Chemical speciation of aluminium in beers

ABSTRACT

Details of analyses of a range of lagers for aluminium and for silica are presented. These permit an estimation of the total levels of aluminium as beer is diluted by saliva and intestinal fluids. These data are combined with databases of formation constants and solubility products and the MINEIR speciation program to calculate the chemical speciation of aluminium from beer through to excretion. Bioavailable species are assumed to be [Al citrate]⁰ and/or [Al phosphate]⁰ but other than a noticeable presence in the small intestine—from which uptake is limited there is not a significant species concentration. With normal kidney action any small traces entering the blood are rapidly cleared.     

Speciation studies of Co(II), Ni(II) and Cu(II) complexes of L-valine in acetonitrile–water mixtures

Abstract

Chemical speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-valine in 0.0-60.0% v/v acetonitrile-water mixtures was studied pH-metrically at an ionic strength of 0.16 mol L^-1 at 303.0 K. The existence of different binary complexes was established from the modelling studies, using the computer program MINIQUAD75. The appropriateness of the model was ascertained by studying the effect of errors in concentrations of the reagents. The trend in variation of stability constants with change in the permittivity of the medium is explained on the basis of electrostatic and non-electrostatic forces. The species distribution diagrams and the plausible equilibria for the formation of the species are also presented.     

Speciation studies of aluminium(III)–acetate complexes under physiological conditions

Abstract

The aluminium complexes of acetic acid (ACT) have been studied using Potentiometric titrations under physiological conditions of temperature (37°C) and ionic strength (0.15 dm^?3 dm^?3 NaCI) and at different ligand to metal ratios. The variations of pH were measured with the help of a glass electrode calibrated daily in hydrogen ion concentrations. Results obtained within the pH range of 2.6–4.2 were analysed to determine stability constants using the SUPERQUAD program. Different complex combinations were considered during the calculation procedure, and evidence was found for ML₂ mononuclear species beside binuclear hydroxo-complexes M₂L(OH)₂ and M₂L(OH)₃ and metal ion hydroxides. Speciation calculations based on the corresponding constants were then used to simulate species distributions.     

Speciation of N-(phosphonomethyl)glycine (glyphosate) in aqueous solutions containing major components of natural fluids

ABSTRACT

Potentiometric measurements in different media and at different temperatures were performed in order to determine protonation constants of glyphosate and formation constants for Ca²⁺ and Mg²⁺ complexes, together with their dependence on ionic strength and ?H⁰ values. Calorimetric measurements were also performed to determine ?H⁰ of protonation. Potentiometric measurements in mixed Ca²⁺ and Mg²⁺ solution allowed us to determine the formation of a mixed metal species. Thermodynamic parameters reported in this work can be used for studying the complete speciation of glp in electrolyte solutions containing the major ionic components of natural fluids.     

Formation and confirmation of binary complexes of calcium(II), magnesium(II ) and zinc(II) with L-histidine in dioxan-water media

Abstract

A computer assisted pH-metric investigation has been carried out on the speciation of binary complexes of Ca(II), Mg(II) and Zn(II) with L-histidine. The titrations are carried out with sodium hydroxide in varying concentrations (0–60% v/v) of dioxan-water mixtures at an ionic strength of 0.16 mol L^-1 and at a temperature of 303 K. Ca(II), Mg(II) and Zn(II) form the binary complexes of ML₂H₄, ML₂H₃, ML₂H₂, ML₂H and ML₂ in dioxan-water mixtures. The effect of systematic errors in the concentrations of the substances on the stability constants is in the order acid > alkali > ligand > metal> Log F. The effect of solvent, dielectric constant of the medium and the electrostatic interactions between the complex species on the stability of the complexes are discussed.     

Chemical speciation of L-proline complexes of Ca(II), Zn(II) and Mn(II) in acetonitrile-water mixtures

Abstract

Chemical speciation of binary complexes of Ca(II), Zn(II) and Mn(II) with L-proline is investigated pH-metrically in acetonitrile-water mixtures. The stability constants are calculated using the computer program MINIQUAD75. The best-fit chemical models are selected based on statistical parameters and residual analysis. The models for the binary species contained ML⁺, MLH²⁺and ML₂H⁺ for Ca(II), Zn(II) and Mn(II). The trend in variation of stability constants with change in the dielectric constant of the medium is explained on the basis of structure forming nature of acetonitrile. Distribution of the species with pH at different variations (0.0-60.0% v/v) in acetonitrile-water mixtures is also presented.     

Glucuronate complexes with Mg2+, Ca2+, Zn2+ and Cd2+ in aqueous chloride solution: a possible chemical speciation model for biochemical understanding

ABSTRACT

Protonation constants and Na⁺-, Mg²⁺-, Ca²⁺-, Zn²⁺- and Cd²⁺-D-Glucuronate complex formation constants have been determined potentiometrically in different ionic strength conditions. Glucuronate forms a very weak complex species with Na⁺ (K ～ 1 dm³ mol^?1), and weak species with Mg²⁺ and Ca²⁺ (K ～ 10 dm³ mol^?1). When glucuronate interacts with Zn²⁺ and Cd²⁺, two species, M(gluc) and M(gluc)₂ (glue = glucuronate) having a stability intermediate between that of mono and dicarboxylate complexes, are formed. This can be due to the involvement of the ethereal oxygen in the coordination. Medium effects are considered in the light of speciation problems.     

Speciation of ternary complexes of lead(II), cadmium(II) and mercury(II) with L-dopa and phenanthroline in propanediol-water mixtures

Abstract

The formation constants of ternary complexes of title systems have been determined pH-metrically in biologically relevant conditions at an ionic strength of 0.16 mol dm^-3 and 303 K. The overall stability constants have been evaluated using MINIQUAD75 computer program. The complexation equilibria have been derived on the basis of species distribution diagram. In the present study L-Dopa and 1, 10-phenanthroline are found to be compatible ligands, proving greater stability of ternary complexes as compared to binary ones. The trend in variation of stability constants with change in dielectric constant of medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of the species with pH at different compositions of propanediol-water mixtures are also presented. The factors responsible for the compatibility of both the ligands have also been discussed.     

Binary complexes of Mg(II) and Ca(II) in water–surfactant mixtures

Abstract

Chemical speciation of Mg(II) and Ca(II) complexes of L-histidine in the presence of water–surfactant mixtures in the concentration range 0.0–2.5% w/v CTAB and SDS, 0.0–5.0% v/v TX-100 maintaining an ionic strength of 0.16 mol dm^?3 at 303 K has been studied pH metrically. The active forms of the ligand are LH₃²⁺, LH₂⁺, LH and L^?. The models containing different numbers of species were refined by using the computer program, MINIQUAD75. The predominant species detected were ML₂H₄⁴⁺, ML₂H₃³⁺, ML₂H₂²⁺, and ML₂. The best fit chemical models were arrived at based on statistical parameters. The trend in variation of complex stability constants with change in the composition of the medium is explained on the basis of electrostatic and non-electrostatic forces. The effect of errors in the stability constants was also studied. Chemical speciation was also discussed based on the distribution diagrams.     

Effect of anionic micelles on speciation of L-glutamine in presence/absence of metals

Abstract

Protonation equilibria of L-glutamine and speciation of its complexes with Co(II), Ni(II) and Cu(II) have been studied in 0–2.5% w/v SLS–water media using pH-metric method. The protonation constants and binary stability constants have been calculated with the computer program MINIQUAD75. Selection of the best fit chemical models is based on standard deviation in stability constants and residual analysis using crystallographic R-factor and sum of squares of residuals in all mass-balance equations. The trend in the variation of stability constants of the complexes with mole fraction of the medium is attributed to the compartmentalisation of complexation equilibria. Distribution of species and effect of influential parameters on chemical speciation have also been presented.     

A rapid non-equilibrium critical precipitation assay to assess aluminium-ligand interactions

Abstract

In many natural situations (e.g. environmental and biological) aqueous metal-ligand interactions occur in complex, dynamic solutions and do not adhere to true equilibrium. Nonetheless, equilibrium-based assays in simple solutions are generally used to model metal-ligand interactions of natural systems. Moreover, these are time consuming and not easily applied or understood by many applied scientists. Here, a ‘critical precipitation assay’ was used to investigate the interaction of common ligands with aluminium at pH 7.0, under non-equilibrium conditions. Results obtained were correlated with literature-derived stability constants for the aluminium-ligand interactions, while high-resolution ¹H nuclear magnetic resonance spectroscopy (¹H NMR) was used to confirm the nature of observed interactions. Weak interaction with aluminium was confirmed for traditional weak ligands (e.g. bicarbonate) as these were unable to compete with the hydroxide ion for aluminium at pH 7.0. Two types of interaction were seen for the ‘stronger’ ligands that could compete with hydroxy-polymerisation. Firstly, distinct aluminium:ligand stoichiometric ratios were observed for ligands such as ethylenediaminetetra-acetic acid (1:1) or 1,3,5-trideoxy-1,3,5-tris( dimethylamino)-cis-inositol (1:2). Secondly, most ligands, including citrate and maltol, did not prevent hydroxy-polymerisation but did maintain more aluminium ‘in solution’ (approximately 2.5:1 aluminium:ligand) than permitted by acceptable aluminium:ligand stoichiometric ratios, suggesting the formation of dynamic metastable hydroxy-bridged aluminium-ligand complexes. ¹H NMR with aluminium and maltol or citrate, supported this idea as complex spectral patterns were observed prior to precipitation. Aluminium maintained in solution at pH 7.0 correlated, with literature-derived stability constants suggesting that non-equilibrium aluminium-ligand interactions approximate to equilibrium and that this assay could be used as a quick screening method for investigation of aluminium-ligand interactions.     

Copper complexation by natural organic matter in contaminated and uncontaminated ground water

Abstract

Ground-water samples were collected from an uncontaminated and a contaminated site. Copper complexation was characterized by ion- selective electrode (ISE), fluorescence quenching (FQ), and cathodic stripping voltammetric (CSV) titrations. All of the samples were titrated at their natural pH values and some of the samples were also titrated at other pH values. For a total Cu concentration of 10^?6 M, the free Cu²⁺ concentrations in the samples from the uncontaminated site were all less than 10^?7 M, while free Cu²⁺ in the samples from the contaminated site were all less than 10^?8 M. For a particular sample and total Cu concentration, the free Cu²⁺ concentration decreased as the pH increased. Relative to ISE, FQ underestimated and CSV overestimated the degree of Cu²⁺ binding. The Cu²⁺ -complexing properties of the ground waters are similar to many published results for the same pH and for ligand concentrations normalized to T.O.C. Chemical equilibrium computations indicate that organic complexes would dominate Cu speciation in the uncontaminated ground waters for 10^?7 to 10^?5 M total Cu. In the contaminated ground waters, sulfide complexes would be the predominant Cu species for total Cu less than the total S(?11) concentration. Organic complexes would dominate Cu speciation for total Cu greater than total S(?11).     

Chemical speciation of ternary complexes of L-dopa and 1,10-phenanthroline with Co(II), Ni(II) and Cu(II) in low dielectric media

Abstract

A computer assisted pH-metric investigation has been carried out on the speciation of complexes of Co(II), Ni(II) and Cu(II) with L-dopa and 1,10-phenanthroline. The titrations were performed in the presence of different relative concentrations (M:L:X = 1.0:2.5:2.5; 1.0:2.5:5.0; 1.0:5.0:2.5) of metal (M) to L-dopa (L) and 1,10-phenanthroline (X) with sodium hydroxide in varying concentrations (0-60% v/v) of 1,2-propanediol-water mixtures at an ionic strength of 0.16 mol L^-1 and at a temperature of 303.0 K. Stability constants of the ternary complexes were refined using MINIQUAD75. The species MLXH, MLX, ML₂X and MLX₂H for Co(II) and Cu(II) and MLXH, MLX and MLX₂H for Ni(II) were detected. The extra stability of ternary complexes compared to their binary complexes was believed to be due to electrostatic interactions of the side chains of ligands, charge neutralisation, chelate effect, stacking interactions and hydrogen bonding. The species distribution with pH at different compositions of 1, 2-propanediol-water mixtures and plausible equilibria for the formation of species were also presented. The bioavailability of the metal ions is explained based on the speciation.     

Complexation of trace metals with humic acids from soil,sediment and sewage

ABSTRACT

Metal—humate interactions in aqueous and terrestrial ecosystems control the speciation of trace metals and hence, their bioavailability and toxicity. The present study investigated the complexation interactions of copper, cadmium and lead, in their divalent states, with humic acids extracted from three different sources: the treated sewage from a treatment plant, Yamuna river bed sediment, and Yamuna river flood plain soil, all at Okhla, Delhi, employing ion selective electrode potentiometry. The conditional stability constants of the complexes were computed from Scatchard plots. The influences of the two important metal speciation factors, viz., pH and ionic strength of the reaction medium on the conditional stability constants were ascertained by investigating the reactions under three different pH: 5.0, 6.0 and 7.0 and three different ionic strengths: 0.01, 0.03 and 0.1. Stabilities of metal—humic acid (HA) complexes follow the order: Cu-HA > Pb-HA > Cd-HA for humic acids from any single source and are found to increase with a rise in pH and fall in a ionic strength of the medium. The humic acids extracted from the soil and the sediment emerged as stronger complexing agents, as compared to that extracted from sewage.     

Speciation studies of ternary complexes of some essential divalent metal ions with L-histidine and L-glutamic acid in DMSO-water mixtures

Abstract

Chemical speciation of ternary complexes of Ca(II), Mg(II) and Zn(II) ions with L-histidine as the primary ligand (L) and L-glutamic acid as the secondary ligand (X) has been studied pH metrically in the concentration range of 0.0-60.0% v/v DMSO-water mixtures maintaining an ionic strength of 0.16 mol L^-1 using sodium chloride at 303.0 K. Titrations were carried out in different relative concentrations (M:L:X = 1.0:2.5:2.5, 1.0:2.5:5.0, 1.0:5.0:2.5) of metal (M) to L-histidine to L-glutamic acid with sodium hydroxide. Stability constants of ternary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The predominant species detected for Ca(II), Mg(II) and Zn(II) are ML₂XH₂, MLXH₂ and MLX₂. Extra stability of ternary complexes compared to their binary complexes was explained to be due to electrostatic interactions of the side chains of ligands, charge neutralisation, chelate effect, stacking interactions and hydrogen bonding. The species distribution with pH at different compositions of DMSO and the plausible equilibria for the formation of species are discussed.     

Chemical speciation of 2,3-dihydroxybenzoic acid complexes with some biologically essential metal ions in 1, 2-propanediol–water mixtures

Abstract

Chemical speciation of Co(II), Ni(II), Cu(II) and Zn(II) complexes of 2,3-dihydroxybenzoic acid in 0.0-60.0% v/v 1, 2-propanediol-water mixtures maintaining an ionic strength of 0.16 mol dm^-3 at 303±0.1 K has been studied pH metrically. The predominant complexes formed are ML, ML₂ and ML₂H₂ for Co(II), Ni(II) and Zn(II) and ML, ML₂, ML₂H and ML₂H₂ for Cu(II). Models containing different numbers of species were refined by using the computer program MINIQUAD75. Selection of the best fit chemical models was based on statistical parameters and residual analysis. The trend in variation of complex stability constants with dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces. Distributions of species, formation equilibria and effect of influential parameters on the stability constants have been presented. The possible structures of the various species are elucidated on the basis of the analysis of the pH-metric data.     

Novel chelating agents as manganese and zinc fertilisers: characterisation,theoretical speciation and stability in solution

Abstract

Mineral, complex and chelated micronutrient fertilisers are widely used in agriculture. However, there have been few studies on manganese and zinc fertilisers. In fact, specific chelating agents to provide these micronutrients to plants have not been found, in contrast to iron. This work considers the interactions of novel and traditional ligands in micronutrient mixtures used in hydroponics and fertigation. Theoretical speciation studies comparing the stability in solution have been carried out to simulate the possible interactions that can affect Fe, Mn and Zn in aqueous formulations containing these micronutrients. Unknown stability constants of ligands with Zn and Mn have been determined. Also, theoretical speciation investigations in hydroponic conditions have been carried out. It has been found that the new chelating agents, IDHA and EDDS, and the poorly studied o,p-EDDHA, can be good alternatives to the traditional sources such as EDTA, HEEDTA and DTPA principally for Zn fertilisers. The Mn and Zn chelates with o,p-EDDHA and complexes with lignosulfonate and gluconate have also shown high stability in a hydroponic nutrient solution, maintaining more than 80% Mn in solution until pH 10. The presence of o,o-EDDHA/Fe³⁺ and o,p-EDDHA/Fe³⁺ enhances the stability of Zn in solution in the mixed fertilisers. More studies with substrates are necessary to confirm these results and to extend them to other agronomic conditions.     

Chemical speciation of oxalato complexes of indium(III)

Abstract

Chemical speciation of binary complexes of indium(III) with oxalic acid has been investigated pH metrically at 303 K and at an ionic strength of 0.2 mol dm^?3. The approximate formation constants have been calculated with the computer program SCPHD utilizing the experimental data obtained by monitoring H⁺ ion concentration. The formation constants thus obtained are refined with the computer program, MINIQUAD75 using primary alkalimetric data. The selection of the best-fit chemical model is based on the statistical parameters and residual analysis. The major complexes formed are In(C₂O₄)₂^?, In(C₂O₄)₃^3?, [In(C₂O₄)₂OH]^2? and [In(C₂O₄)₂ (OH)₂]^3?. The distribution patterns of the different species with the pH values showed that In(C₂O₄)₂^? is the predominant species.     

Computer-augmented modeling studies of Pb(II) and Cd(II) complexes with maleic acid in ethylene glycol–water mixture

Chemical speciation of binary complexes of Pb(II) and Cd(II) ions with maleic acid have been studied pH metrically in the concentration range of 0–50% v/v ethylene glycol (EG)–water mixtures maintaining an ionic strength of 0.16 molL^?1 at 303 K. Alkalimetric titrations were carried out in different relative concentrations of metal and maleic acid. Stability constants of various models of binary complexes were refined with MINIQUAD75. The best-fit chemical models were selected based on statistical parameters and residual analysis. The species detected are ML₂, ML₃, and ML₂H for Pb(II) and Cd(II). The chemical speciation, metal bioavailability, and transportation are explained based on the distribution diagrams.     

Chemical speciation in wound fluid leading to enhanced bioavailability for healing

ABSTRACT

ECCLES computer modelling is used to speciate Ca²⁺, Zn²⁺, Cu²⁺, Mn²⁺ and Fe³⁺ in wound fluid samples analysed for total metal content using Potentiometric stripping analysis. Bioavailability of metals, related to lipid soluble net-neutral complexes, was assessed and found to be broadly similar to the speciation in blood plasma. These appear to be benefits worthy of clinical investigation of keeping the wound fluid at pH = 6.4 and of raising the total cysteine concentration levels in wound fluid.