Dresden 2011 – scientific programme
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MO: Fachverband Molekülphysik
MO 1: Biomolecules
MO 1.8: Talk
Monday, March 14, 2011, 12:15–12:30, TOE 317
Onset of α-helical preference on gas-phase Ac-Alan-LysH+: insights from ab initio theory — •Mariana Rossi, Volker Blum, Xinguo Ren, and Matthias Scheffler — Fritz-Haber-Institut der MPG, Faradayweg 4-5, D-14195, Berlin
The smallest size of polypeptides to form helices in the gas phase can be matched between theory and experiment, and brings us essential information about the intrinsic stability of this well-known secondary structure motif. For the case of the alanine-based Ac-Alan-LysH+ series in the gas phase, indirect measurements from single water adsorption experiments[1] have indicated helix onset at n=8. We here focus on determining quantitatively, based on density-functional theory (DFT), the structural and energetic properties of exactly this series. Starting from a force field conformational screening, we fully relax more than 1000 conformers using the van der Waals (vdW) corrected[2] PBE exchange-correlation (xc) potential. α-helical preference is found to start between n=7-8, in agreement with experiment, but only if vdW interactions are taken into account. For a few of the lowest energy conformers for n=4-8, we test different vdW corrected xc functionals and benchmark our results against explicitly correlated methods, by developing and using a numeric atom-centered basis set which allows us to converge energy differences. Finally, the qualitatively different energetic contributions (H-bonds, vdW, electrostatics) for this helix onset are dissected, explaining the stability of these structures. [1] Kohtani and Jarrold, JACS 108, 8454 (2004); [2] Tkatchenko and Scheffler, PRL 102, 073055 (2009)