix[2]arene[2]triazines were synthesised by inserting different flexible linkers in between the macrocyclic skeleton and carboxylate. The anion-π directed self-assembly of these building units in solution and in gas phase was systematically investigated by concentration and temperature variable 1H NMR, diffusion-ordered NMR spectroscopy (DOSY), dynamic light scattering (DLS) and ESI-MS.

Synthesis, Structure, Property, and Dinuclear Cu(II)Complexation of Tetraoxacalix[2]arene[2]phenanthrolines

A number of novel tetraoxacalix[2]arene[2]phenanthrolines 7-11 containing phenanthroline and diverse aromatic linkages were conveniently synthesized by a one-pot protocol between a series of dihydroxy arenes and 1,10-phenanthroline derivatives. Single-crystal diffraction analysis revealed that the resulting macrocycles possess diverse conformational and cavity structures which are regulated by the different aromatic linkages. In line with the length of the aromatic linkages, the distance between the two phenanthroline moieties ( dN-N) gradually increases from 6.92 to 13.30 Å, respectively. The physicochemical properties of these macrocyclic compounds were investigated by spectroscopic, CV, and DPV measurements. Owing to the coordination ability of the phenanthroline moieties and the tunable conformational structure, the macrocyclic hosts can form distinct dinuclear complexation with Cu2+. Typically, with a short aromatic linkage the 7b-2Cu(II) complex gives an O-bridged dicopper structure, while with long linkage the 11b-2Cu(II) complex possesses two discrete copper centers. The spectroscopic structure and the redox property of the dicopper complexes were investigated by XPS, CV, and DPV techniques. This work hence provides a platform to access biomimetic copper-containing small-molecule models with well-defined structures.

Tritopic ion-pair receptors based on anion–π interactions for selective CaX2 binding

Selective ion-pair binding of CaX2 (X = Br-, I-) was realized by a tritopic receptor containing homoditopic anion-π binding sites and a pentaethylene glycol site. The receptor formed an unusual solvent-separated ion-pair complex with CaI2 and a contact one with CaBr2, and can be applied to selectively dissolve calcium halides in organic solvents.