Frešer Franjo, Bren Urban, Hostnik Gregor
Faculty of Chemistry and Chemical Technology, University of Maribor, Smetanova 17, SI-2000, Maribor, Slovenia.
Faculty of Chemistry and Chemical Technology, University of Maribor, Smetanova 17, SI-2000, Maribor, Slovenia; Faculty of Mathematics, Natural Sciences and Information Technologies, University of Primorska, Glagoljaška 8, SI-6000, Koper, Slovenia; Institute of Environmental Protection and Sensors, Beloruska 7, SI-2000, Maribor, Slovenia.
Spectrochim Acta A Mol Biomol Spectrosc. 2024 May 15;313:124079. doi: 10.1016/j.saa.2024.124079. Epub 2024 Feb 24.
Tannins represent secondary plant metabolites that are used to control bacterial populations by chelation of essential metal ions. Their presence in food also affects the bioavailability of iron. This study investigates the influence of ellagitannins (vescalin, castalin, vescalagin, castalagin) structure and pH on the stoichiometry and formation constants of ellagitannin-Fe(II) coordination compounds. We demonstrated that ellagitannins are stable for at least one hour at pH values lower than 7.25. The spectra of neutral compounds were measured and explained with the help of TDDFT calculations. Furthermore, the pH-dependence of the ellagitannins UV-Vis spectra was examined to obtain insight into their protolytic equilibrium. Using Job's method in the pH range 3.50-5.51, the stoichiometry of the formed ellagitannin-Fe(II) ions complexes was determined. A model explaining interactions between ellagitannins and Fe(II) ions, that took into account the protolytic equilibrium of ellagitannins, was fitted globally to all four Job plots, whereby the corresponding formation constants were obtained.
单宁是植物的次生代谢产物，可通过螯合必需金属离子来控制细菌数量。它们在食物中的存在也会影响铁的生物利用度。本研究调查了鞣花单宁（vescalin、castalin、vescalagin、castalagin）的结构和pH值对鞣花单宁 - Fe(II)配位化合物的化学计量比和形成常数的影响。我们证明了鞣花单宁在pH值低于7.25时至少稳定一小时。借助TDDFT计算对中性化合物的光谱进行了测量和解释。此外，研究了鞣花单宁紫外 - 可见光谱的pH依赖性，以深入了解其质子解离平衡。在3.50 - 5.51的pH范围内使用乔布氏法，确定了形成的鞣花单宁 - Fe(II)离子络合物的化学计量比。一个解释鞣花单宁与Fe(II)离子之间相互作用的模型，该模型考虑了鞣花单宁的质子解离平衡，对所有四个乔布氏图进行了全局拟合，从而获得了相应的形成常数。
