Thermal behavior of some new triazole derivative complexes

A series of new complexes with mixed ligands of the type [ML(C₃H₃O₂)₂]·nH₂O (((1) M=Mn, n=1; (2) M=Co(II), n=2; (3) M=Ni(II), n=4; (4) M=Cu(II), n=1.5; (5) M=Zn(II), n=0; L=3-amino-1,2,4-triazole and (C₃H₃O₂)=acrylate anion) were synthesized and characterised by chemical analysis and IR data. In all complexes the 3-amino-1,2,4-triazole acts as bridge while the acrylate acts as bidentate ligand except for complex (5) where it is found as unidentate. The thermal behaviour steps were investigated in nitrogen flow. The thermal transformations are complex processes according to TG and DTG curves including dehydration, acrylate ion and 3-amino-1,2,4-triazole degradation respectively. The final products of decomposition are the most stable metal oxides, except for complex (4) that leads to metallic copper.     

Sensitive and selective detection of alcohols via fluorescence modulation

Reported herein is the selective detection of aliphatic alcohols using cyclodextrin-promoted, proximity-induced fluorescence modulation of a high-quantum yield fluorophore. This fluorescence modulation occurred when the analyte was held in close proximity to the fluorophore via non-covalent cyclodextrin–analyte–fluorophore interactions, and led to unique modulation responses for each analyte, fluorophore and cyclodextrin investigated. These changes in fluorescence were used for the generation of an array using linear discriminant analysis that successfully generated unique pattern identifiers for 99% of the investigated analytes, and could detect alcohols at micromolar concentrations. These results represent a fundamentally new detection approach for these challenging analytes, and have significant potential in the development of novel detection schemes.     

Synthesis and Crystal Structures of Two Schiff Bases of 2-(Methylthio)aniline with Halogenated Salicylaldehydes

Abstract  

The crystal structures of the new compounds 5-bromo-N-[2-(methylthio)-phenyl]salicylaldimine (1), and 3,5-dichloro-N-[2-(methylthio)phenyl]salicylaldimine (2) were obtained by single crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic space group P2₁/c with a = 14.1479(14) ?, b = 5.3058(3) ?, c = 19.104(3) ?; β = 106.218(10)°; and Z = 4. Compound 2 crystallizes in the triclinic space group $ P\bar{1} $ P\bar{1} with a = 11.2249(10) ?, b = 13.863(2) ?, c = 13.9055(9) ?; and α = 99.378(15)°, β = 102.866(7)°, γ = 91.375(11)°; and Z = 6. Details of the synthesis, structures, and spectroscopic properties of the new compounds are discussed.     

Copper(II) ion hydrolysis in aqueous solution

A copper(II) ion-selective-electrode potentiometric method was used to determine the first and second hydrolysis constants of Cu²⁺. Special techniques prevented copper(II) hydroxide precipitation, and copper(II) carbonate and cipper(II) organic complexation during the titration of the experimental solution over the pH range 6.8–8.4. The large change in the total copper concentration during the titration due to adsorption of copper onto the vessel walls was accounted for by measuring the total copper concentration at each pH by atomic absorption spectrophotometry. The two hydrolysis constants were determined at 25°C in 0.7 and 0.05m NaClO₄ media. The measured stability constants are independent of the copper concentration and yield similar zero ionic strength values. Also, the stepwise equilibrium constants decrease as the ligand number increases.     

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.

     

Pressure-dependent Fourier transform infrared spectroscopy of a poly (ester urethane)

The effects of hydrostatic pressure upon (1) a segmented poly (ester urethane), (2) a hydrolytically degraded sample of the same polymer, and (3) models for the polyurethane and polyester segments in this polymer have been studied by Fourier transform infrared spectroscopy using high-pressure diamond anvil cells (DACs). The pressure responses of the vibrational frequencies of specific functional groups of the poly (ester urethane) in the 0-100-kbar range are compared with data for individual segment models and the partially degraded sample. The results indicated that the polymer is highly stable in this pressure regime, with no measurable degradation or phase changes. Differences in the pressure dependency of specific infrared bands between the poly (ester urethane) sample and the partially degraded sample are slight and consistent with changes in hydrogen-bonding interactions and shorter chain lengths in the degraded sample.