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Secondary structure of Ac-Alan-LysH+ polyalanine peptides (n = 5,10,15) in vacuo: Helical or not?

Rossi, M.*; Blum, V.; Kupser, P.; von Helden, G.; Bierau, F.; Pagel, K.; Meijer, G.; Scheffler, M. – 2010

The polyalanine-based peptide series Ac-Alan-LysH+ (n = 5−20) is a prime example that a secondary structure motif that is well-known from the solution phase (here: helices) can be formed in vacuo. Here we revisit the series members n = 5,10,15, using density functional theory (van der Waals corrected generalized gradient approximation) for structure predictions, which are then corroborated by room temperature gas-phase infrared vibrational spectroscopy. We employ a quantitative comparison based on Pendry’s reliability factor (popular in surface crystallography). In particular, including anharmonic effects into calculated spectra by way of ab initio molecular dynamics produces remarkably good experiment−theory agreement. We find the longer molecules (n = 10,15) to be firmly α-helical in character. For n = 5, calculated free-energy differences show different H-bond networks to still compete closely. Vibrational spectroscopy indicates a predominance of α-helical motifs at 300 K, but the lowest-energy conformer is not a simple helix.

Title
Secondary Structure of Ac-Alan-LysH+ Polyalanine Peptides (n = 5,10,15) in Vacuo: Helical or Not?
Author
Rossi, M.*; Blum, V.; Kupser, P.; von Helden, G.; Bierau, F.; Pagel, K.; Meijer, G.; Scheffler, M.
Date
2010
Identifier
10.1021/jz101394u
Source(s)
Citation
J. Phys. Chem. Lett. 2010, 1, 3465-3470
Type
Text
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