Kinetics and Equilibrium of Binding of Fe 3+ by a Fulvic Acid: A Study by Stopped Flow Methods

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. Can. J. Chem. 60,2023Chem. 60, (1982.Models of the species arising from the interaction of hydrous aluminum oxide colloids with humic substances have been prepared by neutralizing AI(II1) stock solutions in the presence of a well-characterized fulvic acid and aging for 24 h. These samples have been examined kinetically using the fluorimetric AI(II1) reagent calcein blue. The rates of formation of Al(II1) calcein blue complexes allows recognition of five kinetically distinguishable components in the mixtures. Some are similar in lability to simple organic chelates of Al(II1). Others are much less labile. Evidence for non-labile colloidal "ternary" complexes of AI(II1) ion species complexed to fulvic acid, and bound to hydrous aluminum oxide colloid is presented. The polydisperse mixture character of fulvic acid is seen in patterns of complex lability much as it is seen in patterns of complex stability.

“…The acid dissociation rate constant of Fe(II1 ) -F A was found to be 7 x s-I at 25°C (16). This is intermediate between the two Al(II1) values.…”

Section: Discussionmentioning

confidence: 81%

A kinetic study of the interaction of hydrous aluminum oxide colloids with a well-characterized soil fulvic acid

Mak¹,

Langford²

1982

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“…In acid solution, a "1:l complex" was found with conditional stability constant showing complex pH dependence (2). In solution at pH = 4, evidence was obtained for "dissolution" of colloidal hydrous ferric oxide by fulvic acid and some reduction of Fe(II1) by fulvic acid was observed (3).…”

Section: Introductionmentioning

confidence: 99%

The interaction of a soil fulvic acid with precipitating hydrous ferric oxide at pH = 6

Langford¹,

Wong²,

Underdown³

1981

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A kinetic method of analysis which distinguishes Fe(II) from Fe(III) and Fe(III) forms of various labilities from each other is based on spectrophotometric monitoring of the reaction of Fe(II) with ferrozine. Reduction of Fe(III) with hydroxylamine hydrochloride allows the single colourimetric reagent to detect all forms of Fe. The method is applied to study of the effects of a well characterized soluble soil organic acid sample, a fulvic acid, on the speciation of Fe(III) under conditions (pH = 6) where Fe(III) forms a colloidal hydrous oxide in the absence of fulvic acid. The effect of fulvic acid is to greatly increase the lability of Fe(III) compared to that in a hydrous oxide colloid. However, ultrafiltration and light scattering experiments indicate that the Fe(III) – fulvic acid species is larger than the hydrous ferric oxide colloid particles. Kinetic studies in the absence of hydroxylamine hydrochloride show that fulvic acid can act as a reducing agent for iron in the presence of an Fe(II) complexing agent like ferrozine but neither kinetic studies with an Fe(III) reagent nor Mössbauer spectra suggest significant initial presence of Fe(II) in the aged Fe(III) – fulvic acid samples.

“…Note that 'free' concentrations in [3] do not distinguish between Fe(OH2)63+ and Fe(OH2)50H2+ nor among GSH2+, GSH, or GS-. All five of these are of significance in the p H range under study.…”

Section: (A) Kinetic Evaluation Of Bindingmentioning

confidence: 96%

“…Table 2 and Fig. 3 show the best values estimated for the 'observed' constant defined by [3] as a function sf pH.…”

Section: (A) Kinetic Evaluation Of Bindingmentioning

confidence: 99%

“…Interest in kinetic methods of analysis using stopped flow spectrometers has developed recently (1)(2)(3). It is useful for identification of individual components of mixtures where components can react to give an easily detectabie common product such that differential rutes of reaction to that common product allow for distinction among components.…”

Section: Introductionmentioning

confidence: 99%

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Kinetic and spectrophotometric studies of binding of iron(III) by glutathione

Khan¹,

Langford²

1976

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. Can. 9. Chem. 54, 3192 (1976).In this report, determination of unbound aquo iron species is accomplished by a kirretic n~et/7oc/involving reaction with sulfosalicylic acid (SSA) on a time ssale which is very short with respect to reaction of SSA with the glutathione complexes of iron. The data are used to calculate conditional binding constants for Fe(lI1) to glutathione. Binding constants in 0.1 M ionic strength media were obtained between p H 1 and 2.4 by the kinetic method. and near p H = 3 by spectrophotometry arrd by examillation of the ratio of rate of complex formation and dissociation. The conditional binding 'constant' betweetz p H 1 and 3 is represented as pK = -1.96 -O.5OpH. This is consistent with the importance of reactions involving only very limited proton release. Spectrophotometric data show that the -OH group on Fe(OH)*-is lost on glutathione complexing. Kinetics of the complex formation reaction between aquo iron(I1I) species and glutathione are slower than rates of reaction of iron (111) with simple ligands.The glutathione system is regarded as a model system important to natural water chemistry because it is a widely distributed biological sulfur-containing chelating agent. Des donnkes spectrophotomCtriques demontrent que le groupe OH du Fe(OH)2+ est perdu lors de la complexation avec du glutathion. La cinktique de la reaction de formation du complexe entre les espkces aquo-ferriques et le glutathion sont plus faibles que les vitesses de rkaction du fer(II1) avec des ligands simples.On considkre que le systkme de glutathion est un systkme n~odkle important pour la chinlie de l'eau naturelle parce que c'est un agent biologique chelata~~t contenant du soufre qui est distribui trks largement.[Traduit par le journal]