title: Electronic effects on the fluorescence of tyrosine in small peptides.
abstract: It is shown for a series of tyrosine-derivatives and tyrosine-containing peptides that the amide group in combination with electron-withdrawing substituents quenches the fluorescence of the phenol moiety. The ammonium group has the strongest electron-withdrawing effect and thus the largest influence on the quenching rate. The peptide group itself does not quench the fluorescence. In a series of peptides with an increasing number of alanines the decreasing quenching efficiency of the peptide group due to the greater distance of the ammonium group is demonstrated. In tyrosine-containing di- and tripeptides a linear correlation between the 13C-NMR chemical shift delta of the C alpha atom of various aliphatic amino acids and the fluorescence-quenching constant confirms the hypothesis that electron-withdrawing and -donating groups are modulating the fluorescence-quenching efficiency of the peptide group. In small peptides the fluorescence lifetime of tyrosine is characteristic for the neighboring amino acids. Using model substances the redox properties of a peptide group and the phenol ring were studied electrochemically. The highest occupied molecular orbital of the tyrosine (1.4 V vs saturated calomel electrode [SCE]) and the lowest unoccupied molecular orbital of the peptide group (-3.12 V vs SCE) have appropriate energies for a photoinduced electron transfer reaction. For solute-quenching experiments quencher molecules can be systematically selected.
authors.affiliation: Physikalisch-Chemisches Institut, Universität Heidelberg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Seidel
authors.forename: A
authors.initials: A
authors.lastname: Orth
authors.forename: K O
authors.initials: KO
authors.lastname: Greulich
mesh_terms: D000595:Amino Acid Sequence; D004151:Dipeptides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence / Q000379:methods; D014443:Tyrosine
chemical_list: D004151:Dipeptides; D009842:Oligopeptides; D014443:Tyrosine