Regensburg 2007 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 14: Biological Systems

CPP 14.3: Talk

Tuesday, March 27, 2007, 10:30–10:45, H47

How finite (Ala)_n polypeptides are stabilized by H bond cooperativity: A numeric atom-centered orbital based first-principles study — •Volker Blum, Joel Ireta, and Matthias Scheffler — Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin

An infinite alpha-helical polypeptide (Ala)_∞ is clearly stable over a fully extended conformation. This stabilization is brought about by hydrogen bonds. In finite polypeptide chains, the strength of these crucial bonds depends on the length and environment of the helix, so that, e.g., a short α-helical polypeptide segment (Ala)₄ is actually less stable than a fully extended conformation. We here use all-electron density functional calculations in the PBE generalized gradient approximation by a recently developed, computationally efficient numeric atom-centered orbital based code¹ to investigate this H-bond cooperativity that is intrinsic to Alanine-based polypeptides (Ala)_n (n=1-20,∞). We compare finite and infinite prototypical helical conformations (α, π, 3₁₀) on equal footing, with both neutral and ionic termination for finite (Ala)_n peptides. Moderately sized NAO basis sets allow to capture E_hb with meV accuracy, revealing a jump in E_hb (cooperativity) when two H-bonds first appear in line, followed by slower and more continuous increase of E_hb towards n→∞. ¹ V. Blum, R. Gehrke, P. Havu, V. Havu, X. Ren, M. Scheffler, The FHI Ab Initio Molecular Simulations (aims) Project, Fritz-Haber-Institut, Berlin (2006).