Poly(L-proline) II Helix Propensities in Poly(L-lysine) Dendrigraft Generations from Vibrational Raman Optical Activity

Vibrational Raman optical activity (ROA), measured as small circularly polarized components in Raman scattering from chiral molecules, was applied to study the backbone conformations of the first five generations of poly(L-lysine) dendrigrafts (DGLs) in water. Generation 1 was found to support predominantly the poly(L-proline) II (PPII) conformation, the amount of which steadily decreased with increasing generation, with a concomitant increase in other backbone conformations. This behavior may be due to increasing crowding of the lysine side chains, together with suppression of backbone hydration, with increasing branching. In contrast, the ROA spectra of a series of linear poly(L-lysine)s in water show little change with increasing molecular weight. Our results may have implications for the nonimmunogenic properties of DGLs.