Plumbagin as colorimetric and ratiometric sensor for arginine

Abstract

A simple and selective naphthoquinone based fluorescent probe involving plumbagin (Pn=1,4-naphthoquinone) which is a naturally occurring phytochemical is reported for sensing of arginine in aqueous medium. The sensing probe Pn upon binding to Arg, induced a visible color change from light yellow to pink. The 1:1 Pn/Arg complex was characterized by Job's plot, ESI-MS and DFT calculations. This naked eye colorimetric sensing is insensitive to other amino acids namely Asp, Glu, Thr, Lys, His, Cys, Met, Ser and Phe. In the absence of arginine, excited state intramolecular proton transfer (ESIPT) occurs and when arginine is added, intermolecular proton transfer from Pn to arginine takes place resulting in colorimetric and ratiometric response.