Proton Binding Characteristics of Dissolved Organic Matter Extracted from the North Atlantic.

Marine dissolved organic matter (DOM) presents key thermodynamic properties that are not yet fully constrained. Here, we report the distribution of binding sites occupied by protons (i.e.

Interactions of humic acid with pristine poly (lactic acid) microplastics in aqueous solution.

Microplastics and natural organic matter are present in the aquatic environment and their reciprocal interaction plays important roles in the transport and behavior of nutrients and contaminants. Nevertheless, we lack mechanistic understanding on these interactions, especially in the case of biodegradable plastics. Here we investigate the adsorption of a commercial humic acid onto poly (lactic acid) (PLA) microplastics in aqueous solution.

Seasonal Variations in Proton Binding Characteristics of Dissolved Organic Matter Isolated from the Southwest Baltic Sea.

The physicochemical characteristics of dissolved organic matter (DOM) strongly influence its interactions with inorganic species such as protons and trace elements in natural waters. We collected water samples at Boknis Eck, a time series station in the Baltic Sea with a low exposure to freshwater inputs, to investigate how seasonal fluctuations impact the proton binding properties of the isolated DOM. We used potentiometric titrations to assess the binding properties of solid-phase extracted DOM (SPE-DOM) over a seasonal cycle.

Speciation of Inorganic Compounds in Aquatic Systems Using Diffusive Gradients in Thin-Films: A Review.

The speciation of trace metals in an aquatic system involves the determination of free ions, complexes (labile and non-labile), colloids, and the total dissolved concentration. In this paper, we review the integrated assessment of free ions and labile metal complexes using Diffusive Gradients in Thin-films (DGT), a dynamic speciation technique. The device consists of a diffusive hydrogel layer made of polyacrylamide, backed by a layer of resin (usually Chelex-100) for all trace metals except for Hg.

Acid-base properties of dissolved organic matter extracted from the marine environment.

Marine dissolved organic matter (DOM) plays a key role in the current and future global carbon cycle, which supports life on Earth. Trace metals such as iron, an essential micronutrient, compete with protons and major ions for the binding to DOM. These competitive effects and the DOM binding capacity are related to the DOM acid-base properties, which also influence DOM transport and reactivity in marine waters.

Time weighted average concentrations measured with Diffusive Gradients in Thin films (DGT).

Time weighted average (TWA) concentrations can improve the assessment of water quality. DGT (Diffusive Gradients in Thin films) devices have been suggested as simple tools to measure TWA metal concentrations, but the connection of TWA with c has not been rigorously discussed. It is shown here that c is the average DGT-labile concentration along the deployment, which suggests that it is well suited to correlate with toxicity effects.

Dissolution and Phosphate-Induced Transformation of ZnO Nanoparticles in Synthetic Saliva Probed by AGNES without Previous Solid-Liquid Separation. Comparison with UF-ICP-MS.

The variation over time of free Zn ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37 °C was followed in situ (without solid-liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). Under these conditions, ZnO NPs are chemically unstable due to their reaction with phosphates.

Effect of polymer coating composition on the aggregation rates of Ag nanoparticles in NaCl solutions and seawaters.

The aggregation behaviour of polymer-coated silver nanoparticles (AgNPs) was characterized in NaCl solutions, and in two seawaters of different salinities and dissolved organic matter (DOM) contents. Representative organic coatings i.e.

Extending the Use of Diffusive Gradients in Thin Films (DGT) to Solutions Where Competition, Saturation, and Kinetic Effects Are Not Negligible.

DGT (Diffusion Gradients in Thin films) was designed to sample trace metals in situ at their natural concentrations. The setup and the experimental deployment conditions were established to allow interpretation of a linear accumulation of metal with time, using a simple expression based on a steady-state flux under perfect sink conditions. However, the extension of DGT to a wide range of analytes and its use under varied conditions has shown that, in some situations, these conditions are not fulfilled, so that accumulations with time are nonlinear.

Accumulation of Mg to Diffusive Gradients in Thin Films (DGT) Devices: Kinetic and Thermodynamic Effects of the Ionic Strength.

Availability of magnesium is a matter of concern due to its role in many environmental and biological processes. Diffusive Gradients in Thin Films (DGT) devices can measure Mg availability in situ. This work shows that Mg accumulation in water largely increases when ionic strength (I) decreases.

Influence of the settling of the resin beads on diffusion gradients in thin films measurements.

Binding resin beads used in DGT (diffusion gradients in thin films) tend to settle to one side of the resin during casting. This phenomenon might be relevant for metal accumulation when partially labile complexes dominate the metal speciation, especially after recognizing the important role played by complex dissociation in the resin domain. The influence of the inhomogeneity of the binding agent distribution on metal accumulation is here assessed by numerical simulation of DGT devices with binding beads in only one half of the resin disc, as a reasonable model of the standard resin discs.

Suitability of analytical methods to measure solubility for the purpose of nanoregulation.

Solubility is an important physicochemical parameter in nanoregulation. If nanomaterial is completely soluble, then from a risk assessment point of view, its disposal can be treated much in the same way as "ordinary" chemicals, which will simplify testing and characterisation regimes. This review assesses potential techniques for the measurement of nanomaterial solubility and evaluates the performance against a set of analytical criteria (based on satisfying the requirements as governed by the cosmetic regulation as well as the need to quantify the concentration of free (hydrated) ions).

Systematic investigation of the physicochemical factors that contribute to the toxicity of ZnO nanoparticles.

ZnO nanoparticles (NPs) are prone to dissolution, and uncertainty remains whether biological/cellular responses to ZnO NPs are solely due to the release of Zn(2+) or whether the NPs themselves have additional toxic effects. We address this by establishing ZnO NP solubility in dispersion media (Dulbecco's modified Eagle's medium, DMEM) held under conditions identical to those employed for cell culture (37 °C, 5% CO2, and pH 7.68) and by systematic comparison of cell-NP interaction for three different ZnO NP preparations.

Limits of the linear accumulation regime of DGT sensors.

A key question for the practical application of DGT (Diffusive Gradients in Thin films) as dynamic sensors in the environmental monitoring of trace metals is the influence of pH and dissolved ligands over the linear accumulation regime. Protons compete with metal ions for the binding to the DGT resin sites at relatively low pH, whereas high affinity dissolved ligands compete with resin sites for the binding of metals. Any of the two phenomena can lead to a departure from the linear accumulation regime and an underestimation of the actual species concentration in solution.

Experimental evidences for a new model in the description of the adsorption-coupled reduction of Cr(VI) by protonated banana skin.

This work reports experimental evidences, not previously considered, to evaluate the Cr(VI) removal by protonated banana skin biomass. Variations in the number of hydroxyl groups, quantified by potentiometric titrations, and CO2 evolution during experiments, were attributed mainly to the oxidation of hydroxylic entities present in the studied material. The results indicate that these groups together with the carboxylic moieties are the main functionalities involved on the adsorption-coupled reduction process.

A semi-grand canonical Monte Carlo simulation model for ion binding to ionizable surfaces: proton binding of carboxylated latex particles as a case study.

In this paper, we present a computer simulation study of the ion binding process at an ionizable surface using a semi-grand canonical Monte Carlo method that models the surface as a discrete distribution of charged and neutral functional groups in equilibrium with explicit ions modelled in the context of the primitive model. The parameters of the simulation model were tuned and checked by comparison with experimental titrations of carboxylated latex particles in the presence of different ionic strengths of monovalent ions. The titration of these particles was analysed by calculating the degree of dissociation of the latex functional groups vs.

Full description of copper uptake by algal biomass combining an equilibrium NICA model with a kinetic intraparticle diffusion driving force approach.

In this work kinetic and equilibrium studies related to copper binding to the protonated macroalga Sargassum muticum are reported. An intraparticle-diffusion linear driving force (LDF) model has been chosen for the quantitative description of the kinetics at several initial metal concentrations. Copper intraparticle homogeneous diffusion coefficient (D(h)) obtained is in the range 0.

Model-independent link between the macroscopic and microscopic descriptions of multidentate macromolecular binding: relationship between stepwise, intrinsic, and microscopic equilibrium constants.

The binding of ions or other small molecules to macromolecules and surfaces can be macroscopically characterized by means of the stepwise (or stoichiometric) equilibrium constants, which can be obtained experimentally from coverage versus concentration data. The present work presents a novel, simple, and direct interpretation of the stepwise constants in terms of the microscopic, site-specific, stability constants. This formalism can be applied to the most general case, including the heterogeneity of the sites, interactions among them, multicomponent adsorption, and so forth, and, in particular, to chelate complexation.

Effective affinity distribution for the binding of metal ions to a generic fulvic acid in natural waters.

The effective distribution of affinities (Conditional Affinity Spectrum, CAS) seen by a metal ion binding to a humic substance under natural water conditions is derived and discussed within the NICA-Donnan model. Analytical expressions for the average affinity of these distributions in general multi-ion mixtures are reported here for the first time. These expressions enable a simple evaluation of the effect of all interfering cations on the affinity distribution of a given one.

Acid-base equilibria of phthalic acid in saline media: ion association from Pitzer equations.

The protonation constants of 1,2-benzenedicarboxylic acid (phthalic acid) at 25 degrees C in NaCl and CaCl(2) (ionic strengths ranging from 0.1 to 2 mol kg(-1)) were determined potentiometrically, and the results were analyzed by means of Pitzer equations. The values of the logarithm of the first and second dissociation constants ranged from 2.

Competitive Cd2+/H+ complexation to polyacrylic acid described by the stepwise and intrinsic stability constants.

Stepwise constants can be used to describe competitive proton and metal binding to macromolecules with a large number of sites. With the aim of accessing information on the microscopic binding model, we report an expression that connects the stepwise constants to the site-specific metal constants. This expression holds for a very general complexation model including heterogeneity, interactions, and chelate complexation.

Competitive ion complexation to polyelectrolytes: determination of the stepwise stability constants. The Ca2+/H+/polyacrylate system.

This work presents a new methodology aimed at obtaining the stepwise stability constants corresponding to the binding of ions (or other small molecules) to macromolecular ligands having a large number of sites. For complexing agents with a large number of sites, very simple expressions for the stepwise stability constants arise. Such expressions are model-independent; that is, they allow the determination of the stepwise stability constants without making any previous assumption of the detailed complexation mechanism.

Transport properties of the ionic liquid 1-ethyl-3-methylimidazolium chloride from equilibrium molecular dynamics simulation. The effect of temperature.

We present here equilibrium molecular dynamics simulation results for self-diffusion coefficients, shear viscosity, and electrical conductivity in a model ionic liquid (1-ethyl-3-methylimidazolium chloride) at different temperatures. The Green-Kubo relations were employed to evaluate the transport coefficients. When compared with available experimental data, the model underestimates the conductivity and self-diffusion, whereas the viscosity is overpredicted, showing only a semiquantitative agreement with experimental data.

Removal of inorganic mercury from aqueous solutions by biomass of the marine macroalga Cystoseira baccata.

The ability of Cystoseira baccata algal biomass to remove Hg(II) from aqueous solutions is investigated. The mercury biosorption process is studied through batch experiments at 25 degrees C with regard to the influence of contact time, initial mercury concentration, solution pH, salinity and presence of several divalent cations. The acid-base properties of the alga are also studied, since they are related to the affinity for heavy metals.