Main binding sites involved in Fe(III) and Cu(II) complexation in humic-based structures

• Published in: Journal of geochemical exploration Vol. 129; pp. 14 - 17
• Main Authors: Fuentes, Marta, Olaetxea, Maite, Baigorri, Roberto, Zamarreño, Angel M., Etienne, Philippe, Laîné, Philippe, Ourry, Alain, Yvin, Jean-Claude, Garcia-Mina, Jose M.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.2013
• Subjects: Bark; Binding sites; Carboxylic groups; Complexation; Copper complexation; Electron paramagnetic resonance; Humic substances; Iron complexation; Mathematical analysis; Organic chemistry; Phenol groups; Polymerization; Principal component analysis; Stability complexation constants; Phenol groups; Stability complexation constants; Iron complexation; Carboxylic groups; Copper complexation; Humic substances
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2012.12.015

The main objective of this study is to investigate the more relevant binding sites (functional groups) involved in the complexation of Fe(III) and Cu(II) by humic-based structures. To this aim we have generated a set of seven humic-based samples (MHA) by the application of a hemi-synthetic process consisting in the oxidative polymerization of different combinations of three sources of natural organic molecules: two humic acids obtained from peat and leonardite, and natural tannin extracted from the quebracho tree (Schinopsis sp.) bark. These MHA were extensively characterized by using complementary analytical techniques (13C NMR, size-exclusion chromatography, electron paramagnetic resonance, and total phenol-reductant content), and their ability to complex Fe(III) and Cu(II) was also calculated by fluorescence quenching method. The data were studied by using general correlation matrix and principal component analysis. The results obtained, taken together, indicated that in a set of humic-based structures presenting carboxylic, phenol and O-alkyl groups, and diverse aliphatic/aromatic character, the complexation of Fe(III) mainly involved specific structural arrangements including carboxylic groups distributed in aliphatic domains. However, Cu(II) complexation involved singular structural arrangements including phenols (and probably substituted phenols) and O-alkyl groups in side chains of aromatic domains.