The stability, persistence and dynamics of the peptide secondary motifs are investigated in a series of poly(gamma-benZyl-L-glutainate)-b-polyalanine (PBLG-b-PAla) polypeptides through a combination of structural (X-rays, NMR) and dynamic (Dielectric Spectroscopy, NMR) probes. The unfavorable enthalpic interactions between the unlike blocks give rise to nanophase separation that results in the destabilization of PAla beta-sheets. Contrary to. this, the overall helicity of PBLG alpha-helices is enhanced. The dynamics of the "defected" amorphous segments and of the more ordered segments are studied by DS and C-13 NMR, respectively. These probes provide information on the time scale and the mechanism of molecular and supramolecular motion.