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Some notes on fluorescence intensity.

M H Winkler1

  • 1Montefiore Hospital and Medical Center, Bronx, New York, and the Protein Foundation, Boston, Massachusetts, USA.

Biophysical Journal
|February 13, 2009
PubMed
Summary
This summary is machine-generated.

Fluorescence quantum yield depends on solvent viscosity, not just dielectric constant. This study reveals viscosity

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Area of Science:

  • Photochemistry
  • Biophysical Chemistry
  • Spectroscopy

Background:

  • Fluorescence properties of molecules like p-aminohippuric acid (PAH) and p-aminobenzoic acid (PABA) are sensitive to their environment.
  • Understanding how solvent properties influence fluorescence is crucial for interpreting experimental data and designing new probes.
  • Previous studies have often linked fluorescence changes primarily to solvent dielectric constant.

Purpose of the Study:

  • To investigate the influence of solvent viscosity on the fluorescent emission spectra and quantum yield of PAH and PABA.
  • To explore the role of collisional quenching and rotational diffusion in fluorescence.
  • To examine fluorescence changes upon antibody binding and their relation to solvent properties.

Main Methods:

  • Measurement of fluorescent emission spectra and quantum yields for PAH and PABA in methyl alcohol/1,2-propanediol mixtures.
  • Systematic variation of solvent viscosity while maintaining a near-constant dielectric constant.
  • Analysis of fluorescence changes in protein-free solutions and in the presence of homologous antihapten antibody.

Main Results:

  • Quantum yield of fluorescence was found to be a function of solvent viscosity, even at constant dielectric constant.
  • A collisional quenching mechanism involving solvent rotational diffusion was proposed to explain viscosity effects.
  • Augmentation of PAH fluorescence upon antibody binding was confirmed, consistent with the proposed mechanism.
  • A small red shift in emission spectra was observed at higher viscosities and upon antibody binding.

Conclusions:

  • Solvent viscosity plays a significant role in modulating fluorescence quantum yield and emission spectra, independent of dielectric constant.
  • Collisional quenching and rotational diffusion are important mechanisms affecting fluorescence in different viscosity regimes.
  • Observed fluorescence changes upon antibody binding do not necessarily indicate a transfer to a lower dielectric environment, challenging some existing interpretations.