Molecular dynamical approach to the conformational transition in peptide nanorings and nanotubes.

We study the conformational transition in d,l-peptide nanorings (PNRs) and nanotubes (PNTs) computationally based on the total energy calculation. Ab initio energy calculation has been carried out to investigate the static states of PNRs, whereas the molecular dynamics (MD) calculation has been employed to examine PNRs' dynamical states. We, then, discuss the time-dependent (TD) feature via the transition process from E-type to B-type and vice versa. The conformational transition occurs easily from E-type equatorial (Eeq) to B-type axial (Bax) but is unreversible for the opposite direction because of a larger activation energy. The TD tracing of the two dihedral angles in the individual amino acid residues reveals that the conformational change propagates along the peptide skeleton ring nearly at the sound velocity. We further expand our study to the tubular forms and reveal that the PNT has an ability to produce the two kinds of homogeneous tubes, being composed of E rings (E-tube) and of B rings (B-tube), and also that these two PNRs should be mixed to produce a binary alloyed PNT.