Tuning Förster Resonance Energy Transfer Efficiency via Functional Group Modulation of Dansyl-Tagged Molecules in Interaction with The Anti-tuberculosis Drug, Rifampicin

Abstract

Förster resonance energy transfer (FRET) is a powerful technique for investigating molecular interactions at close ranges. Identifying the optimal donor–acceptor pair is crucial for maximizing energy transfer efficiency, significantly improving sensitivity and accuracy in measurements. In this study, a library of six functionally tunable dansyl-tagged molecules (C1-C6) was designed, synthesized, and characterized using ¹H NMR, ¹³C NMR, and LC-MS techniques to serve as potential donor fluorophores in FRET with the acceptor drug rifampicin (RF). The synthetic strategy aimed to incorporate two distinct tunable centers, allowing for the introduction of cyclic, aromatic, and aliphatic substituents into the molecular skeleton. The potential of C1-C6 to participate in FRET was evaluated through spectral overlap assessment, steady-state fluorescence measurements, and lifetime analysis. The impact of varying functional substituents on FRET was investigated through FRET efficiency, donor–acceptor distances, and energy transfer rates. Among the synthesized molecules, C1 with both substituents as benzyl groups, exhibited the highest FRET efficiency of 87 ± 1.03 % and the shortest donor–acceptor distance of 2.2 nm, in contrast C6 containing a cyclohexyl group on one end and a benzyl group on the other, showed the lowest FRET efficiency of 51 ± 0.53 %. The feasibility of FRET was validated by analyzing the energy levels of the Frontier Molecular Orbitals (FMOs) of the donor molecules and rifampicin using Density Functional Theory (DFT). A reduction in the HOMO-LUMO gap observed in C1 after interacting with RF further confirmed their interaction, indicating stabilization of the FMOs.