Models for torsion homotopy types

Given an integern>1 and any setP of positive integers, one can assign to each topological spaceX a homotopy universal mapX ^(P,n) →X whereX ^(P,n) is an (n−1)-connected CW-complex whose homotopy groups areP-torsion. We analyze this construction and its properties by means of a suitable closed model category structure on the pointed category of topological spaces. The authors acknowledge financial aid given by the DGICYT under projects PB93-0581-C02-01 and PB94-0725.     

Ab initio SCF and DFT models of met-car adducts: Ti8C12(L)n (L = Cl, NH3, CO, C6H6; N = 4, 8)

The addition of Cl, NH₃, CO, C₆H₆ to Ti₈C₁₂ has been investigated by means of ab initio RHF and DFT calculations. The metallocarbohedrene (met-car) molecule has been modelled as a structure of a tetracapped tetrahedron with T_d symmetry and two distinct metal sites, found to be most stable from previous theoretical investigations. The addition of four molecules to the atoms of the external tetrahedron of metal atoms has been found to be exothermic for all ligands considered. The addition of four extra ligands leading to T₈C₁₂(L)₈ appears easy for L = Cl, and also for L = NH₃. It appears that π-bonding molecules, either non-polar like benzene or weakly polar like CO, have much less affinity for the inner tetrahedron of metal atoms, which makes adducts with eight ligands difficult or impossible to obtain in that case. Those results agree with the recently observed reactivity of met-cars.     

Organometallic derivatives of fullerenes: a DFT study of (eta2-Cx)[Pt(PH3)2]n (x = 60, 70, 84; n = 1-6)

To determine the relationship among curvature, patch type, and reactivity of the C-C site, a series of density functional calculations were performed on several substituted fullerenes. [6:6] pyracylene-type sites are the most reactive sites in all analyzed cages: C(60), C(70), and C(84). The binding energy between the Pt(PH(3))(2) unit and fullerene is almost independent of the size of the cage and of the number of metals coordinated on the fullerene surface. Contrarily, curvature and type of carbon-carbon bond are determinant for the coordination strength. The use of relatively large basis sets is necessary to have consistent energies.     

Identification of phenolic compounds in artichoke waste by high-performance liquid chromatography-tandem mass spectrometry

A new fast and efficient method combining liquid chromatography coupled to ionspray mass spectrometry in tandem mode with negative ion detection is described for the qualitative analysis of artichoke waste. Forty-five phenolic compounds were identified on the basis of their mass spectra in full scan mode, mass spectra in different MS-MS modes, and retention times compared with those of available reference substances. The major compounds were found to be both caffeoylquinic and dicaffeoylquinic acids, luteolin glucuronide, luteolin galactoside, quercetin, and some quercetin glycosides.     

In quest of factors that control the enantioselective catalytic Markovnikov hydroboration/oxidation of vinylarenes

This study attempts to rationalise the unpredictable performance of transition metal catalysed asymmetric hydroboration of vinylarenes on varying the precursor of the catalyst from cationic to neutral species, [M(cod)(L-L)]BF4, [M(mu-Cl)(cod)]2/(L-L), the metal (M=Rh and Ir), and the hydroborating reagent (catecholborane, pinacolborane). The approaches are based on the agreement between experimental data provided by (R)-Binap and (R)-Quinap modified catalytic systems and computational data evidenced by DFT calculations and QM/MM strategies. Unprecedentedly high enantiomeric excesses in the hydroboration/oxidation of vinylarenes with both electron-withdrawing substituents ((R)-(+)-1-p-F-phenylethanol, ee up to 92 %) and electron-releasing substituents ((R)-(+)-1-p-MeO-phenylethanol, ee up to 98 %), can be attributed to a rhodium halide key intermediate.     

Microfabricated PCR-electrochemical device for simultaneous DNA amplification and detection

Microfabricated silicon/glass-based devices with functionalities of simultaneous polymerase chain reaction (PCR) target amplification and sequence-specific electrochemical (EC) detection have been successfully developed. The microchip-based device has a reaction chamber (volume of 8 microl) formed in a silicon substrate sealed by bonding to a glass substrate. Electrode materials such as gold and indium tin oxide (ITO) were patterned on the glass substrate and served as EC detection platforms where DNA probes were immobilized. Platinum temperature sensors and heaters were patterned on top of the silicon substrate for real-time, precise and rapid thermal cycling of the reaction chamber as well as for efficient target amplification by PCR. DNA analyses in the integrated PCR-EC microchip start with the asymmetric PCR amplification to produce single-stranded target amplicons, followed by immediate sequence-specific recognition of the PCR product as they hybridize to the probe-modified electrode. Two electrochemistry-based detection techniques including metal complex intercalators and nanogold particles are employed in the microdevice to achieve a sensitive detection of target DNA analytes. With the integrated PCR-EC microdevice, the detection of trace amounts of target DNA (as few as several hundred copies) is demonstrated. The ability to perform DNA amplification and EC sequence-specific product detection simultaneously in a single reaction chamber is a great leap towards the realization of a truly portable and integrated DNA analysis system.     

Keggin polyoxoanions in aqueous solution: ion pairing and its effect on dynamic properties by molecular dynamics simulations

The dynamics of Keggin polyoxoanions in aqueous solution in the presence of monovalent cations is analyzed through molecular dynamics simulations. Together with structural information yielding the radial distribution functions of Li(+), Na(+), and K(+) with three polyoxometalates (POMs) bearing 3-, 4-, and 5- charges, the diffusion coefficient of these POMs is calculated. We found that the effect of the microscopic molecular details of the solvent is a key aspect to interpreting the structural and dynamic data because a competition between electrostatic interactions between the ions and the stability of the solvation shell is established. Furthermore, we show that solvent-shared structures weakly bound to the POM anion play a crucial role in the determination of the dynamic properties of the anion. The nature of these ion pairs, structurally characterized for the first time, is consistent with experimental data available.