Abstract
Stopped-flow kinetic investigation of reduction of Fe(III)-maltol complex is reported. The rates are dependent on pH in a complex way. On one hand at low pH there is a predominance of Fe(III)(maltol)2 which is easier to reduce compared to Fe(III) (maltol)3 which is more resistant to reduction. On the other hand ascorbate is a stronger reducing agent at higher pH. The rates are also found to be inversely dependent on the concentration of free ligand. These observations are explained by the following rate law:Rate = ((k0 +k1[H+])k2 [Asc-]/ (k-1[HMal] + k2[Asc-])) + k3 [Asc-] ) [FeIII(Mal)3] Here k1 is the rate constant for acid hydrolysis of the Fe(maltol)3 complex to Fe(maltol)2 complex and is directly controlled by H+, k0 is the rate constant for hydrolysis of the Fe(maltol)3 complex to Fe(maltol)2 complex and is an intrinsic process, k-1 is the rate constant of reformation of the tris complex by reaction of the bis complex and the free ligand, k2 is the rate constant for reduction of the bis complex by ascorbate and k3 is the rate constant for the reduction of the tris complex by ascorbate.
Highlights
MALTOL (3-hydroxy-2-Methyl pyran-4-one, CAS No 118-71-8) is similar to ring C of flavonols which are a class of flavanoids having a 3-hydroxy-2-phenylchromen-4-one backbone [1]
The Fe(III) chelating property of Maltol (Structures given in figure 1) has characteristics similar to that of many flavanols [4]
Complexes of maltol have been suggested for use as medicinal agents, e.g. Bis Maltol OxoVanadium (BMOV) in treatment of diabetes and as nutritional supplements [6]
Summary
MALTOL (3-hydroxy-2-Methyl pyran-4-one, CAS No 118-71-8) is similar to ring C of flavonols which are a class of flavanoids having a 3-hydroxy-2-phenylchromen-4-one backbone [1]. Flavanoids in general and flavanols in particular have strong antioxidant properties [2]. The antioxidant properties are attributed to the 3-hydroxy-4-one functionality which makes it a very strong Fe(III) chelator and an inhibitor of Fenton reaction [3]. The Fe(III) chelating property of Maltol (Structures given in figure 1) has characteristics similar to that of many flavanols [4]. Complexes of maltol have been suggested for use as medicinal agents, e.g. Bis Maltol OxoVanadium (BMOV) in treatment of diabetes and as nutritional supplements [6]. There has been some apprehension about its excessive use because of its possible role in Aluminum neurotoxicity [8]
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