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A new fluorescent pH probe for extremely acidic conditions.

Yu Xu1, Zheng Jiang2, Yu Xiao1

  • 1School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China; Taishan College, Shandong University, Jinan 250100, PR China.

Analytica Chimica Acta
|April 22, 2014
PubMed
Summary

Researchers developed a novel fluorescent probe for detecting extremely acidic conditions. This sensitive probe, with a pKa of 2.1, offers rapid and reliable pH measurement, even in biological applications.

Keywords:
CoumarinE. coliFluorescence probeHighly acidic conditionpH

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Area of Science:

  • Analytical Chemistry
  • Chemical Sensing
  • Biophysical Chemistry

Background:

  • Accurate pH monitoring is crucial in various scientific disciplines.
  • Existing probes often lack sensitivity or specificity for extremely acidic environments.
  • Developing reliable indicators for low pH conditions remains a challenge.

Purpose of the Study:

  • To design and synthesize a novel fluorescent probe for detecting extremely acidic conditions (pH < 3.5).
  • To investigate the probe's sensing mechanism and performance characteristics.
  • To evaluate the probe's applicability in biological imaging of acidity.

Main Methods:

  • Synthesis of a coumarin-imidazole based fluorescent probe.
  • Characterization of the probe's photophysical properties (fluorescence and UV-vis spectra).
  • Determination of the probe's pKa and response to varying pH levels.
  • Investigation of the sensing mechanism using 1H NMR and theoretical calculations (molecular orbital).
  • Application of the probe for imaging strong acidity in E. coli bacteria.

Main Results:

  • The developed probe exhibits a pKa of 2.1 and responds to pH values below 3.5 with high sensitivity via fluorescence quenching.
  • Quantitative pH detection is achieved using a specific equilibrium equation.
  • The probe demonstrates a rapid response time (< 1 min), good reversibility, and minimal interference from common metal ions.
  • A two-step protonation process leading to photoinduced electron transfer (PET) was identified as the fluorescence quenching mechanism.
  • Successful imaging of strong acidity within E. coli bacteria was achieved.

Conclusions:

  • A novel, highly sensitive fluorescent probe for extremely acidic conditions has been successfully developed.
  • The probe operates via a PET mechanism triggered by protonation, offering a practical pH indicator.
  • The probe's ability to image acidity in bacteria highlights its potential for biological applications.