Studies on the pauson-khand reaction. Exclusive formation of angularly fused triquinanes from bicyclo[3.3.0]oct-2-ene and propargyl derivatives

Reaction of bicyclo[3.3.0]oct-2-ene with different hexacarbonyl dicobalt complexes of propargyl derivatives leads, under a great variety of experimental conditions, to the exclusive formation of angularly fused triquinanes, the corresponding reduced products being formed if the reaction is run at high temperature. The intermediacy of a π-allyl complex is suggested in order to account for these results, as well as for the presence of minor amounts of Diels-Alder adducts in the reaction mixture.     

Direct entry to the all-cis tricyclo[5.2.1.O4,10]decane (perhydrotriquinacene) skeleton by a cobalt mediated intramolecular cyclization

The perhydrotriquinacene skeleton has been synthesized by a Pauson-Khand bis-annulation process.     

Study of complexation of gliclazide with β-cyclodextrin in solution by nmr techniques

The study of complexation between GL and -CD in liquid medium has been carried out by phase-solubility,¹H and¹³C NMR studies. A formation complex is observed from the phase solubility diagram, being the average association constant of 1094 M^–1, The NMR studies revealed the preferent complexation of the aliphatic moiety of GL. The aromatic moiety is also entrapped, but in minor extent, by the CD molecules.     

Determination of oxygenated and nitro-substituted polycyclic aromatic hydrocarbons by HPLC and electrochemical detection

A method is described for the measurement of oxy- and nitro-substituted polynuclear aromatic hydrocarbons (OXY- and NITRO-PAHs) using high performance liquid chromatography with reductive electrochemical detection. A series of reference OXY- and NITRO-PAHs were separated in a reversed-phase column, conditions for electrochemical detection were established and the compounds were quantified with a sensitivity of 3-0.3 ng injected. Samples of air particulate matter were collected for the analysis of these PAH derivatives and the presence of 9,10-anthraquinone, benz[a]anthracen-7, 12-dione at levels of between 75 and 398 pg/m(3) in the air samples has been confirmed.     

On-line preconcentration system for bismuth determination in urine by flow injection hydride generation inductively coupled plasma atomic emission spectrometry

An on-line bismuth preconcentration and determination system implemented with hydride generation inductively coupled plasma atomic emission spectrometry (HG-ICP-AES) associated to flow injection (FI) was studied. Quinolin-8-ol and Amberlite XAD-7 were used for the retention of bismuth, at pH 4.5. The bismuth complex was removed from the micro-column with nitric acid. The detection limit value for the preconcentration of 100 ml of aqueous solution was 0.02 ng ml(-1) with a relative standard deviation (R.S.D.) of 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for bismuth was linear with a correlation coefficient of 0.999 at levels near the detection limits up to at least 100 ng ml(-1). The method was successfully applied to the determination of bismuth in human urine samples.     

Thermal Study of Different Omeprazole-Γ-CD CO-Ground Systems

Techniques of DSC, TG/DTG, EGD and HSM were used to study and characterize the complex formation and state of dispersion after co-grinding of a 1:1 mixture of omeprazole (OME) and γ-cyclodextrin (γ-CD) under various conditions. The changed crystalline properties of the composites obtained by co-grinding suggested distinct types of interactions between the components, as a consequence of the variations in the grinding procedure. The experimental data clearly revealed that a true solid complex OME-γ-CD was obtained only by wetting the mixture of the components with phosphate buffer during the co-grinding. Other co-grinding procedures yielded only amorphous drug—CD mixtures or their combination with partial complexation.     

An Alternative Approach to Quantify Partition Processes in Confined Environments: The Electrochemical Behavior of PRODAN in Unilamellar Vesicles

Herein, we investigate the behavior of the electroactive molecular probe 6‐propionyl‐2‐dimethyl amino naphthalene (PRODAN) in large unilamellar vesicles (LUV) formed with the phospholipid 1,2‐di‐oleoyl‐sn‐glycero‐3‐phosphatidylcholine (DOPC) by using cyclic voltammetry (CV). The CV studies in pure water confirm our previous spectroscopic results that PRODAN self‐aggregates due to its low water solubility. Moreover, the electrochemical results also reveal that the PRODAN aggregated species are non‐electroactive within the studied electrochemical potential region. In DOPC LUV media, the redox behavior of PRODAN shows how the LUV bilayer interacts with PRODAN aggregated species to form PRODAN monomer species. Moreover, the electrochemical response of PRODAN allows us to propose a model for explaining the electrochemical experimental results and—in conjunction with our measurements—for calculating the value of the partition constant (K_p) of PRODAN between the water and LUV bilayer pseudophases. This value coincides with that obtained through an independent technique. Moreover, our electrochemical model allows us to calculate the diffusion coefficient (D) for the DOPC LUV, which coincides with the D value obtained through dynamic light scattering (DLS). Thus, our data clearly show that electrochemical measurements could be a powerful alternative approach to investigate the behavior of nonionic electroactive molecules embed in a confined environment such as the LUV bilayer. Moreover, we believe that this approach can be used to investigate the behavior of non‐optical molecular drugs embedded in bilayer media.     

Frank Model and Spontaneous Emergence of Chirality in Closed Systems

In a closed system an irreversible enantioselective autocatalysis coupled to a mutual inhibition reaction, corresponding to a fast and low exergonic formation of the heterochiral dimer which reverts to the monomers in the final reaction work‐up, yields absolute asymmetric synthesis even in the absence of chiral polarizations. This is due to the very high chiral amplifications of the initial small statistical deviations from the ideal racemic composition. Moreover, this system is sensitive to very small chiral polarizations (energy differences between transition states below the mJ mol^?1 range). This behaviour can also be observed in reversible exergonic reactions, because the racemization time scale is substantially longer than that of the transformation of the initial reagents. The effect of the presence of other reactions likely to occur (i.e. non‐catalytic transformations, non‐enantioselective catalysis and homodimer formation) is discussed. Even if these decrease the sensitivity of the network in several chemical scenarios, the emergence of kinetically controlled spontaneous symmetry breaking is not hindered. These features, together with the response of the system to a sequential reaction procedure, suggest that a similar type of network is at the heart of the Soai reaction.