Efficient synthesis of [1,2,3]triazolo[5,1-c][1,4]benzoxazines through palladium-copper catalysis

A wide variety of [1,2,3]triazolo[5,1-c][1,4]benzoxazines were synthesized through palladium-copper catalyzed reactions of 1-azido-2-(prop-2-ynyloxy)benzene with aryl/vinyl iodides. A plausible reaction mechanism has also been proposed.     

Facile purification of rare cucurbiturils by affinity chromatography

A practical method for the separation and purification of cucurbituril (CB) hexamers was developed on the basis of affinity chromatography using aminopentylaminomethylated polystyrene beads. This recyclable resin, which can be used repeatedly, facilitates the general preparation of cucurbituril derivatives and compensates for the usually moderate yields and mixed products that characterize the acid-catalyzed synthesis of CB derivatives. This technique allows convenient, rapid isolation of rare substituted cucurbiturils, including hexacyclohexanocucurbit[6]uril and dodecamethylcucurbit[6]uril. [reaction: see text]     

Interaction and solubilization of some phenolic antioxidants in Pluronic® micelles

The solubilization of four phenolic antioxidants, namely p-hydroxybenzoic acid (PHBAA), syringic acid, sinapic acid, and quercetin in micelles of an ethylene oxide (EO)–propylene oxide (PO) triblock copolymer Pluronic^® P104 (EO₂₇–PO₆₁–EO₂₇, PPO mol wt = 3540, % PEO = 40) was examined at different temperatures, pHs, and in the presence of sodium chloride. The nano-size core–shell micelles of P104 characterized by dynamic light scattering had hydrodynamic diameter of about 18–20 nm with low polydispersity. Antioxidants induced micellization and micellar growth were observed. The critical micellar concentration (CMC), critical micellar temperature (CMT), cloud point (CP) of P104 decreased due to solubilization and interactions of antioxidants. The solubilization was favored at higher temperature, pH and in the presence of salt and follows the order PHBA > syringic acid > sinapic acid > quercetin which corresponds to the trend in their aqueous solubility. The location of antioxidant in micelles observed from NOESY spectra. Structure and hydrophobicity of antioxidants were found to be governing factors for their interaction and location in the micelles.     

Unusual Surface Latent Heat Flux Variations and Their Critical Dynamics Revealed before Strong Earthquakes

We focus on the possible thermal channel of the well-known Lithosphere–Atmosphere–Ionosphere Coupling (LAIC) mechanism to identify the behavior of thermal anomalies during and prior to strong seismic events. For this, we investigate the variation of Surface Latent Heat Flux (SLHF) as resulting from satellite observables. We demonstrate a spatio-temporal variation in the SLHF before and after a set of strong seismic events occurred in Kathmandu, Nepal, and Kumamoto, Japan, having magnitudes of 7.8, 7.3, and 7.0, respectively. Before the studied earthquake cases, significant enhancements in the SLHF were identified near the epicenters. Additionally, in order to check whether critical dynamics, as the signature of a complex phenomenon such as earthquake preparation, are reflected in the SLHF data, we performed a criticality analysis using the natural time analysis method. The approach to criticality was detected within one week before each mainshock.     

The water‐promoted Diels–Alder reaction in quaternary ammonium salts

Prevailing classification of salts based on their effect in solubility and stability of proteins in aqueous solution predicts that tetraalkylammonium salts, guanidinium chloride (GnCl), LiClO₄ act as salting‐in (S/I) and LiCl, NaCl act as salting‐out (S/O) in aqueous conditions. In the same context the behaviour of GnCl, LiClO₄ and LiCl are contradictory in polar solvents like ethylene glycol and formamide. In these solvents, expected salt effect shows just opposite nature from their usual expectation. However, in the aqueous solution salts like tetraalkylammonium halide (R₄NX, R = alkyl group, X = Br group) behave like salting‐in salts. The physicochemical origin of the salting in effect of R₄NX type of salts has been discussed elaborately in the present work. The role of cations in terms of substitution of various alkyl groups on R₄NX has been systematically presented here on the basis of experimental kinetic and thermodynamic studies. The abnormal behaviour of R₄NX salts in aqueous solution has also been explained by the Setschenov equation (k_s) and Δμ_solvation values, which highlights their individual nature out of common properties of R₄NX. Copyright © 2015 John Wiley & Sons, Ltd.     

Invoking Pairwise Interactions in Water‐Promoted Diels–Alder Reactions by using Ionic Liquids as Cosolvents

Rate constants and derived activation parameters of organic reactions in aqueous media, in particular Diels–Alder reactions, are sensitive to the presence of cosolvents in water. To enhance the solubility window of water, we introduced ionic liquids as cosolvents in the aqueous Diels–Alder reaction between anthracene‐9‐carbinol and N‐ethylmaleimide. The reactive potentials of the organic compounds are parameterized by using semi‐empirical quantum chemical methods. The principle of Savage–Wood additivity of group interactions is used to quantify the pairwise group interactions among chemically inert ionic liquids and organic reactants, both at initial and transition states of the reaction. The present approach shows promise, as the use of simple calculations from easily available kinetic data can help researchers to understand the versatility of green ionic‐liquid alternatives to volatile organic solvents.     

Magnetic exchange interactions and magneto-structural correlations in heterobridged μ-phenoxo-μ(1,1)-azide dinickel(II) compounds: a combined experimental and theoretical exploration

This investigation presents the syntheses, crystal structures, magnetic properties, and density functional theoretical modeling of magnetic behavior of two heterobridged μ-phenoxo-μ(1,1)-azido dinickel(II) compounds [Ni(II)(2)(L(1))(2)(μ(1,1)-N(3))(N(3))(H(2)O)]·CH(3)CH(2)OH (1) and [Ni(II)(2)(L(2))(2)(μ(1,1)-N(3))(CH(3)CN)(H(2)O)](ClO(4))·H(2)O·CH(3)CN (2), where HL(1) and HL(2) are the [1+1] condensation products of 3-methoxysalicylaldehyde and 1-(2-aminoethyl)-piperidine (for HL(1))/4-(2-aminoethyl)-morpholine (for HL(2)), along with density functional theoretical magneto-structural correlations of μ-phenoxo-μ(1,1)-azido dinickel(II) systems. Compounds 1 and 2 crystallize in orthorhombic (space group Pbca) and monoclinic (space group P2(1)/c) systems, respectively. The coordination environments of both metal centers are distorted octahedral. The variable-temperature (2-300 K) magnetic susceptibilities at 0.7 T of both compounds have been measured. The interaction between the metal centers is moderately ferromagnetic; J = 16.6 cm(-1), g = 2.2, and D = -7.3 cm(-1) for 1 and J = 16.92 cm(-1), g = 2.2, and D(Ni1) = D(Ni2) = -6.41 cm(-1) for 2. Broken symmetry density functional calculations of exchange interaction have been performed on complexes 1 and 2 and provide a good numerical estimate of J values (15.8 cm(-1) for 1 and 15.35 cm(-1) for 2) compared to experiments. The role of Ni-N bond length asymmetry on the magnetic coupling has been noted by comparing the structures and J values of complexes 1 and 2 together with previously published dimers 3 (Eur. J. Inorg. Chem. 2009, 4982), 4 (Inorg. Chem. 2004, 43, 2427), and 5 (Dalton Trans. 2008, 6539). Our extensive DFT calculations reveal an important clue to the mechanism of coupling where the orientation of the magnetic orbitals seems to differ with asymmetry in the Ni-N bond lengths. This difference in orientation leads to a large change in the overlap integral between the magnetic orbitals and thus the magnetic coupling. DFT calculations have also been extended to develop several magneto-structural correlations in this type of complexes and the correlation aim to focus on the asymmetry of the Ni-N bond lengths reveal that the asymmetry plays a proactive role in governing the magnitude of the coupling. From a completely symmetric Ni-N bond length, two behaviors have been noted: with a decrease in bond length there is an increase in the ferromagnetic coupling, while an increase in the bond lengths leads to a decrease in ferromagnetic interaction. The later correlation is supported by experiments. The magnetic properties of 1, 2, and three previously reported related compounds have been discussed in light of the structural parameters and also in light of the theoretical correlations determined here.