Vibrational Spectra of a Linear Alternating L,D Hexapeptide with a Type II β-Turn Structure

Abstract

Raman and infrared spectra of Boc-(D-aIle-L-Ile)₃-OMe (ILEU-6) and its N-deuterated derivative have been measured. Conformationally sensitive amide vibrations have been identified and compared with the observed and calculated frequencies of Pro-Leu-Gly-NH₂ which has a type II β-turn structure. The observed frequencies of ILEU-6 have also been compared with the normal mode calculations of a standard model type II β-turn structure and a good agreement has been found in these comparisons. The additional frequencies observed for this particular structure are assigned to the residues that are not involved in the β-turn.

Key Words:

• Raman spectra
• IR spectra
• Boc-(D-aIle-L-Ile)₃-OMe
• β-turn α-helix
• amide modes
• vibrational assignment