Self-assembly of a tetranuclear Ni4 cluster with an S = 4 ground state: the first 3d metal cluster bearing a mu4-eta2:eta2-O,O carbonate ligand

Reaction of nickel(II) acetate with H(3)L (2-(5-bromo-2-hydroxyphenyl)-1,3-bis[4-(5-bromo-2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) yields [Ni(2)L(OAc)(H(2)O)(2)].3MeCN.2H(2)O (1.3MeCN.2H(2)O), crystallographically characterized. 1 is unstable in solution for a long time and hydrolyzes to give [Ni(2)L(o-OC(6)H(3)BrCHO)(H(2)O)].2.25MeCN.H(2)O (2.2.25MeCN.H(2)O). In addition, 1 uptakes CO(2) from air in a basic methanol/acetonitrile solution, yielding [[Ni(2)L(MeOH)](2)(CO(3))].1.5MeOH.MeCN.H(2)O (3.1.5MeOH.MeCN.H(2)O). The X-ray characterization of 3 reveals that it is a tetranuclear nickel cluster, which can be considered as the result of a self-assembly process from two dinuclear [Ni(2)L](+) blocks, joined by a mu(4)-eta(2):eta(2)-O,O carbonate ligand. The coordination mode of the carbonate anion is highly unusual and, to the best of our knowledge, it has not been described thus far for first-row transition metal complexes or magnetically studied until now. Magnetic characterization of 1 and 3 shows net intramolecular ferromagnetic coupling between the metal atoms in both cases, with S = 2 and S = 4 ground states for 1 and 3, respectively.     

Reversible colorimetric probes for mercury sensing

The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and N749 [(2,2':6',2' '-terpyridine-4,4',4' '-tricarboxylate)ruthenium(II) tris(tetrabutylammonium) tris(isothiocyanate)] are described. It was found that mercury ions coordinate reversibly to the sulfur atom of the dyes' NCS groups. This interaction induces a color change in the dyes at submicromolar concentrations of mercury. Furthermore, the color change of these dyes is selective for mercury(II) when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II). The detection limit for mercury(II) ions--using UV-vis spectroscopy--in homogeneous aqueous solutions is estimated to be approximately 20 ppb for N719 and approximately 150 ppb for N749. Moreover, the sensor molecules can be adsorbed onto high-surface-area mesoporous metal oxide films, allowing reversible heterogeneous sensing of mercury ions in aqueous solution. The results shown herein have important implications in the development of new reversible colorimetric sensors for the fast, easy, and selective detection and monitoring of mercuric ions in aqueous solutions.     

Separation and quantification of double‐ and triple‐layered rotavirus‐like particles by CZE

Virus‐like particles have been successfully used as safe vaccines, as their structure is identical to their native counterparts but devoid of the viral genetic material. However, production of these complex structures is not easy, as recombinant proteins must assemble into virus‐like particles. Techniques to differentiate assembled and soluble proteins, as well as assembly intermediaries often present in a sample, are required. An example of complex virus‐like particles mixture occurs when rotavirus proteins are recombinantly expressed. Rotavirus‐like particles (RLP) can be single (sl), double (dl), or triple layered (tl). The use of RLP preparations as vaccines requires their complete characterization, including separation and quantification of each RLP in a sample. In this work, CZE was evaluated for the separation and quantification of dl and triple‐layered rotavirus‐like particles (tlRLP). A fused‐silica capillary with a deoxycholate running buffer efficiently separated dl and tlRLP in RLP preparations, as they migrated in two discrete peaks with electrophoretic mobilities of 1.24±0.04 and 2.95±0.03 Ti, respectively. Standard curves for dl and tlRLP were generated, and the response was linearly proportional to analyte concentration. The methodology developed was quantitative, specific, accurate, precise, and reproducible. CZE allowed the quantitative characterization of RLP preparations, which is required for evaluation of immunogens, for process development, and for quality control protocols.     

Indoor radon levels and gamma-radiation in dwellings of the Metropolitan Zone of Guadalajara

The present study in the Metropolitan Zone of Guadalajara (MZG) in the state of Jalisco was carried out along 2007. ²²²Rn (radon) and ²²⁰Rn (thoron) levels were measured in single-family dwellings in normal living conditions (open house condition). Measurements were accomplished by Electret Passive Environmental Radon Monitors (E-PERM) in different configurations. At the same time and for the same period, the gamma dose rate was measured by a LiF: Mg, Cu, P+PTFE thermoluminiscent dosimeter. A Quality Assurance Program was improved. Results show a lognormal distribution of annual concentrations and seasonal variations. Mean annual concentrations of radon were lower than US EPA and EEC action values. ²²⁰Rn levels appear to be higher than the typical value determined by the UNSCEAR Reports (1993 and 2000). Performance of different E-PERM configurations accomplishes the US EPA guidelines and yield useful results for diverse situations. Gamma rate dose was higher than that of the Metropolitan Zone of Mexico.     

Characterization of “oil on copper” paintings by energy dispersive X-ray fluorescence spectrometry

Energy dispersive X-ray fluorescence is a common analytical tool for layer thickness measurements in quality control processes in the coating industry, but there are scarce microanalytical applications in order to ascertain semi-quantitative or quantitative information of painted layers. “Oil on copper” painting becomes a suitable material to be analysed by means of X-ray fluorescence spectrometry, due to the metallic nature of substrate and the possibility of applying layered models as used in coating industry. The aim of this work is to study the suitability of a quantitative energy dispersive X-ray fluorescence methodology for the assessment of the areal distribution of pigments and the characterization of painting methods on such kind of pictorial artworks. The method was calibrated using standard reference materials: dried droplets of monoelemental standard solutions laid on a metallic plate of copper. As an example of application, we estimated pigment mass distribution of two “oil on copper” paintings from the sixteenth and eighteenth centuries. Pictorial layers have been complementarily analysed by X-ray diffraction. Apart of the supporting media made of copper or brass, we could identify two different superimposed layers: (a) a preparation layer mainly composed by white lead and (b) the pictorial layer of variable composition depending on the pigments used by the artist on small areas of the painting surface. The areal mass distribution of the different elements identified in the painting pigments (Ca, Cr, Mn, Fe, Zn, Cd, Hg and Pb) have been determined by elemental mapping of some parts of the artworks.     

Adsorption of water-soluble polymers with surfactant character. Dilational viscoelasticity

A brief summary of dilational surface viscoelatic properties of spread and adsorbed surfactant polymer films at the air-water interface is reported. The viscoelastic moduli have been measured as a function of frequency and surface pressure. The combination of several techniques, oscillating drop and barrier experiments and electrocapillary waves (ECW), has allowed us to investigate a broad frequency range. The dynamic elasticity epsilon shows a slight change with frequency and a noticeable pressure dependence for both kinds of monolayers. In the spread films, elasticity increases steeply with surface pressure, and reaches a constant value before the polymer begins to dissolve into the bulk. On the other hand, the adsorbed films exhibit a pronounced elasticity maximum, followed by a considerable decay when a loose surface structure is formed. The position of the maximum depends on the polymer chemical composition and molecular weight. The results on the overlapping surface pressure range confirm the dynamic equivalence of spread and adsorbed monolayers. At low surface concentration, the agreement between static and dynamic elasticity is quite satisfactory, but the values diverge considerably at higher surface pressures. The loss modulus omegakappa decreases monotonically with increasing omega, becoming zero (it can even take apparent negative values) for the highest frequencies. The frequency dependence of the elasticity has been well described by the diffusive control model of Lucassen-van den Tempel (LVT). However, its predictions for omegakappa do not coincide with the experimental data. The differences between experimental and theoretical values increase at low frequencies.     

Heterogeneous colorimetric sensor for mercuric salts

A novel chemical sensor for the colorimetric detection of mercuric salts is described. The sensor is based on a mesoporous nanocrystalline TiO2 film sensitised with a ruthenium dye; immersion of this film in an aqueous solution of Hg2+ results in a rapid colorimetric response, with both a high selectivity and a sub-micromolar sensitivity.     

Volatile constituents of Origanum vulgare L., 'thymol' chemotype: variability in North India during plant ontogeny

Essential oils derived from six different phenophases, namely early vegetative stage, late vegetative stage, early flowering stage, full flowering stage (FFS), late flowering stage and seed shattering stage of Origanum vulgare L. grown in Kumaon region of Uttarakhand, India were investigated by GC and GC-MS. A total of 38 constituents, representing 97.4-99.7% of the total oil composition, were identified. Major components of oils were thymol (40.9-63.4%), p-cymene, (5.1-25.9%), γ-terpinene (1.4-20.1%), bicyclogermacrene (0.2-6.1%), terpinen-4-ol (3.5-5.9%), α-pinene (1.6-3.1%), 1-octen-3-ol (1.4-2.7%), α-terpinene (1.0-2.2%), carvacrol (<0.1-2.1%), β-caryophyllene (0.5-2.0%) and β-myrcene (1.2-1.9%). Thymol, terpinen-4-ol, 3-octanol, α-pinene, β-pinene, 1,8-cineole, α-cubebene and (E)-β-ocimene were observed to be higher during FFS. The study showed that plant stage had a significant effect on the essential oil content and composition of O. vulgare grown in the hilly tracks of Northern India.     

The enantiomeric scaffold approach to highly functionalized 1-oxadecalines: enantio- and regiocontrolled [4 + 2] cycloadditions of 5-alkenyl-eta3-pyranylmolybdenum complexes

TpMo(CO)2(5-alkenyl-eta-2,3,4-pyranyl) diene complexes function as excellent chiral scaffolds for the efficient regio- and enantiocontrolled synthesis of highly functionalized 1-oxadecaline derivatives through a novel transition metal-mediated Diels-Alder reaction. Very good to excellent yields and excellent levels of endo selectivity are obtained, and the reaction gives products with complete retention of enantiomeric purity when carried out with chiral, nonracemic scaffolds. A subtle structural modification on the diene (replacement of an H by a trans-CH3 group) leads to a complete change of regiochemistry, which is discussed from a mechanistic point of view. The role of the eta3-coordinated TpMo(CO)2 moiety is also critical to the further functionalization of the [4 + 2] cycloadducts, as illustrated by the preparation of 20 variously functionalized 1-oxadecaline derivatives (>98% ee when carried out with high enantiopurity scaffolds).     

Synthesis of functionalized carboranes as potential anticancer and BNCT agents

Carboranyl aldehydes react with alpha,beta-unsaturated esters, ketones, and nitriles in the presence of DABCO to provide functionalized carboranyl alcohols in good yields. Acetates of these alcohols undergo a facile isomerization with a variety of nucleophiles and afford structurally interesting carboranes. Biological evaluation of these molecules exhibited impressive antiproliferative activity for brain and breast cancer cells.