Redox activity of caffeic acid towards iron(III) complexed in a polygalacturonate network

• Published in: Plant and soil 1997-03, Vol.190 (2), p.289-299
• Main Authors: Gessa, C. (Bologna Univ. (Italy). Istituto di Chimica Agraria), Deiana, S, Premoli, A, Ciurli, A
• Format: Article
• Language: English
• Subjects: Absorption. Translocation of ions and substances. Permeability; Acid soils; Agronomy. Soil science and plant productions; Bacteria; Biochemistry; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; CHIMIE DU SOL; Degradation products; Economic plant physiology; FER; Fundamental and applied biological sciences. Psychology; HIERRO; ION; IONES; IONS; IRON; Kinetics; MATERIA ORGANICA DEL SUELO; MATIERE ORGANIQUE DU SOL; Metal ions; Mineral components. Ionic and exchange properties; Molecules; Nutrition. Photosynthesis. Respiration. Metabolism; Oxidation; PECTINAS; PECTINE; PECTINS; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Polysaccharides; POTENCIAL REDOX; POTENTIEL REDOX; PROCESOS DE TRANSPORTE EN EL SUELO; QUIMICA DEL SUELO; REDOX POTENTIAL; SOIL CHEMISTRY; SOIL ORGANIC MATTER; Soil science; SOIL TRANSPORT PROCESSES; TRANSPORT DANS LE SOL
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1023/a:1004295719046

The transfer of several metal ions from the soil to the plant absorbing cells is mediated principally by organic molecules of low molecular weight with complexing and reducing activity, among which caffeic acid (CAF) is particularly important. Here we report the results of a survey which deals with the oxidation of CAF by the Fe(III) ions bound to a polygalacturonate network (Fe(III)-PGA network). The interaction between Fe(III) and CAF was studied by using Fe(III)-PGA networks equilibrated in the 2.4-7.0 pH range by means of kinetic and spectroscopic methods. The reducing power was found to depend on the nature of the Fe(III)-PGA network complexes: when the ferric ion was complexed only by the PGA carboxylic groups, a high redox activity was observed, whereas the Fe(III) reduction was found to be lower when a hydroxylic group was inserted in the Fe(III) coordination sphere. The iron complexed in the network was protected from hydrolysis reactions, as shown by the high pH values at which its reduction occurred. Two different fractions of Fe(II) produced were identified, one diffusible and another exchangeable with CaCl₂ 6.0 mM. The existence of the exchangeable form was attributed to the electrostatic interaction of the Fe(II) ions with the carboxylate groups of the fibrils and with the degradation products of CAF. The arrangement of the fibrils was altered following the substitution of Ca(II) by Fe(III) ions and was restored following the reduction of Fe (III) by CAF.