文章基本信息

标题：Dependence of the Fe(II)-Gallic Acid Coordination Compound Formation Constant on the pH
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作者：Franjo Frešer ; Gregor Hostnik ; Jelena Tošović 等
期刊名称：Foods
电子版ISSN：2304-8158
出版年度：2021
卷号：10
期号：11
DOI：10.3390/foods10112689
语种：English
出版社：MDPI Publishing
摘要：One important property of tannins involves their ability to form coordination compounds with metal ions, which is vital for the bioavailability of these ions, as well as for the antibacterial and antioxidative activities of tannins. In this study, the pH dependence of interactions between gallic acid, one of the basic building blocks of tannins, and Fe(II) ions, was investigated using UV/Vis spectroscopy, in conjunction with density functional theory (DFT) calculations. Moreover, two models were developed to explain the processes taking place in the solution. The first model treated the reaction as a simple bimolecular process while the second also considered the protolytic equilibrium, which was proven very successful in discerning the pH dependence of formation constants, and whose assumptions were well supported by DFT calculations. We showed that the two-time deprotonated gallic acid species forms the coordination compound with Fe(II) ions in a 1:1 molar ratio. To gain better insight into the process, the coordination compound formation was also studied using various DFT functionals, which further supported the model results. Furthermore, due to the relatively low sample amounts needed, the methodology developed here will be useful to study compounds that are more difficult to isolate.
关键词：UV/Vis spectra; gallic acid; Fe(II) ions; coordination compounds; modeling; Job diagrams; density functional theory calculations