A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex as an efficient catalyst for oxidation of alcohols with tert-butyl hydroperoxide

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex [PS–(QBIM)₂Cu(II)] was synthesized by functionalization of chloromethylated polystyrene cross-linked with 6.5 % divinyl benzene with 2-(2′-quinolyl)benzimidazole and subsequent treatment with Cu(OAc)₂ in methanol. The complex was characterized by physical, analytical and spectroscopic techniques. Electronic and ESR spectra, together with magnetic susceptibility measurements, indicated that the complex was paramagnetic with distorted octahedral geometry around the copper. The complex was found to be active toward oxidation of various alcohols including phenol, benzyl alcohol and cyclohexanol using 70 % aqueous tert-butyl hydroperoxide under mild conditions. Under the optimized reaction conditions, cyclohexanol gave 100 % conversion to cyclohexanone, benzyl alcohol gave 98 % yield of benzaldehyde and phenol gave 89 % yield of catechol and 4 % of hydroquinone. The complex was recycled five times without much loss in catalytic activity.     

Formation and Degradation of Polymeric Peroxides

An attempt has been made to bring the literature on polymeric peroxides together from all angles in order to present a comprehensive picture about them. Both polyperoxides, where the peroxide group has been attached to the main chain, and polymeric hydroperoxides, where the peroxide group is present as a side chain, have been considered. Various aspects such as formation, thermal decomposition characteristics, photodecomposition, and analysis of peroxides have been discussed.     

Growth,structural, crystallisation,thermal decomposition and dielectric behaviour of melaminium bis(hydrogen oxalate) single crystal

Single crystals of melaminium bis (hydrogen oxalate) (MOX) single crystals have been grown from aqueous solution by slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MOX crystallises in monoclinic system with space group C2/c. The calculated lattice parameters are a = 20.075 ± 0.123 Å b = 8.477 ± 0.045 Å, c = 6.983 ± 0.015 Å, α = 90°, β = 102.6 ± 0.33°, γ = 90° and V = 1,159.73 (Å)³. Thermogravimetric analysis at three different heating rates 10, 15 and 20 °C min^?1 has been done to study the thermal decomposition behaviour of the crystal. Non-isothermal studies on MOX reveal that the decomposition occurs in two stages. Kinetic parameters [effective activation energy (E _a), pre-exponential factor (ln A)] of each stage were calculated by model-free method: Kissinger, Kim–Park and Flynn–Wall method and the results are discussed. A significant variation in effective activation energy (E _a) with conversion progress (α) indicates that the process is kinetically complex. The linear relationship between the ln A and E _a was established (compensation effect). DTA analyses were conducted at different heating rates and the activation energy was determined graphically from Kissinger and Ozawa equation. The average effective activation energy is calculated as 276 kJ mol^?1 for the crystallization peak. The Avrami exponent for the crystallization peak temperature determined by Augis and Bennett method is found to be 1.95. This result indicates that the surface crystallization dominates overall crystallization. Dielectric study has also been done, and it is found that both dielectric constant and dielectric loss decreases with increase in frequency and is almost a constant at high frequency region.     

Studies of third-order optical nonlinearities and optical limiting properties of azo dyes

In order to protect optical sensors and human eyes from debilitating laser effects, the intensity of the incoming laser light has to be opportunely reduced. Here, we report our results on the third-order optical nonlinearity and optical limiting properties of three azo dyes exposed to a 532nm continuous wave laser. We have observed low power optical limiting based on nonlinear refraction in our samples.     

Synergistic Activation of Nitrite and Thiocarbonyl Compounds Affords NO and Sulfane Sulfur via (Per)thionitrite (SNO−/SSNO−)

(Per)thionitrite (SNO⁻/SSNO⁻) intermediates play vital roles in modulating nitric oxide (NO) and hydrogen sulfide (H₂S) dependent bio-signalling processes. Whilst the previous preparations of such intermediates involved reactive H₂S/HS⁻ or sulfane sulfur (S⁰) species, the present report reveals that relatively stable thiocarbonyl compounds (such as carbon disulfide (CS₂), thiocarbamate, thioacetic acid, and thioacetate) react with nitrite anion to yield SNO⁻/SSNO⁻. For instance, the reaction of CS₂ and nitrite anion (NO₂⁻) under ambient condition affords CO₂ and SNO⁻/SSNO⁻. A detailed investigation involving UV/Vis, FTIR, HRMS, and multinuclear NMR studies confirm the formation of SNO⁻/SSNO⁻, which are proposed to form through an initial nucleophilic attack by nitrite anion followed by a transnitrosation step. Notably, reactions of CS₂ and nitrite in the presence of thiol RSH show the formation of organic polysulfides R-S_n-R, thereby illustrating that the thiocarbonyls are capable of influencing the pool of bioavailable sulfane sulfurs. Furthermore, the availability of both NO₂⁻ and thiocarbonyl motifs in the biological context hints at their synergistic metal-free activations leading to the generation of NO gas and various reactive sulfur species via SNO⁻/SSNO⁻.     

Stretched poly(methyl methacrylate) gel aligns small organic molecules in chloroform. stereochemical analysis and diastereotopic proton NMR assignment in ludartin using residual dipolar couplings and 3J coupling constant analysis

Poly(methyl methacrylate) (PMMA) gels prepared by copolymerizing methyl methacrylate (MMA) and various amounts of ethylene glycol dimethacrylate (EGDMA) in the presence of the radical initiator V-70 (2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile)) can orient small organic molecules when swollen in NMR tubes with CDCl(3). The aligning properties of the stretched PMMA gels were evaluated by monitoring the quadrupolar splitting of the (2)H NMR signal of CDCl(3), and the aligning degree is proportional to the cross-linking density. Natural abundance one-bond (1)H-(13)C residual dipolar couplings (RDCs) for menthol measured in the gels depended on the cross-link density. The stereochemistry and assignment of the diastereotopic protons of the gastroprotective and nonsteroidal aromatase inhibitor sesquiterpene lactone ludartin, isolated from Stevia yaconensis var. subeglandulosa, were unambiguously determined using a combination of natural abundance one-bond (1)H-(13)C RDCs measured in a PMMA gel and a (3)J coupling constant analysis.     

Hypolipidemic potential of flowers of Nerium oleander in high fat diet-fed Sprague Dawley rats

Nerium oleander Linn. (NO), an evergreen shrub, is used in folklore medicine as a cardiotonic and exhibits a wide spectrum of bioactivities. Herein, the hypolipidemic potential of the ethanolic extract of flowers of Nerium oleander (ENO) in a minimal dose was assessed. A high fat diet (HFD) resulted in a significant increase in cardiac lipids and lipoproteins and an increase in body weight gain. Simultaneous treatment with ENO significantly lowered the increase in body weight gain, lipid and lipoprotein levels, with a concomitant increase in HDL in the plasma and heart when compared to HFD-fed rats. Likewise, the activities of lipolytic enzymes were also upheld by the ENO treatment in the heart compared to HFD-fed rats. The above findings highlight the possible mechanism of N. oleander as a hypolipidemic agent in its use in folklore medicine as a cardiotonic.     

Adsorption of methylene blue dye from aqueous solution by agricultural waste: Equilibrium,thermodynamics, kinetics,mechanism and process design

The adsorption of methylene blue (MB) dye from aqueous solution onto a cashew nut shell (CNS) was investigated as a function of parameters such as solution pH, CNS dose, contact time, initial MB dye concentration and temperature. The CNS was shown to be effective for the quantitative removal of MB dye, and the equilibrium was reached in 60 min. The experimental data were analysed by two-parameter isotherms (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models) using nonlinear regression analysis. The characteristic parameters for each isotherm and the related correlation coefficients were determined. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were also evaluated, the sorption process was found to be spontaneous and exothermic. Pseudo-first-order, pseudo-second-order and Elovich kinetic models were used to analyze the adsorption process. The results of the kinetic study suggest that the adsorption of MB dye matches the pseudo-second-order equation, suggesting that the adsorption process is presumably chemisorption. The adsorption process was found to be controlled by both surface and pore diffusion. Analysis of adsorption data using a Boyd kinetic plot confirmed that the external mass transfer is a rate determining step in the sorption process. A single-stage batch adsorber was designed for different CNS doses to effluent volume ratios using the Freundlich equation. The results indicated that the CNS could be used effectively to adsorb MB dye from aqueous solutions.     

Synthesis,Characterization and Biological Activity Studies on 6-<Emphasis Type="Italic">p</Emphasis>-Dimethylaminophenyl-5,6-dihydrobenzoimidazo[1,2-<Emphasis Type="Italic">c</Emphasis>]quinazoline: Crystal Structure of the Title Compound and Comparative Study with Related Derivatives

Abstract  

Reaction of o-aminophenylbenzimidazole with p-dimethylaminobenzaldehyde yielded 6-p-dimethylaminophenyl-5,6-dihydrobenzoimidazo[1,2-c]quinazoline, which was characterized by elemental analysis, IR, UV–Vis, ¹H NMR, ¹³C NMR, mass spectral studies and X-ray crystal structure analysis. Studies on the antimicrobial activity of the compound revealed that it is active against fungus Yeast but not Bacillus subtilis. The compound crystallized in the space group P2₁/n with the unit cell parameters a = 10.652(2) ?, b = 11.002(2) ?, c = 15.753(2) ?, β = 109.29(2)° and the structure was refined to an R-factor of 0.0479. The hydropyrimidine ring in the quinazoline moiety is in skew-boat conformation. The dimethylamino group attached to phenyl ring is in conjugation with it. The structure was stabilized by intermolecular C–H–N interactions. A few of the related quinazolines (6-p-hydroxyphenyl-5,6-dihydrobenzoimidazo[1,2-c]quinazoline; 6-phenyl-5,6-dihydrobenzoimidazo[1,2-c]quinazoline; 6-pyridyl-5,6-dihydrobenzoimidazo[1,2-c]quinazoline; 6-furyl-5,6-dihydrobenzoimidazo[1,2-c]quinazoline) were also examined for their biological activity, in addition to their characterization by IR, UV–Vis, ¹H and ¹³C NMR spectral studies along with structural comparison.