Browsing by Author "Pinheiro, J. P."
Now showing 1 - 10 of 42
Results Per Page
Sort Options
- Application of permeation liquid membrane and scanned stripping chronopotentiometry to metal speciation analysis of colloidal complexesPublication . Domingos, R. F.; Benedetti, M. F.; Pinheiro, J. P.The potential of permeation liquid membrane (PLM) to obtain dynamic metal speciation information for colloidal complexes is evaluated by measurements of lead(II) and copper(II) complexation by carboxyl modified latex nanospheres of different radii (15, 35, 40 and 65 nm). The results are compared with those obtained by a well characterized technique: stripping chronopotentiometry at scanned deposition potential (SSCP). Under the PLM conditions employed, and for large particles or macromolecular ligands, membrane diffusion is the rate-limiting step. That is, the flux is proportional to the free metal ion concentration with only a small contribution from labile complexes. In the absence of ligand aggregation in the PLM channels, good agreement was obtained between the stability constants determined by PLM and SSCP for both metals.
- Cd(II) speciation in alginate gelsPublication . Davis, T. A.; Kalis, E. J. J.; Pinheiro, J. P.; Town, R. M.; Van Leeuwen, H. P.Polysaccharides, such as those occurring in cell walls and biofilms, play an important role in metal speciation in natural aqueous systems. This work describes the speciation of Cd(II) in alginate gels chosen as a model system for biogels. The gels are formed by bridging calcium ions at junction zones present along adjacent homopolymeric guluronic acid chain sequences. The free Cd2+ concentration in the gel phase is measured by a novel in situ microelectrode voltammetric technique that monitors the electroactive probe cation Cd2+ by its reduction at a Au-amalgam microelectrode. In situ voltammetric measurement, coupled with total Ca(II) and Cd(II) determinations, as well as potentiometric titration, permits the full reconstruction of the charging environment and the cation binding for the gel phase. Three independent combinations of measuring and modeling the charged gel layer thereby permit accurate prediction of the Donnan potential, ΨD, and the Donnan enrichment coefficient, ΠD. At an ionic strength of 10 mM, Donnan potentials in the gel ranged from approximately −10 to −20 mV, corresponding to an enhancement in the level of free Cd2+ ions in the gel phase relative to the bulk solution by a factor of approximately 3. In contrast, the total level of Cd(II) was found to be enhanced by a factor of approximately 60, resulting predominantly from the specific binding of the Cd by the uronic acids of the alginate gel. These results emphasize that large differences in Cd(II) speciation can arise due to the combination of specific and electrostatic modes of binding. The results of this speciation analysis, for charged biological gels, have important consequences for mechanistic interpretation of metal biouptake processes involved in complex media.
- Comparison of AGNES (absence of gradients and Nernstian equilibrium stripping) and SSCP (scanned stripping chronopotentiometry) for trace metal speciation analysisPublication . Domingos, R. F.; Huidobro, C.; Companys, E.; Galceran, J.; Puy, J.; Pinheiro, J. P.The free metal ion concentrations obtained by SSCP (stripping chronopotentiometry at scanned deposition potential) and by AGNES (absence of gradients and Nernstian equilibrium stripping) techniques have been compared and the usefulness of the combination of both techniques in the same electrochemical cell for trace metal speciation analysis is assessed. The free metal ion concentrations and the stability constants obtained for lead(II) and cadmium(II) complexation by pyridinedicarboxylic acid, by 40 nm radius carboxylated latex nanospheres and by a humic acid extracted from an ombrotrophic peat bog were determined. Whenever possible, the free metal ion concentrations were compared with the theoretical predictions of the code MEDUSA and with the free metal ion concentrations estimated from ion selective electrodes (ISE). SSCP values were in agreement with the ones obtained by AGNES, and both of them agreed reasonably with the ISE values and the theoretical predictions. For the lead(II)-humic acid, it was not possible to obtain the stability constants by SSCP due to the heterogeneity effect. However, using AGNES it is possible to obtain, for these heterogeneous systems, the free bulk metal concentration, which allows us to retrieve the stability constant at bulk conditions.
- Copper removal by algal biomass: biosorbents characterization and equilibrium modellingPublication . Vilar, V. J. P.; Botelho, C. M. S.; Pinheiro, J. P.; Domingos, R. F.; Boaventura, R. A. R.The general principles of Cu(II) binding to algal waste fromagar extraction, composite material and algae Gelidium, and different modelling approaches, are discussed. FTIR analyses provided a detailed description of the possible binding groups present in the biosorbents, as carboxylic groups (d-glucuronic and pyruvic acids), hydroxyl groups (cellulose, agar and floridean starch) and sulfonate groups (sulphated galactans). Potentiometric acid–base titrations showed a heterogeneous distribution of two major binding groups, carboxyl and hydroxyl, following the quasi-Gaussian affinity constant distribution suggested by Sips, which permitted to estimate the maximum amount of acid functional groups (0.36, 0.25 and 0.1mmolg−1) and proton binding parameters (pKH= 5.0, 5.3 and 4.4; mH = 0.43, 0.37, 0.33), respectively for algae Gelidium, algal waste and composite material. A non-ideal, semi-empirical, thermodynamically consistent (NICCA) isotherm fitted better the experimental ion binding data for different pH values and copper concentrations, considering only the acid functional groups, than the discrete model. Values of pKM (3.2; 3.6 and 3.3), nM (0.98, 0.91, 1.0) and p (0.67, 0.53 and 0.43) were obtained, respectively for algae Gelidium, algalwaste and composite material. NICCA model reflects the complex macromolecular systems that take part in biosorption considering the heterogeneity of the biosorbent, the competition between protons and metals ions to the binding sites and the stoichiometry for different ions.
- Determination of diffusion coefficients of nanoparticles and humic substances using scanning stripping chronopotentiometry (SSCP)Publication . Pinheiro, J. P.; Domingos, R. F.; Lopez, R.; Brayner, R.; Fiévet, F.; Wilkinson, K.A methodology, based on a labile metal ion probe using stripping chronopotentiometry at scanned deposition potential (SSCP), is presented for the determination of the diffusion coefficients of nanoparticles and humic matter. The novel methodology was successfully applied to the determination of diffusion coefficients (and thus hydrodynamic diameters) of eight standard nanoparticles with radii ranging from 5 to 129 nm and two samples of colloidal humic substances with hydrodynamic radii of ca. 1 nm. Good agreement was found between the SSCP determinations and results obtained by dynamic light scattering (DLS), transmission electron microscopy (TEM) and fluorescence correlation spectroscopy (FCS). The SSCP technique is critically analysed with respect to its use for the determination of diffusion coefficients of colloidal complexes.
- Dynamics and heterogeneity of Pb(II) binding by SiO 2 nanoparticles in an aqueous dispersionPublication . Goveia, D.; Pinheiro, J. P.; Milkova, V.; Rosa, A. H.; Van Leeuwen, H. P.ABSTRACT: Pb(II) binding by SiO2 nanoparticles in an aqueous dispersion was investigated under conditions where the concentrations of Pb2þ ions and nanoparticles are of similar magnitude. Conditional stability constants (log K) obtained at different values of pH and ionic strength varied from 4.4 at pH 5.5 and I = 0.1Mto 6.4 at pH 6.5 and I = 0.0015 M. In the range of metal to nanoparticle ratios from 1.6 to 0.3, log K strongly increases, which is shown to be due to heterogeneity in Pb(II) binding. For an ionic strength of 0.1 M the Pb2þ/SiO2 nanoparticle system is labile, whereas for lower ionic strengths there is loss of lability with increasing pH and decreasing ionic strength. Theoretical calculations on the basis of Eigen-type complex formation kinetics seem to support the loss of lability. This is related to the nanoparticulate nature of the system, where complexation rate constants become increasingly diffusion controlled. The ion binding heterogeneity and chemodynamics of oxidic nanoparticles clearly need further detailed research.
- Effect of humic acid on Cd(II), Cu(II), and Pb(II) uptake by freshwater algae: kinetic and cell wall speciation considerationsPublication . Lamelas, C.; Pinheiro, J. P.; Slaveykova, V. I.The present study examines the effect of humic acid on the uptake kinetics of Cd(II), Cu(II), and Pb(II) by the freshwater alga Chlorella kesslerii. The results demonstrated that the relative proportion of Pb in the cell wall layer is greater than that of the internalized Pb, while internalized Cd and Cu were comparable or greater than the adsorbed metal concentration. In the presence of 10 mg L-1 humic acid (HA), Cd and Cu uptake kinetics were consistent with that predicted by measured free metal concentrations. For Pb, the uptake flux and amount of lead bound to internalization and adsorption sites were an order of magnitude higher than those found at the same free lead ion concentrations in the presence of citric acid. Chemodynamic modeling suggested that the enhancement of the Pb uptake flux in the presence of HA originates from an increasing amount of Pb bound to the internalization sites through a ternary complex formation between lead-humic acid complex and internalization sites. Cell wall speciation calculations indicated that the lead-humic acid complex is the predominant species in the cell wall layer, while for Cu(II) and Cd(II) metal bound to the internalization (Cu) and adsorption (Cd) sites significantly dominated over the M-HA complex. The findings of the work show the relevance of the cell wall layer concentration and speciation and its key role in defining the local equilibrium conditions between metal and internalizations sites. The results of the present kinetic study have important consequences for improvement of the mechanistic understanding of the role of dissolved organic matter in metal uptake in phytoplankton and biogeochemical cycling of metals in the surface waters.
- 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.
- Effects of copper nanoparticles exposure in the mussel Mytilus galloprovincialisPublication . Gomes, Tânia; Pinheiro, J. P.; Cancio, I.; Pereira, Catarina Guerreiro; Cardoso, Cátia; Bebianno, Maria JoãoCuO NPs are widely used in various industrial and commercial applications. However, little is known about their potential toxicity or fate in the environment. In this study the effects of copper nanoparticles were investigated in the gills of mussels Mytilus galloprovincialis, comparative to Cu(2+). Mussels were exposed to 10 μg Cu·L(-1) of CuO NPs and Cu(2+) for 15 days, and biomarkers of oxidative stress, metal exposure and neurotoxicity evaluated. Results show that mussels accumulated copper in gills and responded differently to CuO NPs and Cu(2+), suggesting distinct modes of action. CuO NPs induced oxidative stress in mussels by overwhelming gills antioxidant defense system, while for Cu(2+) enzymatic activities remained unchanged or increased. CuO NPs and Cu(2+) originated lipid peroxidation in mussels despite different antioxidant efficiency. Moreover, an induction of MT was detected throughout the exposure in mussels exposed to nano and ionic Cu, more evident in CuO NPs exposure. Neurotoxic effects reflected as AChE inhibition were only detected at the end of the exposure period for both forms of copper. In overall, these findings show that filter-feeding organisms are significant targets for nanoparticle exposure and need to be included when evaluating the overall toxicological impact of nanoparticles in the aquatic environment.
- Electrochemical DNA sensor for detection of single nucleotide polymorphismsPublication . Marques, L. P. J.; Cavaco, Isabel Maria Palma Antunes; Pinheiro, J. P.; Ribeiro, Vera; Ferreira, GuilhermeIn recent years there has been an increased interest in using biosensors for the recognition and monitoring of molecule interactions. DNA sensors and gene chips are particularly relevant for directly applying the information gathered from the genome projects. In this work electrochemical techniques are used to develop methodologies to detect DNA polymorphisms in human genes using cytochrome P450 3A4 (CYP3A4) as a model gene. CYP3A4*1B oligonucleotides were immobilized on the surface of a gold electrode and hybridized with fully complementary oligonucleotide sequences as well as with mismatched sequences corresponding to the CYP3A4*1A reference sequence. The methodology developed is based on double-stranded DNA’s ability to transport charge along nucleotide stacking. The perturbation of the double helix pi-stack introduced by a mismatched nucleotide reduces electron flow and can be detected by measuring the attenuation of the charge transfer. The methodology developed could identify CYP3A4*1A homozygotes by the 5 μC charge attenuation observed when compared with DNA samples containing at least one CYP3A4*1B allele.