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.     

Stability indicating RP-HPLC method development and validation for oseltamivir API

The present study describes the development and subsequent validation of a stability indicating reverse-phase HPLC (RP-HPLC) method for the analysis of oseltamivir active pharmaceutical ingredient (API). The proposed RP-HPLC method utilizes Kromasil C(18), 5 microm, 250 mm x 4.6 mm i.d. column (at ambient temperature), gradient run (using acetonitrile and triethylamine as mobile phase), effluent flow rate (1.0 ml/min), and UV detection at 215 nm for analysis of oseltamivir. The described method was linear over the range of 70-130 microg/ml (r(2)=0.999). The precision, ruggedness and robustness values were also within the prescribed limits (<1% for system precision and <2% for other parameters). Oseltamivir was exposed to acidic, basic, oxidative and thermal stress conditions, and the stressed samples were analyzed by the proposed method. Chromatographic peak purity results indicated the absence of co-eluting peaks with the main peak of oseltamivir, which demonstrated the specificity of assay method for estimation of oseltamivir in presence of degradation products. The proposed method can be used for routine analysis of oseltamivir in quality control laboratories.     

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.     

Size dependence of structural, electronic, elastic, and optical properties of selenium nanowires: a first-principles study

We have studied the structural, elastic, and optical properties of selenium nanowires, as well as bulk selenium, by performing first-principles density functional theory calculations. The nanowires are structurally similar to bulk trigonal Se, in that they consist of hexagonal arrays of helices, though there is a slight structural rearrangement in response to the finite size of the nanowires. These small structural changes result in Young's modulus decreasing slightly for progressively thinner nanowires. However, there is a significant effect on electronic structure and optical properties. The thinner the nanowire, the greater the band gap, and the greater the anisotropy in optical conductivity. The latter is due to the effects of finite size being much more marked for the case where the electric field is polarized perpendicular to the helical axis, than in the case where the polarization is parallel to c. For the case of bulk Se, we obtain good agreement with experimental data on the structure, elastic constants, and dielectric function.     

Interplay between bonding and magnetism in the binding of NO to Rh clusters

We have studied the binding of NO to small Rh clusters, containing one to five atoms, using density functional theory in both spin-polarized and non-spin-polarized forms. We find that NO bonds more strongly to Rh clusters than it does to Rh(100) or Rh(111), suggesting that Rh clusters may be good catalysts for NO reduction. However, binding to NO also quenches the magnetism of the clusters. This (local) effect results in reducing the magnitude of the NO binding energy, and also washes out the clear size-dependent trend observed in the nonmagnetic case. Our results illustrate the competition present between the tendencies to bond and to magnetize, in small clusters.     

Development of natural sorbent based micro-solid-phase extraction for determination of phthalate esters in milk samples

In the present study, a natural sorbent based micro-solid phase extraction (μ-SPE) was developed for determination of phthalate esters in milk samples. For the first time, an efficient and cost effective natural material (seed powder of Moringa oleifera) was employed as sorbent in μ-SPE. The sorbent was found to be naturally enriched with variety of functional groups and having a network of interconnected fibers. This method of extraction integrates different steps such as removal of proteins and fatty stuff, extraction and pre-concentration of target analytes into a single step. Thirteen phthalate esters were selected as target compounds for the development and evaluation of method. Some key parameters affecting the extraction efficiency were optimized, including selection of membrane, selection and amount of sorbent, extraction time, desorption solvent, volume of desorption solvent, desorption time and effect of salt addition. Under the optimum conditions, very good linearity was achieved for all the analytes with coefficient of determinations (R²) ranging between 0.9768 and 0.9977. The limits of detection ranged from 0.01 to 1.2 μg L⁻¹. Proposed method showed satisfactory reproducibility with relative standard deviations ranging from 3.6% to 10.2% (n = 7). Finally, the developed method was applied to tetra pack and bottled milk samples for the determination of phthalate esters. The performance of natural sorbent based μ-SPE was better or comparable to the methods reported in the literature.     

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.     

Photopolymers: Synthesis and Characterization of Poly(3‐methacryloyloxystyryl‐2‐naphthyl ketone)

3‐Methacryloyloxystyryl‐2‐naphthyl ketone containing a photosensitive α,β‐unsaturated ketone moiety was synthesized and polymerized in methyl ethyl ketone using benzoyl peroxide as the initiator. The thermally stable polymer was characterized by means of UV, IR and NMR spectroscopy. The molecular weight data as obtained from gel permeation chromatography suggests a high tendency for chain termination by disproportionation. The photosensitivity of the polymer in the presence and absence of photosensitizers and the effect of solvent on the rate of photocrosslinking (see Figure) was also investigated.