Phosphorescence from tryptophan and tryptophan analogs in the solid state

Colin McCaul, Richard D. Ludescher

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Tryptophan phosphorescence provides a long-lived optical signal whose lifetime and quantum yield are sensitive to the local environment of the protein. The phosphorescence from tryptophan analogs, however, has not been studied. We report here data on the room temperature phosphorescence of tryptophan, 4-, 5-, and 6-fluorotryptophan, and 5-bromotryptophan embedded in sucrose glasses. The absorption of the analogs was either blue-shifted (4-F-trp), markedly red-shifted (5-F-trp and 5-Br-trp), or not shifted (6-F-trp) with respect to tryptophan. The phosphorescence emission spectra of all analogs were red-shifted compared to trp (442 nm) with maxima at 446 mn (5-F), 451 nm (6-F), 452 nm (5-Br), and 469 nm (4-F). The 5-F and 6-F analogs had emission intensities similar to tryptophan (relative quantum yields of 0.68 and 0.91, respectively), while the emission intensities of the 4-F and 5-Br analogs were much lower (relative quantum yields of 0.039 and 0.022, respectively). All analogs exhibited complex decay behavior which required several exponentials for an adequate fit. The average lifetimes were all significantly lower than that of trp (2109 ms). The average lifetimes of the fluorinated analogs (5-F: 1496 ms, 6-F: 1004 ms, and 4-F: 87 ms) scaled approximately with the relative quantum yields while that of 5-Br (1.03 ms) was significantly lower.

Original languageEnglish (US)
Pages (from-to)263-268
Number of pages6
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 1998
EventAdvances in Optical Biophysics - San Jose, CA, United States
Duration: Jan 25 1998Jan 26 1998

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


  • Lifetimes
  • Phosphorescence
  • Photophysics
  • Quantum yield
  • Tryptophan
  • Tryptophan analogs


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