Simultaneous determination of five common additives in insulating mineral oils by high‐performance liquid chromatography with ultraviolet and coulometric detection

Dielectric mineral oils are used to impregnate power transformers and large electrical apparatus, acting as both liquid insulation and heat dissipation media. Antioxidants and passivators are frequently added to mineral oils to enhance oxidation stability and reduce the electrostatic charging tendency, respectively. Since existing standard test methods only allow analysis of individual additives, new approaches are needed for the detection of mixtures. For the first time we investigate and discuss the performance of analytical methods, which require or do not require extraction as sample pretreatment, for the simultaneous reversed‐phase high‐performance liquid chromatography determination of passivators (benzotriazole, Irgamet^® 39) and antioxidants (N‐phenyl‐1‐naphtylamine, 2,6‐di‐tert‐butylphenol, 2,6‐di‐tert‐butyl‐p‐cresol), chosen for their presence in marketed oils. Quick easy, cheap, effective, rugged and safe and solid phase extractions were evaluated as sample pretreatments. Direct sample‐injection was also studied. Ultraviolet spectrophotometry and direct‐current coulometry detection were explored. As less prone to additive concentrations variability, the direct‐injection high‐performance liquid chromatography with ultraviolet and coulometric detection method was validated through comparison with Standard Method IEC 60666 and through an ASTM interlaboratory proficiency test. Obtained detection limits are (mg kg^?1): benzotriazole (2.8), Irgamet^® 39 (13.8), N‐phenyl‐1‐naphtylamine (11.9), 2,6‐di‐tert‐butylphenol (13.1), 2,6‐di‐tert‐butyl‐p‐cresol (10.2). Simultaneous determination of selected additives was possible both in unused and used oils, with good precision and accuracy.     

Structural and thermodiffractometric analysis of coordination polymers. Part II: zinc and cadmium derivatives of the Bim ligand [Bim = bis(1-imidazolyl)methane

New polynuclear coordination species containing the ditopic bis(1-imidazolyl)methane (Bim) ligand have been prepared as microcrystalline powders and structurally characterized by ab initio X-ray powder diffraction methods. [Zn(CH3COO)2(Bim)]n contains 1D chains with tetrahedral metal atoms bridged by Bim ligands; [CdBr2(Bim)]n shows a dense packing with hexacoordinated Cd(II) ions and mu-Br and mu-Bim bridges; at variance, the isomorphous [ZnCl2(Bim)]n and [ZnBr2(Bim)]n species contain cyclic dimers based on tetrahedral Zn(II) ions. Thermodiffractometric analysis allowed estimation of the linear thermal expansion coefficients and strain tensors derived there from. Bim-rich phases, with 2:1 ligand-to-metal ratio, were also isolated: ZnBr2(Bim)2(H2O)3 and [Cd(CH3COO)2(Bim)2]n containing cis and trans MN4O2 chromophores, respectively, show 1D polymers built upon M2Bim2 cycles, hinged on the metal ions. In all species the conformation of the Bim ligands is Cs (or nearly so), while in the few sparse reports of similar coordination polymers the alternative C2 one was preferentially observed.     

Method validation for the analysis of 169 pesticides in soya grain, without clean up, by liquid chromatography-tandem mass spectrometry using positive and negative electrospray ionization

Part of a comprehensive study on the comparison of different extraction methods, GC-MS(/MS) and LC-MS/MS detection methods and modes, for the analysis of soya samples is described in this paper. The validation of an acetone-based extraction method for analysis of 169 pesticides in soya, using LC-MS/MS positive and negative electrospray ionisation (ESI) mode, is reported. Samples (5 g) were soaked with 10 g water and subsequently extracted with 100 mL of a mixture of acetone, dichloromethane and light petroleum (1:1:1), in the presence of 15 g anhydrous sodium sulphate. After centrifugation, aliquots of the extract were evaporated and reconstituted in 1.0 mL of methanol, before direct injection of the final extract (corresponding with 0.05 g soya mL(-1)) into the LC-MS/MS system. Linearity, r(2) of calibration curves, instrument limit of detection/quantitation (LOD/LOQ) and matrix effect were evaluated, based on seven concentrations measured in 6-fold. Good linearity (at least r(2)> or =0.99) of the calibration curves was obtained over the range from 0.1 or 0.25 to 10.0 ng mL(-1), corresponding with pesticide concentrations in soya bean extract of 2 or 5-200 microg kg(-1). Instrument LOD values generally were 0.1 or 0.25 ng mL(-1). Matrix effects were negligible for approximately 90% of the pesticides. The accuracy, precision and method LOQ were determined via recovery experiments, spiking soya at 10, 50, 100 microg kg(-1), six replicates per level. In both ESI modes, method LOQ values were mostly 10 or 50 microg kg(-1) and more than 70% of pesticides analysed by each mode met the acceptability criteria of recovery (70-120%) and RSD (< or =20%), at one or more of the three levels studied. A fast, easy and efficient method with acceptable performance was achieved for a difficult matrix as soya, without cleanup.     

Synthesis,crystal structure and antibacterial activity of four mononuclear Schiff base complexes of copper(II) and nickel(II)

Transition Metal Chemistry - Three mononuclear copper(II) complexes, viz. [CuL1] (1), [CuL2] (2), [CuL3] (3), and one nickel(II) complex, viz.[NiL3] (4) where...     

A Dirichlet form approach to MCMC optimal scaling

This paper shows how the theory of Dirichlet forms can be used to deliver proofs of optimal scaling results for Markov chain Monte Carlo algorithms (specifically, Metropolis–Hastings random walk samplers) under regularity conditions which are substantially weaker than those required by the original approach (based on the use of infinitesimal generators). The Dirichlet form methods have the added advantage of providing an explicit construction of the underlying infinite-dimensional context. In particular, this enables us directly to establish weak convergence to the relevant infinite-dimensional distributions.     

Retention of heavy metal ions on SBA-15 mesoporous silica functionalised with carboxylic groups

Three samples of SBA-15 functionalised with -(CH(2))(3)COOH groups have been prepared by co-condensation, starting from solutions of TEOS and 4-(triethoxysilyl)butyronitrile, acting as -(CH(2))(3)COOH precursor, of different molar compositions. Materials were characterised by X-ray diffraction, nitrogen adsorption, and FT-IR spectroscopy. The pK(a) and the acidic capacity were measured for all samples by potentiometric titration. The acidic capacity increases with increasing amount of -COOH precursor in the synthesis mixture only up to 10% molar of total alkoxysilane. The value for the pK(a)(4.75) is independent of the acidic capacity of the material. The sample prepared starting from an amount of -COOH precursor equal to 10% molar of total alkoxysilane was chosen to test selective interactions with heavy metals of environmental importance (Ag(+), Cd(2+), Fe(3+), Cu(2+), Zn(2+)) at different pH values and ionic strengths. The significant and selective adsorption exhibited by the material has been exploited in a preliminary cation-exchange chromatographic application showing the possibility of eluting the metal ions at different retention times.     

Synthesis of Migrastatin Analogues as Inhibitors of Tumour Cell Migration: Exploring Structural Change in and on the Macrocyclic Ring

Migrastatin and isomigrastatin analogues have been synthesised in order to contribute to structure–activity studies on tumour cell migration inhibitors. These include macrocycles varying in ring size, functionality and alkene stereochemistry, as well as glucuronides. The synthesis work included application of the Saegusa–Ito reaction for regio‐ and stereoselective unsaturated macroketone formation, diastereoselective Brown allylation to generate 9‐methylmigrastatin analogues and chelation‐induced anomerisation to vary glucuronide configuration. Compounds were tested in vitro against both breast and pancreatic cancer cell lines and inhibition of tumour cell migration was observed in both wound‐healing (scratch) and Boyden chamber assays. One unsaturated macroketone showed low affinity for a range of secondary drug targets, indicating it is at low risk of displaying adverse side effects.     

Structural basis for the potential antitumour activity of DNA-interacting benzo[kl]xanthene lignans

The biological properties and possible pharmacological applications of benzo[kl]xanthene lignans, rare among natural products and synthetic compounds, are almost unexplored. In the present contribution, the possible interaction of six synthetic benzo[kl]xanthene lignans and the natural metabolite rufescidride with DNA has been investigated through a combined STD-NMR and molecular docking approach, paralleled by in vitro biological assays on their antiproliferative activity towards two different cancer cell lines: SW 480 and HepG2. Our data suggest that the benzo[kl]xanthene lignans are suitable lead compounds for the design of DNA selective ligands with potential antitumour properties.     

Assembly of shape-controlled nanocrystals by depletion attraction

Recently (Baranov et al., Nano Lett., 2010, 10, 743) we demonstrated that depletion attraction between semiconductor nanorods in solution can be employed for both their self-assembly and their separation from spherical nanoparticles. Here we show that depletion attraction can be used to fabricate binary superlattices of nanorods and 3D networks of octapod/tetrapod-shaped nanocrystals.     

Synthesis and characterization of 2-phenylaniline cyclopalladated complexes

Reaction of the dinuclear complex [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}Cl]₂ (1) with ligands (L = 4-picoline, sym-collidine) gave the six-membered palladacycles [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}Cl(L)] (2). The complex 1 reacted with AgX (X = CF₃SO₃, BF₄) and bidentate ligands [L–L = phen (phenanthroline), dppe (bis(diphenylphosphino)ethane), bipy(2,2′-bipyridine) and dppp (bis(diphenylphosphino)propane)] giving the mononuclear orthopalladated complexes [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}(L–L)] (3) [L–L = phen, dppe, bipy and dppp]. These compounds were characterized by physico-chemical methods, and the structure of [Pd{κ2-N2′,C1-2-(2′-NH₂C₆H₄)C₆H₄}Cl(L)] (L = sym-collidine) was determined by single-crystal X-ray analysis.