Maria José Araújo

Spontaneous Vesicle Formation in Catanionic Mixtures of Amino Acid-Based Surfactants: Chain Length Symmetry Effects

The use of amino acids for the synthesis of novel surfactants with vesicle-forming properties potentially enhances the biocompatibility levels needed for a viable alternative to conventional lipid vesicles. In this work, the formation and characterization of catanionic vesicles by newly synthesized lysine- and serine-derived surfactants have been investigated by means of phase behavior mapping and PFG-NMR diffusometry and cryo-TEM methods. The lysine-derived surfactants are double-chained anionic molecules bearing a pseudogemini configuration, whereas the serine-derived amphiphile is cationic and single-chained. Vesicles form in the cationic-rich side for narrow mixing ratios of the two amphiphiles. Two pairs of systems were studied: one symmetric with equal chain lengths, 2C12/C12, and the other highly asymmetric with 2C8/C16 chains, where the serine-based surfactant has the longest chain. Different mechanisms of the vesicle-to-micelle transition were found, depending on symmetry: the 2C12/C12 system entails limited micellar growth and intermediate phase separation, whereas the 2C8/C16 system shows a continuous transition involving large wormlike micelles. The results are interpreted on the basis of currently available models for the micelle-vesicle transitions and the stabilization of catanionic vesicles (energy of curvature vs mixing entropy).

Physicochemical and toxicological properties of novel amino acid-based amphiphiles and their spontaneously formed catanionic vesicles

The design of efficient liposomal systems for drug delivery is of considerable biomedical interest. In this context, vesicles prepared from cationic/anionic surfactants may offer several advantages, mainly due to their spontaneity in formation and long-term stability. There is also an impending need to produce less toxic, more biocompatible amphiphiles, while maintaining the desirable aggregation properties. In this work, we present data for acute toxicity to Daphnia magna (IC(50)), and potential ocular irritation (HC(50)) for some newly prepared ionic surfactants with dodecyl chains, derived from the amino acids tyrosine (Tyr), serine (Ser), hydroxyproline (Hyp) and lysine (Lys). The micellization behavior of the compounds, evaluated from surface tension measurements, is presented and compared to more conventional ionic amphiphiles. Two types of spontaneouly formed catanionic vesicles, composed either by a dodecyltrimethylammonium bromide (DTAB)/Lys-derivative and or Ser-/Lys-derivative mixture, have also been tested for their ecotoxicity and hemolytic potential. All the micelle-forming surfactants as well as the vesicle-containing mixtures are found to have lower ecotoxicity than the reference surfactant DTAB. Moreover, the results from hemolysis and hemoglobin denaturation tests show that the Tyr- and Lys-derivatives are moderately irritant, whereas the Hyp- and Ser- ones are just slightly irritant. Even more significantly, the vesicle-containing mixtures exhibit lower hemolytic activity than the neat surfactants, a positive result for their potential use in liposomal formulations.

In vitro cytotoxicity of a thermoresponsive gel system combining ethyl(hydroxyethyl) cellulose and lysine-based surfactants

The cytotoxicity of three lysine-derived surfactants with a gemini-like structure was evaluated on HeLa cells. The half maximal effective concentration (EC(50)) 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.

Morphology, thermal behavior, and stability of self-assembled supramolecular tubules from lysine-based surfactants.

Synthetic amino acid-based surfactants possess versatile aggregation properties and are typically more biocompatible and biodegradable than surfactants with conventional headgroups. This opens the possibility of a myriad of specialty applications, namely in pharmaceutics, cosmetics, biomedicine, and nanotemplating chemistry. In this work, we have investigated the interfacial and self-assembling properties in aqueous medium of novel double-chained lysine-based surfactants, with particular focus on the behavior of the dodecyl derivative, 12Lys12. Upon cooling from dilute isotropic micellar solutions, this surfactant crystallizes into micrometer-sized tubular structures that induce gelation of the system. The tubules have been characterized in terms of morphology, assembly process, thermal behavior, and stability, by using differential scanning calorimetry, light and scanning electron microscopy, and deuterium NMR. Possible mechanisms for tubule assembly are discussed, on the basis of surfactant molecular shape, H-bonding and electrostatic interactions, and chirality effects.

Lysine-based surfactants as chemical permeation enhancers for dermal delivery of local anesthetics

The aim of this study is to investigate the efficacy of new, biocompatible, lysine-based surfactants as chemical permeation enhancers for two different local anesthetics, tetracaine and ropivacaine hydrochloride, topically administered. Results show that this class of surfactants strongly influences permeation, especially in the case of the hydrophilic and ionized drug, ropivacaine hydrochloride, that is not easily administered through the stratum corneum. It is also seen that the selected permeation enhancers do not have significant deleterious effects on the skin structure. A cytotoxicity profile for each compound was established from cytotoxicity studies. Molecular dynamics simulation results provided a rationale for the experimental observations, introducing a mechanistic view of the action of the surfactants molecules upon lipid membranes.

Crossing borders and linking plural knowledge : biodiversity conservation, ecosystem services and human well-being

The challenges we face today in terms of local, regional and global environmental changes and pressures on biodiversity can only be addressed with a close coupling of approaches from natural and social sciences together with local knowledge. The authors emphasise that biodiversity research and intervention should integrate this new comprehensive perspective, bringing together biological sciences, social sciences and local knowledge. This approach should demystify the traditional dichotomies that still impose epistemological and moral reductionist borders between nature and culture, systematically hiding the heuristic value of the social and cultural dimension of biodiversity loss. In this context, biodiversity is a field dominated by multiple tensions between plural knowledge within science itself and local knowledge (less visible), which brings to the discussion conflicts that are inherent to science, technology, economics, sociology, politics and culture. This is a fundamental dimension to understand and respond to the challenges we are facing on biodiversity loss.

Music and drama in primary schools in the Madeira Island - Narratives of ownership and leadership

A three-year-case study funded by the Foundation for Science and Technology (FCT) from the Portuguese Ministry of Science, Technology and Higher Education was designed to study a 30-year project of music and drama in primary schools in Madeira. This article reports on the narratives of the three main figures in the project as they elaborate on its construction according to the following themes: innovation, philosophies of music education and teacher education. Through the lens of a narrative inquiry, the discourses produced are analysed, taking into account the emerging concepts of ownership and leadership.