Publications

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. © 2012 by World Scientific Publishing Co. Pte. Ltd.

Abstract In the present work, the standard (p degrees = 0.1 MPa) molar enthalpies of formation of xanthydrol, 9-xanthenecarboxylic acid and 9-xanthenecarboxamide, in the gaseous state, at T = 298.15 K, were determined by experimental and computational studies. The experimental techniques used were the static-bomb combustion calorimetry, which enabled the determination of the standard molar enthalpy of formation, in the crystalline state, and the vacuum drop microcalorimetric and the Knudsen effusion techniques used to derive the enthalpy of sublimation. For comparison purposes, we performed standard ab initio molecular orbital calculations, using the G3(MP2)//B3LYP composite procedure, of the enthalpies of several homodesmotic reactions, allowing to extract the standard molar enthalpies of formation, in the gaseous state, of the three xanthene derivatives considered in this work. The calculated results are in good agreement with the experimental data.

Abstract Two antimicrobial cryptopeptides from the N1 domain of bovine lactoferrin, lactoferricin (LFcin17-30) and lactoferrampin (LFampin265-284), together with a hybrid version (LFchimera), were tested against the protozoan parasite Leishmania. All peptides were leishmanicidal against Leishmania donovani promastigotes, and LFchimera showed a significantly higher activity over its two composing moieties. Besides, it was the only peptide active on Leishmania pifanoi axenic amastigotes, already showing activity below 10 mu M. To investigate their leishmanicidal mechanism, promastigote membrane permeabilization was assessed by decrease of free ATP levels in living parasites, entrance of the vital dye SYTOX Green (MW = 600 Da) and confocal and transmission electron microscopy. The peptides induced plasma membrane permeabilization and bioenergetic collapse of the parasites. To further clarify the structural traits underlying the increased leishmanicidal activity of LFchimera, the activity of several analogues was assessed. Results revealed that the high activity of these hybrid peptides seems to be related to the order and sequence orientation of the two cryptopeptide moieties, rather than to their particular linkage through an additional lysine, as in the initial LFchimera. The incorporation of both antimicrobial cryptopeptide motifs into a single linear sequence facilitates chemical synthesis and should help in the potential clinical application of these optimized analogues.

Abstract A low-temperature polymorph of 1,1':3',1 '': 3 '',1''': 3''',1''''-quinquephenyl (m-quinquephenyl), C30H22, crystallizes in the space group P2(1)/c with two molecules in the asymmetric unit. The crystal is a three-component nonmerohedral twin. A previously reported room-temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993). Chem. Commun. pp. 17951797] also crystallizes with two molecules in the asymmetric unit in the space group P-1. The unit-cell volume for the low-temperature polymorph is 4120.5 (4) angstrom(3), almost twice that of the room-temperature polymorph which is 2102.3 (6) angstrom(3). The molecules in both structures adopt a U-shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit-cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C-H center dot center dot center dot pi interactions.

Abstract Solid lipid nanoparticles (SLNs) produced from multiple emulsions technology theoretically enclose an inner aqueous compartment suitable for hydrophilic biomolecules. This paper reports a 3(3) full factorial design study to optimize SLNs formulations for hydrophilic biomolecules. The concentrations of solid lipid, lipophilic and hydrophilic emulsifiers were set as the 3 independent variables. Mean particle size (Z-Ave), polydispersity index (PI) and zeta potential (ZP) were set as the dependent variables. The selected optimized parameters were set as 1.0 wt% of solid lipid, 0.25 wt% of lipophilic emulsifier and 1.5 wt% of hydrophilic emulsifier. The coating of SLNs with sodium alginate was found to improve the ZP of the lipid particles and these results suggest that the ideal concentration was 0.75 wt%. The influence of low pH (i.e.. about 2-3) in the inner aqueous phase was stronger than higher pH values, contributing for the production of larger droplet sizes. Nevertheless, these systems can be useful for the incorporation of biomolecules requiring a pH ranging between 4 and 10. SLNs based on multiple emulsions technology were found to be a promising approach for the incorporation of several hydrophilic drugs, such as proteins and peptides.

Abstract Much stronger binding is seen in aqueous solutions between the anionic polyelectrolyte potassium poly(vinyl sulfate) and the substitution labile aluminium(III) than with the kinetically inert chromium(III). This strongly supports the idea that entropy driven water loss from the hydration sphere of the metal ion plays a major role in driving binding of the trivalent metal ion to the polyelectrolyte.

Abstract Herein a core scaffold of 1-phenylnaphthalenes and 1,8-diphenylnaphthalenes with different substituents on the phenyl rings was used to study substituent effects on parallel-displaced aromatic p...p interactions. The energetics of the interaction was evaluated in gas phase based on the standard molar enthalpies of formation, at T=298.15 K, for the compounds studied; these values were derived from the combination of the results obtained by combustion calorimetry and Knudsen/Quartz crystal effusion. A homodesmotic gas-phase reaction scheme was used to quantify and compare the intramolecular interaction enthalpies in various substituted 1,8-diphenylnaphthalenes. The application of this methodology allowed a direct evaluation of aromatic interactions, and showed that substituent effects on the interaction enthalpy cannot be rationalized solely on classical electrostatic grounds, because no correlation with the smeta or spara Hammett constants was observed. Moreover, the results obtained indicate that aromatic p...p interactions are significantly enhanced by substitution, in a way that correlates with the ability of the interacting aryl rings to establish dispersive interactions. A combined experimental and computational approach for calculation of the true aromatic p...p interaction energies in these systems, free of secondary effects, was employed, and corroborates the rationale derived from the experimental results. These findings clearly emphasize the role of dispersion and dilute the importance of electrostatic forces on this type of interactions.

Abstract An electrochemical sensor for the determination of the chlorophenoxy herbicide MCPA has been developed, based on a combination of multi-walled carbon nanotubes with incorporated beta-cyclodextrin and a polyaniline film modified glassy carbon electrode. The proposed molecular host-guest recognition based sensor has a high electrochemical sensitivity for the determination of MCPA. The electrochemical behaviour of MCPA at the chemically modified electrode was investigated in detail by cyclic voltammetry. The results indicate that the beta-CD/MWCNT modified glassy carbon electrode exhibits efficient electrocatalytic oxidation of MCPA with high sensitivity, stability and lifetime. The analytical characteristics of this film were used for the quantitative determination of MCPA in natural waters. Cyclic voltammetry in phosphate buffer solution at pH 6.0, allowed the development of a method to determine MCPA, without any previous steps of extraction, clean-up, or derivatization, in the range of 10-100 mu mol L-1, with a detection limit of 0.99 mu mol L-1 in water. The results were statistically compared with those obtained through an established high-performance liquid chromatography technique, no significant differences having been found between the two methods.

Abstract The past years have witnessed a persistent deterioration of sexual health, especially among young adults. The most concerning problems are sexually transmitted diseases and non-planned pregnancies that cost millions of dollars in healthcare. Sexually transmitted diseases are usually represented by cutaneous signs which may provide a portal of entry for the transmission of other infections, such as HIV. Skin is a widely used route of delivery of drugs locally, and also potentially promising pathway for systemic targeting. Skin contributes to the physical and chemical protection of the body, providing an important barrier against topical drug administration. However, it may be overcome by nanotechnology-based systems, especially in skin diseases, reducing the side effects. Different approaches have been focused on nanotechnology, not only in the treatment of sexually transmitted diseases, but also in diagnostics and prevention of these infections. The present paper highlights recent advances in the nanotechnology-based systems for the diagnostic, prevention and topical treatment of sexually transmitted diseases.