A DFT study of molecular structure and 1 H NMR, IR, and UV‐Vis spectrum of Zn(II)‐kaempferol complexes: A metal‐flavonoid complex showing enhanced anticancer activity

The polyphenol compound Kaempferol, a relevant member of the class of flavonoids, is a good example where coordination to Zn(II) ion was found to improve the anticancer effects compared to the free ligand. Determination of the metal‐complex molecular structure (and binding sites on Kaempferol) in the liquid phase is fundamental for an understanding of biological activities. Experimental UV‐Vis and EPR data only provide indirect evidence or limited structural information. Therefore, theoretical study of structural and spectroscopic properties of the metal‐polyphenol complex, using computational quantum chemistry methods, is certainly relevant as starting point for the investigation of mechanism of action at a molecular level. In this article, we used the density functional theory (DFT) methodology to predict the molecular structure of [Zn(Kaempferol)(H 2 O) n ] + and [Zn(Kaempferol) 2 (H 2 O) n ] complexes ( n = 0, 2, or 4) and B‐ring nonplanar conformation of flavonoid using as strategy the best match between theoretical and experimental 1 H NMR, IR, and UV‐Vis spectroscopic data in solution. These are valuable information for further studies involving structure‐activity relationship.