Publications

Abstract A water soluble complex of neodymium(III) with CdTe quantum dots nanoparticles was synthesized. The obtained homogeneous solutions were characterized by fluorescence, X-ray photoelectron and energy dispersive X-ray spectroscopies. The effect of the refluxing time of the reaction on the fluorescence intensity and emission wavelength has been studied. It was found that the emission wavelength of the solutions of neodymium(III) complex capped CdTe QDs nanoparticles shifted from about 540 to 735 nm. For an emission wavelength of 668 nm, the most reproducible nanoparticles obtained, the pH effect over the fluorescence emission and its intensity were studied. The purified and lyophilized solid obtained was morphologically characterized by transmission electron microscopy (TEM). The quantitative composition was determined by fluorescence X-ray spectroscopy (EDAX) and the X-ray photoelectron analysis (XPS) confirmed the presence of neodymium(III) at the surface of the CdTe nanoparticles forming a complex with the carboxylate groups from 3-mercaptopropanoic acid of the CdTe QDs. Due to the optical behavior of this complex, it could be of potential interest as a light source in optical devices.

Abstract The firefly oxyluciferin family of fluorophores has been attracting attention from the research community, due to their role on firefly bioluminescence. Moreover, this family exhibits a very efficient fluorescence quenching process. The elucidation of this process is very important, as it may occur inside of the luciferase active site, thereby decreasing the life time of bioluminescence. To this end we have used a computational approach to study the fluorescence quenching of firefly luciferin, the most studied member of the oxyluciferin family of fluorophores. We have found that the fluorescence quenching is due to the excited state protonation of the nitrogen heteroatom of the benzothiazole moiety. This protonation leads to a singlet to triplet intersystem crossing to triplet excited states, which explains the quenching of fluorescence.

Abstract Two series of novel cationic gemini surfactants based on the amino acid serine have been synthesized. These compounds contain long alkyl chains linked to the nitrogen atoms of the amino acid residues, as well as spacers interconnecting two carboxylic acid groups, through amide or ester bonds. The most efficient synthetic pathway was established; it involves the introduction of the spacers into the N, N-dialkylated monomeric precursors by peptide condensation methods with diamines or diols, with subsequent methylation and deprotection to yield the final target surfactants. The effects of molecular structure, type of spacer linkage, and spacer length on the interfacial and cytotoxic properties of these gemini surfactants are reported and discussed; studies on gemini surfactants with amine linkages and other relevant homologous compounds (conventional bis-quat gemini and monomeric surfactants) are also included. Overall, it is shown that cationic serine-based gemini surfactants have enhanced interfacial properties and low cytotoxicities, offering potential use in technical and biological applications.

Abstract Sol-gel molecularly imprinted materials (MIMs) are traditionally obtained by grinding and sieving of a monolith formed by bulk polymerization. However, this process has several drawbacks that can be overcome if these materials are synthesized directly in the spherical format. This work aimed at the development of two efficient methods to prepare spherical glycylglycine-templated silica ("whole-imprinted" and surface-imprinted) through a combination of sol-gel and emulsion techniques. The synthesis of the microspheres was optimized regarding emulsion and sol-gel parameters. Imprinting efficiency of the prepared materials was studied by solid phase extraction and flow microcalorimetry. The particles prepared with glycylglycine and functional monomer, in basic medium (using cyclohexane as non-polar continuous medium) presented the highest imprinting factor - 2.5 - and the respective surface-imprinted material presented an imprinting factor of 1.5. The results of flow microcalorimetry confirmed the action of different mechanisms of glycylglycine adsorption: entropically-controlled interactions were present for the "whole-imprinted" material, indicating adsorption inside small imprinted pores; enthalpically-controlled interactions were observed for the surface-imprinted material, a behaviour more compatible with a template/surface-only interaction. Globally, the two approaches allowed for a successful imprinting effect which was more extensive for the "whole-imprinted" material, whereas the surface-imprinting feature confers to the surface-imprinted xerogel advantages regarding mass transfer kinetics. Overall, the spherical particles obtained by both approaches presented characteristics, such as sphericity, mesoporosity, easy/fast accessibility to imprinted sites, important indicators that these materials maybe candidates for stationary phases for efficient, selective chromatographic separation.

Abstract The cytotoxicity of three lysine-derived surfactants with a gemini-like structure was evaluated on HeLa cells. The half maximal effective concentration (EC50) was estimated from the dose-response curves and the values indicated an increase in toxicity with the increase in alkyl chain length. The shorter chain length surfactant (C-6) was shown to be less cytotoxic than sodium dodecyl sulfate (SDS), and all the lysine-derived surfactants were less toxic than the cationic cetyl trimethylammonium bromide (CTAB). The presence of ethyl (hydroxyethyl) cellulose (EHEC), shown previously to form thermoresponsive gels in combination with these surfactants, was found to contribute to a lower toxicity on HeLa cells. The conjecture is that the polymer-surfactant interactions in forming mixed micelles are the key contributors to the enhanced biocompatibility of the hydrogels. The most promising results were obtained in the presence of either the most hydrophilic surfactant or in the presence of the longest chain-length surfactant. For the latter, very low concentrations are needed to induce a sol-gel transition of EHEC semi-dilute solutions.

Abstract Due to their role in the metabolism of monoamine neurotransmitters, MAO-A and MAO-B present a significant pharmacological interest. For instance the inhibitors of human MAO-B are considered useful tools for the treatment of Parkinson Disease. Therefore, the rational design and synthesis of new MAOs inhibitors is considered of great importance for the development of new and more effective treatments of Parkinson Disease. In this work, Quantitative Structure Activity Relationships (QSAR) has been developed to predict the human MAO inhibitory activity and selectivity. The first step was the selection of a suitable dataset of heterocyclic compounds that include chromones, coumarins, chalcones, thiazolylhydrazones, etc. These compounds were previously synthesized in one of our laboratories, or elsewhere, and their activities measured by the same assays and for the same laboratory staff. Applying linear discriminant analysis to data derived from a variety of molecular representations and feature selection algorithms, reliable QSAR models were built which could be used to predict for test compounds the inhibitory activity and selectivity toward human MAO. This work also showed how several QSAR models can be combined to make better predictions. The final models exhibit significant statistics, interpretability, as well as displaying predictive power on an external validation set made up of chromone derivatives with unknown activity (that are being reported here for first time) synthesized by our group, and coumarins recently reported in the literature.

Abstract Objectives With the aim of finding the structural features governing binding activity and selectivity against adenosine receptors (ARs), several 3-subtituted coumarins with amide (compounds 36) and carbamate (79) functions were synthesized. To study its possible influence on the binding activity and selectivity, a hydroxyl substituent was also introduced at position 4 of the coumarin moiety. Methods A new series of coumarins (39) were synthesized and evaluated by radioligand binding studies towards ARs. Key findings None of the 4-hydroxy derivatives (4, 8 and 9) showed binding affinity for any of the ARs. None of the compounds interacted with the hA2B AR (Ki > 100 000 nm). Compounds 3, 5, 6 and 7 had different activity profiles with dissimilar binding affinity and selectivity towards human A1, A2A and A3 ARs. Conclusions The most remarkable derivative is compound 7, which presents the best affinity and selectivity for the A3 adenosine receptor (Ki = 5500 nm).