A water-soluble 1,8-naphthyridine-based imidazolium molecular gripper for fluorescence sensing and discriminating of GMP

Abstract

A selective receptor for sensing and discriminating of GMP is useful not only in the energy metabolism but also in the processes of DNA replication and transcription-related to GMP; such a receptor is presently rare especially in a pure water environment. Herein, a novel 1,8-naphthyridine-based tripodal imidazolium gripper-like molecular served as a “turn-on” fluorescent receptor (TINP) was designed and synthesized for selective sensing and discriminating GMP from structurally similar GNPs (N = D and T) and XMPs (X = U, T, A, and C) in 100% aqueous solution. TINP consists of 1,8-naphthyridines and imidazolium cations. 2-acetylamino-1,8-naphthyridine was chosen as fluorophore and tri-hydrogen bonds interactions sites for the nucleobase guanine. Imidazolium cations were identified as the phosphate part receiving moieties and communicators, while the three imidazolium cations also served as indispensable water-soluble parts. GMP caused a remarkable fluorescence enhancement (ca. 6.5-fold) with a quantum yield (Φf) of 0.26 at 399 nm, displaying an efficient “turn on” behavior. The sensing mechanisms and fluorescence response were explained by Job's plot, NMR spectroscopic analysis, and theoretical calculations. The “turn-on” fluorescent property for GMP can be attributed to photoinduced electron transfer (PeT) transitions with some mixed intraligand charge-transfer (ILCT) transitions. Finally, the preliminary results of cell experiments show that the receptor can be applied for the imaging of GMP in living mammalian cells.