Syntheses, kinetics and thermodynamics of BODIPY-based fluorescent probes with different kinds of hydrophilic groups for the detection of biothiols

A series of BODIPY-based fluorescent probes incorporating different kinds of hydrophilic groups were synthesized for the detection of biothiols (GSH as a representative target), namely BDP (control), BDP-OH (acidic), BDP-OEG (neutral and hydrophilic) and BDP-QA (cationic). The incorporation of nitroolefin unit (-CH=CH-NO2) to the BODIPY core enabled the OFF-ON fluorescent probes. The results indicated that the absorption and fluorescence emission spectra of the probes were essentially not affected by the hydrophilic groups attached on the para position of the meso phenyl group. The reaction rate constants were affected by the hydrophilicity of probes. It was highly worth noting that the cationic BDP-QA had the fastest response toward biothiols owing to the best water solubility and the possible formation of ion pairs with thiolate (R-S ). Thermodynamics illustrated that the reactions of probes with GSH all had negative enthalpy changes and negative entropy changes. Moreover, BDP-QA had the highest affinity toward GSH (K = 2.54 x 10(4) M-1) and the smallest LOD value (182 nM), which benefited from its best water solubility. This work has primarily elucidated the effects of hydrophilic groups from the kinetic and thermodynamic perspectives. It will promote better design of fluorescent probes with fast response and high affinity.