Synthesis And Spectral Properties Of A Neutral Nitrogen-based PH Fluorescent Probe

Intracellular pH plays a pivotal role in the life and have potential values for the diagnosis of special disease.The normal value of H+ in cell is about 40nmol/L(pH7.4)and varies by about 5nmol/L(pH=7.35-7.45).Deviation by 0.10-0.20 pH units can cause cardiopulmonary and neurologic problems,and more extreme variations can be fatal.The close relation between intracellular pH values and cell function means that the accurate measurement of intracellular pH values can provide key information for the study of the physiology and pathology process of a single cell organelle.The optical measurement method of pH by fluorescent probe based on protonation or deprotonation is attracting more and more attention due to its unique advantages such as easy operation,quick response,high sensitivity and non-invasiveness to cells.In this paper,we designed and synthesized three series of indolizine pH fluorescent probes with hydrazone and thiol acting as receptor group.We also studied fluorescence emission spectra and UV-Vis absorption spectra properties of these compounds.It provided new information for designing and synthesizing novel pH fluorescent probe.1.Four indolizine pH fluorescent probes with hydrazone acting as receptor group,named Q-1?Q-4,were synthesized.The experimental results show that Q-1?Q-4 all have the ability of H+ recognition.The fluorescence of Q-1?Q-3 are strongly quenched in both strong acid and strong basic solution.However,Q-4 has low fluorescence intensity in both nearly neutral and basic solution,while the fluorescence intensity increases significantly at lower pH and is stronger than Q-1?Q-3 obviously.The pKa value of Q-4 is 1.51.2.Two indolizine pH fluorescent probes with two thiols acting as receptor group,named D-1 and D-2,were synthesized.The experimental results show that D-l and D-2 both have the ability of H+ recognition,and both exhibit distinct changes of fluorescence intensity in its range of response.The pKa values of D-1 and D-2 are 3.95 and 4.78 respectively.They both have the potential application value for testing the pH changes of acid organelles such as lysosome.3.Four indolizine pH fluorescent probes with thiol acting as receptor group,named S-1-S-4,were synthesized.The experimental results show that S-1?S-3 have stronger ability of H+ recognition than S-4.S-1?S-3 all exhibit obvious changes of fluorescence intensity in the range of response respectively.And the pKa values of S-1?S-2 and S-3 are 9.45?10.35 and 5.58 respectively.Although S-4 doesn't respond to H+ obviously,it has higher fluorescence quantum efficience than others.