Structural properties and photophysical behavior of conformationally constrained hexapeptides functionalized with a new fluorescent analog of tryptophan and a nitroxide radical quencher.
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.
Venanzi
Mariano
M
Department of Chemical Sciences and Technologies, University of Tor Vergata, 00133 Rome, Italy. venanzi@uniroma2.it
Valeri
Alessandro
A
Palleschi
Antonio
A
Stella
Lorenzo
L
Moroder
Luis
L
Formaggio
Fernando
F
Toniolo
Claudio
C
Pispisa
Basilio
B
D000975:Antioxidants / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009589:Nitrogen Oxides / Q000737:chemistry*; D009842:Oligopeptides / Q000737:chemistry*; D010777:Photochemistry; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D013055:Spectrophotometry, Infrared; D014364:Tryptophan / Q000031:analogs & derivatives*
D000975:Antioxidants; D009589:Nitrogen Oxides; D009842:Oligopeptides; D014364:Tryptophan; C039900:nitroxyl