Synthesis of highly stable silver nanoparticles by photoreduction and their size fractionation by phase transfer method

In this report we demonstrate a green chemical approach for the synthesis of stable silver nanoparticles in aqueous medium using tyrosine as an efficient photoreducing agent. A narrow size distribution of silver nanoparticles can be achieved by this simple photoirradiation method without using any additional stabilizing agents or surfactants. Two different irradiation sources have been explored resulting in a different particle size distribution pattern in each case. Further, we show that starting from a polydisperse tyrosine synthesized silver nanoparticles sample, it is also possible to fractionate them into different size ranges. The size fractionation was achieved by a 2 stage phase transfer method employing different organic solvents. The nanoparticles synthesized were characterized using UV-vis spectroscopy, Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques.     

Achiral banana-shaped mesogenic bidentate ligands and their Cu(II) and Pd(II) complexes

The first achiral bent-core banana-shaped bidentate ligands and their Cu(II) and Pd(II) metal complexes have been synthesized and investigated for mesomorphic behaviour. The bidentate ligands exhibit only one enantiotropic mesophase. The ligand having C6 -alkoxy chains shows a mesophase that has been assigned as a two-dimensional B1 phase while the C8 and C10 homologues stabilize the fluid B2 mesophase showing antiferroelectric switching characteristics. In constrast, their corresponding Cu(II) and Pd(II) metal complexes are non-mesomorphic.     

Light-Front BRST Quantization of the Vector Schwinger Model with a Photon Mass Term

Vector Schwinger model with a mass term for the photon, describing 2D electrodynamics with mass-less fermions, studied by us recently (UK, Mod. Phys. Lett A22, 2993 (2007), PoS LC2008, 008 (2008), UK and DSK, Int. J. Mod. Phys. A22, 6183 (2007), UK, Mod. Phys. Lett A27, 1250157 (2012)), represents a new class of models. This theory becomes gauge-invariant when studied on the light-front. This is in contrast to the instant-form theory which is gauge-non-invariant. The light-front Hamiltonian and path integral quantization of this theory has been studied recently by one of us (UK, Mod. Phys. Lett. A27 (No. 27) 1250157 (2012)). In the present work we study the light-front Becchi-Rouet-Stora and Tyutin (BRST) quantization of this theory under appropriate light-cone BRST gauge-fixing. Here the BRST (gauge) symmetry of the theory is maintained even under BRST-gauge-fixing which is in contrast to its Hamiltonian and path integral quantization where the gauge symmetry of the theory necessarily gets broken under gauge-fixing.     

Thermal decomposition characteristics of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide-tri n-butyl phosphate–nitric acid systems

Thermal stability of neat octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OΦD[IB]CMPO) and TRUEX solvent composition (0.2M OΦD[IB]CMPO-1.2M tri n-butyl phosphate-in n-dodecane) in the presence and absence of nitric acid has been studied in ambient air in a closed vessel, employing an adiabatic calorimeter. Enthalpies and kinetic parameters for the decomposition reaction were derived wherever possible and are reported for the first time. Neat OΦD[IB]CMPO was found to be thermally stable up to 633 K and exhibited an exothermic decomposition later. It decomposed at lower temperatures (376–386 K) depending on the nitric acid concentration. The exothermic rise in temperature and pressure increased exponentially, while activation energies exhibited exponential decrease for the decomposition reactions with increase in nitric acid content. TRUEX solvent was found to be stable up to 661 K in the absence of nitric acid while in the presence of 8 and 4M HNO₃, it decomposed between 387 and 413 K. All these samples on decomposition formed incompressible gases and viscous black liquids. The results also indicate that the neat OΦD[IB]CMPO and the TRUEX solvent are thermally more stable than neat tri n-butyl phosphate (TBP), PUREX solvent (1.1M TBP/n-DD), neat diamyl amyl phosphonate (DAAP) and 1.1M DAAP/n-DD, triisoamyl phosphate (TiAP) and 1.1M TiAP/n-DD.     

High carrier density and capacitance in TiO2 nanotube arrays induced by electrochemical doping

The paper describes the electronic charging and conducting properties of vertically oriented TiO 2 nanotube arrays formed by anodization of Ti foil samples. The resulting films, composed of vertically oriented nanotubes approximately 10 mum long, wall thickness 22 nm, and pore diameter 56 nm, are analyzed using impedance spectroscopy and cyclic voltammetry. Depending on the electrochemical conditions two rather different electronic behaviors are observed. Nanotube array samples in basic medium show behavior analogous to that of nanoparticulate TiO 2 films used in dye-sensitized solar cells: a chemical capacitance and electronic conductivity that increase exponentially with bias potential indicating a displacement of the Fermi level. Nanotube array samples in acidic medium, or samples in a basic medium submitted to a strong negative bias, exhibit a large increase in capacitance and conductivity indicating Fermi level pinning. The contrasting behaviors are ascribed to proton intercalation of the TiO 2. Our results suggest a route for controlling the electronic properties of the ordered metal-oxide nanostructures for their use in applications including supercapacitors, dye-sensitized solar cells, and gas sensing.     

Recipe for new diorganostannates, [R2Sn(OS(O)2R1)4]2-, bearing alkanesulfonate groups using dialkyl sulfite as the reagent

A one-pot reaction between di-n-propyl/di-n-butyltin oxide, dialkyl sulfite, and triethylamine or tetra-n-alkylammonium iodide proceeds under ambient conditions (110-120 degrees C, 20 h) via sulfur-centered Arbuzov rearrangement to afford the corresponding dianionic tetraalkanesulfonato diorganostannates [R2Sn(OSO2Me)4].2Et3NMe [R = n-Pr (1), n-Bu (2)] as well as [n-Bu(2)Sn(OSO(2)R(1))(4)].(2)R(2)(4)N [R(1) = Me, Et, n-Pr; R(2) = Et (3, 5, and 7), n-Bu (4, 6, and 8)]. X-ray crystal structures of 2 and 3 reveal a monomeric motif of the dianion, with methanesulfonate groups acting as unidentate ligands. The (119)Sn NMR spectral studies suggest the existence of pentacoordinated tin species in solution.     

Selective Functionalisation of 5-Methylcytosine by Organic Photoredox Catalysis

The epigenetic modification 5-methylcytosine plays a vital role in development, cell specific gene expression and disease states. The selective chemical modification of the 5-methylcytosine methyl group is challenging. Currently, no such chemistry exists. Direct functionalisation of 5-methylcytosine would improve the detection and study of this epigenetic feature. We report a xanthone-photosensitised process that introduces a 4-pyridine modification at a C(sp³)−H bond in the methyl group of 5-methylcytosine. We propose a reaction mechanism for this type of reaction based on density functional calculations and apply transition state analysis to rationalise differences in observed reaction efficiencies between cyanopyridine derivatives. The reaction is initiated by single electron oxidation of 5-methylcytosine followed by deprotonation to generate the methyl group radical. Cross coupling of the methyl radical with 4-cyanopyridine installs a 4-pyridine label at 5-methylcytosine. We demonstrate use of the pyridination reaction to enrich 5-methylcytosine-containing ribonucleic acid.     

Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13C NMR Spectroscopy

Mesogens that vary in shape anisometry have been investigated by ¹³C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (S_zz) values for the phenyl rings of the rod-like mesogen are 0.65–0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit phenyl rings, S_zz is ~0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the S_zz value for the side arm phenyl rings is ~0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of S_zz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of λ shape is proposed in the liquid crystalline phase.     

Simultaneous quantification of (E) and (Z) isomers of rilpivirine and four degradation products in bulk and tablets by reversed-phase ultra-high-performance liquid chromatography and confirmation of all by molecular weight

The (E)-isomer of rilpivirine is an approved antiretroviral drug used to treat human immunodeficiency virus. A simple, fast, accurate, and precise analytical method is required to confirm the quality, purity, efficacy, and safety of drug substances and drug products containing rilpivirine. This research article offers a comprehensive ultra-high performance liquid chromatography method for the simultaneous separation and quantification of (E) and (Z) isomers of rilpivirine, including two amide impurities, one nitrile impurity, and one dimer impurity, in both bulk and tablet forms. After complete validation, the proposed reversed-phase ultra-high-performance liquid chromatography method has proven to be simple, fast, linear, accurate, and precise, with a lower limit of quantification and detection of 0.05 and 0.03 μg/ml, respectively, for all six analytes. Separation was achieved on a Waters Acquity ethylene bridged hybrid Shield RP18 (150 × 2.1 mm, 1.7 μm) column maintained at 35.0°C using a gradient elution of acetonitrile and 0.05% formic acid in 10 mM ammonium formate at a flow rate of 0.30 ml/min. A systematic forced degradation study on the undissolved rilpivirine revealed the formation of acid-base hydrolyzed amide impurities (Impurity-A and Impurity-B), oxidative nitrile impurities (Impurity-C), and Z-isomer and dimer impurities of rilpivirine (Impurity-D and Impurity-E) due to alkaline hydrolysis and photodegradation. The proposed method is primarily appropriate for applications requiring the precise determination of desired and undesired isomers of rilpivirine and its degradation products, such as those involving the safety, efficacy, and quality roles of rilpivirine in bulk and tablet forms. Additionally, the proposed ultra-high-performance liquid chromatography method in combination with a mass spectrometer and photo-diode array detector is helpful for the confirmation and correct identification of all analytes.     

Equilibrium structure and dynamics of (2R, 3R)-(+)-bis(decyloxy)succinic acid at the air-water interface

A twin-tailed, twin-chiral fatty acid, (2R,3R)-(+)-bis(decyloxy)succinic acid was synthesized and its two dimensional behavior at the air-water interface was examined. The pH of the subphase had a profound effect on the monolayer formation. On acidic subphase, stable monolayers with increased area per molecule due to hydrogen bonding and bilayers at collapse pressures were observed. Highly compressible films were formed at 40 degrees C, while stable monolayers with increased area were observed at sub-room temperatures. Langmuir monolayers formed on subphases containing 1 mM ZnCl2 and CaCl2 revealed two dimensional metal complex formation with Zn2+ forming a chelate-type complex, while Ca2+ formed an ionic-type complex. Monolayers transferred from the condensed phase onto hydrophilic Si(100) and quartz substrates revealed the formation of bilayers through transfer-induced monolayer buckling. Compression induced crystallites in 2D from monolayers and vesicle-like supramolecular structures from multilayers were the noted LB film characteristics, adopting optical imaging and electron microscopy. The interfacial monolayer structure studied through molecular dynamics simulation revealed the order and packing at a molecular level; monolayers adsorbed at various simulated specific areas of the molecule corroborated the (pi-A) isotherm and the formation of a hexagonal lattice at the air-water interface.