Speciation of Mixtures of Copper (I) and Copper (II) Mixed Ligand Complexes by X-Ray Absorption Fine Structure Spectroscopy

Studies on speciation have been done in the mixtures of mixed ligand copper complexes. Three heterogeneous mixtures have been studied, each having one Cu(I) complex and one Cu(II) complex. The Cu(I) complex is [Cu(thu)Cl 0.5H₂O] (1) and the Cu(II) complexes are [Cu(L-phen)(bpy) H₂O] (2), [Cu(L-tyr)(phn) 2.5H₂O] (3), and [Cu(dien)(ina) 4H₂O.1/2SO₄] (4) (where thu = thiourea, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine, tyr = tyrosine, dien = diethylenetriamine, and ina = isonicotinate anion). The mixtures have been prepared by mixing the Cu(I) complex with each of the Cu(II) complexes in the ratio of 1:1 by mole percentage. The X-ray absorption fine structure (XAFS) spectra have been recorded at the K-edge of copper in the mixtures as well as in the complexes, separately. The aim of the present work is to make a study of the different methods of speciation using XAFS, viz., principal component analysis (PCA) and the target transformation (TT) method, the linear combination fitting (LCF) method, derivative spectra methods, and normalized difference absorption edge spectra (NDAES) analysis. It has been shown that these methods can be used to determine the relative quantity of the mixed ligand complexes in their mixtures.     

XAFS study of aqua (diethylenetriamine)(isonicotinato)‐copper(II) complex – inference of square‐pyramidal geometry

X‐ray absorption fine structure (XAFS) of aqua (diethylenetriamine) (isonicotinato) copper(II) complex has been investigated. The crystal structure of the complex is unavailable. The X‐ray absorption near edge structure (XANES) spectrum of the complex has been compared with those of the standard compounds to estimate the coordination geometry and oxidation state of copper. This study indicates that the copper center has +2 oxidation state and that it may be penta or hexa‐coordinated. The spectrum has been further compared with those of the earlier studied complexes having square‐pyramidal geometry. Similarity has been observed between them indicating that the complex should have penta‐coordinated square‐pyramidal geometry. The same inference has been obtained from the study of the characteristic pre‐edge and XANES features. This inference has been further examined by analysis of the extended X‐ray absorption fine structure (EXAFS) spectrum. The experimental EXAFS data has been fitted with three different theoretical models for tetra‐coordination, penta‐coordination, and hexa‐coordination. The tetra model is unable to provide a satisfactory fit so it has been ignored. Although the penta and hexa models give comparable results, the parameters obtained indicate that the penta‐coordinated model fits better to the experimental data than the hexa‐coordinated model. This penta‐coordinated model has been further fitted to the experimental data by allowing the coordination number to vary. Such fitting also shows that the penta‐coordinated model is a satisfactory model for the studied complex. The obtained values of mean‐square disorder indicate that the force constants are different for the equatorial and axial bonds. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrochemically Tunable Proton‐Coupled Electron Transfer in Pd‐Catalyzed Benzaldehyde Hydrogenation

Acid functionalization of a carbon support allows to enhance the electrocatalytic activity of Pd to hydrogenate benzaldehyde to benzyl alcohol proportional to the concentration of Brønsted‐acid sites. In contrast, the hydrogenation rate is not affected when H₂ is used as a reduction equivalent. The different responses to the catalyst properties are shown to be caused by differences in the hydrogenation mechanism between the electrochemical and the H₂‐induced hydrogenation pathways. The enhancement of electrocatalytic reduction is realized by the participation of support‐generated hydronium ions in the proximity of the metal particles.     

Methane production in a 100-L upflow bioreactor by anaerobic digestion of farm waste

Manure waste from dairy farms has been used for methane production for decades, however, problems such as digester failure are routine. The problem has been investigated in small scale (1-2 L) digesters in the laboratory; however, very little scale-up to intermediate scales are available. We report production of methane in a 100-L digester and the results of an investigation into the effect of partial mixing induced by gas upflow/recirculation in the digester. The digester was operated for a period of about 70 d (with 16-d hydraulic retention time) with and without the mixing induced by gas recirculation through an internal draft tube. The results show a clear effect of mixing on digester operation. Without any mixing, the digester performance deteriorated within 30-50 d, whereas with mixing continuous production of methane was observed. This study demonstrates the importance of mixing and its critical role in design of large scale anaerobic digesters.     

Xyloccensin X and Y, two new limonoids from xylocarpus molluccensis: NMR investigation in mixture

Two new limonoids, xyloccensin X (1) and xyloccensin Y (2), have been identified in mixture using NMR spectroscopy. Both limonoids were isolated in mixture from the fruit of the plant Xylocarpus molluccensis. The structures of these were proposed after extensive 2D NMR analyses in mixture.     

Characterization of stable and reactive metabolites of piperine formed on incubation with human liver microsomes

Black pepper, though commonly employed as a spice, has many medicinal properties. It consists of volatile oils, alkaloids, pungent resins, etc., of which piperine is a major constituent. Though safe at low doses, piperine causes alteration in the activity of drug metabolising enzymes and transporters at high dose and is known to precipitate liver toxicity. It has a potential to form reactive metabolite(s) (RM) owing to the presence of structural alerts, such as methylenedioxyphenyl (MDP), α, β‐unsaturated carbonyl group (Michael acceptor), and piperidine. The present study was designed to detect and characterize stable and RM(s) of piperine formed on in vitro incubation with human liver microsomes. The investigation of RMs was done with the aid of trapping agents, viz, glutathione (GSH) and N‐acetylcysteine (NAC). The samples were analysed by ultra‐high performance liquid chromatography coupled with high resolution mass spectrometry (UHPLC‐HRMS) using Thermo Scientific Q Exactive Plus Orbitrap. Full scan MS followed by data‐dependent MS² (Full MS‐ddMS²) mode was used to establish mass spectrometric fragmentation pathways of protonated piperine and its metabolites. In total, four stable metabolites and their isomers (M1a‐c, M2a‐b, M3a‐c, and M4a‐b) were detected. Their formation involved removal of carbon (3, M1a‐c), hydroxylation (2, M2a‐b), hydroxylation with hydrogenation (3, M3a‐c), and dehydrogenation (2, M4a‐b). Out of these metabolites, M1, M2, and M3 are reported earlier in the literature, but their isomers and two M4 variants are novel. In addition, six novel conjugates of RMs, including three GSH conjugates of m/z 579 and three NAC conjugates of m/z 435, were also observed.     

Polymer‐Supported Sulfonic Acid‐Catalyzed Candid Synthesis and Photophysical Properties of 2H‐indazolo[2,1‐b]phthalazinetriones

Polystyrene‐supported sulfonic acid has been found to be an efficient catalyst for the one‐pot, three‐component synthesis of 2H‐indazolo[2,1‐b]phthalazinetriones in greener solvent glycerol. Use of greener solvent glycerol along with a polymer‐supported, low toxic, and inexpensive catalyst renders the method eco‐friendly. High yields, simple product isolation procedure, and fluorescent and electroluminescent natures of the products are the noteworthy aspects of this protocol.