Modulation of Excited-State Proton Transfer Dynamics in a Model Lactim-Lactam Tautomeric System by Anisotropic Gold Nanoparticles

The past few decades have witnessed significant advances in the development of functionalized gold nanoparticles (GNPs) for diverse applications in various fields such as chemistry, biology, pharmacy, and physics. However, a recent in vivo toxicity study of GNPs in Drosophila melanogaster demonstrated that GNPs are capable of inducing mutagenesis. Considering mutagenicity and tautomerism (lactim-lactam and amine-imine) of DNA base pairs are correlated with each other, a recent theoretical study reveal the modification of double-proton-transfer process of guanine-cytosine DNA base pairs upon interaction with the gold surface (Au(111)). However, there is a dearth of experimental data about the proton-transfer (PT) process in isolated base pairs on gold nanosurface. In this particular work, we have chosen a model lactim-lactam tautomeric system, namely, 1-(2-hydroxy-S-chloro-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b] isoindole (ADCL), and carried out for the first time a comprehensive study of the modification of excited-state PT dynamics in the presence of synthesized isotropic (spherical) and anisotropic (trianglular, rod, and trigonal bipyramidal) GNPs by means of steady-state and time-resolved fluorescence spectroscopy. The PT process operative in ADCL was experimentally found to be accelerated on the anisotropic gold nanosurface, whereas spherical-shaped GNPs showed little impact on the dynamics of the above-mentioned photophysical phenomenon. Therefore, our experimental results regarding the modification of lactim-lactam tautomerism of a model compound on the gold nanosurface are an indirect evidence of mutation caused by GNPs.