Solvent Geometry Regulated J- and H-Type Aggregates of Photoswitchable Organogelator: Phase-Selective Thixotropic Gelation and Oil Spill Recovery.

We demonstrate supramolecular polymerization and formation of 1D nanofiber of azobenzene based organogelator (AZO-4) in cyclic hydrocarbon solvents (toluene and methylcyclohexane). The AZO-4 exhibits J- and H-type aggregates in toluene: MCH (9 : 1) and MCH: toluene (9 : 1) respectively. The type of aggregate was governed by the geometry of the solvents used in the self-assembly process. The J-type aggregates with high thermal stability in toluene is due to the enhanced interaction of AZO-4 π- surface with the toluene π-surface, whereas H-aggregate with moderate thermal stability in MCH was due to the interruption of the cyclic hydrocarbon in van der Waals interactions of peripheral chains of AZO-4 molecule. The light induced reversible photoisomerization is observed for both J- and H-aggregates. The macroscopic property revealed spontaneous and strong gelation in toluene preferably due to the strong interactions of the AZO-4 nanofibers with the toluene solvent molecules compared to the MCH. The rheological measurements revealed thixotropic nature of the gels by step-strain experiments at room temperature. The thermodynamic parameter (ΔHm) of gel-to-sol transition was determined for all the gels to get more insight into the gelation property. Furthermore, the phase selective gelation property was extended to the oil spill recovery application using diesel/water and petrol/water mixture.

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.

Enhancing the optical response and biosensing capabilities of bioinspired peptide micro-waveguides exploiting chromatic aberration.

Bioinspired peptide waveguides of mesoscopic length scales have established a new paradigm in photonics with possible applications in precision bioimaging, sensing, and diagnostics. Here, we improve the efficiency of coupling various constituent colors of a white light source into single self-assembled microtube-shaped passive peptide waveguides by employing chromatic aberration. Thus, we use a chromatically aberrated microscope objective lens to couple light into peptide waveguides. Using both numerical simulation and experiments, we show that the waveguide response displays higher quality factor, wavelength selectivity, and axial coupling range compared to a chromatically corrected standard plan-fluoritic objective lens. We also demonstrate absorption and refractive index-based sensing by studying the changes in the optical responses of the peptide tubes in the presence of a wide concentration range of the absorptive Congo red, and the nonabsorptive Coumarin dyes. The former understandably display a much higher response than the latter due to the low finesse of the waveguides. We obtain a detection limit of around 10 nM for Congo red, and 10 mM for Coumarin. Our study opens up possibilities for deploying such peptide microtubes for various biosensing applications utilizing spectral and waveguide characteristics.

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.

Topology-Controlled AIEE of Iminocoumarin Luminophores.

Aggregation-induced emission enhancement (AIEE) is an unusual phenomenon where luminophores show a higher photoluminescence efficiency in the aggregated and solid state. We report the design and synthesis of a series of luminophores 1-4 with imine functionality at 6 position of coumarin and studied their AIE propensities on self-assembly. The effect of the topology of the phenolic hydroxyl group on the emission behaviour of the luminophores has been investigated. The imines show significant solvatochromism with high emission in non-polar solvents, whereas the emission gets quenched in the polar solvent. The fluorescence in the toluene-hexane mixture arises due to the aggregation of fluorophores and falls under the category of AIEE. Not only the solution state emission of the isomeric iminocoumarin luminophores is notably varied, but also their solid-state emission found to be significantly different from each other. Moreover, the iminocoumarin 1 selectively recognizes Fe(III) over Fe(II) with a prominent color change. In situ oxidation of Fe(II) with H2 O2 exhibits the same effect like Fe(III) and developed a chemical combinational logic gate.

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.