Stabilization of NH tautomers of quinolines by osmium and ruthenium

Complexes OsH2Cl2(PiPr3)2 and RuH2Cl2(PiPr3)2 promote the tautomerization of quinoline and 8-methylquinoline to NH tautomers, which lie about 44 kcal.mol-1 above the usual CH tautomers. The NH tautomers are stabilized by coordination to the metal center and by means of a Cl...HN interaction. As a consequence, the six-coordinate elongated dihydrogen complexes OsCl2{kappa-C2-(HNC9H5R)}(eta2-H2)(PiPr3)2, the five-coordinate derivatives RuCl2{kappa-C2-(HNC9H5R)}(PiPr3)2, and the six-coordinate dihydrogen compounds RuCl2{kappa-C2-(HNC9H5R)}(eta2-H2)(PiPr3)2 (R = H, Me) have been isolated and characterized.     

Combination of mid- and near-infrared spectroscopy for the determination of the quality properties of beers

The combination of infrared (MIR) and near-infrared (NIR) spectroscopy has been employed for the determination of important quality parameters of beers, such as original and real extract and alcohol content. A population of 43 samples obtained from the Spanish market and including different types of beer, was evaluated. For each technique, spectra were obtained in triplicate. In the case of NIR a 1 mm pathlength quartz flow cell was used, whereas attenuated total reflectance measurements were used in MIR. Cluster hierarchical analysis was employed to select calibration and validation data sets. The calibration set was composed of 15 samples, thus leaving 28 for validation. A critical evaluation of the prediction capability of multivariate methods established from the combination of NIR and MIR spectra was made. Partial least squares (PLS) and artificial neural networks (ANN) were evaluated for the treatment of data obtained in each individual technique and the combination of both. Different parameters of each methodology were optimized. A slightly better predictive performance was obtained for NIR-MIR combined spectra, and in all the cases ANN performs better than PLS, which may be interpreted from the existence of some non-linearity in the data. The root-mean-sqare-error of prediction (RMSEP) values obtained for the combined NIR-MIR spectra for the determination of real extract, original extract and ethanol were 0.076% w/w, 0.14% w/w and 0.091% v/v.     

Chemical radiation studies of 8-bromo-2'-deoxyinosine and 8-bromoinosine in aqueous solutions

The reactions of hydrated electrons (e(aq) (-)) with 8-bromo-2'-deoxyinosine (8) and 8-bromoinosine (12) have been investigated by radiolytic methods coupled with product studies and have been addressed computationally by means of BB1K-HMDFT calculations. Pulse radiolysis revealed that one-electron reductive cleavage of the C--Br bond gives the C8 radical 9 or 13 followed by a fast radical translocation to the sugar moiety. Selective generation of a C5' radical occurs in the 2'-deoxyribo derivative, whereas in the ribo analogue the reaction is partitioned between the C5' and C2' positions with similar rates. Both C5' radicals undergo cyclizations, 10-->11 and 14-->15, with rate constants of 1.4 x 10(5) and of 1.3 x 10(4) s(-1), respectively. The redox properties of radicals 10 and 11 have also been investigated. A synthetically useful photoreaction has also been developed as a one-pot procedure that allows the conversion of 8 to 5',8-cyclo-2'-deoxyinosine in a high yield and a diastereoisomeric ratio (5'R)/(5'S) of 4:1. The present results are compared with data previously obtained for 8-bromoadenine and 8-bromoguanine nucleosides. Theory suggests that the behavior of 8-bromopurine derivatives with respect to solvated electrons can be attributed to differences in the energy gap between the pi*- and sigma*-radical anions.     

Separation of carbon nanotubes in aqueous medium by capillary electrophoresis

A robust and reproducible method for the dispersion of carbon nanotubes, either single-walled or multi-walled is presented. Dispersion of nanotubes was achieved as surfactant-coated species of sodium dodecyl sulphate. The addition of small amounts of hydroxypropyl methyl cellulose (HPMC) together with the surfactant, sodium dodecyl sulphate, was found critical to achieve reproducible nanotubes dispersion and to obtain an homogeneous and stable solution. This solution is further analyzed by capillary electrophoresis using a background electrolyte solution containing a polymer, 0.025% (w/v) HPMC solution prepared in 5 mM ammonium acetate at pH 8.03. This electrophoretic method presents a high reproducibility between runs, being an interesting alternative to study nanotube size distribution or characterization after synthesis. In addition, the methodology developed allowed the study of the interaction of the different types of carbon nanotubes with a molecular probe such as pentachlorophenol. This procedure was showed effective to detect small differences on the chemical/physical surface properties of the nanotubes. The different interaction behavior found within the two SWNTs selected was critically discussed.     

C-H bond activation and subsequent C-C bond formation promoted by osmium: 2-vinylpyridine-acetylene couplings

Complex OsH2Cl2(PiPr3)2 promotes the C-H activation of 2-vinylpyridine and subsequently couples the activated substrate with a second 2-vinylpyridine and two acetylene molecules. In the absence of 2-vinylpyridine, the activated substrate is coupled with an acetylene unit to afford a 2-butadienylpyridine derivative.     

Ligand effects on the structures of extended networks of dicyanamide-containing transition-metal ions

The structural characterization of a series of complexes of formula [M(dca)2L]n, where dca = dicyanamide, L = 1,10-phenanthroline (phen) [1-4] and 2,9-dimethylphenanthroline (2,9-dmphen) [9-12], and M = Mn (1 and 9), Fe (2 and 10), Co (3 and 11), and Ni (4 and 12), has revealed the effect of the presence of the methyl substituents of L on the resulting network. The structure of [Mn(dca)2(phen)]n (1), which is identical to those of 2-4, together with the investigation of its magnetic properties in the temperature range of 77-300 K were reported elsewhere. The use of the 4,7-dimethylphenanthroline (4,7-dmphen) as the co-ligand yielded a series of compounds of formula [M(dca)2(4,7-dmphen)]n [M = Mn (5), Fe (6), Co (7), and Ni (8)], which are isostructural with 1-4. Compounds containing phen (1-4) and 4,7-dmphen (5-8) are made of two-dimensional grids of metal atoms, each metal atom being linked to three other metal centers through single (three metal atoms involved) and double (two metal atoms involved) dca bridges exhibiting the mu-1,5 coordination mode. The isostructural complexes [M(dca)2(2,9-dmphen)]n (9-12) also have a sheetlike structure, the metal atoms in each layer being linked by two single and one double mu-1,5-dca units, as in 1-8. However, the topology of the network in 9-12 is different from that in 1-8 because of the different arrangement of the two single mu-1,5 dca bridges: cis in 1-8 versus trans in 9-12. The magnetic study of compounds 1-12 in the temperature range of 1.9-290 K has revealed the occurrence of weak ferromagnetic (M = Ni) and antiferromagnetic interactions (M = Mn, Fe, and Co). The different magnetic behavior in 1-12 was analyzed in the light of their structures, and the values of the magnetic interactions were compared to those of related systems.     

The nicholas approach to natural product hybrids

The intermolecular Nicholas reaction of terpene-based scaffolds is an excellent access to natural product hybrid compounds. These intermolecular reactions have a low selectivity and are scarcely efficient for non-conjugated cations, but they are highly efficient to produce new terpene structures through an intramolecular reaction pathway. The use of cations derived from natural product derived [Co(2)(CO)(6)]-enyne complexes is, in contrast, a highly efficient regio- and stereoselective procedure to prepare very complex structures, incorporating diverse densely functionalized or labile moieties. Thus, beta-pinene-diterpene-alkaloid or homohybrids can be accessed in totally stereo-, regio- and siteselective fashion. This approach efficiently discriminates between different propargylic positions by selecting the nature of the alcohol, being the enyne-derived cations the most reactive. The chimera 38 with a steroid-terpene-indole skeleton was prepared in this way.     

Self-assembled FePt nanocrystals with large coercivity: reduction of the fcc-to-L1(0) ordering temperature

Herein we report the synthesis and properties of Fe(55)Pt(45) nanoparticles, both monodisperse and self-assembled into hexagonal close-packed and cubic arrays of 4.0 +/- 0.2 nm size in an L1(0) structure, obtained by a modified polyol process. The new synthetic route improved the control over the particle composition, thereby reducing the temperature required to convert from face-centered cubic (fcc) to face-centered tetragonal (fct) phase by some 30-50 degrees C without additives. Annealing at 550 degrees C for 30 min converts the self-assembled nanoparticles into ferromagnetic nanocrystals with large coercivity, H(C) = 11.1 kOe. Reducing the fcc-to-fct (L1(0)) ordering temperature avoided particle coalescence and decreased the loss in particle positional order without compromising the magnetic properties, as is generally observed when additives are used.     

Determination of benzene in gasoline using direct injection-mass spectrometry

A high-speed determination of benzene in gasoline samples using a non-separative method based on direct injection into the mass spectrometer is proposed. The results obtained are very similar to those provided with fast GC-MS.The calibration set was made up of gasoline samples in which the benzene was determined chromatographically and samples of gasoline subjected to a process of evaporation - until the complete disappearance of the original benzene - to which known concentrations of this compound had been added. A PLS1 multivariate calibration model was constructed. Cross-validation was used to select the optimum number of PLS components. The prediction capacity of the model was checked with an additional group of gasoline samples that had not been used either in the construction or in the validation of the model.With the direct injection method proposed here it was possible to analyse 24 samples over a period of 1 h. The direct injection method is rapid, simple and - in view of the results - highly suitable for the determination of benzene in gasoline samples.     

High-nuclearity ruthenium carbonyl cluster complexes derived from 2-amino-6-methylpyridine: synthesis of nonanuclear derivatives containing mu4- and mu5-oxo ligands

Nonanuclear cluster complexes [Ru9(mu3-H)2(mu-H)(mu5-O)(mu4-ampy)(mu3-Hampy)(CO)21] (4) (H2ampy = 2-amino-6-methylpyridine), [Ru9(mu5-O)2(mu4-ampy)(mu3-Hampy)2(mu-CO)(CO)20] (5), [Ru9(mu5-O)2(mu4-ampy)(mu3-Hampy)2(mu-CO)2(CO)19] (6), and [Ru9(mu4-O)(mu5-O)(mu4-ampy)(mu3-Hampy)(mu-Hampy)(mu-CO)(CO)19] (7), together with the known hexanuclear [Ru6(mu3-H)2(mu5-ampy)(mu-CO)2(CO)14] (2) and the novel pentanuclear [Ru5(mu4-ampy)(2)(mu-CO)(CO)12] (3) complexes, are products of the thermolysis of [Ru3(mu-H)(mu3-Hampy)(CO)9] (1) in decane at 150 degrees C. Two different and very unusual quadruply bridging coordination modes have been observed for the ampy ligand. Compounds 4-7 also feature one (4) or two (5-7) bridging oxo ligands. With the exception of one of the oxo ligands of 7, which is in a distorted tetrahedral environment, the remaining oxo ligands of 4-7 are surrounded by five metal atoms. In carbonyl metal clusters, quadruply bridging oxo ligands are very unusual, whereas quintuply bridging oxo ligands are unprecedented. By using 18O-labeled water, we have unambiguously established that these oxo ligands arise from water.