Characterization of citrate capped gold nanoparticle-quercetin complex: Experimental and quantum chemical approach

• Elemental analysis and IR spectroscopy of GNP indicates presence of C and O atoms and OH groups in GNP.
• Method of preparation of GNP suggests incorporation of citrate groups as capping elements.
• Quantum chemical studies indicate important role of citrate capping.
• These establish that the citrate-capped GNP interacts with quercetin.
• In vivo studies indicated GNP-quercetin complex can penetrate cell membrane.

Quercetin and several other bioflavonoids possess antioxidant property. These biomolecules can reduce the diabetic complications, but metabolize very easily in the body. Nanoparticle-mediated delivery of a flavonoid may further increase its efficacy. Gold nanoparticle is used by different groups as vehicle for drug delivery, as it is least toxic to human body. Prior to search for the enhanced efficacy, the gold nanoparticle-flavonoid complex should be prepared and well characterized. In this article, we report the interaction of gold nanoparticle with quercetin. The interaction is confirmed by different biophysical techniques, such as Scanning Electron Microscope (SEM), Circular Dichroism (CD), Fourier-Transform InfraRed (FT-IR) spectroscopy and Thermal Gravimetric Analysis (TGA) and cross checked by quantum chemical calculations. These studies indicate that gold clusters are covered by citrate groups, which are hydrogen bonded to the quercetin molecules in the complex. We have also provided evidences how capping is important in stabilizing the gold nanoparticle and further enhances its interaction with other molecules, such as drugs. Our finding also suggests that gold nanoparticle-quercetin complex can pass through the membranes of human red blood cells.