Interaction of aryldiazonium salts with some schiff-base complexes of cobalt and ruthenium

The interaction of aryldiazonium ions with some Schiff-base complexes of cobalt and ruthenium have been studied. With cobalt, one-electron oxidation of [Co(II)Salen] occurred; with [Co(I)Salen] the corresponding Co(III)-aryl complexes were isolated. In the case of ruthenium oxidation also occurs, [Ru(Salen)(CO)py] gave the corresponding monocation. The results, especially for ruthenium, are in contrast to the stabilisation of both nitrosyl and aryldiazonium adducts in analogous porphyrin complexes.     

Intramolecular "Aryl-metal chelate ring" pi,pi-interactions as structural evidence for metalloaromaticity in (aromatic alpha,alpha'-diimine)-copper(II) chelates: molecular and crystal structure of aqua(1,10-phenanthroline)(2-benzylmalonato)copper(II) three-hydrate

By reaction of Cu(2)CO(3)(OH)(2), 2-benzylmalonic acid (H(2)Bzmal), and 1,10-phenanthroline (phen), [Cu(Bzmal)(phen)(H(2)O)] x 3H(2)O (compound 1) has been obtained and characterized by thermal, spectral, magnetic, and X-ray diffraction methods. The molecular structure of 1 is remarkably similar to that of [Cu(Bzmal)(bipy)(H(2)O)] x 2H(2)O (compound 2, bipy = 2,2'-bipyridine). In both complexes, the aryl(Bzmal) ring produces an unexpected pi,pi-stacking interaction with the Cu(II)-(aromatic alpha,alpha'-diimine) chelate ring, at an average distance d(pi)(-)(pi) of 3.40 A, involving roughly parallel and smoothly slipped rings. This insight is discussed as new structural evidence for metalloaromaticity of Cu(II)-(aromatic alpha,alpha'-diimine) chelate rings. Interestingly, 1 recognizes itself by a weak intermolecular pi,pi-stacking interaction between aryl(Bzmal) ligands to give pairs of complex molecules. In contrast, there is an intermolecular pyridyl-pyridyl pi,pi-stacking interaction also forming pairs of complex molecules in 2.     

Setting up of recovery profiles: A tool to perform the compliance with recovery requirements for residue analysis

The use of the recovery term has presented some confusion in Analytical Chemistry. Recent IUPAC recommendations propose to distinguish between two terms: recovery or recovery factor, ℜ, and apparent recovery, ℜ*. Apparent recovery includes recovery factor and a new recovery term proposed in this paper, named calibration recovery, ℜ^C, which depends of the type of systematic error due to the matrix effect (constant and/or proportional) and is related to the applied calibration methodology. This paper highlights the dependence of the calibration recovery on the sample analyte concentration and, for extension, of the apparent recovery, defines the recovery profile, and makes evident the need to determine a “fit for purpose” analyte concentration interval to comply with a regulated recovery requirements. An approach to estimate the calibration recovery and its associated uncertainty in relation to the above-mentioned dependence is presented. The usefulness of the proposed methodology has been shown in the quantification of a pesticide by GC-ECD for assessing dermal exposure.     

Purification of neutral protease by dye affinity chromatography

Twenty triazinic dyes were assayed as ligands for the chromatographic affinity purification of a neutral protease from Flavourzyme^™, a commercial preparation. Screening at pH 4.0 allowed the selection of eight dyes on the basis of their high protease adsorption. When the pH was set to 5.0 in order to increase selectivity, only Yellow HE-4R, Red HE-3B, and Cibacron Blue F3G-A maintained protease adsorption at high values. Neither maximum capacities nor dissociation constants calculated from isotherms measured at 8 and 25°C showed great differences. By contrast, a strong temperature effect was evidenced in the elution step: elution at 8°C allowed 70, 81, and 98% recovery of adsorbed protease with Yellow HE-4R, Red HE-3B, and Cibacron Blue F3G-A, respectively, whereas only 20% recovery was attained at 25°C. Based on the results obtained, a purification process for the neutral protease contained in Flavourzyme with Cibacron Blue F3G-A as the affinity ligand was developed, yielding 96% of electrophoretically pure enzyme in a single step, the specific activity rising from 850 to 3650 U/mg.     

Optimization of chromatographic parameters for the determination of biogenic amines in wines by reversed-phase high-performance liquid chromatography

A method suitable for the determination of eight biogenic amines (histamine, tyramine, phenylethylamine, tryptamine, cadaverine, putrescine, spermidine and spermine) in wines has been developed. The method involves derivatization of the amines by treatment with dabsyl chloride, after which the derivates were analysed by reversed-phase liquid chromatography with gradient elution and spectrophotometric detection at 446 nm. Different variables affecting separation were optimized. Validation of the method included calibration experiments, the addition of standards amines for the determination of recovery and repeatability tests. Good linearity of the responses was obtained up to 500 microg l(-1), except for putrescine (up to 2100 microg l(-1)). The detection limits ranged between 10 and 60 microg l(-1) for standard solutions. The method was successfully applied to the analysis of five Spanish wines.     

Molecular Imprinting in Sol-Gel Materials: Recent Developments and Applications

Since its inception five decades ago, imprinted sol-gel materials went practically unnoticed, until in the 1970s the conceptual introduction of molecular imprinting in synthetic polymers triggered a new interest in this field. The recent growth in interest in organic–inorganic hybrid materials prepared by sol-gel chemistry and the development of a variety of new strategies for imprinting polymeric matrices have led to a growing activity in what became known as molecularly imprinted sol-gel materials. This paper intends to give an overview of recent progress in molecular imprinting in sol-gel matrices, the potential analytical applications of these tailor-made materials and their limitations, with the aim of drawing attention to useful information and to enhancing interest in this practically unexplored but promising field.     

Determination of the amino acid tryptophan and the biogenic amine tryptamine in foods by the heavy atom induced-room temperature phosphorescence methodology

Very simple and selective methods are presented to determine the amino acid tryptophan (Trp) and the biogenic amine tryptamine (Tryp), both compounds with an indole-type molecular structure by the methodology named Heavy Atom Induced-Room Temperature Phosphorescence (HAI-RTP) which constitutes the first time that HAI-RTP has been used to detect compounds with non-naphthalenic structures in their molecules. Different variables affecting the phosphorescence signal (heavy atom perturber and sodium sulfite concentration) were carefully studied. The analytical curves give a linear dynamic range of 15-100 ng ml(-1) and a detection limit of 4 ng ml(-1) for Trp and 94-400 ng ml(-1) and 28 ng ml(-1) for Tryp. The methods have been successfully applied to the analysis of complex food matrices such as the presence of tryptophan in yoghurt and tryptamine in bottled beer. A single alkaline hydrolysis to release Trp from yoghurt proteins and two methods for extracting Tryp from beer samples are proposed and optimised. A total Trp content of 374 mg of Trp per kg of yoghurt was quantified by the standard addition method of calibration and a recovery of 90% was obtained for 250 ng ml(-1) of Tryp in spiked non-alcoholic beer samples.     

Understanding the catalytic role of flexible chiral δ-amino alcohols: the 1-(2-aminoethyl)norbornan-2-ol model

An empiric first approach to the knowledge about the structural factors influencing the catalytic behavior of conformationally flexible δ-amino-alcohol-based ligands, for the enantioselective addition of dialkylzincs to prochiral carbonyl groups, has been applied using the 1-(2-aminoethyl)norbornan-2-ol moiety as the model chiral system, and the asymmetrically catalyzed addition of diethylzinc to benzaldehyde as the test reaction. For this purpose, a selected small library of seven norbornane-based chiral ligands, bearing well-defined structural variations to allow a comparative study, that is, variation of the relative configuration and steric hindrance at the C(2), C(3) and/or C(7) norbornane positions, has been synthesized and probed in the mentioned test reaction. The experimental results obtained have been rationalized empirically using diastereomeric Noyori-like transition states, demonstrating that the conformational flexibility of the δ-amino-alcohol ligands, contrary to the more studied and rigid β-amino-alcohols, plays a crucial role on the catalytic behavior of such ligands (stereochemical sense and degree of the stereodifferentiation in the asymmetric process), which makes such structural factors, important for the improved design of new related chiral catalysts. In this sense, a robust crude empirical model for the prediction of the catalytic behavior of such δ-amino-alcohol-based ligands is proposed.     

Room-temperature synthesis and conductivity of the pyrochlore type Dy2(Ti1−yZry)2O7 (0?y?1) solid solution

Different compositions in a solid solution of general formula Dy₂(Ti_1−yZr_y)₂O₇, showing high oxygen ion conductivity, have been successfully prepared at room temperature via mechanochemical synthesis. Stoichiometric mixtures of the constituent oxides were dry milled together in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by X-ray diffraction and revealed that, in all cases and after milling for 19 h, the powder mixtures consisted of a single phase. Electrical properties were measured on sintered pellets as a function of frequency, temperature and zirconium content, revealing an increase in conductivity of more than one order of magnitude for y?0.4, which, as observed in the similar Y₂(Ti_1−yZr_y)₂O₇, has been related with the onset of disordering of the anion sublattice. Despite increasing structural disorder with increasing Zr content, conductivity remains almost constant for y>0.6, reaching a maximum value of ∼5×10⁻³ for Dy₂Zr₂O₇ at 900 °C.     

The modulating possibilities of dicarbollide clusters: optimizing the Kharasch catalysts

exo-Cluster dicarbollides substitution has allowed tuning of the E degrees (Ru(II)/Ru(III)) potential to obtain the best-performing Kharasch catalyst. We postulate that this is possible through the to-and-fro electron movement between the boron cluster and the sulfonium moieties.