Asymmetric rotations and dimerization driven by normal to modulated phase transition in 4-biphenylcarboxy coupled L-phenylalaninate

Amongst the derivatives of 4-biphenylcarboxylic acid and amino acid esters, the crystal structure of 4-biphenylcarboxy-(L)-phenylalaninate is unusual owing to its monoclinic symmetry within a pseudo-orthorhombic lattice. The distortion is described by disparate rotational property around the chiral centers ($\varphi_{\mathrm{chiral}}$ $\simeq$ -129 degrees and 58 degrees) of the two molecules in the asymmetric unit. Each of these molecules comprise of planar biphenyl moieties ($\varphi_{\mathrm{biphenyl}}$ = 0 degrees). Using temperature dependent single crystal X-ray diffraction experiments we show that the compound undergoes a phase transition below $T$ $\sim$ 124 K that is characterized by a commensurate modulation wave vector, $\mathbf{q}$ = $\delta(101)$, $\delta$ = $\frac{1}{2}$. The (3+1) dimensional modulated structure at $T$ = 100 K suggests that the phase transition drives the biphenyl moieties towards non coplanar conformations with significant variation of internal torsion ($\varphi^{\mathrm{max}}_{\mathrm{biphenyl}}$ $\leq$ $20$ degrees). These intramolecular rotations lead to dimerization of the molecular stacks that are described predominantly by intermolecular tilts and small variations in intermolecular distances. Atypical of modulated structures and superstructures of biphenyl and other polyphenyls, the rotations of individual molecules are asymmetric ($\Delta$$\varphi_{\mathrm{biphenyl}}$ $\approx$ 5 degrees) while $\varphi_{\mathrm{biphenyl}}$ of one independent molecule is two to four times larger than the other. Crystal-chemical analysis and phase relations in superspace suggest multiple competing factors involving intramolecular steric factors, intermolecular H--C${\cdot}{\cdot}{\cdot}$C--H contacts and weak C--H${\cdot}{\cdot}{\cdot}$O hydrogen bonds that govern the distinctively unequal torsional property of the molecules

Mopping up the Oil, Metal, and Fluoride Ions from Water

The recycle, cleaning, and reuse of water are highly important for environmental remediation. This issue is addressed by creating a fluorescent zwitterionic spirocyclic Meisenheimer complex with high chelating propensity for toxic metals using low-cost starting materials and a one-pot synthesis technique. The resulting material is able to detect fluoride up to 12.8 ppb level and remove 82% aqueous fluoride from 1000 mL of 100 ppm fluoride solution in a single contact. The material demonstrates rapid kinetics and is capable of dropping the toxic metal ion (Pb/Hg/Cd) concentration below 0.2 ppb within 10 min. A resin-free, precipitation-free, and reusable technique has been developed for the removal of toxic metal ions and fluoride from extremely polluted water. Moreover, utilizing its extreme hydrophobicity, polystyrene sponges have been coated with the Meisenheimer complex to mop up oil spill and organic solvents from a biphasic mixture

Mopping up the Oil, Metal, and Fluoride Ions from Water

The recycle, cleaning, and reuse of water are highly important for environmental remediation. This issue is addressed by creating a fluorescent zwitterionic spirocyclic Meisenheimer complex with high chelating propensity for toxic metals using low-cost starting materials and a one-pot synthesis technique. The resulting material is able to detect fluoride up to 12.8 ppb level and remove 82% aqueous fluoride from 1000 mL of 100 ppm fluoride solution in a single contact. The material demonstrates rapid kinetics and is capable of dropping the toxic metal ion (Pb/Hg/Cd) concentration below 0.2 ppb within 10 min. A resin-free, precipitation-free, and reusable technique has been developed for the removal of toxic metal ions and fluoride from extremely polluted water. Moreover, utilizing its extreme hydrophobicity, polystyrene sponges have been coated with the Meisenheimer complex to mop up oil spill and organic solvents from a biphasic mixture

Mopping up the Oil, Metal, and Fluoride Ions from Water

The recycle, cleaning, and reuse of water are highly important for environmental remediation. This issue is addressed by creating a fluorescent zwitterionic spirocyclic Meisenheimer complex with high chelating propensity for toxic metals using low-cost starting materials and a one-pot synthesis technique. The resulting material is able to detect fluoride up to 12.8 ppb level and remove 82% aqueous fluoride from 1000 mL of 100 ppm fluoride solution in a single contact. The material demonstrates rapid kinetics and is capable of dropping the toxic metal ion (Pb/Hg/Cd) concentration below 0.2 ppb within 10 min. A resin-free, precipitation-free, and reusable technique has been developed for the removal of toxic metal ions and fluoride from extremely polluted water. Moreover, utilizing its extreme hydrophobicity, polystyrene sponges have been coated with the Meisenheimer complex to mop up oil spill and organic solvents from a biphasic mixture

Mopping up the Oil, Metal, and Fluoride Ions from Water

The recycle, cleaning, and reuse of water are highly important for environmental remediation. This issue is addressed by creating a fluorescent zwitterionic spirocyclic Meisenheimer complex with high chelating propensity for toxic metals using low-cost starting materials and a one-pot synthesis technique. The resulting material is able to detect fluoride up to 12.8 ppb level and remove 82% aqueous fluoride from 1000 mL of 100 ppm fluoride solution in a single contact. The material demonstrates rapid kinetics and is capable of dropping the toxic metal ion (Pb/Hg/Cd) concentration below 0.2 ppb within 10 min. A resin-free, precipitation-free, and reusable technique has been developed for the removal of toxic metal ions and fluoride from extremely polluted water. Moreover, utilizing its extreme hydrophobicity, polystyrene sponges have been coated with the Meisenheimer complex to mop up oil spill and organic solvents from a biphasic mixture

1-(2-Aminophenyl)-3H-[1,2,3] triazole-4-carboxylic acid: activity against Gram-positive and Gram-negative pathogens including Vibrio Cholerae

Figures ESI S1, S2, S3; synthesis scheme and characterization of compounds, 1H NMR, 13C NMR and Mass spectrum : Figure S1-S11

α,ε-Hybrid Peptide Foldamers: Self-Assembly of Peptide with Trans Carbon–Carbon Double Bonds in the Backbone and Its Saturated Analogue

The effect of geometrically rigid trans α,β-unsaturated ε-amino acids on the structure, folding, and assembly of α,ε-hybrid peptide foldamers has been reported. From single-crystal diffraction analysis, the unsaturated tetrapeptide <b>1</b> has stapler-pin-like structure but without intramolecular hydrogen bond. The asymmetric unit has two molecules that are stabilized by multiple intermolecular hydrogen bonding interactions as well as π–π stacking interactions between the aromatic rings of 3-aminocinnamic acid. Peptide <b>1</b> does not form organogel. But on hydrogenation, peptide <b>1</b> provides the saturated α,ε-hybrid peptide foldamer <b>2</b>, which forms instant gel in most of the aromatic solvents. The gel exhibits high stability. The unsaturated peptide <b>1</b> has porous microsphere morphology, but saturated analogue <b>2</b> has ribbonlike morphology. The gel has been used efficiently for removal of cationic organic pollutants from waste water

Hydrazine-Modified Topology-Dependent Conductivity of Cyclic NDI as a Molecular Circuit

Significant conductance enhancement can be achieved by topology modification of n-type semiconducting naphthalenediimide (NDI) as a molecular circuit. Hydrazine not only reduces electron-deficient NDI to NDI(center dot-)radical anions but also modifies the topology by selectively replacing the amino acid methyl esters from NDI 1 and forms a cyclic NDI nanorim. On treatment with hydrazine, the NDI 1 emission band at 525 nm gradually disappears, and a new band appears at 607 nm, presumably due to NDI oligomer formation. Eventually, a shiny black, almost insoluble precipitate of the NDI nanorim appeared. The cyclic NDI nanorim was characterized by powder X-ray diffraction, high-resolution mass spectrometry, Fourier transform infrared, and C-13 CP-MAS NMR spectroscopy. Cyclic voltammetry (CV) of NDI 1 possesses two sequential one-electron cathodic waves at -0.4661 and -0.9456 V versus Ag/Ag+ due to NDI center dot- and NDI2- formation. However, CV of the NDI nanorim reveals four distinct reversible one-electron waves due to electronic communication between the four NDI redox centers within the nanorim. The I-V measurements show sevenfold conductance enhancements by topology modification from linear NDI to a nanorim