Publications

Abstract A phase transition study, including vapour pressure determinations of odd fluorotelomer alcohols {oFTOH; CF3(CF2)(n)CH2OH, with n = 5 to 9}, is reported in order to explore the effect of the successive introduction of -CF2- groups into the molecule on the thermodynamic properties related to (solid + liquid, solid + gas, and liquid + gas) equilibria. An odd-even effect on the thermodynamic parameters of fusion and sublimation was observed in the homologous series of odd fluorotelomer alcohols indicating an increase of the stability in the crystal packing for the members with an odd number of carbon atoms. The vaporization parameters of o-FTOH were compared with the literature data for their alkane analogues and the results showed a higher volatility of liquid fluorotelomer alcohols than their congeners. The higher molecular conformation restriction of perfluorinated alcohols and/or the higher molar mass seems to contribute to their higher entropy of vaporization which drives the volatility of the 1H,1H-perfluorinated alcohols.

Abstract High-precision heat capacities at 298.15 K of the [C(n)C(1)im][Ntf(2)] ionic liquid series were measured with an uncertainty of less than +/- 0.3%, using a drop heat capacity apparatus that was recently updated. The dependence of the c(p)(o) values on the alkyl side chain length for the extended ionic liquid series [C(n)C(1)im][Ntf(2)] (with n = 2 to 8, 10, and 12) displays a trend shift at [C(6)C(1)im][Ntf(2)], which is taken as an evidence for percolation limit. Above this limit there is an increase in the methylene group contribution to the molar heat capacity which is in agreement with the higher molar absolute entropies change observed from the (liquid + vapor) equilibrium results. The obtained experimental results support the model that the ionic liquids tend to be segregated into a polar network and non-polar domains, being followed by an increase of the entropy contribution of the non-polar domains.

Abstract The synthesis of novel cationic gemini surfactants based on serine, with long lipophilic alkyl chains and a spacer linked to the nitrogen atom of the amino acid residue by amine linkages, is described. The most efficient synthetic pathway involves introduction of the spacer into the monomeric precursors, N-alkyl derivatives, by reductive amination of dialdehydes followed by methylation and deprotection. Characterization of the basic micellization properties of the new compounds was carried out by tensiometry and conductimetry. These surfactants present enhanced interfacial properties compared to the monomeric analogues, and show improved performance, namely lower critical micelle concentration (cmc), lower surface tension at cmc and increased micellar ionization, with respect to conventional bis-quaternary ammonium salts (bis-quats).

Abstract We report within this paper the development of a fiber-optic based sensor for Hg(II) ions. Fluorescent carbon nanoparticles were synthesized by laser ablation and functionalized with PEG(200) and N-acetyl-L-cysteine so they can be anionic in nature. This characteristic facilitated their deposition by the layer-by-layer assembly method into thin alternating films along with a cationic polyelectrolyte, poly(ethyleneimine). Such films could be immobilized onto the tip of a glass optical fiber, allowing the construction of an optical fluorescence sensor. When immobilized on the fiber-optic tip, the resultant sensor was capable of selectively detecting sub,micromolar concentrations of Hg(II) with an increased sensitivity compared to carbon dot solutions. The fluorescence of the carbon dots was quenched by up to 44% by Hg(II) ions and interference from other metal ions was minimal.

Abstract Salt-free catanionic surfactants form in water binary systems, thus differing from pseudo-ternary equimolar catanionic mixtures, where salt is present. A miscibility gap, an unusual phenomenon in binary systems, is observed for the lamellar phase of the catanionic surfactant hexadecyltrimethylammonium octylsulfonate. Experimental data show the coexistence of a swollen and a collapsed lamellar phase in a wide two-phase region, while linear swelling is observed for each phase. This phase behavior is suggested to stem mainly from a concentration dependence of the charge density of catanionic bilayer, driven by the much higher solubility of the short chain ionic counterpart (octylsulfonate). Thus, a theoretical cell model based on combined DLVO and short range repulsive potentials is presented in order to provide physical insight into the miscibility gap. Furthermore, the surfactant forms at high dilution a solution phase and exhibits a very low critical micelle concentration (0.0035 wt%). The dilute lamellar phase is in equilibrium with the isotropic solution, and small vesicles can also be observed, apparently as a dispersion of the swollen lamellae in the solution. Upon temperature increase, a vesicle-to-micelle transition occurs. These unusual equilibria can also be qualitatively rationalized by the short chain solubility model.

Abstract Neurodegenerative disorders are becoming more prevalent given the increase in the aging population. This has inspired active research in the development of new drugs that could mark an important advance in the treatment of complex diseases such as Alzheimer's and Parkinson's. With the aim of finding new MAO-B-selective inhibitors, we report the synthesis, in vitro evaluation, and docking simulation of a new series of 3-arylcoumarins variously substituted at the 8-position. Most of the studied compounds show high affinity and selectivity for the hMAO-B isoform, with IC50 values in the low micro- to nanomolar range. Some of them have greater hMAO-B inhibitory activity and selectivity than the reference compound, selegiline. Compounds 7 and 8 are the most active of this series, with compound 8 being fivefold more potent against MAO-B and severalfold more selective than selegiline. Docking experiments were carried out with hMAO-B crystal structures, providing new information about the enzymeinhibitor interaction and the potential therapeutic application of the new 8-substituted 3-arylcoumarins.

Abstract Density and viscosity experimental data for binary mixtures of 1-alkyl-3-methylimidazolium alkylsulfates + water are reported using four ionic liquids: 1-butyl-3-methylimidazolium hydrogensulfate [C(4)mim][HSO4], 1-butyl-3-methylimidazolium methylsulfate [C(4)mim] [C1SO4], 1-ethyl-3-methylimidazolium methylsulfate [C(2)mim] [C1SO4], and 1-ethyl-3-methylimidazolium methylsulfate [C(2)mim][C2SO4]. The choice of the ionic liquids allows us to compare the effects of incrementing the alkyl chain length in the cation and the anion on the measured thermophysical properties behavior. The Gardas and Coutinho group contribution methods were applied to the description of the pure component densities and viscosities allowing the estimation of new group contribution parameters, to extend the applicability of these methods to new ILs. Excess molar volumes and viscosity deviations were calculated and correlated by Redlich-Kister polynomial expansions. .

Abstract A full account is given for the total synthesis and the cytotoxic activity against the human lung tumoral cell line NCI-H460 of (+/-)-7-deoxy-pancratistatin and its 2-epi- and 2,4-diepi- unnatural analogues.

Abstract 2-Methoxymethylpyrrolidine best performed, among several other proline derivatives, to control the enantioselective [3+3] annulation of beta-(hetero)aryl-alpha-nitro-alpha,beta-enals with commercial 2,2-dimethyl-1,3-dioxan-5-one, a procedure that renders highly oxygenated nitrocyclohexanes endowed with five new stereocenters. Use of this reaction allowed the development of a total synthesis of the antitumoral natural product (+)-pancratistatin; it also converted our previous racemic route to tetrodotoxin into an enantioselective one.

Abstract This work reports the first data for the vapor pressures at several temperatures of the ionic liquids, [C(N/2)C(N/2)im][NTf2] (N = 4, 6, 8, 10, 12) measured using a Knudsen effusion apparatus combined with a quartz crystal microbalance. The morphology and the thermodynamic parameters of vaporization derived from the vapor pressures, are compared with those for the 1-alkyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide series, [C(N-1)C(1)im][NTf2] (N = 3 - 9, 11, and 13). It was found that the volatility of [C(N/2)C(N/2)im][NTf2] series is significantly higher than the asymmetric cation ILs with the same total number of carbons in the alkyl side chains, [C(N-1)C(1)im][NTf2]. The observed higher volatility is related with the lower enthalpy of vaporization. The symmetric cation, [C(N/2)C(N/2)im][NTf2], presents lower entropies of vaporization compared with the asymmetric [C(N-1)C(1)im][NTf2], indicating an increase of the absolute liquid entropy in the symmetric cation ILs, being a reflection of a change of the ion dynamics in the IL liquid phase. Moreover both the enthalpy and entropy of vaporization of the [C(N/2)C(N/2)im][NTf2] ILs, present a clear odd-even effect with higher enthalpies/entropies of vaporization for the odd number of carbons in each alkyl chain ([C(3)C(3)im][NTf2] and [C(5)C(5)im][NTf2]).