Ion-exchange properties and electrochemical characterization of quaternary ammonium-functionalized silica microspheres obtained by the surfactant template route

Porous silica spheres functionalized with quaternary ammonium groups have been prepared by co-condensation of N-((trimethoxysilyl)propyl)-N,N,N-trimethylammonium chloride (TMTMAC) and tetraethoxysilane (TEOS) in the presence of cetyltrimethylammonium as a template and ammonia as a catalyst. The physicochemical characteristics of the resulting ion exchangers have been analyzed by various techniques and discussed with respect to the amount of organofunctional groups in the materials. For comparison purposes, both an ordered MCM-41 type mesoporous silica and two silica gels of different pore size have been grafted with TMTMAC. The ion-exchange capabilities were first evaluated from batch experiments (determination of anion-exchange capacities) and then by ion-exchange voltammetry at carbon paste electrodes modified with these hybrid materials. Effective concentration of Fe(CN)(6)(3)(-) species in the anion exchangers was pointed out, while no significant accumulation of Ru(NH(3))(6)(3+) was observed. The preconcentration efficiency was discussed on the basis of the organic group content in the materials as well as their structure and porosity. A second series of materials displaying zwitterionic surfaces was finally prepared and characterized with respect to their physicochemical properties and ion-exchange voltammetric behavior. They consisted of sulfonic acid-functionalized mesoporous silica samples resulting from the oxidation of thiol-functionalized silica spheres obtained by co-condensation of mercaptopropyl-trimethoxysilane (MPTMS) and TEOS, which were then grafted with TMTMAC at various functionalization levels. Possible interactions between the ammonium and sulfonate moieties in the confined medium were pointed out from X-ray photoelectron spectroscopy. The competitive accumulation-rejection of Fe(CN)(6)(3)(-) and Ru(NH(3))(6)(3+) redox probes was finally studied by cyclic voltammetry.     

Spectroscopic Studies on TiO<Subscript>2</Subscript> Enhanced Binding of Hypocrellin B with DNA

The binding of Hypocrellin B-TiO₂ chelate with DNA has been studied by using absorption, steady state fluorescence, cyclic voltammetry, time resolved fluorescence and laser flash photolysis measurements. The experimental results show that the presence of TiO₂ nanoparticles increases the binding of Hypocrellin B with DNA. The groove binding mode is confirmed by spectroscopic and docking studies. Laser flash photolysis studies confirm the presence of electrons in the conduction band of TiO₂ which will produce active oxygen species and results in damage of DNA indicating the potential application of Hypocrellin B-TiO₂ chelate in the field of photodynamic therapy (PDT).     

Investigation of the upper rim binding of triphenylpyrylium cation with p-sulfonatocalix[4]arene

The interaction of 2,4,6-triphenylpyrylium cation with p-sulfonatocalix[4]arene is studied using absorption, emission, NMR and electrochemical techniques. The increase in the absorption is observed with the increase in the concentration of p-sulfonatocalix[4]arene. The emission intensity of 2,4,6-triphenylpyrylium cation is also enhanced in the presence of p-sulfonatocalix[4]arene. The electrochemical titration reveals the presence of host–guest interaction. The NMR analysis explains the upper rim interaction of 2,4,6-triphenypyrylium cation with p-sulfonatocalix[4]arene. The mode of binding is studied using computational methods. The quantum chemical simulations reveal the binding orientation of cationic TPP with p-SC4. The calculated complexation energy (??33.19 kcal mol^?1) indicates the strong binding nature of 2,4,6-triphenylpyrylium cation with p-sulfonatocalix[4]arene.     

Interfacial dilatational elasticity and viscosity of beta-lactoglobulin at air-water interface using pulsating bubble tensiometry

The ability of proteins to provide stability in foams is greatly influenced by their interfacial dilatational rheological properties. Surface tension response of a pulsatingbubble with an adsorbed layer of beta-lactoglobulin was measured for different frequencies and protein concentrations using a pulsating bubble tensiometer. A methodology, accounting for adsorption/desorption as well as variation of surface concentration due to expansion/contraction, was developed for the evaluation of surface dilatational elasticity and viscosity at different frequencies from these measurements. The adsorption rate constants were inferred from the surface pressure dynamics of protein adsorption using a Langmuir minitrough. The desorption rates were shown to be negligible for beta-lactoglobulin from the surface pressure response of a spread monolayer when subjected to compression in a Langmuir minitrough. The proposed model was employed to infer the interfacial dilatational viscosity and elasticity of an adsorbed beta-lactoglobulin layer at the air-water interface from experimental pulsating bubble data for protein concentrations in the range of 0.01-0.5 wt % at pH 7. As expected, the interfacial dilatational rheological properties were found to be higher at higher protein concentrations, this effect being less pronounced for dilatational elasticity. Heating at 80 degrees C for 30 min was found to result in higher interfacial dilatational viscosity and lower interfacial dilatational elasticity though this difference was within experimental error. The traditional approach for the inference of interfacial dilatational rheological properties is found to overpredict the interfacial dilatational elasticity whereas the viscosity values do not differ significantly from those obtained using the current analysis.     

Synthesis,characterization and spectral studies of various newer 4‐benzyloxy‐1H‐indole‐2‐carboxylic acid (arylidene)‐hydrazides

4‐Benzyloxyindole‐2‐carboxylic acid hydrazide reacts with aromatic and heterocyclic aldehydes in alcoholic medium in refluxing conditions to give 4‐benzyloxy‐1H‐indole‐2‐carboxylic acid (arylidene)‐hydrazides, important synthetic intermediates for the synthesis of a newer class of pharmacologically active compounds. We describe here the synthesis of various 4‐benzyloxy‐1H‐indole‐2‐carboxylic acid (arylidene)‐hydrazides by conventional as well as microwave irradiation techniques. The structures of these compounds have been confirmed by spectroscopic techniques (FTIR, NMR and MS). Some of the interesting features of the electron impact mass spectral fragmentation pattern of these compounds are also discussed.     

Di- and tri-nuclear molybdenum-palladium complexes bearing strong π-acceptor “P-N-P” ligands, MeN{P(OR)2}2 (R = CH2CF3 or Ph)

The dipalladium complexes, [PdCl(μ-MeN{P(OR)₂}₂)]₂ (R = CH₂CF₃, 1a; Ph, 1b) react with [Mo₂(η⁵-C₅H₅)₂(CO)₆] in boiling benzene to afford the molybdenum-palladium heterometallic complexes, [(η⁵-C₅H₅)(CO)Mo(μ-MeN{P(OR)₂}₂)₂PdCl] (R = CH₂CF₃, 3a; Ph, 3b), [(η⁵-C₅H₅)Mo(μ₃-CO)₂(μ-MeN{P(OR)₂}₂)₂Pd₂Cl], (R = CH₂CF₃, 5a; Ph, 5b), [(η⁵-C₅H₅)(Cl)Mo(μ₂-CO)(μ₂-Cl)(μ-MeN{P(OR)₂}₂)PdCl], (R = CH₂CF₃, 6a; Ph, 6b) and also the mononuclear complex [Mo(CO)Cl(η⁵-C₅H₅)(κ²-MeN{P(OR)₂}₂)], (R = Ph, 4b). These complexes have been separated by column chromatography and are characterised by elemental analysis, IR, ¹H, ³¹P{¹H} NMR data. The structures of 1a, 3a, 4b, 5b and 6a have been confirmed by single crystal X-ray diffraction. The CO ligands in 5b and 6a adopt a semi-bridging mode of bonding; the Mo-CO distances (1.95-1.97 Å) are shorter than the Pd-CO distances (2.40-2.48 Å). The Pd-Mo distances fall in the range, 2.63-2.86 Å. The reaction of [Mo₂(η⁵-C₅H₅)₂(CO)₆] with MeN{P(OPh)₂}₂ in toluene gives [Mo₂(CO)₄(η⁵-C₅H₅)₂(κ¹-MeN{P(OPh)₂}₂)₂] (2) in which the diphosphazane acts as a monodentate ligand.     

Instabilities in block copolymer films induced by compressible solvents

We combine a simple lattice-gas model for fluid mixtures along with polymer mean-field theory for block copolymer melts to study the stability of thin films of diblock copolymers in the presence of compressible fluid solvents. Using a free energy analysis, the stable and unstable thicknesses of a copolymer thin film are obtained for given solvent conditions. Our results suggest that the interplay between confinement, the compressibility of the solvent, and its selectivity to polymer component can lead to significant changes on the ordering and stability of the diblock copolymer thin films. Our results are in qualitative agreement with recent experimental results.     

Controlling the solid-state luminescence of gold(I) N-heterocyclic carbene complexes through changes in the structure of molecular aggregates

Thermally stable, solid-state luminescent organic materials are highly desired for the development of practical applications.Herein we synthesized new gold(I) complexes with N-heterocyclic carbene ligands, which have the ability to form strong metalorganic bond. Consequently, their thermochemical stability is enhanced at temperatures around 300 °C. Precise design of the molecular structure of the ligands, with a focus on ensuring low steric hindrance around Au atoms in order to limit disturbances to Au/Au interactions, provided a complex with a densely packed crystal with a shorter intermolecular Au–Au distance(3.17 ?)than the typical distance. In the solid state, this complex exhibited strong aurophilic interactions, which generated intense phosphorescence even in air at room temperature(quantum yield=16%) in spite of absence of any phosphorescence in solution.This behavior is characteristic for solid-state luminescence referred to as aggregation-controlled emission. Furthermore, the gold(I) complex displays capacity for mechano-and vapo-chromism—that is, the ability to change color reversibly in response to the application of external stimuli. We believe that the proposed design framework, which involves controlling thermal stability and luminescence property separately, provides a new opportunity for the development of practical applications using solid-state luminescent organic molecules.     

Antioxidant activity of phenolic compounds from extracts of Eucalyptus globulus and Melaleuca styphelioides and their protective role on D-glucose-induced hyperglycemic stress and oxalate stress in NRK-49Fcells

Phytochemicals serve as potential therapeutic agents for the prevention and treatment of diseases. In this study, we elucidate the renoprotective activity of compounds isolated from Eucalyptus globulus and Melaleuca styphelioides extracts in glucose- and oxalate-challenged NRK-49F cell model. The antioxidant potential of isolated compounds was evaluated based on their effect on antioxidant enzyme activities and lipid peroxidation levels. The results demonstrated that exposure of NRK-49F cells to glucose and oxalate stress augmented cell damage and attenuated antioxidant enzyme activities. The phytochemicals 2,2,8-trimethyl-6-formyl-chrom-3-ene-7-O-β-D-glucopyranoside, Cornusiin B and tellimagrandin I treatment restored antioxidant enzyme activity, significantly lowered lipid peroxidation levels and effectively protected cells from glucose and oxalate stress equivalent to the known antioxidant, N-acetyl cysteine. Pterocarinin A significantly reversed cellular damage owing to glucose stress. In conclusion, the compounds isolated from E. globulus and M. styphelioides showed potential cytoprotective and anti-oxidative property against glucose- and oxalate-induced oxidative stress in NRK-49F cells.     

Cobalt‐Catalyzed Cyclization of N‐Methoxy Benzamides with Alkynes using an Internal Oxidant through C−H/N−O Bond Activation

The cyclization of substituted N‐methoxy benzamides with alkynes in the presence of an easily affordable cobalt complex and NaOAc provides isoquinolone derivatives in good to excellent yields. The cyclization reaction is compatible with a range of functional group‐substituted benzamides, as well as ester‐ and alcohol‐substituted alkynes. The cobalt complex [Co^IIICp*(OR)₂] (R=Me or Ac) serves as an efficient catalyst for the cyclization reaction. Later, isoquinolone derivatives were converted into 1‐chloro and 1‐bromo substituted isoquinoline derivatives in excellent yields in the presence of POCl₃ or PBr₃.