Thermal behavior of Ni,Co and Fe succinates embedded in silica matrix

This paper presents the thermal behavior of Co, Ni and Fe succinates obtained by sol-gel synthesis using Co(II), Ni(II) and Fe(III) nitrates, 1,4-butanediol and tetraethyl orthosilicate as reactants. The thermal analysis revealed the formation of succinates at 413–453 K and their decomposition to ferrites at 503–623 K. The rate constants for the decomposition of succinates to ferrites, calculated using the isotherms at 473, 523, 573 and 623 K, were used to determine the activation energy of each ferrite (NiFe₂O₄, Ni_0.3Co_0.7Fe₂O₄, Ni_0.7Co_0.3Fe₂O₄ and CoFe₂O₄) embedded in the silica matrix. By increasing the Ni content in the mixed Ni–Co ferrites, the activation energy decreases from 13.530 to 1.944 kJ mol^?1. The formation and decomposition of succinate precursors and the formation of silica matrix were confirmed by FT-IR spectroscopy, while the formation of CoFe₂O₄ and NiFe₂O₄ single-phases embedded in the silica matrix was confirmed by X-ray diffraction analysis. The nanocrystallites size decreases from 31.7 (CoFe₂O₄) to 18.5 nm (NiFe₂O₄). The optical band gap of mixed Co–Ni ferrites was significantly higher than that corresponding to CoFe₂O₄. The photocatalytic activity of the samples was evaluated against Rhodamine B under visible light. All the samples have photocatalytic activities, the best performance being obtained in the case of Ni_0.7Co_0.3Fe₂O₄.

     

Efficient Detection of Phthalate Esters in Human Saliva via Fluorescence Spectroscopy

The detection of phthalates in human biologic fluids remains an important research objective because it provides an important measure of an individual’s exposure to this class of compounds, which have known deleterious health effects. Moreover, the ability to accomplish such detection in fluids that are easy to collect, such as saliva and urine, provides additional practical advantages. Reported herein is the application of cyclodextrin-promoted fluorescence energy transfer and fluorescence modulation to accomplish precisely such detection: the development of sensitive and selective florescence-based detection methods for phthalates in saliva, an easily collectable human biologic fluid. Such saliva-based detection methods occur with high levels of selectivity (100% differentiation) and sensitivity (limits of detection as low as 0.089?µM), and provide significant potential in the development of practical phthalate detection devices.     

Colloidally Stable CdS Quantum Dots in Water with Electrostatically Stabilized Weak-Binding,Sulfur-Free Ligands

Colloidal quantum dot (QD) photocatalysts have the electrochemical and optical properties to be highly effective for a range of redox reactions. QDs are proven photo-redox catalysts for a variety of reactions in organic solvents but are less prominent for aqueous reactions. Aqueous QD photocatalysts require hydrophilic ligand shells that provide long-term colloidal stability but are not so tight-binding as to prevent catalytic substrates from accessing the QD surface. Common thiolate ligands, which also poison many co-catalysts and undergo photo-oxidative desorption, are therefore often not an option. This paper describes a framework for the design of water-solubilizing ligands that are in dynamic exchange on and off the QD surface, but still provide long-term colloidal stability to CdS QDs. The binding affinity and inter-ligand electrostatic interactions of a bifunctional ligand, aminoethyl phosphonic acid (AEP), are tuned with the pH of the dispersion. The key to colloidal stability is electrostatic stabilization of the monolayer. This work demonstrates a means of mimicking the stabilizing power of a thiolate-bound ligand with a zwitterionic tail group, but without the thiolate binding group.     

ZnCl2-mediated stereoselective addition of terminal alkynes to D-(+)-mannofuranosyl nitrones

[reaction: see text] An optimized process for the addition of terminal alkynes to chiral nitrones using ZnCl2 and NEt3 in toluene is reported. The new reaction protocol is facile to perform and cost-effective. The resulting optically active propargyl N-hydroxylamines are isolated in good to excellent yield and high diastereoselectivity.     

Ultrafast dynamics of shock compression of molecular monolayers

Femtosecond laser-driven approximately 1 GPa shock waves are used to compress monolayers of hydrocarbon chains. Vibrational sum-frequency generation spectroscopy probes the orientation of the terminal methyl groups. With an odd number (15) of carbon atoms, shock compression is an elastic process that causes the methyl groups to tilt. With an even number (18) of carbon atoms, shock compression is viscoelastic, creating single and double gauche defects. When the shock unloads, single gauche defects remain while double defects relax in 30 ps to single-defect states with more upright methyl groups.     

Using hydrogen bonds to direct the assembly of crowded aromatics

This Minireview details the design, synthesis, and self-assembly of a new class of crowded aromatics that form columnar superstructures. The assembly of these subunits produces helical and polar stacks, whose assembly can be directed with electric fields. In concentrated solutions, these self-assembled helical rods exhibit superhelical arrangements that reflect circularly polarized light at visible wavelengths. Depending on the side chains employed, spin-cast films yield either polar monolayers or isolated strands of molecules that can be visualized with scanning probe microscopy. Also detailed herein are methods to link these mesogens together to produce monodisperse oligomers that fold into defined secondary conformations.     

Activation of muscarinic acetylcholine receptors elicits pigment granule dispersion in retinal pigment epithelium isolated from bluegill

Background

In fish, melanin pigment granules in the retinal pigment epithelium disperse into apical projections as part of the suite of responses the eye makes to bright light conditions. This pigment granule dispersion serves to reduce photobleaching and occurs in response to neurochemicals secreted by the retina. Previous work has shown that acetylcholine may be involved in inducing light-adaptive pigment dispersion. Acetylcholine receptors are of two main types, nicotinic and muscarinic. Muscarinic receptors are in the G-protein coupled receptor superfamily, and five different muscarinic receptors have been molecularly cloned in human. These receptors are coupled to adenylyl cyclase, calcium mobilization and ion channel activation. To determine the receptor pathway involved in eliciting pigment granule migration, we isolated retinal pigment epithelium from bluegill and subjected it to a battery of cholinergic agents.

Results

The general cholinergic agonist carbachol induces pigment granule dispersion in isolated retinal pigment epithelium. Carbachol-induced pigment granule dispersion is blocked by the muscarinic antagonist atropine, by the M₁ antagonist pirenzepine, and by the M₃ antagonist 4-DAMP. Pigment granule dispersion was also induced by the M₁ agonist 4-[N-(4-chlorophenyl) carbamoyloxy]-4-pent-2-ammonium iodide. In contrast the M₂ antagonist AF-DX 116 and the M₄ antagonist tropicamide failed to block carbachol-induced dispersion, and the M₂ agonist arecaidine but-2-ynyl ester tosylate failed to elicit dispersion.

Conclusions

Our results suggest that carbachol-mediated pigment granule dispersion occurs through the activation of M_odd muscarinic receptors, which in other systems couple to phosphoinositide hydrolysis and elevation of intracellular calcium. This conclusion must be corroborated by molecular studies, but suggests Ca²⁺-dependent pathways may be involved in light-adaptive pigment dispersion.

     

Transient rheology of discotic mesophases

This paper presents an analysis of the role of orientation on the rheology of discotic mesophases subjected to slow shear start-up flows, using a projection of the Landau-de Gennes equations of nematodynamics. Analysis of the shear stress surface as a function of tilt and twist orientation with respect to the shear plane shows that the stress surface is dense in well-oriented and periodically located sets of maxima and minima. Thus overshoots and undershoot stress responses to shear-start up are predicted to be the rule rather than the exception. In-plane (within the shear plane) shear start-up stress responses can exhibit multiple, single, or no overshoots, depending on the number of maxima traversed on the way to steady state. Responses originating from orientations close to the vorticity axis lead to stress undershoots. Complex stress responses, such as a weak overshoot-strong undershoot sequence, are found for intermediate tilt-twist initial states. In-plane modes lead to amplitude and strain scaling. Out-of-plane modes do not display amplitude or strain scaling. These results provide will be useful to interpret and use transient shear rheological data of carbonaceous mesophases and highly filled suspensions of disc-like particles.