Metallation modulates the properties of Curcumin: An ultrafast dynamics overview

Abstract

Turmeric, the golden yellow spice of India, is considered to be one of the most efficacious herbal plants due to its prolific content of natural phenols such as curcuminoids. Curcumin is the principal curcuminoids of turmeric, exhibiting varieties of medicinal applications including the use as an anticancer agent, anti-Alzheimer agent, anti-Parkinson disease neuroprotective agent. The behavior of curcumin as a chelating ligand to bivalent metal ions leads to formation of metallo-curcumin complexes. These complexes often demonstrate enhancement of soly. and activity. However, this ligation property sometime shows a contrasting effect as curcumin can effectively chelates toxic heavy metal ions. Herein, we have first evaluated the synthesis and optical characterization of metallo-curcumin complexes of Cu(II) and Zn(II). The photo-induced electron transfer processes from curcumin to the metal ions have been obsd. Using femtosecond upconversion technique. In order to investigate the antioxidant activity of the complexes, we have performed 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay which reveal an enhanced and recyclable antioxidant activity of Cu(II)-curcumin complex. However, the Zn(II) complex has a higher soly. and stability in aq. media. To address stability vs. functionality issues, we have suggested a facile metal exchange method that shows improved bioavailability as well as better activity of curcumin in aq. media. Further, we attempted to fabricate ZnO based nanoprobes to detect heavy metal contaminated curcumin. The mol. level interaction was confirmed by picosecond-resolved PL-quenching of ZnO NR due to Förster Resonance Energy Transfer (FRET) from donor ZnO NR to the acceptor curcumin moieties. The attachment proximity of ZnO NR and curcumin moieties depend on size of metals which is confirmed by FRET as well as using DFT calcns. These have been further applied for fabrication of photovoltaic device to detect heavy metal contaminated curcumin. Our results provide detail phys. insight of interfacial processes present in metallo-curcumin complexes and thus expected to find vast applications.