The remarkable effect of amino hydrogen on membrane permeability and organelle staining of 1,8-naphthalimide dyes

Abstract

Membrane permeability and intracellular diffusion of fluorescent probes determine staining selectivity of intracellular substructures. However, the relationship between the molecular structure of fluorescent probes and their membrane permeability and intracellular distribution is poorly understood. In this paper, we reported a series of 1,8-naphthalimide dyes and carried out cell imaging experiments, and found that the presence of amino hydrogen in these dyes played a crucial role in their cell membrane permeability and intracellular distribution. The secondary amino group containing compounds 1–4 show excellent membrane permeability and strong fluorescence in living cells. While the tertiary amine containing dyes 5 and 6 can hardly permeate the cell membrane though they show extremely similar structure with compounds 2–4. Compound 1 can selectively image lipid droplets by selecting the wavelength of excitation light. With the specificity for lysosomes, 2 and 4 have been used in long-term time-lapses imaging of lysosomal dynamics and tracking the process of lysosome–lysosome interaction, fusion and movement. The effect of hydrogen-containing amino substituent on the cell membrane permeability of fluorescent molecules is promising for the development of better biocompatible probes.