Lifetime measurements of SO2 below the Clement's A-band

High resolution laser induced fluorescence spectrum of jet-cooled SO(2) is recorded toward the blue side of the Clement's A-Band in the region of 314-319 nm. Time resolved fluorescence measurements have been carried out for all the prominent peaks in this region. Most of the peaks exhibited double exponential decay profiles. Some of the rovibronic bands exhibited quantum beats with strong quantum beats observed at 315.261 and 315.271 nm. This is the first observation of quantum beats in SO(2) in the absence of any external magnetic or electric fields. The decay profiles of the beating rovibronic bands were fitted using a four-level model by least-squares fitting method. The fitting shows that all the measured bands were double exponential with a similar first lifetime of approximately 3 mus and a varying second lifetime of the order of 1 micros-100 ns with a beating frequency of approximately 1 MHz. These quantum beats, in the absence of any external field, indicate rotational level mixing between the A (1)A(2) and the B (1)B(1) vibronic states which are near resonant due to the high density of states of these two states.     

Liquid chromatography-mass spectrometry-based quantification of steroidal glycoalkaloids from Solanum xanthocarpum and effect of different extraction methods on their content

A new liquid chromatography-mass spectrometry (LC-MS)-based method coupled with pressurized liquid extraction (PLE) as an efficient sample preparation technique has been developed for the quantification and fingerprint analysis of Solanum xanthocarpum. Optimum separations of the samples were achieved on a Waters MSC-18 XTerra column, using 0.5% (v/v) formic acid in water (A) and acetonitrile (ACN):2-propanol:formic acid (94.5:5:0.5, v/v/v) (B) as mobile phase. The separation was carried out using linear gradient elution with a flow rate of 1.0mL/min. The gradient was: 0min, 20% B; 14min, 30% B; 20min, 30% B; 27min, 60% B and the column was re-equilibrated to the initial condition (20% B) for 10min prior to next injection. The steroidal glycoalkaloids (SGAs) which are the major active constituents were isolated as pure compounds from the crude methanolic extract of S. xanthocarpum by preparative LC-MS and after characterization were used as external standards for the development and validation of the method. Extracts prepared by conventional Soxhlet extraction, PLE and ultrasonication were used for analysis. The method was validated for repeatability, precision (intra- and inter-day variation), accuracy (recovery) and sensitivity (limit of detection and limit of quantitation). The purpose of the work was to develop a validated method, which can be used for the quantification of SGAs in commercialized S. xanthocarpum products and the fingerprint analysis for their routine quality control.     

Phosphine-free Pd-salen complexes as efficient and inexpensive catalysts for Heck and Suzuki reactions under aerobic conditions

Phosphine-free palladium-salen complexes, N,N′-bis(salicylidene)-ethylenediamino-palladium and N,N′-bis(salicylidene)-1,2-phenylenediamino palladium, are found to be highly active catalysts for the Heck olefination of aryl iodides and Suzuki reaction of aryl iodides and bromides giving excellent yields (70-90%) of products under aerobic conditions, in short reaction times (10-60 min).     

Facile synthesis methodology and characterization studies of silica-decorated hybridized anisotropic nanotubes and nanosheets

Carbonaceous nanomaterials and their derivatives have been inspired tremendous enthusiasm in the scientific community. They have been excogitated as the encouraging attributes and the qualified dispersed phase to develop multi-functional composites. Particularly, graphene and carbon nanotube (anisotropic fillers) have gained substantial research interest owing to their promising characteristics. This highlights an innovative technique to synthesize hybridized nanotube and nanosheet. Initially, parent materials have been synthesized: The pristine CNT has been modified by acid mixture solution, and reduced graphene oxide has been prepared by chemical reduction method. Henceforth, the self-assembly in situ sol–gel technique has been endorsed here. The synthesized nanohybrids have been characterized by different spectroscopic techniques: FTIR, Raman, UV, and XPS to confirm the attachment of multifunctionalities; meanwhile, the composition and stability have been investigated from XRD and TGA plots. The magnitude of surface charge and particle size distribution have been evaluated for the parent and hybridized products; further, morphology of all the samples has been authenticated from FESEM and TEM.     

Ruthenium(II), rhodium(III) and iridium(III) based effective catalysts for hydrogenation under aerobic conditions

The new cationic mononuclear complexes [(η⁶-arene)Ru(Ph-BIAN)Cl]BF₄ [η⁶-arene = benzene (1), p-cymene (2)], [(η⁵-C₅H₅)Ru(Ph-BIAN)PPh₃]BF₄ (3) and [(η⁵-C₅Me₅)M(Ph-BIAN)Cl]BF₄ [M = Rh (4), Ir (5)] incorporating 1,2-bis(phenylimino)acenaphthene (Ph-BIAN) are reported. The complexes have been fully characterized by analytical and spectral (IR, NMR, FAB-MS, electronic and emission) studies. The molecular structure of the representative iridium complex [(η⁵-C₅Me₅)Ir(Ph-BIAN)Cl]BF₄ has been determined crystallographically. Complexes 1–5 effectively catalyze the reduction of terephthaldehyde in the presence of HCOOH/CH₃COONa in water under aerobic conditions and, among these complexes the rhodium complex [(η⁵-C₅Me₅)Rh(Ph-BIAN)Cl]BF₄ (4) displays the most effective catalytic activity.     

Kinetics and mechanism of oxidation of benzoic acid hydrazide by bromate catalyzed by octamolybdomanganate(II)

Oxidation of benzoic acid hydrazide by bromate in the presence of octamolybdomanganate(II), [Mn^IIMo₈O₂₇]⁴⁻, was studied in hydrochloric acid medium. The mechanism of the reaction involves oxidation of the catalyst to [Mn^IVMo₈O₂₇]²⁻ by bromate which then forms a complex with the unoxidized catalyst. Both the complex and [Mn^IVMo₈O₂₇]²⁻ react with the substrate in rate-determining steps to generate an intermediate acyl diimide, RCONNH. The reaction of water with the diimide then leads to the formation of benzoic acid and nitrogen as products through an NH–NH intermediate. There was no formation of free radical, indicating the involvement of only two-electron transfer steps in the mechanism. The order of more than unity in catalyst concentration is due to the formation of complex between the catalyst and the oxidized form of the catalyst. A rate law explaining all the kinetic results has been derived and verified. The effects of ionic strength and solvent polarity have also been studied, and the thermodynamic parameters were determined. A less solvated transition state as a result of interaction between the complex and oxidized form of the catalyst satisfactorily explains all the effects observed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Role of superheated water in the dissolution and perturbation of hydrogen bonding in the crystalline lattice of polyamide 4,6

Here, we demonstrate that water, in the superheated state, is a solvent for polyamide 4,6 (PA4,6) and that the water molecules can strongly influence hydrogen bonding. In the presence of superheated water, the melting temperature of PA4,6 can be suppressed by nearly 100 degrees C. The depression in the melting temperature follows the Flory-Huggins principle. The instantaneous dissolution of the polymer hardly influences the molar mass of the polymer. However, if the polymer is retained in solution above the dissolution temperature for more than 10 min, hydrolysis occurs. These findings suggest that the dissolution of the aliphatic polymer in superheated water is mainly a physical process as opposed to a chemical process. Time resolved X-ray studies show that the dissolution occurs prior to the Brill transition temperature, as reported earlier. Crystals grown from the water solution show a lath-like morphology with interchain and intersheet distances that are similar to the distances obtained for crystals grown from other known solvents. Electron diffraction further confirmed that the crystals grown from superheated water are single crystals, where the chains are perpendicular to the ab-plane. SAXS performed on dried sedimented water grown single crystals showed a lamellar thickness of 6 nm. The lamellar thickness is in accordance with other reported studies on PA4,6, confirming that the single crystals incorporate four repeat units between re-entrant folds with an amide group incorporated in the tight fold. Solid state NMR studies performed on mats of these single crystals showed two different mobilities of the proton associated with the amide groups: a higher mobility linked to the amide protons in the fold and a reduced mobility of the hydrogen bonded amide protons within the crystal. Additionally, the solid state NMR studies on the dried water crystallized single crystals show the presence of water molecule(s) in the vicinity of the amide groups. This was confirmed by infrared studies that conclusively demonstrated the appearance of two new bands arising due to the binding of a water molecule in the vicinity of the amide group (i.e., NH3(+) and COO(-) bands that disappear upon heating at approximately 200 degrees C). Additionally, DSC traces of the water crystallized PA4,6 show an exothermic event in the same temperature region (i.e., in the vicinity of the Brill transition temperature, where the bound water exits from the lattice). Furthermore, this event was corroborated by TGA data.     

Colon targeted delivery systems of metronidazole based on osmotic technology: development and evaluation

Colon targeted delivery systems of metronidazole (MTZ) based on osmotic technology were developed. The developed systems consisted of osmotic core (drug, osmotic agent and wicking agent), coated with semipermeable membrane (SPM) containing guar gum as pore former, coated core were then further coated with enteric coating to protect the system from acidic environment of stomach. The effect of various formulation variables namely the level of wicking agent (sodium lauryl sulphate), osmotic agent in the osmotic core, the level of pore former (guar gum) in SPM, and the thickness of SPM, were studied on physical parameters and drug release characteristics of developed formulations. MTZ release was inversely proportional to SPM thickness, but directly related to the level of pore former, wicking agent and osmotic agent. On the other hand burst strength of the exhausted shells was decreased with the increase in level of pore former in the membrane but increased with the increase in the thickness of SPM. The drug release from the developed formulations was independent of pH, and agitation intensity, but dependent on the osmotic pressure of the release media. The thickness of enteric coating could prevent formation of delivery pores before contact with simulated colonic fluid, but had no effect on drug release. Result of SEM studies showed the formation of in-situ delivery pores in the membrane from where the drug release occurred, and the number of pores formed were directly related to the initial level of pore former (guar gum) in SPM. The manufacturing procedure was found to be reproducible and formulations were found to be stable during 3 months of accelerated stability studies.     

Betterment in EDXRF analytical results for compositional characterization of mixed uranium thorium oxide samples with bead specimens compared with pressed pellet specimens

A comparative study on the energy dispersive X‐ray fluorescence analytical results of uranium determinations, in uranium and uranium–thorium mixed oxides, using specimens in the form of fused beads and pressed pellets, has been made. It was observed that in case of fusion bead specimens, the intensity of the analyte lines was approximately 1.6 times of that observed in pellet specimens under identical instrumental conditions. In case of uranium oxide samples, the analytical results with bead specimens were slightly better compared with the pellet specimens. However, in case of the uranium–thorium oxide mixtures, the average precision obtained with bead specimen was significantly better (1%, 1 s) in comparison with that achieved using pellet specimens (7%, 1 s). This difference may be due to the hardness of thorium oxide compared with uranium oxide, which affects the homogeneity of the pellet specimens prepared. In fusion bead method of sample preparation, even highly refractory material like ThO₂ forms uniform glass beads. Addition of internal standard further improves the analytical results, with reduction in the percent deviation of energy dispersive X‐ray fluorescence results from the expected values to 3% from 7% compared with that obtained using without internal standard. The fusion bead method of sample preparation will be very useful for characterization of sintered (U,Th)O₂ pellets, which are highly refractory and difficult to dissolve. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis,Crystal Structure,and Electrochemical Properties of a Simple Magnesium Electrolyte for Magnesium/Sulfur Batteries

Most simple magnesium salts tend to passivate the Mg metal surface too quickly to function as electrolytes for Mg batteries. In the present work, an electroactive salt [Mg(THF)₆][AlCl₄]₂ was synthesized and structurally characterized. The Mg electrolyte based on this simple mononuclear salt showed a high Mg cycling efficiency, good anodic stability (2.5 V vs. Mg), and high ionic conductivity (8.5 mS cm^?1). Magnesium/sulfur cells employing the as‐prepared electrolyte exhibited good cycling performance over 20 cycles in the range of 0.3–2.6 V, thus indicating an electrochemically reversible conversion of S to MgS without severe passivation of the Mg metal electrode surface.