ELECTRONIC EFFECTS ON THE FLUORESCENCE OF TYROSINE IN SMALL PEPTIDES |
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Authors: | Claus Seidel Andreas Orth Karl-Otto Greulich |
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Institution: | Physikalisch-Chemisches Institut der Universität Heidelberg, Im Neuenheimer Feld 253, D-6900 Heidelberg, Germany |
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Abstract: | 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 or 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 δ of the C2 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. |
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