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Cooligopeptides containing aromatic residues spaced by glycyl residues. IX. Fluorescence properties of tryptophan‐containing peptides
Author(s) -
Wiget Peter,
Luisi Pier Luigi
Publication year - 1978
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1978.360170113
Subject(s) - chemistry , tryptophan , quantum yield , fluorescence , fluorophore , aromatic amino acids , circular dichroism , quenching (fluorescence) , stereochemistry , yield (engineering) , aromaticity , phenylalanine , stacking , crystallography , amino acid , molecule , organic chemistry , biochemistry , physics , materials science , quantum mechanics , metallurgy
The fluorescence properties of several cooligopeptides of glycine, phenylalanine, and tryptophan, containing one or two aromatic residues, are investigated. In particular, a detailed analysis is made of the influence of pH upon the quantum yield and the position of the emission maximum (λ max ) in H‐Trp‐Trp‐OH, H‐Trp‐Gly‐OH, H‐Gly‐Trp‐OH, H‐Gly‐Trp‐Gly‐OH, H‐Trp‐Trp‐OH, H‐Trp‐Trp‐Gly‐OH, H‐Gly‐Trp‐Trp‐OH, H‐Phe‐Trp‐OH, H‐Phe‐Trp‐Gly‐OH, H‐Gly‐Phe‐Trp‐OH, and H‐Gly‐ X ‐(Gly) n ‐Trp‐Gly‐OH, with X = Phe or Trp, and n = 0,1,2. It is shown that raising the pH from ca. 2 to 11 results in a red shift of λ max, and an increase in the quantum yield. These changes, mostly structure dependent, are in most cases attributable to electronic perturbations acting directly upon the λ max of the fluorophore(s) and upon the quenching efficiency of the free amino and carbonyl groups. For the compounds having two adjacent tryptophyl residues, it is shown that the two fluorophores do not appear to have the same emission properties and the quantum yield is lower than expected. The causes of this behavior are discussed in terms of conformational effects, stacking interactions, and radiationless energy transfer. Finally, an attempt is made to correlate fluorescence data with previous circular dichroism data which had indicated the occurrence of a conformationally rigid structure for some of the compounds having two adjacent aromatic residues.