Free Metal Ion In Solution Research Articles

Ga Ion-Enhanced and Particle Shape-Dependent Generation of Reactive Oxygen Species in X-ray-Irradiated Composites.

The reported results test the effects of the collective behavior hypothesized to contribute to the production of more reactive oxygen species (ROS) in vitro and result in an enhanced radiosensitization. The role of particle shape in composites with gallium oxyhydroxide (GaOOH) particles and Matrigel is studied. Particles of two different shapes are embedded into the gel to understand only the materials effect on the generation of ROS rather than cell penetrating variations. The paper reports materials characterization by scanning electron microscopy and X-ray diffraction. The stability of the particles within the composite is assessed by quantification of leached metal using inductively coupled plasma mass spectrometry. The amount of ROS in each construct under variable radiation conditions is quantified in the presence and absence of PC12 cells seeded on top of the composites. The viability of cells is also recorded under different in vitro conditions. The collective materials characterization and the results from the bioassays are used to explain the role of anisotropy on the radiosensitization of nanostructures containing Ga. The presence of Ga ions in composites can have a radiosensitizing effect, and the amount of the available Ga3+ determines the magnitude of the radiosensitization. The shape of the particles determines the stability in aqueous solutions and release of Ga3+ that triggers ROS production. The concentration and shape of Ga-containing materials can be combined to generate an additive effect by increasing the amount of available free metal ions in solution. The studies with GaOOH containing composites enable one to explore the role of key parameters that lead to an increased efficiency of radiation treatments.

In situ hydrogel formation for biomedical applications using acoustic cavitation from high intensity focused ultrasound

There is a growing interest in polymer mechanochemistry for their industrial applications. For example, stress-induced crosslinking gel formation from polymer networks is a rapidly growing field of study. Recent work utilizes a variety of different polymer structures and crosslinking mechanisms. However, these polymers are typically soluble in only organic solvents and require the use of a sonicating probe or bath at frequencies below 100 kHz. These requirements limit their use in biomedical applications that require in situ gel formation within a patient (e.g., blocking of varicose veins, internal wound healing, etc.). Here we report on the development of a water soluble block copolymer that forms a hydrogel in the presence of acoustic cavitation from high intensity focused ultrasound. These block copolymers are comprised of hydrophilic polyethylene glycol methyl methacrylate units and hydrophobic tridentate crosslinkers. The tridentate crosslinker forms bonds with free metal ions in solution only in the presence of acoustic cavitation induced mechanical stress. We show that the block copolymer is capable of forming a hydrogel in under 90 seconds and will also block a liquid channel formed in an agarose cylinder.

Ratiometric Bioluminescence-Based Zinc Biosensor with Nanomolar Sensitivity

In recent years, we and other workers have developed fluorescence-based sensors and biosensors for Zn2+ and other free metal ions in solution, which have proven valuable as tools for the study of the biology of metal ions. Using the sensors in some applications such as in vivo molecular imaging has been challenging, owing to the difficulty of exciting fluorophores deep in tissues which scatter and absorb exciting light effectively. One approach used by investigators to minimize this problem is the use of bioluminescent labels for in vivo imaging, which perforce require no exciting light. We have employed a bioluminescence resonance energy transfer approach with our carbonic anhydrase-based zinc biosensor to produce a ratiometric bioluminescence-based zinc biosensor.

Fast separation, characterization, and speciation of gold and silver nanoparticles and their ionic counterparts with micellar electrokinetic chromatography coupled to ICP-MS.

In this study, a method for separation, size characterization, and speciation of gold and silver nanoparticles was developed through the use of micellar electrokinetic chromatography (MEKC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) for the first time. Figures of merit in this proof-of-principle study include peak area precision of 4-6%, stable migration times (1.4% with internal standard), and capillary recoveries on the order of 72-100% depending on species and nanoparticle size, respectively. Detection limits are currently in the sub-microgram per liter range. For example, a total of 1500 50-nm-sized gold nanoparticles were successfully detected. After careful optimization, MEKC-ICP-MS was used to separate engineered nanoparticles (ENPs) of different composition. Speciation analysis of ENPs and free metal ions in solution was feasible using a complexing agent (penicillamine). Gold speciation analysis of a dietary supplement, which contained approximately 6-nm-sized gold nanoparticles, was demonstrated.

Humic acid complexation to Zn and Cd determined with the new electroanalytical technique AGNES

Environmental context. Humic substances are complex mixtures that play an important role in trace metal bioavailability in soils and aquatic environments. The bioavailability of a metal depends on what chemical forms, or species, it is in. We need to know how much of the metal is present as a free metal ion in solution, and how much is bound up in complexes with humic acids, for example. This work reports the complexation of Cd and Zn to humic acids by means of a simple and robust technique, AGNES (absence of gradients and Nernstian equilibrium stripping). Abstract. AGNES (absence of gradients and Nernstian equilibrium stripping), an emerging electroanalytical technique specifically designed for the determination of the free concentration of heavy metals in aqueous solutions, is here implemented to characterise the binding of CdII and ZnII to a soil humic acid. A set of metal titration experiments were performed by adding Cd or Zn to a purified humic acid (Aldrich) at pH 4, 5, 6 and 7 and measuring the free metal concentration by AGNES. The application of a program with two potential steps along the deposition stage allows for the reduction of the deposition time in the humic titration. The polyelectrolytic effects of the macromolecular ligand were taken into account through the Donnan model. Data free of electrostatic effects were reasonably described by the NICA isotherm, which accounts for heterogeneity, considering just a monomodal distribution (because of the range of pH covered). The obtained affinity parameters indicate a similar strength for Zn and Cd binding to the purified humic acid.

Determination of the metal complexation capacity of natural waters by ligand titration in the presence of complexing resins

The complexation properties of some drinking waters for U(VI), Al(III) and Cu(II) are determined by ligand titration (LT) with the metal ions, using a new method for monitoring, i.e. the sorpion of metal ion on complexing resins. The concentration of the free metal ion in solution is evaluated from the concentration of sorbed metal ion and from the quantity K * , which is the ratio of the concentration of the metal ion sorbed on the resin to the concentration of free metal ion in solution, and can be independently evaluated. The concentration of the ligands in solution (c I ) and the conditional stability constant (K M(I) ) are obtained by the Ruzic linearization. Different resins, i.e. the iminodiacetic resin Chelex 100, the carboxylic resin Amberlite CG 50 and the anion exchange resin AG1X8 were used for monitoring the titration, since they have different sorbing properties, and in principle they allow the detection of different ligands. Ligands at low concentration and with very high complexation constants were detected in the considered samples. Particularly in the case of U(VI), they are able to complex the metal ion much more strongly than the ligands that are usually considered in aqueous solution, i.e. carbonate and hydroxyl.

The Challenges of Hazard Identification and Classification of Insoluble Metals and Metal Substances for the Aquatic Environment

The OECD is currently harmonizing procedures for aquatic hazard identification of substances. Such a system already exists in Europe where it is recognized that special consideration must be given to sparingly soluble metals and metal compounds (SSMMCs) because standard hazard testing procedures designed for organic chemicals do not accommodate the characteristics of SSMMCs. Current aquatic hazard identification procedures are based on persistence, bioaccumulation, and toxicity (PBT) measurements. Persistence measurements typically used for organic substances (biodegradation) do not apply to metals. Alternative measurements such as complexation and precipitation are more appropriate. Metal bioaccumulation is important in terms of nutritional sufficiency and potential food chain transfer and toxicity. Unlike organic substances, metal bioaccumulation potential cannot be estimated using log octanol-water partition coefficients. Further, bioaccumulation and bioconcentration factors are often inversely related to exposure concentration for most metals and organisms, and hence are not reliable predictors of chronic toxicity or food chain accumulation. Metal toxicity is due predominately to the free metal ion in solution. In order to assess the toxicity of SSMMCs, the rate and extent of transformation to a soluble form must be measured.

Determination of the complexing properties of drinking waters toward copper(II) and aluminium(III) by ligand titration

The complexing capacity of some drinking waters for aluminium(III) and copper(II) is determined by a ligand titration with metal ions based on the use of complexing resins. The resins used in the titration are the iminodiacetic resin Chelex 100, the carboxylic resin Amberlite CG50 and the anionic exchange resin AG1X8. They allow the detection of ligands forming complexes of different stability with the metal ions used for the titration, since they have different sorbing properties. After equilibration with the resin, the concentration of the free metal ion in solution is evaluated from the concentration of sorbed metal ion and from the quantity K ∗, which is the ratio of the concentration of the metal ion sorbed on the resin to the free metal ion in solution. It strongly depends on the conditions, but it can be evaluated, at the considered conditions, from the sorption equilibria of the metal ion on the resin. The concentration of the ligands in solution and the conditional stability constant are obtained from the Ruzik linearization procedure. Very strong ligands of copper(II) and aluminium(III) were detected in a tap water sample at concentrations ranging from 10 −7 to 10 −6 mol kg −1, and forming complexes having conditional complexation constants K cI=2.3×10 17 (pH=6.77) and 4.5×10 16 (pH=6.24), respectively, for copper(II) and aluminium(III). Weaker ligands were detected using the less strongly sorbing resins Amberlite CG50 and AG1X8, but at a concentration equal to that of the strong ligands. This was ascribed to the presence of competing metals in solution, not sorbed by the weak resins. Two other drinking waters had completely different complexing properties both towards copper(II) and aluminium(III), containing much weaker ligands.

Determination of the metal complexing capacity of aqueous solutions containing ligands by titration in the presence of complexing resins

The feasibility of ligand titrations with metal ions using complexing resins as sorbing solids is evaluated. The resins considered were the iminodiacetic resin Chelex 100, the carboxilic resin Amberlite CG50, and the anion exchange resin AG1X8, whose sorbing properties for aluminium(III) and copper(II) were known from previous investigations. Synthetical solutions containing known concentrations of ligands, EDTA and IDA were titrated separately with aluminium(III) and copper(II), by adding known concentration of titrant metal, and measuring the concentration of metal ion sorbed on the resin, c. The concentration of free metal ion was evaluated from c by the relationship: [M] = cV/ K* w. K* is the ratio of the concentration of metal ion sorbed on the resin to the free metal ion in solution, and strongly depends on the conditions. In the case of the resins used in this investigation it can be calculated since the sorption equilibria of the metal ions are known. The total concentration of the ligands and the conditional stability constants are evaluated by a linearization procedure, previously proposed and widely used for ligand titrations, based on the hypothesis that only a 1 to 1 metal to ligand complex is formed. Accurate results are always obtained if the titration is properly carried out, i.e. using the appropriate resin, and adding the required excess of titrant. Some criteria are suggested to evaluate the results obtained, which can be useful when solutions of unknown composition are titrated. For these evaluations the sorption equilibria of metal ions on the resin at the considered conditions must be exactly known. In this paper they were evaluated from the sorbing properties of the resins, previously investigated according to the Gibbs–Donnan model. This is very convenient, since it avoids the experimental determination at each particular set of conditions, which is often even impossible, yet giving acceptable results.

Kinetically Labile Equilibrium Shifts Induced by the Electrospray Process

The complexation reactions between the alkaline earth metal ions and EDTA were studied by electrospray mass spectrometry to measure the change in concentration of the metal ion-EDTA complex (MY(2)(-)) in the gas phase relative to the solution-phase equilibrium concentration. This work focused on the solution pH range from 4 to 7 where there exists free metal ions in solution at equilibrium. The equilibrium shift, measured through quantitation of the increased abundance of the MY(2)(-) species in the gas phase, was largest for barium and smallest for magnesium. The cause of the net equilibrium shift of the MY(2)(-) species is the combined effect of an electrolytic increase in pH within the capillary plus an additional shift within the evaporating droplets. In a thin diffusion-limited layer created by the products of electrolysis mixing with the bulk solution at the ES capillary tip, the labile species reequilibrate at a new, higher pH. In the evaporating droplets, the formation of new labile species due to increased solute concentrations is kinetically controlled because the ion residence time in the droplet prior to desorption is only ∼5 μs. These results are briefly discussed with respect to the potential for utilizing electrospray mass spectrometry for kinetically labile equilibrium studies.

Investigation of the speciation of aluminium in drinking waters by sorption on a strong anionic-exchange resin AG1X8

The sorption properties of the strong anion exchange resin AG1X8 towards aluminium(III) were investigated in view of the study of the speciation of this metal ion in drinking waters. This was done by determining the side reaction coefficients of the metal ion in the sample solution in the presence of the resin. It was found that aluminium(III) is sorbed on AG1X8 by the formation of Al(OH) 3 and Al(OH) − 4. The exchange coefficients were determined at different conditions and the intrinsic complexation constants were evaluated on the basis of the Gibbs–Donnan model. From the exchange coefficients the ratio of metal ion sorbed on the resin to the free metal ion in solution, K * was evaluated. It is a measure of the sorbing properties of a resin towards a metal ion at a given pH. AG1X8 was used for the determination of total aluminium(III) concentration in drinking water samples by the resin titration (RT) method at pH 7.5 and 6.2. In the first case the total concentration obtained by RT was equal to that determined directly, showing that all aluminium is either quantitatively sorbed or in equilibrium with AG1X8. The side reaction coefficient α M(I) was evaluated to be around 10 12 in the considered drinking water samples at this pH. Not any aluminium(III) was sorbed on AG1X8 from the considered drinking water samples at pH=6.2 suggesting that aluminium is present here as species with α M(I)>10 7. These results were compared with those obtained using Chelex 100, which is able to sorb aluminium(III) also at pH 6.2. More information about the speciation of aluminium can be obtained by comparing the results from two different sorbing resins.

Uptake of Lipophilic Organic Cu, Cd, and Pb Complexes in the Coastal Diatom Thalassiosira weissflogii

Short-term uptake experiments using the coastal diatom Thalassiosira weissflogii demonstrated that low molecular weight, lipophilic, organic Cu, Cd, and Pb complexes enter the cell by diffusion across the plasma membrane. This passive uptake mechanism acts in parallel to facilitated transport, which involves an equilibrium between free metal ions in solution and surface transport sites. Neither the observed permeability coefficents nor the calculated theoretical permeability coefficents for these lipophilic organic compleres account for the increased cellular Cu concentration observed over 5 h. Furthermore, permeability measwements cannot explain the discrepancy in cellular concentrations between Cu, Cd, and Pb in the lipophilic organic metal treatments

27] Measurements of cation transport with metallochromic indicators

Publisher Summary This chapter reviews that sensitive and accurate kinetic measurements of ionized metal ions are central for the understanding of ion transport in biological systems. Among the various cations interacting with biological materials, H + , Ca 2+ , and Mg 2+ have a key role in regulating enzyme activity and cellular functions. Hence, the study of H + , Ca 2+ , and Mg 2+ transport acquires particular significance for the understanding of (1) energy transduction and cellular events such as contraction, secretion, fusion, and excitation and (2) more complex events such as vision and hormone and neurotransmitter action. The chapter also discusses the methods for measuring H + , Ca 2+ , and Mg 2+ , which includes isotope distribution, atomic absorption spectroscopy, specific electrodes, photoluminescent, fluorescence, and absorbance indicators. All of these methods present advantages and disadvantages with respect to selectivity, specificity, time resolution, and sensitivity. It also reviews that metallochromic indicators are substances that undergo color changes when the concentration of free metal ion in the solution changes. The color difference between the free indicator and the indicator-metal ion complex is often very large and can be used for quantitative determination of the concentration of free metal ion in solution.

A Study of Manganous Complexes by Paramagnetic Resonance Absorption

THE paramagnetic resonance absorption of unstable metal complexes in aqueous solution has been explored and has been applied to the measurement of dissociation constants of such complexes. The method has the obvious limitation, in common with other magnetic methods, that direct measurements are confined to those ions and molecules which are paramagnetic. On the other hand, the method, in common with other spectroscopic methods, has the advantage that it can measure directly and rapidly the concentration of the free metal ion in solution without disturbing any pre-existing equilibrium state.