Tris(pentafluorophenyl)borane: a mild and efficient catalyst for the chemoselective tritylation of alcohols

An efficient acid-catalyzed protection of alcohols as trityl ethers is described using triphenylmethanol in the presence of tris(pentafluorophenyl)borane (3 mol %) in dichloromethane at room temperature. The chemoselectivity of this protocol is demonstrated by studying the tritylation of a primary alcohol in the presence of a secondary alcohol and also the mildness of this catalyst was studied with substrates containing acid labile protecting groups.     

Determination of overall kinetic constants for mediated electrochemical oxidation of phenol from CO<Subscript>2</Subscript> measurements

Mediated electrochemical oxidation is the latest achievement in environmental electrochemistry for the complete oxidation of organic pollutants. Transition or inner transition elements in an acid medium are usually employed as the mediator-electrolyte combination. The organic pollutants upon oxidation are completely converted to carbon dioxide and water. Since the oxidizing ability of the medium is so vigorous, the changes in the reactant concentrations or intermediates formed are usually difficult to analyze, but the product formed (CO₂) can be measured and quantified in most of the cases. Therefore, in MEO reactions the kinetics can be followed either by monitoring the oxidant concentration changes or by measuring the product concentrations. In real applications the oxidant is regenerated continuously in situ and, hence, the oxidant concentration is maintained throughout the system. Therefore, in continuous organic feeding reactions, the product CO₂ could be monitored and kinetics could be followed. We report in this paper a simple procedure for the calculation of the overall kinetic constants for the destruction of phenol from CO₂ measurements. The procedure is based on the summation of the difference between the total amounts of organic added to the system and reacted to obtain CO₂ evolution patterns. The CO₂ patterns were then fitted with the experimental results to obtain the overall kinetic constants. Thermodynamic parameters have been obtained for phenol destruction from the overall kinetic constants.     

Influence of the electronics of the phosphine ligands on the H-H bond elongation in dihydrogen complexes

Five new monocationic dihydrogen complexes of ruthenium of the type trans-[RuCl(eta(2)-H(2))(PP)(2)][BF(4)] (PP = bis-1,2(diarylphosphino)ethane, aryl = p-fluorobenzyl, 1a, benzyl, 2a, m-methylbenzyl, 3a, p-methylbenzyl, 4a, p-isopropylbenzyl, 5a) have been prepared by protonating the precursor hydride complexes trans-[RuCl(H)(PP)(2)] using HBF(4).OEt(2). The dihydrogen complexes are quite stable and have been isolated in the solid state. The intact nature of the H-H bond in these derivatives has been established from the short spin-lattice relaxation times (T1, ms) and observation of substantial H, D couplings in the HD isotopomers. The H-H bond distances (dHH, A) increase systematically from 0.97 to 1.03 A as the electron-donor ability of the substituent on the diphosphine ligand increases from the p-fluorobenzyl to the p-isopropylbenzyl moiety. The d(HH) in trans-[Ru(eta(2)-H(2))(Cl)((C(6)H(5)CH(2))(2)PCH(2)CH(2)P(CH(2)C(6)H(5))(2))(2)][BF(4)], 2a, was found to be 1.08(5) A by X-ray crystallography. In addition, two new 16-electron dicationic dihydrogen complexes of the type [Ru(eta(2)-H(2))(PP)(2)][OTf](2) (PP = (ArCH(2))(2)PCH(2)CH(2)P(CH(2)Ar)(2), Ar = m-CH(3)C(6)H(4-), 6a, p-CH(3)C(6)H(4)-, 7a) have also been prepared and characterized. These derivatives were found to possess elongated dihydrogen ligands.     

Electrodeposited three dimensional tin nano wire anode for thin film Li-Ion micro batteries

The tin wire grown over anodic aluminium oxide template is used as anode for Li ion batteries. This work entails porous template formation through double step electrochemical oxidation method optimized by design of experiment and Tafel polarization. The X-ray diffraction results of different anodized specimens show amorphous alumina layer formation. The pores in alumina matrix and the filamentous outward projection of Sn wires are observed from micrographs. The initial discharge capacity of Sn wire and Sn planar thin film is observed to be around 850 and 531 mA h/g respectively. The 50th cycle capacity of Sn wire is observed to be around 494 mA h/g which is very high when compared to theoretical capacity of graphite anodes.     

Experimental and computational studies of the recognition of amino acids by galactosyl-imine and -amine derivatives: an attempt to understand the lectin-carbohydrate interactions

A galactosyl-naphthyl-imine-based derivative, 1-(beta-D-galactopyranosyl-1'-deoxy-1'-iminomethyl)-2-hydroxynaphthalene (GNI), and a galactosyl-naphthyl-amine-based derivative, 1-(galactopyranosyl-1'-deoxy-1'-aminomethyl)-2-hydroxynaphthalene (GNA), possessing an ONO binding core were studied for their recognition of naturally occurring amino acids using fluorescence and absorption spectroscopy, and the corresponding association constants were derived for the complexes formed. The complexes formed between GNI/GNA and amino acids were supported by electrospray ionization mass spectrometry (ESI/MS). The structures of the complexes were optimized by computational studies using density functional theory, and stabilization energies were computed for the complexes to substantiate the interactions present between GNI/GNA and amino acid. The interactions were found to be primarily hydrogen bonding in nature. These interactions are reminiscent of those present in the lectin-carbohydrate and glycosidase substrate. Thus, the carbohydrate moiety present in GNI shows high specificity toward the -COOH group of the amino acid, which may be relevant to such interactions present between the carbohydrates and the polypeptides.     

Design and optimization of photonic crystal based eight channel dense wavelength division multiplexing demultiplexer using conjugate radiant neural network

In this paper, two dimensional photonic crystal, based eight-channel demultiplexer is proposed and designed for DWDM applications. The performance parameters of the demultiplexer such as transmission efficiency, channel spacing, spectral line width, Q factor, and crosstalk have been evaluated. The proposed demultiplexer comprises of bus waveguide, drop waveguide and parellogram resonant cavity (PRC). The bus waveguide transmits light to the PRC and exits through respective drop waveguide. The PRC consists of a parellogram resonator with a nano ring cavity that is used for dropping eight specific wavelength for ITU-T G 694.1 standard with 50 GHz channel spacing. The circular ring resonator is placed above the PRC wherein a resonant air hole (Cr) is positioned for desired channel selection. The channel selection is done by altering the radius of the air hole. In addition, a conjugate radiant neural network is implemented for optimizing the radii of resonant air holes to select the required channel wavelength. The proposed device is very compact and it could be considered for implementing the photonic integrated circuits.     

Fungal based synthesis of silver nanoparticles—An effect of temperature on the size of particles

A simple and effective approach to aqueous based biosynthesis of silver nanoparticles was demonstrated and the effect of temperature on controlling size of silver nanoparticles was studied. The morphology and uniformity of silver nanoparticles were investigated by UV–Vis spectroscopy, X-ray diffraction and HrTEM. The functional group of protein molecule was identified using FTIR. Increase in reaction temperature leads to decrease in size of silver nanoparticles and increase in monodispersity.     

Wavelength assignment for all-to-all broadcast in bidirectional WDM optical ring with limited drops

All-to-all broadcast is to disseminate a unique message from each node to every other node in a network. This problem is significant in the context of control plane design as it relates to status information dissemination. In this paper, a wavelength assignment method to reduce the number of wavelengths is proposed to establish all-to-all broadcast in a bidirectional WDM ring network. The network model is an all-optical network, in which a message from source node can be dropped (or split) only at a limited number of destination nodes along a light path due to power loss of dropping optical signals. An expression for the upper bound on the number of wavelengths required to support all-to-all broadcast is derived for certain cases of WDM ring while for other cases, an attractive algorithm is given to identify the lengths of connection sets that can be grouped together with suitable wavelength assignment strategies. Numerical results are computed to show that the results obtained are close to the lower bound.     

Investigations on the geometrical isomers of astaxanthin: Raman spectroscopy of conjugated polyene chain with electronic and mechanical confinement

Recent research interests in geometrical isomers of astaxanthin (AST) are motivated by their metabolic activities in aquatic animals and human. It has been established that cis‐isomers of AST are selectively absorbed in human plasma during the metabolic process; however, exact absorption mechanism is still unclear. Hence, a detailed investigation of the structural and optical properties of geometrical isomers of AST is required. Among the techniques available for the study of AST and other carotenoids, Raman spectroscopy has been much acclaimed. Raman spectra have been shown to be influenced by the electronic and mechanical confinement effects arising from the conjugated polyene chain of carotenoids. In this work, we present Raman studies of geometrical isomers of AST, along with their optical absorption characteristics. Geometrical isomers of AST were prepared by heating all trans‐AST in solution form, and the isomers were separated using high performance liquid chromatography. Optical absorption spectra of cis‐isomers of AST showed hypsochromic shifts in the main absorption band and formation of new bands at lower wavelengths. A detailed Raman spectral analysis performed on the cis‐isomers of AST showed new modes which have not been observed and accounted for so far. In addition, we demonstrate that the electronic and mechanical confinement effects in the polyene chain of AST play an important role in the Raman spectra of geometrical isomers of AST. It is anticipated that this work will demonstrate that Raman spectroscopy is an important diagnostic tool in distinguishing and identifying the geometrical isomers of AST. Copyright © 2014 John Wiley & Sons, Ltd.