Abstract
Chemometric techniques were applied to the study of the interaction of iron(III) and tannic acid (TA). Modeling the interaction of Fe(III)–TA is a challenge, as can be the modeling of the metal complexation upon natural macromolecules without a well-defined molecular structure. The chemical formula for commercial TA is often given as C76H52O46, but in fact, it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12. Therefore, the data treatment cannot be based on just the stoichiometric approach. In this work, the redox behavior and the coordination capability of the TA toward Fe(III) were studied by UV-vis spectrophotometry and fluorescence spectroscopy. Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) and Parallel Factor Analysis (PARAFAC) were used for the data treatment, respectively. The pH range in which there is the redox stability of the system Fe(III)–TA was evaluated. The binding capability of TA toward Fe(III), the spectral features of coordination compounds, and the concentration profiles of the species in solution as a function of pH were defined. Moreover, the stability of the interaction between TA and Fe(III) was interpreted through the chemical models usually employed to depict the interaction of metal cations with humic substances and quantified using the concentration profiles estimated by MCR-ALS.
Highlights
Tannic acid (TA) is a naturally derived polyphenolic compound
The chemical formula for commercial TA is often given as C76H52O46, which corresponds to decagalloyl glucose, with a 1,701.20 g mol−1 molecular weight, but it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12
The UV-vis spectra of the solutions were recorded after 2 h from the preparation, the time needed for a stable color development
Summary
Tannic acid (TA) is a naturally derived polyphenolic compound. It is able to complex or cross-link macromolecules through multiple interactions, such as hydrogen and ionic bonding and hydrophobic interactions (Heijmen et al, 1997; Shutava et al, 2005; Erel-Unal and Sukhishvili, 2008). It can coordinate metal ions through the oxygenated functions and the coordination capability was exploited to form TA–metal networks (Ejima et al, 2013; Guo et al, 2014). The chemical formula for commercial TA is often given as C76H52O46, which corresponds to decagalloyl glucose, with a 1,701.20 g mol−1 molecular weight, but it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12
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