Energetic, conformational and vibrational features of the tripeptide (Gly)3. Data from MP2 and DFT calculations

Abstract

The conformational and vibrational properties of the structurally simplest tripeptide (Gly)3 were analyzed using the MP2 and DFT methods. Cationic and zwitterionic species of (Gly)3 were embedded in a polarizable continuum (PCM), mimicking a bulk water environment. Initial conformers having β-strand, helical, polyproline-II, classic and inverse γ-turn conformations, were geometry optimized. Except β-strand, which was transformed into a quasi-planar extended chain, all other conformers maintained their structural integrity at the MP2 level. Amongst the eleven functionals (B3LYP, CAM-B3LYP, B97-1, B97-2, B97-D3, B98, ωB97XD, PBE0, APF-D, M062X and MN15) used in DFT calculations, only ωB97XD was able to assure the stability of all the ordered structures in both cationic and zwitterionic species. The backbone terminal charged groups were shown to have a great influence on the energy landscape of the optimized conformers. A multiconformational approach was used to calculate the Raman spectra of the zwitterionic species.