Structural properties and photophysical behavior of conformationally constrained hexapeptides functionalized with a new fluorescent analog of tryptophan and a nitroxide radical quencher

Biopolymers. 2004 Oct 5;75(2):128-39. doi: 10.1002/bip.20110.

Abstract

The influence of the conformational properties on the photophysics of two de novo designed hexapeptides was studied by spectroscopic measurements (ir, NMR, steady-state, and time resolved fluorescence) and molecular mechanics calculations. The peptide sequences comprise two nonproteinogenic residues: a beta-(1-azulenyl)-L-alanine (Aal) residue, obtained by formally functionalizing the Ala side chain with the azulene chromophore, and a Calpha-tetrasubstituted alpha-amino acid (TOAC), incorporating a nitroxide group in a cycloalkyl moiety. Aal represents a new fluorescent, quasi-isosteric Trp analog and TOAC a stable radical species, frequently used as a paramagnetic probe in biochemical studies. The peptide chains differ in the sequence position of the two probes and are heavily based on Aib (alpha-aminoisobutyric acid) residues to generate conformationally restricted helical structures, as confirmed by both spectroscopic and computational results. The conformationally controlled, excited state interactions, determining the photophysical relaxation of the Aal*/TOAC pair, are also discussed.

MeSH terms

  • Antioxidants / chemistry*
  • Magnetic Resonance Spectroscopy
  • Nitrogen Oxides / chemistry*
  • Oligopeptides / chemistry*
  • Photochemistry
  • Protein Structure, Secondary
  • Spectrometry, Fluorescence
  • Spectrophotometry, Infrared
  • Tryptophan / analogs & derivatives*

Substances

  • Antioxidants
  • Nitrogen Oxides
  • Oligopeptides
  • Tryptophan
  • nitroxyl