A Systematic Design and Synthesis of PET‐based Fluorescent Probes for Monitoring pH During Mitophagy

Abstract

Mitochondria are the powerhouse of the cell and function at pH ~8.0. Dysfunctions of mitochondria, includes mitochondrial damage, leading to pH alteration. Hence, researchers aim to develop efficient pH probes for tracking mitochondrial pH dynamics. Herein, we developed a PETbased fluorescent probe for pH monitoring during mitochondrial dysfunctions. Three derivatives were synthesized with a variable spacer's length in pentacyclic pyridinium fluorophores (PM-C2, PM-C3, and PM-C6). An efficient electron transfers from the receptor (tertiary amine) was observed in the case of PM-C2 compared to the other two derivatives. This PET process was inhibited when tertiary amine was protonated in acidic pH. However, PM-C3 showed minimal fluorescence intensity at similar conditions and almost negligible change in case of PM-C6, suggesting poor PET process for both the derivatives. Furthermore, DFT/TD-DFT quantum chemical calculation well supported this optical phenomena and PET process. Biocompatible, photostable, and mitochondria-specific PM-C2 could monitor pH dynamics during mitochondrial damage which were engulfed by lysosome, also known as mitophagy. This mitophagy process were induced by rapamycin and starvation, which can be monitored by turn-on fluorescence enhancement. This process was further validated by tracking Parkin-protein translocation from cytoplasm to damaged mitochondria using our developed probe.

Chronological development of functional fluorophores for bio-imaging

“…19a). 162 This process was later inhibited upon protonation of the tertiary amine under acidic pH conditions. The biocompatible, photostable, and mitochondria-specific PM-C2 probe monitored pH dynamics during mitophagy via a turn-on fluorescence response.…”

Ratiometric fluorescent probes for pH mapping in cellular organelles

“…[6][7][8][9] Fluorescence imaging offers a unique platform to visualize the bio-components involved in a bioprocess. [10][11][12][13][14] Thus, biological events in living cells have become much clear, especially with the advancement in imaging techniques. [15][16][17][18][19][20] Direct visualization of cells and organelles and their dynamics can be monitored and quantitatively analyzed through their emission color intensity, which changes reversibly or irreversibly depending on the interactions with the analytes and receptors of fluorophores in the cellular microenvironment.…”

A Ratiometric Fluorescent Probe for Hypochlorite and Lipid Droplets to Monitor Oxidative Stress

“…A ratiometric fluorescent probe can overcome a few drawbacks compared to turn on/off by self-calibration, and can emerge as an attractive tool in the bio-imaging field [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. However, designing a ratiometric probe and simultaneously targeting two analytes is always challenging [ 34 ].…”