title: Fluorescence and phosphorescence of tryptophan in peptides of different length and sequence.
abstract: To interpret accurately protein fluorescence and phosphorescence, it is essential to achieve a better understanding of the luminescence properties of tryptophan (Trp, or W) in peptides. In published literature data on luminescence of peptides of varied length are scarce. This article describes studies of fluorescence and phosphorescence properties of the eight Trp-containing synthetic peptides: WAK, AWK, SWA, KYLWE, AVSWK, WVSWAK, WAKLAWE, and AVSWAKLARE. The aim was to investigate which factors influence the fluorescence yield and phosphorescence-spectra and lifetimes. Absorption spectra, room temperature fluorescence emission and corresponding excitation spectra and time-resolved phosphorescence spectra (77K) have been recorded; the dependence of the fluorescence quantum yield on the specific peptide and its variation with the wavelength of excitation has been studied. The changes in fluorescence yield and shape of phosphorescence spectra are explained in terms of internal electron and proton transfer. The structured phosphorescence spectrum originates from proton transfer occurring upon excitation of Trp, while electron transfer gives rise to a non-structured luminescence spectrum. There is also electron transfer from higher vibronic S1 states. In the peptides there is higher probability of electron transfer than in Trp alone. The obtained data are interpreted in light of the peptides' sequence, length and conformation.
authors.affiliation: Institute for Multidisciplinary Research, University of Belgrade, Kneza Višeslava 1, 11000, Belgrade, Serbia. Electronic address: xenia@imsi.rs.
authors.forename: Ksenija
authors.initials: K
authors.lastname: Radotić
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway. Electronic address: thor.melo@ntnu.no.
authors.forename: Thor Bernt
authors.initials: TB
authors.lastname: Melø
authors.affiliation: Department of Chemistry, University of Miami, FL, United States. Electronic address: rml@miami.edu.
authors.forename: Roger M
authors.initials: RM
authors.lastname: Leblanc
authors.affiliation: Department of Chemistry, Yarmouk University, Irbid, Jordan. Electronic address: yaserhaj@hotmail.com.
authors.forename: Yaser A
authors.initials: YA
authors.lastname: Yousef
authors.affiliation: Department of Physics, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway.
authors.forename: K Razi
authors.initials: KR
authors.lastname: Naqvi
mesh_terms: D010455:Peptides / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D010455:Peptides; D014364:Tryptophan
keywords: Luminescence; Peptides; Phosphorescence; Steady state fluorescence; Time resolved fluorescence; Tryptophan