A spectroscopic and molecular mechanics investigation on a series of AIB-based linear peptides and a peptide template, both containing tryptophan and a nitroxide derivative as probes
✍ Scribed by Basilio Pispisa; Lorenzo Stella; Mariano Venanzi; Antonio Palleschi; Fernando Marchiori; Alessandra Polese; Claudio Toniolo
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 2000
- Tongue
- English
- Weight
- 188 KB
- Volume
- 53
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Linear Aib-based hexapeptides, of the general formula Ac-Toac-(Aib) n -Trp-(Aib) r -OtBu [T(Aib) n Trp], where n ϩ r ϭ 4, and Toac is a nitroxide spin-labeled C ␣,␣ -disubstituted glycine, were investigated by steady-state and time-resolved fluorescence measurements in different solvent media. A related peptide, i.e., cyclo-{Orn-[(Aib) -cyclo-Trp], was also studied by the same techniques. It is a L-Orn, L-Asp diketopiperazine template, to which two Aib-based chains are covalently attached, each one containing one chromophore only, i.e., Trp or Toac. Whatever the solvent, in the former series of peptides quenching of the excited Trp exhibits three lifetime components and proceeds on a time scale from subnanoseconds to a few nanoseconds, while in the case of the template the same process occurs entirely on the nanoscale time scale, exhibiting two lifetimes only. The ir absorption spectral patterns suggest that the backbone of the peptides examined is in the 3 10 -helical conformation, as earlier determined by x-ray diffraction for T(Aib) 3 Trp in the crystal state. In all cases, the fluorescence results are satisfactorily described by a dipole-dipole interaction mechanism, in which