Effect of pH and α-, β- and γ-cyclodextrin on the spectral properties of etoricoxib: spectroscopic and molecular dynamics study

The spectral properties of etoricoxib (ETR) at pH 2.0, 6.0 and 10.0 in the presence of cyclodextrins (CDs) were investigated. The absorption spectrum of ETR in acidic medium exhibited two bands centered at 236 and 273 nm, while in basic medium it exhibited two bands centered at 236 and 285 nm. No change in the spectrum was observed in the presence of CDs. The fluorescence emission spectra of ETR in acidic and basic media exhibited one band at 380 nm and another one at 484 nm. The emission band at 484 nm was enhanced when ETR was complexed with β-CD and γ-CD at pH 2.0, 6.0 and 10.0, while the band at 380 nm was enhanced selectively when ETR was complexed with α-CD at pH 2.0. Molecular dynamics simulations computations revealed that at pH 2.0, the sulfonyl moiety of H₂ETR²⁺ is preferentially included within the α-CD cavity, which is believed to cause the enhancement of the band at 380 nm. Moreover, at pH 6.0 and 10.0, the enhancement of the band at 484 nm was related to the inclusion of the chloropyridinyl and methylpyridinyl groups of the bipyridine moiety of HETR⁺ and ETR within β-CD and γ-CD cavities. Benesi–Hildebrand analysis showed that the ETR/β-CD complex adopts a 1:1 stoichiometry with association constant of K ₁₁?=?64.8 at pH 2.0, K ₁₁?=?105.4 at pH 6.0 and K ₁₁?=?520.5 at pH 10.0.     

Ultrasound-accelerated aromatisation of trans- and cis-pyrazolines under heterogeneous conditions using claycop

A simple, efficient and eco-friendly procedure has been developed for the aromatisation of various pyrazolines in heterogeneous media using clay-supported copper(II) nitrate (claycop) under ultrasound activation. The reaction rate enhancement and the sonication effect are discussed.     

New salts of graphite,C12+HF2− & C24+SiF5− and the treshold for the oxidative intercalation of graphite

Third row transition metal hexafluorides (MF₆) for which the electron affinity exceeds 130 kcal/mole (M = Os, Ir, Pt) have been found to intercalate graphite with electron oxidation of the host lattice, whereas those with inferior electron affinities (M = W, Re) do not intercalate¹. This behavior can be rationalized on kinetic or thermodynamic grounds; arguing for the latter, a simple Born-Haber cycle may be used which suggests an electron affinity threshold of 120–130 kcal/mole for the MF₆ intercalation reaction. For the general case of intercalation reactions by metal fluorides (with or without added fluorine), wherein the graphite lattice is oxidized, the threshold is determined by the free energy of the half-reaction which produces the intercalating fluoro-anion. The lattice energy of the graphite salt must also be taken into account when comparing free energy thresholds for large (e.g., MF₆) and small (e.g. HF₂^?) intercalating species.We have evaluated the free energy of formation of a number of fluoro-anions from the heats of formation and lattice energies of salts which contain them. These studies indicate a threshold free energy of ca. 110 kcal/mole for graphite intercalation. Two ‘borderline’ second stage compounds, C₂₄⁺SiF₅^? and C₁₂⁺HF₂^?, have been synthesized.     

Individual single-walled nanotubes and hydrogels made by oxidative exfoliation of carbon nanotube ropes

Single-walled carbon nanotubes were oxidized by a technique previously developed for the oxidation of graphite to graphite oxide (GO). This process involves treatment with concentrated H(2)SO(4) containing (NH(4))(2)S(2)O(8) and P(2)O(5), followed by H(2)SO(4) and KMnO(4). Oxidation results in complete exfoliation of nanotube ropes to yield individual oxidized tubes that are 40-500 nm long. The C:O:H atomic ratio of vacuum-dried oxidized nanotubes is approximately 2.7:1.0:1.2. XPS and IR spectra show evidence for surface O-H, C=O, and COOH groups. The oxidized nanotubes slowly form viscous hydrogels at unusually low concentration (>or=0.3 wt %), and this behavior is attributed to the formation of a hydrogen-bonded nanotube network. The oxidized tubes bind readily to amine-coated surfaces, on which they adsorb as smooth and dense monolayer films. Thin films of the oxidized nanotubes show ohmic current-voltage behavior, with resistivities in the range of 0.2-0.5 Omega-cm.     

Nanowires as building blocks for self-assembling logic and memory circuits

The concept of assembling electronic circuits from metal nanowires is discussed. These nanowires are synthesised electrochemically by using porous membranes as templates. High aspect ratio wires, which range from 15 to 350 nm in diameter and contain "stripes" of different metals, semiconductors, colloid/polymer multilayers, and self-assembling monolayers have been made by this technique. By using the distinct surface chemistry of different stripes, the nanowires can be selectively derivatized and positioned on patterned surfaces. This allows the current-voltage properties of single and crossed nanowire devices to be measured. Nanowire conductors, rectifiers, switches, and photoconductors have been characterized. Techniques are still being developed for assembling sublithographic scale nanowires into cross-point arrays for memory and logic applications.     

Motility of catalytic nanoparticles through self-generated forces

Small-scale synthetic motors capable of generating their own motive forces by exploiting the chemical free energy of their environment represent an important step in developing practical nanomachines. Catalytic particles are capable of generating concentration and other gradients that can be used to self-propel small objects. However, the autonomous movement of catalytic nanoparticles by self-generated forces is a relatively unexplored area in colloid and interfacial chemistry. This paper explores the potential of catalytically self-generated forces for propulsion of small objects through fluids.     

A high-throughput optical screening method for the optimization of colloidal water oxidation catalysts

A high-throughput method has been developed for screening and optimization of colloidal water oxidation catalysts. The catalysts are irradiated in parallel by visible light from an overhead projector in solutions containing tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) and persulfate. The array of reaction solutions is held in a 96-well plate, and absorbance readings are taken intermittently using a bioassay plate reader. The absorbance at 430 nm is indicative of the amount of Ru(bpy)(3)(2+) remaining in solution. The best catalysts give the most persistent absorbance, because the oxygen evolution reaction is kinetically competitive with decomposition of Ru(bpy)(3)(3+). Reagent concentrations were varied using a factorial design-of-experiment approach in order to optimize reaction conditions for a IrO(2).xH(2)O colloidal catalyst. A higher colloid concentration, a lower Ru(bpy)(3)(2+) concentration, and a higher pH buffer doubled the number of turnovers relative to the original conditions. Metal oxide colloids consisting of IrO(2).xH(2)O doped with varying amounts of Pt, Ru, and Os were made using a parallel microwave synthesis technique and were tested both by the parallel screening method and by direct measurement of oxygen evolution. The correlation between the two methods was good, with Ir-Pt-Os oxide compositions showing the highest activity. The effect of adding small amounts of Pt and Os to IrO(2).xH(2)O appears to be predominantly to reduce the particle size of the colloids.     

Photosensitized production of doubly reduced methylviologen followed by highly efficient methylviologen radical formation using self-assembling ruthenium(II) complexes

Supramolecular fibers of Ru(II) complexes act as efficient photosensitizers, photochemically generating methylviologen radical (MV.+) and then converting it quantitatively to doubly reduced methylviologen, (MV0), in the presence of triethanolamine.