Browsing by Author "Alves, Nuno G."
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- Effect of monomer organization on the behavior of PSS-PS micellesPublication . Alves, Nuno G.; Rocha, Luciana S.; Moreira, José; Costa, Ana M. Rosa da; Pinheiro, J. P.Six copolymers of styrenesulfonate-styrene (SS-S) of varying molecular weights were prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization and proven to give rise to micelles in aqueous solution. Three are diblock copolymers (PSS-b-PS), while the other three have a random distribution of the two monomers, probably forming a gradient (PSS-co-PS). The latter ones form micelles of smaller sizes and present lower critical micellar concentrations (CMC) than the former. The morphologic and dimensional features of the micelles were obtained by TEM analysis and their CMC were determined by fluorescence spectroscopy.The trace metal ion removal ability of these micelles was tested. Thus the complexation capacity of PSS-b-PS and PSS-co-PS micelles towards Cd and Pb was evaluated using an electro-analytical stripping technique (AGNES). Both micelles performed similarly yielding percentages of metal removal that varied between 85 and 97% and 95-99%, for Cd(II) and Pb(II) respectively. Both copolymers demonstrate a good potential for future application in metal removal from water, namely on Micellar Enhanced Ultrafiltration techniques. (C) 2016 Elsevier B.V. All rights reserved.
- Investigating the binding heterogeneity of trace metal cations with SiO2 nanoparticles using full wave analysis of stripping chronopotentiometry at scanned deposition potentialPublication . Rotureau, Elise; Rocha, Luciana S.; Goveia, Danielle; Alves, Nuno G.; Pinheiro, José PauloSilica oxides nano- and microparticles, as well as silica-based materials, are very abundant in nature and industrial processes. Trace metal cation binding with these bulk materials is generally not considered significant in speciation studies in environmental systems. Nonetheless, this might change for nanoparticulate systems as observed in a previous study of Pb(II) with a very small SiO2 particle (7.5 nm diameter). Besides, metal binding by those nanoparticles is surprisingly characterized by a heterogeneity that increases with the decrease of metal-to-particle ratio. Therefore, it is interesting to extend this study to investigate different trace metals and the influence of the nanoparticle size on the cation binding heterogeneity. Consequently, the Cd(II), Pb(II), and Zn(II) binding by two different sized SiO2 nanoparticles (Ludox LS30 and TM40) in aqueous dispersion was studied for a range of pH and ionic strength conditions, using the combination of the electroanalytical techniques Scanned Stripping ChronoPotentiometry and Absence of Gradients and Nernstian Equilibrium Stripping. The coupling of these techniques provides the free metal concentration in the bulk (AGNES) and information of the free and complex concentration at the electrode surface for each Stripping Chronopotentiometry at Scanned deposition Potential (SSCP). A recent mathematical treatment allows the reconstruction of a portion of the metal to ligand binding isotherm with the included heterogeneity information using the full SSCP wave analysis. In this work, we observed that the Zn(II) binding is homogeneous, Cd(II) is slightly heterogeneous, and Pb(II) is moderately heterogeneous, whereas the results obtained with the 7.5 nm diameter nanoparticle are slightly more heterogeneous than those obtained with the one of 17 nm. These findings suggest that the Zn(II) binding is electrostatic in nature, and for both Cd(II) and Pb(II), there should be a significant chemical binding contribution.
- Ligand size polydispersity effect on SSCP signal interpretationPublication . Rocha, Luciana S.; Botero, Wander G.; Alves, Nuno G.; Moreira, José; Costa, Ana M. Rosa da; Pinheiro, J. P.The present study aims to establish unambiguously the conditions required for the validity of the average diffusion (D) approximation in fully labile systems with significant ligand size polydispersity. The average diffusion coefficient is a key parameter in mass transfer that affects signal interpretation in dynamic electroanalytical techniques. To achieve this goal, the binding of Cd(II) and Pb(II) to binary and ternary mixtures containing chemically homogenous (PSS)n-COOH polymers (ligand excess conditions were required) of different sizes (4, 10 and 30 KDa) was evaluated. It was experimentally evidenced that the average diffusion coefficient (D), can indeed be computed as the weighted average of several metal-polymer complexes of diverse sizes.
- Selective synthesis of 3-(1H-Tetrazol-5-yl)-indoles from 2H-Azirines and ArynesPublication . Grosso, Carla; Alves, Cláudia; Sase, Terver J.; Alves, Nuno G.; Cardoso, Ana L.; Melo, Teresa M. V. D. Pinho e; Lemos, AmericoA new selective synthetic approach to indole derivatives bearing a tetrazole moiety has been developed. Arynes, generated in situ from o-(trimethylsilyl)aryl triflates and KF, reacted smoothly with 2-(2-benzyl-2H-tetrazol-5-yl)-2H-azirines to give 3-(2-benzyl-2H-tetrazol-5-yl)-indole derivatives with high selectivity. Deprotection of the tetrazole moiety gave 3-(1H-tetrazol-5-yl)-indole derivatives.
- Sistemas conjugados: importância na ação e potenciação de fármacos.Publication . Alves, Nuno G.; Brigas, Amadeu F.Os sistemas conjugados apresentam uma reatividade própria devido à deslocalização das suas ligações. Esta reatividade torna-os importantes não só ao nível da indústria química mas também em questões farmacológicas e toxicológicas. Existem bastantes fármacos que exercem a sua função farmacológica devido à capacidade alquilante inerente aos seus sistemas conjugados, podendo a alquilação dar-se por uma reação tipo-Michael ou por uma substituição nucleofílica assistida por um sistema conjugado, como ocorre com compostos com sistemas alílicos. Muitos fármacos citotóxicos ou antibióticos atuam por um mecanismo de alquilação, seja pela alquilação do DNA ou pela modificação covalente de enzimas e outras proteínas. Estas alquilações interferem com os processos celulares levando à apoptose da célula. Por outro lado, existem muitos fenómenos de toxicidade que têm vindo a ser associados ao desenvolvimento de diversas doenças, que ocorrem também devido à alquilação de proteínas e do DNA por moléculas com um sistema conjugado na sua estrutura. Estas alquilações podem levar a respostas imunológicas e à diminuição de função de algumas proteínas endógenas, por alterarem a estrutura destas. No caso da alquilação do DNA, podem provocar mutações que podem causar um descontrolo do ciclo celular dando origem ao desenvolvimento de uma neoplasia. O conhecimento dos mecanismos pelo qual os fármacos e outras moléculas com atividade biológica contendo sistemas conjugados na sua estrutura atuam, a nível endógeno, é bastante relevante tanto na compreensão de determinadas patologias, como na criação de novas moléculas com uma atividade farmacológica melhorada.