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

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.

Constructing D-π-A-π dye to obtain red-emission fluorescent probe for structured illumination microscopy imaging of lipid droplet dynamics

Lipid droplets(LDs)are dynamic organelles interacting with a variety of intracellular organelles.Tracking intracellular LD dynamics employing synthetic small molecules is crucial for biological studies.Fluorescence imaging in the red and near infrared(NIR)region is more suitable for biological imaging due to its low phototoxicity and high signal-to-noise ratio.However,available LD-dyes in the red region with remarkable environmental sensitivity,selectivity for LDs staining are limited.Here,we constructed a red-emission D-π-A-π type LDdye LD 688P with higher environmental sensitivity and suitable“calculated log P”(Clog P)for LDs dynamic imaging.LD 688P was proved to be highly selective and photostable for tracing LD fusion including multiple consecutive fusions and fusions in a centrosymmetric manner by super-resolution microscopy.We believe that the D-π-A-π skeleton would be an efficient strategy to construct red and even NIR-emission dyes.