A combined spectroscopic and ab initio study of the transmetalation of a polyphenol as a potential purification strategy for food additives.

Recently, metal exchange (transmetalation) techniques have become popular for the post-synthesis modification of metal organic complexes (MOCs). Here, we have explored the possibility of toxic metal ion (mercury (Hg)) exchange from a model polyphenol, curcumin, which is a very important food additive, using a much less toxic counterpart (copper). While the attachment of different metals on the polyphenol was confirmed using a picosecond resolved fluorescence technique, the surface plasmon resonance (SPR) band of the Ag nanoparticle (NP) was employed as a tool to detect uncoupled Hg ions in aqueous media. Furthermore, a microscopic understanding of the experimental observations was achieved through density functional theory (DFT) based theoretical studies. The presence of Cu ions in the vicinity of Hg-curcumin, upon ground state optimization, was observed to extrude most of the Hg from the curcumin complex and replace its position in the complex. The study may find relevance in the development of a purification strategy for food additives heavily contaminated with toxic metals.