We present a molecular dynamics simulation study od the stability of alanine- (A) and Lysine- (K) based hexapeptides in water. Sixteen runs of 2 ns long each are performed in explicit solvent and in the NPT ensamble. The simulated sequences are AAAAAA, AKAAAK, KAAAAK and KKKKKK. The main results are: I) The a-helix conformation of these peptides have similar stability at 300 K. II) This stability is noticeably high for peptides of this size when compared with previus simulations. The observed stability is in line with with the s value of A and K residues in the Zimm-Brag theory of helix-coil transitions. We also discuss the interations that stabilize tha a-helix conformation of this peptides and the importance of multiple runs to achieve consisten results.
