Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 37: Biopolymers (joint session CPP/BP)

CPP 37.2: Vortrag

Donnerstag, 26. März 2009, 14:45–15:00, ZEU 114

Secondary structure of polyalanine peptides [Ac-Ala_nLysH⁺ (n=5, 10, 15)] in vacuo – part II (density functional theory) — •Mariana Rossi, Volker Blum, Peter Kupser, Gert von Helden, Frauke Bierau, Gerard Meijer, and Matthias Scheffler — Fritz-Haber-Institut, D-14195 Berlin, Germany

Predicting the conformation(s) of biomolecules from first principles is an important challenge, requiring both an accurate energetic description of single conformers and an efficient strategy to explore the combinatorial explosion of potential candidate structures. We here study the secondary structure of Ac-Ala_nLysH⁺ (n=5, 10, 15) polyalanine peptides in vacuo, based on density-functional theory in the generalized gradient approximation with van der Waals corrections (GGA+vdW), using the FHI-aims code [1]. We verify our results by comparing calculated vibrational spectra with experimental room-temperature multi-photon IR spectra obtained using the FELIX free-electron laser. We use a force field (OPLS) to screen roughly the conformational energetics of as many structure candidates as possible (>10⁴ in practice), following up with GGA+vdW for a wide range of low-energy conformers. Consistent with earlier indications [2], we find that Ac-Ala₅LysH⁺ is helical, with a close energetic competition between α- and 3₁₀-like conformers. We show how the LysH⁺ termination acts to induce helices also for longer peptides, and that the inclusion of vdW contributions is critical to decide the detailed energy hierarchy. [1] V. Blum, et al., Comput. Phys. Comm., accepted (2008). [2] R. Hudgins et al., JACS 120, 12974 (1998).