We have shown solvent-and substrate-dependent chiral inversion of a few glycoconjugate supramolecules. (Z)-F-Gluco, in which d-glucosamine has been attached chemically to Cbz-protected l-phenylalanine at the C terminus, forms a self-healing hydrogel through intertwining of the nanofibers wherein the gelators undergo lamellar packing in the β-sheet secondary structures with a single chiral handedness. Dihybrid (Z)-F-gluco nanocomposite gel was prepared by in-situ formation of silver nanoparticles AgNPs in the gel; this enhances the mechanical properties of the composite gel through physical crosslinking without altering the packing pattern. In contrast, (Z)-L-gluco bearing an l-leucine moiety does not form a hydrogel but an organogel. Interestingly, the chiral handedness of the aggregates of (Z)-L-gluco can be reversed by choosing suitable solvents. In addition to selfhealing behavior, (Z)-L-gluco gel revealed shape persistency. Further, (Z)-F-gluco hydrogel is benign, nontoxic, nonimmunogenic, and non-allergenic in animal cells. AgNPloaded (Z)-F-gluco hydrogel showed antibacterial activity against both Gram-positive and Gram-negative bacteria.

No abstract

Here, we studied the self‐assembly and chiroptical properties of four C2‐symmetric molecules bearing terephthaloyl (TLF−C4 and TLF−C12) and benzene‐1,4‐dicarbonyl core (BLF−C4 and BLF−C12). β‐turn in the aggregates of TLF−C4 and TLF−C12 was found irrespective of the amount of water as anti‐solvent in methanol (MeOH). Interestingly, chiroptical properties can be switched from β‐turn to twisted β‐sheet secondary structure in BLF−C4 and BLF−C12 beyond a certain amount of water in MeOH. Detailed studies suggested lamellar arrangement of the TLF−C4 gelators with a β‐turn led to the formation of right‐handed coiled‐coil helical fibers. However, left‐handed coiled‐coil twisted fibers were formed by lamellar packing (twisted β‐sheet) of BLF−C4. In addition, TLF−C12 gel in methylcyclohexane (MCH) revealed shape persistent gelation. Rapid dynamic equilibrium between association and dissociation of non‐covalent interactions in BLF−C12 gel in MCH resulted in thixotropic and, in turn, injectable behavior.

A new 3D manganese(II) coordination polymer, formulated as [Mn3(HL)6] (1) (where H2L = 6-hydroxypicolinic acid), has been hydrothermally synthesized and characterized by single-crystal X-ray crystallographic analysis along with other spectroscopic and magnetic techniques. Structural analysis shows that the compound crystallizes in the monoclinic C2/c space group and is a non-porous 3D coordination polymer formed by three different Mn(II) centres connected by 6-hydroxypicolinic acid ligands in their keto form. Each Mn(II) centre shows a distorted octahedral coordination environment. Neighbouring Mn(II) centres are connected by two different syn-anti bridging carboxylate groups to form regular coordination chains. There are two different [Mn2(RCOO)2] units along the chain, formed by two crystallographically independent Mn centres (Mn1 and Mn2). These chains are further connected by HL− ligands to form a 3D coordination network. Interestingly, both the hydroxy and the carboxylate groups of the ligands are deprotonated and coordinated to the metal centres, whereas the pyridyl group is protonated and uncoordinated, although it participates in strong hydrogen bonding interactions with oxygen atoms of the HL− ligand, as shown by the Hirshfeld surface analysis. Both the absorption and emission spectra of the compound have also been measured. Variable temperature magnetic studies reveal the presence of a spin-canted antiferromagnetic behaviour with a high coercivity of 40 mT at 2 K and an ordering temperature of 14 K.

Catalyst development for water splitting to afford hydrogen as a green source of energy is one of the major areas of research in the pursuit of sustainable energy technology solution. Herein, the electrocatalytic water oxidation behaviour of two different Co‐pdc (H2pdc=pyridine‐2,5‐dicarboxylic acid) based metal‐organic frameworks (MOFs) of different dimensionalities (2D and 1D) is reported. 2D‐MOF {[Co(pdc)(H2O)2] ⋅ H2O}n acts as the mother which transforms into daughter 1D‐MOF {[Co(pdc)(H2O)2] ⋅ 7H2O}n via consecutive dehydration and rehydration. Within 2D‐MOF, the Co2+ shows six coordinated octahedral geometry with two coordinated water molecules and for the 1D‐MOF, Co2+ shows five coordinated square pyramidal geometry having two coordinated water molecules and one open metal site. Both the MOFs show excellent stability over a pH range of 3 to 11 even after 24 hours and show OER activity from neutral to alkaline medium. The MOFs retain their crystalline structure even after OER at neutral pH but eventually gets decomposed; but they are converted into their (oxy)hydroxides at pH 14. Interestingly, 1D MOF shows superior activity in both neutral and alkaline medium over the 2D framework for OER due to presence of open metal sites, better electrical conductivity and larger electrochemically active surface area.

No abstract

No abstract