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The potential of composts produced from different origin residues to be used in environmentally friendly agriculture is addressed in this work. Seven composts obtained from different raw materials and composting methodologies are compared using elemental, thermal and spectroscopic characterization data. Despite the stabilization of the organic matter in all composts being adequate for agricultural applications, they display distinct elemental and structural compositions. Likewise, the fertilisers have very different effects on lettuce growth. Despite the observed differences, some common features were found, namely a mass loss (TGA) of 25.2 g per mol C, association between groups of elements (Fe, Al, Ni, Co, Cr, Cu and S; Mg, Na, K and P, C, Coxi, N and Pb) and correlations between the amount of carbon nanostructures and the characteristic aromaticity parameters. These results suggest that the tuning of the compost features for specific cultures may be possible for sustainable food production., This work was financially supported by the Interreg VA Spain-Portugal Programme (EU) through the project Res2ValHum (0366_RES2VALHUM_1_P). A.C. Silva acknowledges receipt of a PhD grant (UMINHO/BD/40/2016) financed by the Operational Programme Norte 2020 (through the Project “NORTE-08-5369-FSE-000033”). A. Teixeira acknowledges the grant (Res2ValHum 01/2018) to develop experimental work for 11 months on the project. J. Antelo and S. Fiol are also grateful for the financial support provided by Xunta de Galicia—Consellería de Educación e Ordenación Universitaria de Galicia (Consolidation of Competitive Groups of Investigation; GI-1245, ED431C 2018/12 and CRETUS AGRUP2015/02, ref. 2018-PG10).

International audience; Alkaline extractions from humic material are used to risk assessment in soils. However, there are questions about the type of extraction most suitable for this evaluation. Thus, this work evaluated different soil extractions in search of realistic environmental conditions (simulated rain). The parameters obtained revealed significant differences between the levels and structural characteristics of organic matter, depending on the extractant used, reinforcing the importance of developing methodologies and analytical procedures that minimize structural changes and may be more representative of the molecular structures of organic matter found in soils. The results showed that the material extracted by simulated rain is similar to the fulvic acids of the soil organic matter extracted by alkaline extraction showing the importance of this type of extraction for risk assessment studies in soils.

Hypothesis Charge descriptors of aquatic nanoparticles (NPs) are evaluated from proton titration curves measured at different salt concentrations and routinely analysed by the Non-Ideal Competitive Adsorption-Donnan (NICAD) model. This model, however, suffers from approximations regarding particle electrostatics, which may bias particle charge estimation. Implementation of Poisson-Boltzmann (PB) theory within consistent treatment of NPs protolytic data is expected to address NICAD shortcomings. Experiments An alternative to NICAD is elaborated on the basis of nonlinearized PB equation for soft particle electrostatics to properly unravel the electrostatic and chemical components of proton binding to NPs. A numerical package is developed for automated analysis of proton titration curves and proton affinity spectra at different salt concentrations. The performance of the method is illustrated for humic matter nanoparticles with different charge and size, and compared to that of NICAD. Findings Unlike NICAD, PB-based treatment successfully reproduces particle charge dependence on pH for practical salt concentrations from the thin to thick electric double layer limit. Donnan representation in NICAD leads to moderate to dramatic misestimations of proton affinity and binding heterogeneity depending on particle size to Debye layer thickness ratio. Interpretation of NPs protolytic properties with PB theory further avoids adjustment of the ‘particle Donnan volume’ empirically introduced in NICAD.

The aim of this study was to develop an analytical method to determine free concentrations of Europium (Eu(III)) in natural waters. Europium(III) in solution was detected using cathodic stripping voltammetry after complexation with N-nitroso-N-phenylhydroxylamine (cupferron). Optimization of analytical parameters allowed us to detect nanomolar levels of Eu(III) in solution. Free Eu(III) in solution was measured using the Donnan membrane technique in which a natural solution (the “donor”, containing various ligands) is separated from a ligand-free solution (the “acceptor”) by a cation-exchange membrane. This membrane allows only non-colloidal cationic species to pass through it, and after an adequate time equilibrium is reached between both compartments. Total Eu(III) concentration can then be quantified in the acceptor solution and related to free Eu(III) in the natural sample. Due to its high valency, free Eu(III) tends to adsorb strongly to the cation-exchange membrane. In order to determine the physicochemical conditions minimizing this adsorption, we analyzed solutions of different Eu(III) and Ca(II) (as background ion) concentrations. Results showed that 100 mM of Ca(II) were necessary to make adsorption of Eu(III) onto the membrane negligible. The optimized setup was then used to quantify Eu(III) complexation in a Eu(III)-dissolved organic matter solution.

Free indium concentrations can be determined using AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) with no relevant hindrance from the irreversibility of the In3+/In° redox couple at a mercury electrode. The electroactivity, high lability and mobility of the In hydroxy species help in reaching AGNES conditions for a relatively moderate ratio (deposition time):(gain), which decreases with increasing pH due to the growing contribution of the hydroxy species. In the related technique SSCP (Scanned Stripping ChronoPotentiometry), points corresponding to more positive deposition potentials are said to be “at the foot of the wave”. Some of these points can reach equilibrium along the fixed SSCP deposition time, so that these points are effectively AGNES experiments, and free metal ion concentrations (such as those of free indium) can also be computed from them provided sufficiently accurate data are available. A new representation of the SSCP wave allows for the diagnosis of the potential region where AGNES conditions are fulfilled.

International audience; Electrochemical stripping techniques are interesting candidates for carrying out onsite speciation of environmentally relevant trace metals due to the existing low-cost portable instrumentation available and the low detection limits that can be achieved. In this work, we describe the initial analytical technique method development by quantifying the total metal concentrations using Stripping Chronopotentiometry (SCP). Carbon paste screen-printed electrodes were modified with thin films of mercury and used to quantify sub-nanomolar concentrations of lead and cadmium and sub-micromolar concentrations of zinc in river water. Low detection limits of 0.06 nM for Pb(II) and 0.04 nM for Cd(II) were obtained by the standard addition method using a SCP deposition time of 180 s. The SCP results obtained for Pb(II) and Cd(II) agreed with those of inductively coupled plasma mass spectrometry (ICP-MS). The coupling of SCP with screen-printed electrodes opens up excellent potential for the development of onsite speciation of trace metals. Due to the low analysis throughput obtained for the standard addition method, we also propose a new, more rapid screening Cd(II) internal standard methodology to significantly increase the number of samples that can be analyzed per day.

International audience; 1 deposition potential (SSCP): obtaining binding curves in labile 2 heterogeneous macromolecular systems for any metal-to-3 ligand ratio. 4 5 Abstract 12 The different deposition potentials applied in Scanned Stripping ChronoPotentiometry 13 (SSCP) probe different values of the free metal and complex concentrations at the 14 electrode surface. The knowledge of these concentrations gives access to a relevant 15 window of the binding curve of a metal to a homogeneous or heterogeneous ligand. 16 Here, a suitable mathematical treatment for the determination of these surface 17 concentrations, when using a mercury thin film rotating disk electrode, is reported. The 18 proposed procedure does not require ligand excess conditions and takes advantage of 19 the knowledge of the free metal ion concentration in the bulk solution provided by the 20 technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). It is 21 experimentally shown that the information derived from the SSCP points (i.e. at 22 different deposition potentials in a unique solution) is consistent with the speciation 23 results yielded by the technique AGNES in pertinent solutions prepared within a range 24 of metal-to-ligand ratios. Successful examples with polystyrene sulfonate, Laurentian 25 Fulvic acid and a peat humic acid are reported. It is concluded that, by running 26 consecutively SSCP and AGNES in a single solution, speciation information 27 corresponding to different compositions (i.e. those locally generated at the electrode 28

The free metal ion concentration and the dynamic features of the metal species are recognized as key to predict metal bioavailability and toxicity to aquatic organisms. Quantification of the former is, however, still challenging. In this paper, it is shown for the first time that the concentration of free copper (Cu2+) can be quantified by applying AGNES (Absence of Gradients and Nernstian equilibrium stripping) at a solid gold electrode. It was found that: i) the amount of deposited Cu follows a Nernstian relationship with the applied deposition potential, and ii) the stripping signal is linearly related with the free metal ion concentration. The performance of AGNES at the vibrating gold microwire electrode (VGME) was assessed for two labile systems: Cu-malonic acid and Cu-iminodiacetic acid at ionic strength 0.01 M and a range of pH values from 4.0 to 6.0. The free Cu concentrations and conditional stability constants obtained by AGNES were in good agreement with stripping scanned voltammetry and thermodynamic theoretical predictions obtained by Visual MinteQ. This work highlights the suitability of gold electrodes for the quantification of free metal ion concentrations by AGNES. It also strongly suggests that other solid electrodes may be well appropriate for such task. This new application of AGNES is a first step towards a range of applications for a number of metals in speciation, toxicological and environmental studies for the direct determination of the key parameter that is the free metal ion concentration. Funding for this work was provided by (i) Fundação para a Ciência e Tecnologia (FCT, Portugal): Science 2008 IST-CQE3 “Environmental Chemistry” Assistant Researcher position to RFD and Project PTDC/AAC-AMB/110595/2009, and (ii) ANR (Agence national de recherché) - FCT project N°12-IS06-0001 - SPECIES: “Mesure in situ de la spéciation des métaux trace”, by ANR Project NormaRHIZO. JG acknowledges financial support from the Spanish Ministry of Education and Science (project CTM2013-48967).

The geochemical fate of indium in natural waters is still poorly understood, while recent studies have pointed out a growing input of this trivalent element in the environment as a result of its utilisation in the manufacturing of high-technology products. Reliable and easy-handling analytical tools for indium speciation analysis are, then, required. In this work, we report the possibility of measuring the total and free indium concentrations in solution using two complementary electroanalytical techniques, SCP (Stripping chronopotentiometry) and AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) implemented with the TMF/RDE (Thin Mercury Film/Rotating Disk Electrode). Nanomolar limits of detection, i.e. 0.5 nM for SCP and 0.1 nM for AGNES, were obtained for both techniques in the experimental conditions used in this work and can be further improved enduring longer experiment times. We also verified that AGNES was able (i) to provide robust speciation data with the known In-oxalate systems and (ii) to elaborate indium binding isotherms in presence of humic acids extending over 4 decades of free indium concentrations. The development of electroanalytical techniques for indium speciation opens up new routes for using indium as a potential tracer for biogeochemical processes of trivalent elements in aquifers, e.g. metal binding to colloidal phases, adsorption onto (bio) surfaces, etc. This work has been supported by the French National Research Agency through the national program “Investissements d’avenir” with the reference ANR-10-LABX-21-01/LABEX RESSOURCES21. We thank the contribution of Jérémy Gloux, Paco Iglesias and Mirella Dammous from University of Lorraine in the preliminary experimental work. Funding from the Spanish Ministry of Economy, Industry and Competitiveness MINECO, project CTM2016-78798 (EC, PPV, JG) is acknowledged. PPV thanks Generalitat de Catalunya for a doctoral FI-AGAUR fellowship.

Silver nanoparticles (Ag NPs) have emerged as one of the most commonly used NPs in a wide range of industrial and commercial applications. This has caused increasing concern about their fate in the environment as well as uptake and potential toxicity towards aquatic organisms. Accordingly, mussels Mytilus galloprovincialis were exposed to 10 μg L(-1) of Ag NPs and ionic silver (Ag+) for 15 days, and biomarkers of oxidative stress and metal accumulation were determined. Accumulation results show that both Ag NPs and Ag+ accumulated in both gills and digestive glands. Antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) were activated by Ag NPs and Ag+, showing different antioxidant patterns in both gills and digestive glands. Moreover, metallothionein was inducted in gills, directly related to Ag accumulation, while in the digestive glands only a small fraction of Ag seems to be associated with this protein. Lipid peroxidation was higher in gills exposed to Ag NPs, whereas in the digestive glands only Ag+ induced lipid peroxidation. Ag NPs and Ag+ cause oxidative stress with distinct modes of action and it's not clear if for Ag NPs the observed effects are attributed to free Ag+ ions associated with the nanoparticle effect. REEQ/700/CTM/2005, PTDC/AACAMB/121650/2010 info:eu-repo/semantics/publishedVersion

Determining the environmental risk of metals requires an in-depth understanding of the environmental matrices composition, which currently also includes the presence of manufactured metallic nanoparticles (NPs) usually, stabilized by a polymer surface coating. As a consequence, is necessary to take into account effects of the NP core, the polymer surface coating and their mutual interaction as well as with other environmental components. The release of metal ions from metallic NPs is a well-known outcome, however, the effect of the presence of the NP polymer coating in the NPs solubilization mechanism is not well understood. In this study the dynamic speciation of Cd and Pb in presence of a polyacrylic acid (PAA)-stabilized CdTe/CdS NP was quantified by scanned stripping chronopotentiometry (SSCP). It was found that although the NP solubility was 5.8× larger at pH 8.5 than at pH 6.0, the amount of free Cd ions was much smaller (2.4 % at pH 8.5 vs. 57 % at pH 6.0). The concentration of free Cd and Pb ions in solution was larger in presence of the PAA-shells than when in presence of the same amount of polymer but when this is at the surface of the NP. This effect is attributed to the metal ions interaction with the particle itself. The effect is notably larger for Pb ions and might results from the exchange of Cd by Pb ions at the particle surface since PbS is less soluble than CdS.

Genetically engineered microorganisms are alternatives to physicochemical methods for remediation of metal-contaminated aquifers due to their remarkable bioaccumulation capacities. The design of such biosystems would benefit from the elaboration of a sound quantitative connection between performance in terms of metal removal from aqueous solution and dynamics of the multiscale processes leading to metal biouptake. In this work, this elaboration is reported for Escherichia coli cells modified to overexpress intracellular metallothionein (MTc), a strong proteinaceous metal chelator. Depletion kinetics of Cd(II) from bulk solution following biouptake and intracellular accumulation is addressed as a function of cell volume fraction using electroanalytical probes and ligand exchange-based analyses. It is shown that metal biouptake in the absence and presence of MTc is successfully interpreted on the basis of a formalism recently developed for metal partitioning dynamics at biointerfaces with integration of intracellular metal speciation. The analysis demonstrates how fast sequestration of metals by intracellular MTc bypasses metal excretion (efflux) and enhances the rate of metal depletion to an extent such that complete removal is achieved at sufficiently large cell volume fractions. The magnitude of the stability constant of nanoparticulate metal–MTc complexes, as derived from refined analysis of macroscopic bulk metal depletion data, is further confirmed by independent electrochemical measurement of metal binding by purified MTc extracts.

Nanoparticles (NPs) exhibit unique reactivity features that stem from the spatial confinement of their reactive sites to the particle body, which typically carries electric charges. Accordingly, association of ions and molecules with NPs takes place in a local environment that may be very different from that prevailing in the bulk aqueous medium. We present a critical overview of a conceptual framework that describes the dynamic features of metal ion, M, association with different types of NPs, i.e. impermeable (hard, 2D), coreshell, and permeable (soft, 3D). The interpretation identifies the crucial role played by the particulate electric field, and elucidates the factors that determine which step in the overall association/dissociation process is the rate-limiting one. The scope encompasses delineation of the distribution of NP-associated metals, M-NP, over various intraparticulate forms, as well as description of the influence of the intraparticulate spatial distribution of reactants on the complex formation/dissociation kinetics. The connection between the chemodynamic features of M-NP entities at the intraparticulate level and their reactivity at the macroscopic scale is elaborated. These relationships are used to derive analytical expressions for the lability of M-NP entities at reactive interfaces, such as sensors and organisms. Such knowledge is required to make mechanistic links with bioavailability and ensuing toxicity. The interpretation includes formulation of the operational reaction layer at the macroscopic interface and the significance of partial size exclusion of the NP body therefrom. The concepts are illustrated by confrontation with sets of experimental data for different types of natural and engineered NPs.

Environmental contextStudying the mechanism of binding between metals and natural organic matter is fundamental to understanding the transport and availability of these contaminants in the environment. The influence of sample treatment on the purification of organic matter showed significant differences in the interaction with metals. The results will contribute to improved modelling of metal binding to organic matter in soils, thereby providing a basis for a more realistic risk assessment. AbstractWe studied the changes in metal binding characteristics of extracted humic acids induced by HF/HCl treatment followed by dialysis, i.e. the last step of the International Humic Substances Society (IHSS) extraction protocol. We performed metal binding experiments with both the alkaline-extracted material (AE) and the fully purified (FP) humic acid using the electrochemical stripping technique (AGNES) and modelled the results using the NICA-Donnan model. The results showed an increase of free Zn, Cd and Pb concentrations of similar to 1 order of magnitude for the AE compared with the FP. These differences may be mostly explained by the different carbon content (51.3% FP and 36.5% AE) associated with an AE/FP carboxyl ratio of 0.5. Simulations using the NICA-Donnan model showed that halving the amount of carboxylic groups (Q(max,1)) for the FP reduced this difference to 0.25 log units for Cd and Zn and to 0.15 log unit for Pb. There is a clear need for further research on the differences between purified v. less-disturbed natural organic material, which will contribute to improved modelling of metal binding to organic matter in soils, hence providing a basis for a more realistic risk assessment. Coordenadoria de Aperfeicoamento do Pessoal de Nivel Superior (CAPES CSF) [981313-6] Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq PVE) [400572/2013-3] French national research agency (ANR) [ANR-10-LABX-21-01/LABEX RESSOURCES 21] Portuguese national funding agency for science, research and technology [FCT-ANR/AAG-MAA/0065/2012] Region Lorraine

The lability of a complex species between a metal ion M and a binding site S, MS, is conventionally defined with respect to an ongoing process at a reactive interface, for example, the conversion or accumulation of the free metal ion M by a sensor. In the case of soft charged multisite nanoparticulate complexes, the chemodynamic features that are operative within the micro environment of the particle body generally differ substantially from those for dissolved similar single-site complexes in the same medium. Here we develop a conceptual framework for the chemodynamics and the ensuing lability of soft (3D) nanoparticulate metal complexes. The approach considers the dynamic features of MS at the intraparticulate level and their impact on the overall reactivity of free metal ions at the surface of a macroscopic sensing interface. Chemodynamics at the intraparticulate level is shown to involve a local reaction layer at the particle/medium interface, while at the macroscopic sensor level an operational reaction layer is invoked. Under a certain window of conditions, volume exclusion of the nanoparticle body near the medium/sensor interface is substantial and affects the properties of the reaction layer and the overall lability of the nanoparticulate MS complex toward the reactive surface.

Green microalgae are well known to bioaccumulate potentially toxic metals, which can be magnified along the trophic chain. Therefore, they also have the potential to be used as bioadsorbents for removal of toxic metals. Interaction of Hg(II) with live Chlamydomonas reinhardtii was investigated for the first time by stripping chronopotentiometry, enabling the quantification of the reactive metal fractions in presence of the microalgae. This approach allowed the computation of the Hg(II) fraction able to dissociate from metal-cell surface complexes due to the concentration gradient imposed by the deposition potential applied to the working electrode. Equilibrium was reached in 120 min. Biosorption isotherms at pH 4.0, 5.0 and 6.0 were fitted using the Langmuir-Freundlich equation, showing the highest biosorption capacity, (3.3 ± 0.9) mmol g− 1, at pH 4.0. The mass balance of Hg(II) in filtered solution plus in digested microalgae (102 ± 8%) indicated that most Hg(II) was retained in the cells instead of being released to the surrounding environment, an interesting feature for biosorbents. However, for initial Hg concentrations > 20 μmol L− 1 the determined Hg(II) concentrations in presence of the cells were 2 to 6 times higher than those determined in the filtered solutions, suggesting a partial lability of the surface-bound Hg(II) which should be considered in bioremediation technologies.

The improvement of knowledge about the toxicity and even processability, and stability of quantum dots (QD) requires the understanding of the relationship between the QD binding head group, surface structure, and interligand interaction. The scanned stripping chronopotentiometry and absence of gradients and Nernstian equilibrium stripping techniques were used to determine the concentration of Cd dissolved from a polyacrylate-stabilized CdTe/CdS QD. The effects of various concentrations of small organic ligands such as citric acid, glycine, and histidine and the roles of pH (4.5–8.5) and exposure time (0–48 h) were evaluated. The highest QD dissolution was obtained at the more acidic pH in absence of the ligands (52 %) a result of the CdS shell solubility. At pH 8.5 the largest PAA ability to complex the dissolved Cd leads to a further QD solubility until the equilibrium is reached (24 % of dissolved Cd vs. 4 % at pH 6.0). The citric acid presence resulted in greater QD dissolution, whereas glycine, an amino acid, acts against QD dissolution. Surprisingly, the presence of histidine, an amino acid with an imidazole functional group, leads to the formation of much strong Cd complexes over time, which may be non-labile, inducing variations in the local environment of the QD surface.

International audience; In this work, the impact of electrostatics on the stability constant, the rate of association/dissociation, and the lability of complexes formed between Cd(II), Pb(II), and carboxyl-modified polymer nanoparticles (also known as latex particles) of radius similar to 50 nm is systematically investigated via electroanalytical measurements over a wide range of pHs and NaNO3 electrolyte concentrations. The corresponding interfacial structure and key electrostatic properties of the particles are independently derived from their electrokinetic response, successfully interpreted using soft particle electrohydrodynamic formalism, and complemented by Forster resonance energy transfer (FRET) analysis. The results underpin the presence of an similar to 0.7-1 nm thick permeable and highly charged shell layer at the surface of the polymer nanoparticles. Their electrophoretic mobility further exhibits a minimum versus NaNO3 concentration due to strong polarization of the electric double layer. Integrating these structural and electrostatic particle features with recent theory on chemodynamics of particulate metal complexes yields a remarkable recovery of the measured increase in complex stability with increasing pH and/or decreasing solution salinity. In the case of the strongly binding Pb(II), the discrepancy at pH > 5.5 is unambiguously assigned to the formation of multidendate complexes with carboxylate groups located in the particle shell. With increasing pH and/or decreasing electrolyte concentration, the theory further predicts a kinetically controlled formation of metal complexes and a dramatic loss of their lability (especially for lead) on the time-scale of diffusion toward a macroscopic reactive electrode surface. These theoretical findings are again shown to be in agreement with experimental evidence.

International audience; Metal binding to natural soft colloids is difficult to address due to the inherent heterogeneity of their reactive polyelectrolytic volume and the modifications of their shell structure following changes in e.g. solution pH, salinity or temperature. In this work, we investigate the impacts of temperature- and salinity-mediated modifications of the shell structure of polymeric ligand nanoparticles on the thermodynamics of divalent metal ions Cd(II)-complexation. The adopted particles consist of a glassy core decorated by a fine-tunable poly(N-isopropylacrylamide) anionic corona. According to synthesis, the charges originating from the metal binding carboxylic moieties supported by the corona chains are located preferentially either in the vicinity of the core or at the outer shell periphery (p(MA-N) and p(N-AA) particles, respectively). Stability constants (KML) of cadmium-nanoparticle complexes are measured under different temperature and salinity conditions using electroanalytical techniques. The obtained KML is clearly impacted by the location of the carboxylic functional groups within the shell as p(MA-N) leads to stronger nanoparticulate Cd complexes than p(N-AA). The dependence of KML on solution salinity for p(N-AA) is shown to be consistent with a binding of Cd to peripheral carboxylic groups driven by Coulombic interactions (Eigen–Fuoss mechanism for ions-pairing) or with particle electrostatic features operating at the edge of the shell Donnan volume. For p(MA-N) particulate ligands, a scenario where metal binding occurs within the intraparticulate Donnan phase correctly reproduces the experimental findings. Careful analysis of electroanalytical data further evidences that complexation of metal ions by core–shell particles significantly differ according to the location and distribution of the metal-binding sites throughout the reactive shell. This complexation heterogeneity is basically enhanced with increasing temperature i.e. upon significant increase of particle shell shrinking, which suggests that the contraction of the reactive phase volume of the particulate ligands promotes cooperative metal binding effects.

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. Agence National de Recherché ANR- FCT, project N◦ 12-IS06-0001 − SPECIES: “Mesure in situ de la spéciation des métaux trace”

International audience; Up to now, different approaches have been proposed for in situ trace metal speciation, based on the deployment of in situ devices such as Donnan Membrane device (DMT) and then analysis by ICP-MS [1], or by means of preconcentration systems hyphenated wih electrochemical detection such as gel integrated microelectrode (GIME) probe [2] or a direct in situ electrochemical stripping speciation method such as Absence Gradient Nernstian Equilibrium Stripping (AGNES) [3]. Although numerous in situ methods have been proposed, currently there is no reliable in situ probe for trace metal speciation at concentration levels present in natural systems. Regarding autonomy problems of in situ probes, electrochemical devices have the advantage of being easily available in smaller sizes and with the possibility to be operated with batteries. This work presents the probe ISIDORE developped for in situ trace metal speciation [4]. This probe is based on the hyphenation between a DMT and a screen-printed electrode through a flow-cell (Figure 1), allowing a direct in situ detection and avoiding thus all problems inherent to sampling, transport and storage. The acceptor solution of the DMT was first optimized for electrochemical detection with a composition of 3 mmol L-1 Ca(NO 3) 2 and 3 mmol L-1 of sodium acetate buffer at pH 4.5. Under these conditions, the simultaneous determination of Zn, Pb and Cd is possible at low detection limits. The lower volume of the acceptor solution yielded a much faster equilibrium time, 6 h, as compared with the common 36 to 48 h deployment needed to reach equilibrium. The possibility of using the accumulation slope with ISIDORE is studied to further reduce the analysis time and obtain dynamic information on the nature of the metal complexes [5].

Given the wide use of CuO nanoparticles in various industrial and commercial applications they will inevitably end up in the aquatic environment. However, little information exists on their biological effects in bivalve species. Accordingly, mussels Mytilus galloprovincialis were exposed to 10 μg Cu L(-1) as CuO nanoparticles and Cu(2+) for 15 days, and biomarkers of oxidative stress (superoxide dismutase, catalase and glutathione peroxidase), damage (lipid peroxidation) and metal exposure (metallothionein) were determined along with Cu accumulation in the digestive glands of mussels. Cu was linearly accumulated with time of exposure in mussels exposed to CuO nanoparticles, while in those exposed to Cu(2+) elimination was significant by day 15. Both forms of Cu cause oxidative stress with distinct modes of action. Exposure to CuO nanoparticles induces lower SOD activity in digestive glands compared to those exposed to Cu(2+), while CAT was only activated after 7 days of exposure to nano and ionic Cu, with contradictory effects after 15 days of exposure and GPX activities were similar. Lipid peroxidation levels increased in both Cu forms despite different antioxidant efficiency. Moreover, a linear induction of metallothionein was detected with time in mussels exposed to CuO nanoparticles, directly related to Cu accumulation, whereas in those exposed to Cu(2+) metallothionein was only induced after 15 days of exposure. Since only a small fraction of soluble Cu fraction was released from CuO nanoparticles, the observed effects seem to be related to the nano form of Cu, with aggregation as a key factor. Overall, our results show that the digestive gland is susceptible to CuO nanoparticles related oxidative stress, and is also the main tissue for their accumulation.

The contribution of electrochemical methods to the knowledge of dynamic speciation of toxic trace elements in marine waters is critically reviewed. Due to the importance of dynamic considerations in the interpretation of the electrochemical signal, the principles and recent developments of kinetic features in the interconversion of metal complex species will be presented. As dynamic electrochemical methods, only stripping techniques (anodic stripping voltammetry and stripping chronopotentiometry) will be used because they are the most important for the determination of trace elements. Competitive ligand ex- change-adsorptive cathodic stripping voltammetry, which should be considered an equilibrium technique rather than a dynamic method, will be also discussed because the complexing parameters may be affected by some kinetic limitations if equilibrium before analysis is not attained and/or the flux of the adsorbed complex is in fluenced by the lability of the natural complexes in the water sample. For a correct data interpretation and system characterization the comparison of results obtained from different techniques seems essential in the articulation of a serious discussion of their meaning.

We prepared anionic multistimuli responsive core-shell polymer nanoparticles with very low size dispersity. By using either acrylic acid (AA) or methacrylic acid (MA) as a comonomer in the poly(N-isopropyl acrylamide) (PNIPAM) shell, we are able to change the distribution of negative charges in the nanoparticle shell. The particle size, volume phase transition temperature, and aggregation state can be modulated using temperature, pH, or ionic strength, providing a very versatile platform for applications in sensors, medical diagnostics, environmental remediation, etc. The nanoparticles have a glassy poly(methyl methacrylate) (PMMA) core of ca. 40 nm radius and a cross-linked PNIPAM anionic shell with either AA or MA comonomers. The particles, p(N-AA) and p(MA-N), respectively, have the same total charge but different charge distributions. While the p(MA-N) particles have the negative charges preferentially distributed toward the inner shell, in the case of the p(N-AA) particles the charge extends more to the particle outer shell. The volume phase transition temperature (T(VPT)) of the particles is affected by the charge distribution and can be fine-tuned by controlling the electrostatic repulsion on the particle shell (using pH and ionic strength). By suppressing the particle charge we can also induce temperature-driven particle aggregation.

CuO 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.

The Model of Uptake with Instantaneous Adsorption and Efflux, MUIAE, describing and predicting the overall Cd uptake by the metal-resistant bacterium Cupriavidus metallidurans CH34, is presented. MUIAE takes into account different processes at the bacteria-medium interface with specific emphasis on the uptake and efflux kinetics and the decrease in bulk metal concentration. A single set of eight parameters provides a reasonable description of experimentally determined adsorbed and internalized Cd, as well as the evolution of dissolved Cd concentrations with time, for an initial Cd concentration between 10(-8) and 10(-4) M, covering the situation of contaminated environments and heavily polluted effluents. The same set of parameters allowed successful prediction of the internalized and adsorbed Cd as a function of the measured free Cd ion concentration in the presence of natural and anthropogenic ligands. The findings of the present study reveal the key role of Cd efflux and bulk depletion on the overall Cd uptake by C. metallidurans, and the need to account for these processes to understand and improve the efficiency of the metal removal from the contaminated environment.

In this work, polyelectrolyte coatings assembled on glassy carbon/thin mercury film electrodes, as an adsorbed layer of poly(sodium 4-styrenesulfonate) (PSS), were studied. The goal was to search for the best conditions for the production of stable PSS-coated electrodes that could present high negative charge densities within the thin polymeric film, providing a fast and significant electrostatic cation accumulation. Square-wave anodic stripping voltammetry was applied to measure the amount of incorporated lead used as the reference cation. The influence of the composition of the PSS solution, the amount of deposited PSS, molecular weight and of the ionic strength of the electrolyte solution, on the features of the PSS coatings for ion-exchange voltammetry was studied. The PSS films morphology was assessed by SEM. The best PSS coating performance was found for the electrodes prepared from water solutions with a molecular weight of at least 70,000, and a mass loading of ca. 8 μg mm−2. In these conditions a three fold increase was observed in low ionic strength (0.0032 M) media. However, this improvement was not sufficient for the application of direct ion-exchange voltammetry, thus different strategies to obtain polymer films with higher charge densities have to be envisaged.

Made available in DSpace on 2018-12-11T16:40:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-05-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) In this work we propose a trace metal speciation methodology to determine the total, free and ultrafiltered (

In this work, the performance and applicability of the thin mercury film electrode (TMFE) in the heavy metal speciation, by stripping chronopotentiometry (SCP), were exploited. The TMFE thickness was optimized and a 7.6 nm mercury film was selected. This TMFE was mechanically stable and able to perform 60 SCP consecutive measurements, with no significant variation in the analytical signal of lead(II) (RSD less than 2%). Due to the small electrode thickness the measurements were performed under conditions of complete depletion over a wide oxidation current ( I s ) range, i.e., within the interval [75–500] × 10 −9 A. The limit of detection (3 σ ) for lead(II) was 2.4 × 10 −9 M for a deposition time of 40 s and an oxidation current of 75 × 10 −9 A. The TMFE was successfully applied to the construction of SSCP experimental waves, which were in conformity to those predicted by the theory. The stability constant calculated ( K ′) for the Pb(II)-carboxylated latex nanospheres system using a TMFE, agreed with the one obtained using the HMDE, for identical experimental conditions.

International audience; 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.

International audience; This work presents the development of a new probe (ISIDORE probe) based on the hyphenation of a Donnan Membrane Technique device (DMT) to a screen-printed electrode through a flow-cell to determine the free zinc, cadmium and lead ion concentration in natural samples, such as a freshwater river. The probe displays many advantages namely: (i) the detection can be performed on-site, which avoids all problems inherent to sampling, transport and storage; (ii) the low volume of the acceptor solution implies shorter equilibration times; (ii) the electrochemical detection system allows monitoring the free ion concentration in the acceptor solution without sampling.

Ex-situ plated Bi film electrodes (Bi-FE) have been employed, for the first time, to measure the free concentration of Pb(II) in aqueous solutions using AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) with Stripping Chronopotentiometry (SCP) quantification. The amount of deposited Pbº, below a certain threshold, follows a Nernstian relationship with the applied potential. This threshold can be interpreted as the frontier of transition from surface deposition to solid (bulk) formation of Pbº. AGNES with Bi-FE yielded a very good detection limit (3σ) for Pb(II) of 6.0×10-9 M with an applied gain of 398 and a deposition time of 400 s. The ability of the Bi film electrode to perform speciation measurements was demonstrated for Pb(II)-PSS and Pb(II)-IDA systems. The measured values with the Bi-FE were in good agreement with the values obtained using the Hg film electrode and/or the values reported in the literature. The authors thank Nuno G. Alves, Ana M. Rosa da Costa, and José A. Moreira for the synthesis of polystyrenesulfonate polymer. This work is supported by Portuguese funding through Fundação para a Ciência e a Tecnologia (Grant FCTANR/AAG-MAA/0065/2012), Faculdade de Ciências e Tecnologia (Grants Pest-OE/EQB/LA0023/2013 and PEst- OE/QUI/UI4023/2014), and by the Spanish Ministry of Science (Projects CTM2012-39183 and CTM2013-48967). L.S. Rocha also thanks FCT Project FCTANR/AAG-MAA/ 0065/2012 for her grant.

This work aimed to produce improved polymer coatings for the modification of thin mercury film electrodes (TMFEs). The goal is to obtain sensitive, reproducible, mechanically stable and antifouling devices suitable for the determination of trace metal cations in complex media. Therefore, novel mixed coatings of two sulfonated cation-exchange polymers of dissimilar characteristics-Nafion (NA) and poly(sodium 4-styrenesulfonate) (PSS)-were produced by solvent evaporation onto glassy carbon electrodes. The effect of the mass ratio (NA:PSS) on the film morphology was studied by scanning electron microscopy, revealing the formation of biphasic polymer systems, where PSS bead-shaped clusters appeared randomly dispersed into a uniform and compact NA environment. The permselectivity/ion-exchange features of the mixed films onto glassy carbon were evaluated using cathecol, urate, and dopamine. To allow trace metal analysis, thin mercury films were plated through the NA/PSS coatings, being the reproducibility and ion-exchange features of the mixed coatings-TMFE evaluated using lead ions. The best NA/PSS coating was found for the mass ratio of 5.3. Analytical performance of the NA/PSS-TMFE yielded a detection limit of 5.5 nM (3sigma), and the application of this modified electrode to an untreated polluted estuarine water sample produced significant improvements in the quality of the signal compared with that for a bare TMFE.

We investigate the dynamic nature of metal speciation in colloidal dispersions using a recently proposed theory [J.P. Pinheiro, M. Minor, H.P. Van Leeuwen, Langmuir, 21 (2005) 8635] for complexing ligands that are situated on the surface of the particles. The new approach effectively modifies the finite rates of association/dissociation of the colloidal metal complexes, thus invoking consideration of the two basic dynamic criteria: the association/dissociation kinetics of the volume complexation reaction (the “dynamic” criterion), and the interfacial flux of free metal to a macroscopic surface due to dissociation of complex species (the “lability” criterion). We demonstrate that the conventional approach for homogeneous systems that assume a smeared-out ligand distribution, overestimates both the dynamics and the lability of metal complexes when applied to colloidal ligands. It is also shown that the increase of lability with increasing particle radius, as expected for a homogeneous solution, is moderated for spherical microelectrodes and practically eliminated for planar electrodes.

This work describes the electrochemical methodology for the determination of the Donnan potential from diffusion-limited steady-state voltammograms of acrylamide gels. The technique is based upon the measurement of gel–sol systems that have reached Donnan equilibrium and contain Cd 2+ as a probe ion. Au-amalgam microelectrodes are used to measure the Cd concentration in the gel phase relative to the solution phase, thus permitting comparison of the Cd voltammograms obtained in both phases. This approach yields two independent measures of the Donnan potential resulting from (i) the potential shift relative to the reference electrode, and (ii) the enhancement of the Cd 2+ wave. Two suites of acrylamide gels containing 0.2% and 0.5% Na-acrylate were studied as a function of ionic strength by varying [NaNO 3 ] and maintaining a constant concentration of the electroactive probe ion, [Cd 2+ ] = 1 × 10 −5 mol/L in the equilibrating solutions. Independent model predictions of the Donnan potential as a function of ionic strength that consider the effects of differential swelling on the charge density, the influence of a mixed electrolyte on the potential developed in the gel at the limit of low ionic strength and the effects of incomplete dissociation of the carboxylic functional groups were in agreement with the Donnan potentials independently measured by the twofold steady-state voltammetric approach.

The general principles of cation binding to humic matter and the various aspects of modeling used in general-purpose speciation programs are discussed. The discussion will focus on (1) the discrimination between chemical and electrostatic interactions, (2) the binding site heterogeneity, (3) the models for the electrostatic interactions, such as the Donnan model and (4) the complications inherent to ion binding in multi-component systems, including a different stoichiometry for different ions. The basic NICA (non ideal competitive adsorption) model addresses issues (1), (2) and (4) and ensures thermodynamic consistency. The electrostatic interactions (3) can be included using the ion activity adjacent to the binding sites. To compute this activity it is necessary to use an electrostatic model that relates the particle charge and the characteristic particle potential. Several simplifications to arrive at such a relation are analyzed. The Donnan model is proposed as the most convenient model. A short derivation of the NICA–Donnan model is presented to illustrate that the derivation is quite straightforward once it is clear which assumptions should be made. The main parameters of the NICA model are the site density, the median affinity constants for the different ions, the ion stoichiometry and the width of the generic affinity distribution. All these parameters are intrinsic properties that are independent of pH, salt concentration or metal concentration. The key parameter of the Donnan model is the Donnan volume, for which an empirical relation with one adjustable parameter is advised. The NICA–Donnan model has been used in several studies. To illustrate the capabilities of the model some results obtained for purified humic acid are presented together with model predictions. Key features of the model are its ability to adjust to different heterogeneities and binding stoichiometries and its predictive abilities with respect to metal ion–proton and metal–metal ion competition. With the application the model should be regarded as semi-empirical because assumptions have been made for its derivation that are not met in practice. Both for this reason and since it is difficult, if not impossible, to find a unique set of parameters for a given system the interpretation of the parameter values may be difficult. A brief discussion is given on the generic NICA–Donnan description of fulvic and humic acids presented by Milne et al. [C.J. Milne, D.G. Kinniburgh, E. Tipping, Environ. Sci. Technol. 35 (2001) 2049; C.J. Milne, D.G. Kinniburgh, W.H. van Riemsdijk, E. Tipping, Environ. Sci. Technol. 37 (2003) 958]. Finally a brief literature review is presented on the use of the NICA–Donnan model for other heterogeneous natural sorbent systems.

A method is presented for analyzing the dynamic speciation features of metal complexes based on stripping chronopotentiometry at a scanned deposition potential (SSCP). The shift in the SSCP half-wave deposition potential, ΔEd,1/2, is straightforwardly related to the complex stability, K, irrespective of the degree of lability; the limiting wave height, τ*, quantifies the metal species accumulated in the electrode and thus depends on both the lability and mass transport properties of the metal complex species in solution. For complexes with a lower diffusion coefficient than the free metal ion, K calculated from ΔEd,1/2 will be the same as that derived from the relative τ* values so long as the system is fully labile. Discrepancies between ΔEd,1/2-derived and τ*-derived K values indicate loss of lability. We show that this approach is a sensitive indicator of lability, as illustrated by analysis of cadmium and lead binding by carboxylated nanospheres.

Environmental health hazards of Quantum Dots (QDs) are of emergent concern, but limited data is available about their toxicokinetics (TK) and tissue distribution in marine bivalves. This study investigated the QDs behavior in seawater, their TK and tissue distribution in Mytilus galloprovincialis, in comparison with soluble Cd. Mussels were exposed to CdTe QDs and soluble Cd for 21 days at 10 μgCd L(-1) followed by a 50 days depuration. TK of QDs in mussels is related to the homo-aggregate uptake, surface charge, aggregation and precipitation as key factors. There were tissue- and time-dependent differences in the TK of both Cd forms, and soluble Cd is the most bioavailable form. Digestive gland is a preferential site for QDs storage and both Cd forms are not eliminated by mussels (t1/2>50 days). Results indicate that the TK model of CdTe QDs in marine mussels is distinct from their soluble counterparts. Science Without Borders Program from the Brazilian National Council for Scientific and Technological Development (CNPq) 239524/2012-8 info:eu-repo/semantics/publishedVersion

International audience; The hydrogel/water partitioning of the various species in the cadmium(II)/soil humic acid (HA) system is studied for two types of gel, using in situ microelectrodic voltammetry. Under the conditions of this work, with HA particles of ca. 25 and 125 nm radius, the CdHA complex is shown to be close to nonlabile toward a 12.5 μm radius microelectrode. This implies that its kinetic contribution to Cd2+ reduction at the medium/microelectrode interface is practically negligible. The polyacrylamide (PAAm) gels equilibrate with the aqueous medium under significant sorption of HA at the gel backbone/gel medium interface, which in turn leads to induced sorption of Cd(II) in the form of immobilized gel-bound CdHA. The rather high total Cd content of the PAAm gel suggests that the binding of Cd2+ by the hydrophobically gel-bound HA is stronger than that for dispersed HA particles. Still, the intraparticulate speciation of Cd(II) over Cd2+ and CdHA corresponds to an intrinsic stability constant similar to that for simple monocarboxylate ligands such as acetate. Alginate gels are negatively charged, and their free [Cdaq2+] is higher than that in the medium by the corresponding Donnan coefficient. On top of that, Cd2+ is specifically sorbed by the gel backbone/gel medium interface to reach accumulation factors as high as a few tens. HA and CdHA accumulate in the outer 20 μm film of gel at the gel/water interface of both gels, but they do not penetrate into the bulk of the alginate gel. Overall, the gel/water interface dictates drastic changes in the speciation of Cd/HA as compared to the aqueous medium, with distinct features for each individual type of gel. The results have broad significance, for example, for predictions of reactivity and bioavailability of metal species which inherently involve partitioning and diffusion into diverse gel layers such as biointerfacial cell walls, biofilm matrices, and mucous membranes.

International audience; Particles consisting of a glassy poly(methyl methacrylate) core (ca. 40 urn in radius) decorated with a poly(N-isopropylacrylamide) anionic corona are synthesized using either methacrylic acid (MA) or acrylic acid (AA) as reactive comonomers in the shell. The different reactivity ratios of MA and AA toward N-isopropylacrylamide originates p(MA-N) and p(N-AA) particles with carboxylate charges supposedly located, preferentially, in the close vicinity of the core and at the shell periphery, respectively. The corresponding Swelling features of these nanoparticles are addressed over a broad range of pH values (4 to 7.5), NaNO3 concentrations (3 to 200 mM), and temperatures (15 to 45 degrees C) by dynamic light scattering (DLS) and small angle neutron scattering (SANS). DLS shows that the swelling of the particle shells increases their thickness from similar to 10 to 90 nm with decreasing temperature, ionic strength, or increasing pH, with the effect being more pronounced for p(N-AA) whose lower critical solution temperature is shifted to higher values compared to that of p(MA-N). Potentiometric titration and electrokinetic results further reflect the easier dissociation of carboxyl groups in p(N-AA) and a marked heterogeneous interfacial swelling of the latter with decreasing solution salt content. The DLS response of both particles is attributed to the multiresponsive nature of a peripheral dilute shell, while SANS only probes the presence of a quasi-solvent-free dense polymer layer, condensed on the core surface. The thickness of that layer slightly increases from similar to 6 to 9.5 mu with increasing temperature from 15 to 45 degrees C (at 15 mM NaNO3 and pH 5) due to the collapse of the outer dilute shell layer. Overall, results evidence a nonideal brush behavior of p(MA-N) and p(N-AA) and their microphase segregated shell, structure, which supports some of the conclusions recently formulated from approximate self-consistent mean-field computations.

International audience; Temperature effects on metal speciation dynamics were studied using Stripping Chronopotentiometry at Scanned deposition Potential (SSCP). The temporal and spatial scales of this study are respectively O(10(-1) s) and O(10(-5) M), characteristics of the thin mercury film rotating disk, used as working electrode. The lability degree and the association rate constant were evaluated in the temperature interval of 15-40 degrees C for a significantly non-labile system, cadmium binding by nitrilotriacetic acid, and a quasi-labile system, lead binding by iminodiacetic acid. The results for both systems reveal that the lability of the metal complex significantly increases with temperature. This lability gain results from the thermal augmentation of the association rate constant and the broadening of the diffusion layer thickness.An evaluation of the metal calibration methodology for SSCP at different temperatures was conducted. It was found that although the variation of diffusion layer thickness can be correctly predicted, changes in standard reduction potential of the metals cannot, thus a calibration must be performed for each temperature studied.This work constitutes a first step toward the comprehension of the effect of temperature on metal chemodynamics.

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.

The nuclease activity of VO(acac)2 (1, acac = acetylacetone) and its derivatives VO(hd)2 (2, hd = 3,5-heptanedione), VO(Cl-acac)2 (3, Cl-acac = 3-chloro-2,4-pentanedione), VO(Et-acac)2 (4, Et-acac = 3-ethyl-2,4-pentanedione) and VO(Me-acac)2 (5, Me-acac = 3-methyl-2,4-pentanedione), is studied by agarose gel electrophoresis, UV-visible spectroscopy, cyclic and square wave voltammetry and (51)V NMR. The mechanism is shown to be oxidative and associated with the formation of reactive oxygen species (ROS). Hydrolytic cleavage of the phosphodiester bond is also promoted by 1, but at much slower rate which cannot compete with the oxidative mechanism. The generation of ROS is much higher in the presence of phosphate buffer when compared with organic buffers and this was attributed to the formation of a mixed-ligand complex containing phosphate, (V(IV)O)(V(V)O)(acac)2(HnPO4(n-3)), presenting a quasi-reversible voltammetric behavior. The formation of this species was further observed by Electrospray Ionization Mass Spectrometry (ESI-MS). Phosphate being an essential species in most biological media, the importance of the formation of mixed-ligand species in other vanadium systems is emphasized.