Synthesis and Structural Investigation of Foldamer-Based Iodine-Supported Artificial Glycosidases.

Glycosidases are a type of enzyme that hydrolytically cleave carbohydrates and form glycans for biologically important processes. The inadequacies of glycosidases or their genetic abnormalities are responsible for various diseases. Thus, the development of glycosidase mimetics is of great importance. We have designed and synthesized an enzyme mimetic containing l-phenylalanine, α-aminoisobutyric acid (Aib), l-leucine, and m-Nifedipine. From X-ray crystallography, the foldamer adopts a ß-hairpin conformation stabilized by two 10-member and one 18-member NH⋅⋅⋅O=C hydrogen bonds. Moreover, the foldamer was found to be highly efficient in hydrolysing ethers and glycosides in the presence of iodine at room temperature. Further, X-ray analysis shows the backbone conformation of the enzyme mimetic to be almost unchanged after the glycosidase reaction. This is the first example of iodine-supported artificial glycosidase activity with an enzyme mimic at ambient conditions.

Effect of Symmetry and Increasing Hydrophobicity on the Self-Assembly and Function of Benzoylurea Derivatives.

A novel series of benzoylurea derivatives containing benzoic acid, m-dibenzoic acid, and benzene 1,3,5-tricarboxylic acid were designed with increasing hydrophobicity. The aggregation behavior of the derivatives was studied by several spectroscopic methods. The porous morphology of the resulting aggregates was examined by polar optical microscopy and field emission scanning electron microscopy. From X-ray single-crystal analysis, it is observed that N,N'-dicyclohexylurea containing compound 3 lost C3 symmetry and adopted a "bowl"-shaped conformation and self-assembles to form a supramolecular honeycomb-like framework that is stabilized by multiple intermolecular hydrogen bonds. However, compound 2 with C2 symmetry had a kink-like conformation and self-assembled to form a sheet-like structure. Discotic compound 3 coated paper, cloth, or glass surfaces, repealed water, and behaved like a self-cleaning material. Discotic compound 3 is also able to separate the oil and water from oil-water emulsion.

Proof of Concept: Interface of Recyclable Organogels with Embedded Palladium Nanoparticles Catalyzing Suzuki-Miyaura Coupling in Water at Room Temperature.

A sustainable approach for C-C cross-coupling reaction at room temperature in water has been developed to avoid tedious Pd separation, reduce the carbon footprint, and save energy. Another important aspect is the catalyst recycling and easy product separation. α,γ-Hybrid peptides were designed to selectively use as a ligand for C-C cross-coupling catalysts as well as to form organogels. The peptides form antiparallel sheet-like structures in the solid state. The peptide containing m-aminobenzoic acid, glycine, and dimethylamine forms a whitish gel in toluene, and co-gelation with Pd(OAc)2 results in light brown gel, which acts as a biphasic catalyst for Suzuki-Miyaura cross-coupling at room temperature in water by mild shaking. The organic-inorganic hybrid gel was characterized by rheology, field-emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray analyses. On completion of the cross-coupling reaction, the basic aqueous layer (containing products) above the gel can be simply decanted and the intact organic-inorganic hybrid gel can be recycled by topping-up fresh reactants multiple times. The reaction permitted a range of different substitution patterns for aryl and heterocyclic halides with acid or phenol functional groups. Both electron-donating- and electron-withdrawing-substituted substrates exhibited good results for this transformation. The findings inspire toward a holistic green technology for Suzuki-Miyaura coupling reaction and an innovative avenue for catalyst recycling and product isolation.

White-Light-Emitting Supramolecular Polymer Gel Based on ß-CD and NDI Host-Guest Inclusion Complex.

Supramolecular polymer formed by non-covalent interactions between complementary building blocks entraps solvents and develops supramolecular polymer gel. A supramolecular polymer gel was prepared by the heating-cooling cycle of ß-cyclodextrin (ß-CD) and naphthalenedimide (NDI) solution in N,N-dimethylformamide (DMF). The host-guest inclusion complex of ß-CD and NDI 1 containing dodecyl amine forms the supramolecular polymer and gel in DMF. However, ß-CD and NDI 2, having glutamic acid, fail to form the supramolecular polymer and gel under the same condition. X-ray crystallography shows that the alkyl chains of NDI 1 are complementary to the hydrophobic cavity of the two ß-CD units. From rheology, the storage modulus was approximately 1.5 orders of magnitude larger than the loss modulus, which indicates the physical crosslink and elastic nature of the thermo-responsive gel. FE-SEM images of the supramolecular polymer gel exhibit flake-like morphology and a dense flake network. The flakes developed from the assembly of smaller rods. Photophysical studies show that the host-guest complex formation and gelation have significantly enhanced emission intensity with a new hump at 550 nm. Upon excitation by a 366 nm UV-light, NDI 1 and ß-CD gel in DMF shows white light emission. The gel has the potential for the fabrication of organic electronic devices.

Acid-responsive fibrillation and urease-assisted defibrillation of phenylalanine: a transient supramolecular hydrogel.

The aggregation of proteins and peptides into fibrils is associated with many neurodegenerative diseases in humans, including Alzheimer's disease, Parkinson's disease and non-neurological type-II diabetes. A better understanding of the fibril formation process and defibrillation using biochemical tools is highly important for therapeutics. Under physiological conditions, acidic pH promotes the formation of toxic fibrils. Here, a mimic of living systems has been achieved by the acid-responsive assembly of benzyloxycarbonyl-l-phenylalanine to fibrils, as well as the urease-assisted disassembly of the said fibrils. The simultaneous incorporation of the two triggers helped to prepare a transient supramolecular hydrogel from benzyloxycarbonyl-l-phenylalanine-entangled fibrils with a high degree of control over the self-assembly lifetime and mechanical properties. Further, under acidic pH, the compound formed the O-HO[double bond, length as m-dash]C hydrogen-bonded dimer. The dimers were further self-assembled by intermolecular N-HO[double bond, length as m-dash]C hydrogen bonds and π-π stacking interactions to form fibrils with high mechanical properties, from this simple molecule. However, the self-assembly process is dynamic. Hence, the in situ-generated NH3 uniformly increased the pH and led to the homogeneous disassembly of the fibrils. Thus, this report provides a valuable approach to defibrillation.

Urea-Appended Amino Acid To Vitalize Yeast Growth, Enhance Fermentation, and Promote Ethanol Production.

The development of sustainable protocols for enhancing the production of ethanol is highly important for its utilization in automotive transportation and energy sector. Up to 15% ethanol can blend with diesel to make e-diesel that can be used in fuel compression ignition engine. Urea-modified amino acids can be used as a very good vitalizer for yeast (Saccharomyces cerevisiae, Baker's yeast (ATCC 204508)) growth and thus promote ethanol production. A simple, one-step, room-temperature synthetic procedure has been developed for urea-appended α-amino acids from amino acid by treatment with KCNO. Single-crystal X-ray studies confirm the successful synthesis and molecular structures of the urea-appended α-amino acids. Out of 20 urea-appended amino acids, Arg-, Pro-, His-, and Gln-containing compounds promote yeast growth significantly after 12 h at pH 6.8 and 38 °C. These compounds are nontoxic. The urea-appended Arg shows 2-fold increase of yeast growth. However, urea-appended m-aminobenzoic acid and p-aminobenzoic acid inhibit yeast growth. NMR experiments confirmed the enhanced production of ethanol by glucose fermentation in the presence of 2.5 µmol urea-appended Arg. Not only glucose but also commercially available sugars and feedstock of the starch slurry drained out after boiling of rice exhibit significant enhancement of ethanol production under same conditions.