Publications

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.

Abstract Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans. Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this article, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential (ZP) were 500 nm and -34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography, were 99.06 +/- 0.3 and 17.48 +/- 0.05, respectively. Effective incorporation of PZQ into the particles was confirmed by small angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room temperature (25 degrees C) and at 4 degrees C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days. Results showed a relatively long-term physical stability after storage at 4 degrees C, without drug expulsion.

Abstract Antimicrobial peptides (AMPS) take part in the immune system by mounting a first line of defense against pathogens. Recurrent structural and functional aspects are observed among peptides from different sources, particularly the net cationicity and amphipathicity. However, the membrane seems to be the key determinant of their action, either as the main target of the peptide action or by forming a barrier that must be crossed by peptides to target core metabolic pathways. More importantly, the specificity exhibited by antimicrobial peptides relies on the different lipid composition between pathogen and host cells, likely contributing to their spectrum of activity. Several mechanisms of action have been reported, which may involve membrane permeabilization through the formation of pores, membrane thinning or micellization in a detergent-like way. AMPs may also target intracellular components, such as DNA, enzymes and even organelles. More recently, these peptides have been shown to produce membrane perturbation by formation of specific lipid-peptide domains, lateral phase segregation of zwitterionic from anionic phospholipids and even the formation of non-lamellar lipid phases. To countermeasure their activity, some pathogens were successful in developing effective mechanisms of resistance to decrease their susceptibility to AMPs. The functional and integral knowledge of such interactions and the clarification of the complex interplay between molecular determinants of peptides, the pathogen versus host cells dichotomy and the specific microenvironment in which all these elements convene will contribute to an understanding of some elusive aspects of their action and to rationally design novel therapeutic agents to overcome the current antibiotic resistance issue.

Abstract Antioxidants are additives largely used in industry for delaying, retarding, or preventing the development of oxidative deterioration. Propyl gallate (E310) is a phenolic antioxidant extensively used in the food, cosmetics, and pharmaceutical industries. A series of lab experiments have been developed to teach students about the importance and significance of antioxidants in industry. In the first laboratory, the antioxidant propyl gallate is obtained and the structure identified. Students become acquainted with laboratory techniques such as extraction, crystallization, and thin-layer chromatography. In the second laboratory, spectroscopic data (IR, H-1 and C-13 NMR) is acquired and interpreted. Students become familiar with the basic concepts of organic compound identification. In the third laboratory, the antioxidant activity of the synthesized additive and gallic acid is evaluated by DPPH (2,2-diphenyl-1-picrythydrazyl) assay using trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) as standard. Concepts such as free radical chemistry, preparation of analytical samples, calibration methods, and UV-vis spectrophotometry, are reviewed. This series of experiments can also be used to explore the effect of substituents on radical stability because structurally related compounds were found to have qualitatively different antioxidant profiles.

Abstract The measurement of aryl-naphthyl rotational barriers, Delta G(double dagger), in various solvents for two substituted 1,8-diarylnaphthalenes by dynamic H-1 NMR showed that Delta G(double dagger) trends in aromatic systems can be fully rationalized only when considering the different types of aromatic interactions that can be established in the ground and transition states, namely, intramolecular interactions involving the aromatic rings and specific solvation interactions.

Abstract The chlorophenoxy herbicide MCPA(4-chloro-2-methylphenoxyacetic acid), widely used for the control of broad-leaf weeds primarily in cereal and grass seed crops, still remains one of the most often used herbicides in Portugal. As the formation of inclusion complexes with cyclodextrins can improve its solubility properties, the interaction between the herbicide MCPA and beta-cyclodextrin was investigated. The stability constants describing the extent of formation of the complexes have been determined by phase-solubility studies. Different analytical techniques [ultraviolet-visible spectroscopy (UV-Vis), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (H-1 NMR)] were employed for a thorough investigation of the structural characteristics of the obtained complexes, which exhibited distinct features and properties from both "guest" and "host" molecules. FTIR and H-1 NMR data obtained for the MCPA/beta-CD complexes gave information about the interaction between MCPA and the nonpolar cyclodextrin cavity. The dramatic change observed in band frequency and proton displacements of OCH2 group and H6 aromatic proton confirmed the inclusion of MCPA in beta-CD. The formation of an inclusion complex between MCPA and beta-CD increased the aqueous solubility of this herbicide which could be a particularly advantageous property for some specific applications, namely to improve commercial formulation and for environmental protection.