Determination of organochlorine compounds in human biological samples by GC-MS/MS

A study was undertaken to determine the extent of organochlorine pesticide (OP) and polychlorinated biphenyl (PCB) contamination in infant formula milk and in the human milk, fat and serum of women from an agricultural area in Southern Spain. A procedure is proposed that simultaneously detects trace levels of lindane, endosulfan-ether, vinclozolin, aldrin, endosulfan-lactone, endosulfan-alpha, 4,4'DDE, 2,4'DDT, endosulfan-beta, 4,4'DDT, kepone, endosulfate-sulfate, methoxychlor, mirex, 2,3,4 PCB, 2,2',4,5 PCB, 2,3,4,5 PCB and 2,2',3,3',6,6'PCB. After liquid-liquid or solid-liquid extraction, the extract of the sample was cleaned by high performance liquid chromatography (HPLC) and the fi rst eluted fraction was analysed by gas chromatography (GC) with mass spectrometry (MS) detector in tandem mode. To evaluate the validity of the method the following parameters were studied: linearity, detection limits, quantification limits, specificity, percentage recovery and precision. A study of the uncertainty associated with the analytical method was also carried out.     

Theoretical study of electronic spectra of [Pt3(μ‐CO)3(CO)3] (n = 3–5) complexes

The platinum‐platinum attraction and the spectroscopic properties of [Pt₃(μ‐CO)₃(CO)₃] (n = 3–5) were studied at the PBE level. Theoretical calculations are in agreement with experimental geometries. The absorption spectra of these platinum complexes were calculated by the single excitation time‐dependent (TD) density functional method. All complexes showed MLCT transitions interrelated with the intertriangular complexes. The values obtained at the PBE level are in agreement with the experimental color range. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Oriented immobilization of a membrane-bound hydrogenase onto an electrode for direct electron transfer

The interaction of redox enzymes with electrodes is of great interest for studying the catalytic mechanisms of redox enzymes and for bioelectronic applications. Efficient electron transport between the biocatalysts and the electrodes has achieved more success with soluble enzymes than with membrane enzymes because of the higher structural complexity and instability of the latter proteins. In this work, we report a strategy for immobilizing a membrane-bound enzyme onto gold electrodes with a controlled orientation in its fully active conformation. The immobilized redox enzyme is the Ni-Fe-Se hydrogenase from Desulfovibrio vulgaris Hildenborough, which catalyzes H(2)-oxidation reversibly and is associated with the cytoplasmic membrane by a lipidic tail. Gold surfaces modified with this enzyme and phospholipids have been studied by atomic force microscopy (AFM) and electrochemical methods. The combined study indicates that by a two-step immobilization procedure the hydrogenase can be inserted via its lipidic tail onto a phospholipidic bilayer formed over the gold surface, allowing only mediated electron transfer between the enzyme and electrode. However, a one-step immobilization procedure favors the formation of a hydrogenase monolayer over the gold surface with its lipidic tail inserted into a phospholipid bilayer formed on top of the hydrogenase molecules. This latter method has allowed for the first time efficient electron transfer between a membrane-bound enzyme in its native conformation and an electrode.     

The role of aromaticity on the building of nanohybrid materials functionalized with metalated (Au(III), Ag(III), Cu(III)) extended porphyrins and single‐walled carbon nanohorns: A theoretical study

An ab initio, systematic study on the aromaticity involving the group of metalated extended porphyrins, termed meso‐hexakis(pentafluorophenyl)‐substituted[26]hexaphyrin(1.1.1.1.1.1) (HP), was performed for the first time. The aromatic behavior of the system shifted to antiaromatic in the [28]HP analogue, due to the presence of hydrogen atoms that break the orbital symmetry. The absorption bands observed in the experiment were assigned to an intraligand charge transfer, where the intrametallic character is also important. The excited states reveal the absorption of visible light and the possibility of electronic transfer to different systems. We propose a system such as single‐walled carbon nanohorns (SWCNHs), due to their special electronic properties, and predict a novel nanohybrid material. The evidence of electronic communication between both species is presented in this work. The HP aromaticity and the spatial configuration of the interaction with SWCNHs are also related to the strength of electronic transfer among the systems, making the HP metalated antiaromatic species and their corresponding nanohybrids potential candidates to be used as building blocks in photovoltaic cell materials. © 2012 Wiley Periodicals, Inc.     

Curvature and conjugate points in Lorentz symmetric spaces

We give some relations between conjugate points and curvature in a locally symmetric Lorentzian manifold. In the compact case, we show that the sectional curvature of timelike planes is non positive, and the lightlike sectional curvature of null planes is non negative. We also compute the lightlike conjugate loci of Cahen–Wallach manifolds, which are an important family of symmetric Lorentzian spaces.     

Effects of the Au(I)–Au(I) closed‐shell attraction on the electronic and phosphorescent properties in a series of coordination compounds: A theoretical study

The Au(I)–Au(I) closed‐shell or aurophilic attraction has been the subject of interest in the experimental and theoretical chemistry fields, due to the intriguing properties associated to it. The presence of phosphorescence in “aurophilic” compounds has been addressed to a wide range of applications, but it has not yet been fully understood. A theoretical study on the electronic and phosphorescent properties of the following series of dinuclear gold complexes has been performed: [Au₂(dmpm) (i‐mnt)] ( 1 ), [Au₂(μ‐Me‐TU) (μ‐dppm)] ( 2 ), and [Au₂(μ‐G)(μ‐dmpe)] ( 3 ). Full geometry optimizations at the second‐order Møller–Plesset perturbation theory (MP2) were carried out for each of the species. These calculations made evident that, at the ground‐state geometry, the Au(I) cations allocated at the center of the ring show a short Au–Au distance below the sum of the van der Waals radii, at the range of the aurophilic attraction. An intermolecular Au(I)–Au(I) closed‐shell attraction for a pair of the systems under study is found. This attraction is comparable to that of the hydrogen bonds. The phosphorescent properties experimentally observed for this series were also characterized through ab initio techniques. The obtained results allow to fit reasonably the excitation energies with the experimental data and to identify a correlation between the strength of the Au(I)–Au(I) interaction and the phosphorescent behavior. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011