Understanding guest and pressure‐induced porosity through structural transition in flexible interpenetrated MOF by Raman spectroscopy

Interpenetrating metal organic frameworks are interesting functional materials exhibiting exceptional framework properties. Uptake or exclusion of guest molecules can induce sliding in the framework making it porous or non‐porous. To understand this dynamic nature and how framework interaction changes during sliding, metal organic framework (MOF) 508 {Zn(BDC)( 4,4′‐Bipy)_0.5 · DMF(H₂O)_0.5} was selected for study. We have investigated structural transformation in MOF‐508 under variable conditions of temperature, pressure and gas loading using Raman spectroscopy and substantiated it with IR studies and density functional theory (DFT) calculations. Conformational changes in the organic linkers leading to the sliding of the framework result in changes in Raman spectra. These changes in the organic linkers are measured as a function of high pressure and low temperature, suggesting that the dynamism in MOF‐508 framework is driven by ligand conformation change and inter‐linker interactions. The presence of Raman signatures of adsorbed CO₂ and its librational mode at 149 cm⁻¹ suggests cooperative adsorption of CO₂ in the MOF‐508 framework, which is also confirmed from DFT calculations that give a binding energy of 34 kJ/mol. Copyright © 2015 John Wiley & Sons, Ltd.     

Porosity Switching in Polymorphic Porous Organic Cages with Exceptional Chemical Stability

Porous solids that can be switched between different forms with distinct physical properties are appealing candidates for separation, catalysis, and host–guest chemistry. In this regard, porous organic cages (POCs) are of profound interest because of their solution‐state accessibility. However, the application of POCs is limited by poor chemical stability. Synthesis of an exceptionally stable imine‐linked (4+6) porous organic cage ( TpOMe‐CDA ) is reported using 2,4,6‐trimethoxy‐1,3,5‐triformyl benzene (TpOMe) as a precursor aldehyde. Introduction of the ‐OMe functional group to the aldehyde creates significant steric and hydrophobic characteristics in the environment around the imine bonds that protects the cage molecules from hydrolysis in the presence of acids or bases. The electronic effect of the ‐OMe group also plays an important role in enhancing the stability of the reported POCs. As a consequence, TpOMe‐CDA reveals exceptional chemical stability in neutral, acidic and basic conditions, even in 12 m NaOH. Interestingly, TpOMe‐CDA exists in three different porous and non‐porous polymorphic forms (α, β, and γ) with respect to differences in crystallographic packing and the orientation of the flexible methoxy groups. All of the polymorphs retain their crystallinity even after treatment with acids and bases. All the polymorphs of TpOMe‐CDA differ significantly in their properties as well as morphology and could be reversibly switched in the presence of an external stimulus.     

Design,Synthesis, and Anticancer Activity of Bis-isoxazole Incorporated Benzothiazole Derivatives

Russian Journal of General Chemistry - A novel series of bis-isoxazole incorporated benzothiazole derivatives has been designed and synthesized. Molecular structures of the compounds have been...     

Triclabendazole: An Intriguing Case of Co‐existence of Conformational and Tautomeric Polymorphism

The crystal polymorphism of the anthelmintic drug, triclabendazole ( TCB ), is described. Two anhydrates (Forms I and II), three solvates, and an amorphous form have been previously mentioned. This study reports the crystal structures of Forms I ( 1 ) and II ( 2 ). These structures illustrate the uncommon phenomenon of tautomeric polymorphism. TCB exists as two tautomers A and B. Form I (Z′=2) is composed of two molecules of tautomer A while Form II (Z′=1) contains a 1:1 mixture of A and B. The polymorphs are also characterized by using other solid‐state techniques (differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), PXRD, FT‐IR, and NMR spectroscopy). Form I is the higher melting form (m.p.: 177 °C, ΔH_f=≈105±4 J g^?1) and is the more stable form at room temperature. Form II is the lower melting polymorph (m.p.: 166 °C, ΔH_f=≈86±3 J g^?1) and shows high kinetic stability on storage in comparison to the amorphous form but it transforms readily into Form I in a solution‐mediated process. Crystal structure analysis of co‐crystals 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 further confirms the existence of tautomeric polymorphism in TCB . In 3 and 11 , tautomer A is present whereas in 4 , 5 , 6 , 7 , 8 , 9 , 10 the TCB molecule exists wholly as tautomer B. The DFT calculations suggest that the optimized tautomers A and B have nearly the same energies. Single point energy calculations reveal that tautomer A (in Form I) exists in two low‐energy conformations, whereas in Form II both tautomers A and B exist in an unfavorable high‐energy conformation, stabilized by a five‐point dimer synthon. The structural and thermodynamic features of 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 are discussed in detail. Triclabendazole is an intriguing case in which tautomeric and conformational variations co‐exist in the polymorphs.     

Raman and X-ray investigations of ferroelectric phase transition in NH4HSO4

Temperature-dependent Raman spectroscopy and X-ray diffraction studies have been carried out on NH(4)HSO(4) single crystals in the temperature range 77-298 K. Two structural transitions driven by the molecular ordering and change in crystal symmetries are observed below 263 and 143 K. These phase transitions are marked by the anomalies in the temperature dependence of wavenumber and fwhm of several internal vibrational modes. The Raman spectra and X-ray data enable us to understand the nature of the molecular ordering resulting in the ferroelectric phase below 263 K, sandwiched between two nonferroelectric phases. The crystal structure of the ferroelectric phase is determined correctly as Pc, which has been earlier solved in Ba symmetry. The temperature dependent Raman and X-ray results suggest that the disorder to order transition leading to lower symmetry below 263 K is driven by the change in HSO(4)(-) ions and that below 143 K is driven by the change in both HSO(4)(-) and NH(4)(+) ions.     

Stoichiometry-controlled cycloaddition of azomethine ylide with dipolarophiles: chemoselective and regioselective synthesis of bis- and tris-spirooxindole derivatives

A new series of bis- and tris-spirooxindole derivatives have been synthesized by controlling the molar equivalent of in situ generated azomethine ylides in [3+2]-cycloaddition reactions with dipolarophiles. The structural elucidation on the basis of IR, ¹H NMR, ¹³C NMR, and mass spectral data of these compounds established the highly chemoselective and regioselective formation of spirooxindole derivatives. Single crystal X-ray analysis of compound 4g and 2D NMR analysis of compound 5a confirmed the structures of bis- and tris-spirooxindole derivatives.     

Design,synthesis, antitubercular and antibacterial activities of pyrrolo[3,2-b]pyridine-3-carboxamide linked 2-methoxypyridine derivatives and in silico docking studies

Abstract

A novel series pyrrolo[3,2-b]pyridine-3-carboxamide linked 2-methoxypyridine derivatives have been designed, synthesized and confirmed by FT-IR, ¹H NMR, ¹³C NMR, ¹⁹F NMR, MS, and elemental analysis. The synthesized compounds were screened for their antitubercular activity using microplate alamar blue assay method and antibacterial activity. Among the tested compounds, 4- fluorophenyl (8m), 4- chlorophenyl (8n) and 4-methoxyphenyl (8i) showed potent anti-TB activity (3.12?µg/mL) in comparison with reference drug, Pyrazinamide ((3.12?µg/mL). In addition, all compounds were docked into DprE1 (PDB code: 4KW5) to explore their binding interactions at the active site. The compounds exhibited essential key interactions as that of reported DprE1 inhibitors and hence, the synthesized compounds may be considered as molecular scaffolds for antitubercular activity. Compounds, 4-chlorophenyl (8n) and 4-flurophenyl (8m) showed significant antibacterial activity against Escherichia coli and Staphylococcus aureus strains. In silico prediction of toxicities, druglikeness and drug score profiles of the tested compounds are promising.     

Spin-reorientation, ferroelectricity, and magnetodielectric effect in YFe(1-x)Mn(x)O3(0.1 ≤ x ≤ 0.40)

We report the observation of magnetoelectric and magnetodielectric effects at different temperatures in Mn-substituted yttrium orthoferrite, YFe(1-x)Mn(x)O(3)(0.1 ≤ x ≤ 0.40). Substitution of Mn in antiferromagnetic YFeO(3)(T(N) = 640 K) induces a first-order spin-reorientation transition at a temperature, T(SR), which increases with x whereas the Néel temperature (T(N)) decreases. While the magnetodielectric effect occurs at T(SR) and T(N), the ferroelectricity appears rather at low temperatures. The origin of magnetodielectric effect is attributed to spin-phonon coupling as evidenced from the temperature dependence of Raman phonon modes. The large magnetocapacitance (18% at 50 kOe) near T(SR) = 320 K and high ferroelectric transition temperature (～115 K) observed for x = 0.4 suggest routes to enhance magnetoelectric effect near room temperature for practical applications.     

Synthesis,Characterization, and Anticancer Activity of Novel Imidazo[1,2-a]pyridine Linked 1,2,3-Triazole Derivatives

Russian Journal of General Chemistry - A novel series of imidazo[1,2-a]pyridine linked 1,2,3-triazole derivatives has been designed, synthesized and the structures have been confirmed by 1H and 13C...