BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 5

offer a perspective on the future of research in the field of peptide-based
copolymers.
2. Bulk Self-assembled Structures from Polypeptide-based Conjugates
2.1. Diblock copolymer architectures
Polydiene-based diblock copolymers
One of the first reports on the nanoscale solid-state structure of peptide-synthetic
hybrid block copolymers was published by Gallot et al. [11] in 1976. In
this publication, the solid-state structure of a series of polybutadiene- block -
poly( ȳ -benzyl L -glutamate) (PB- b -PBLG) and polybutadiene- block -poly( N 5 -
hydroxyethyl L -glutamine) (PB- b -PHLGln) diblock copolymers was investigated
using a combination of techniques, including infrared and circular dichroism
(CD) spectroscopy, x-ray scattering (SAXS), and transmission electron
microscopy (TEM). The block copolymers covered a broad composition range
with peptide contents ranging from 19 to 75%. Interestingly, SAXS and TEM
revealed a well-ordered lamellar superstructure characterized by up to four
higher-order Bragg spacings for all of the investigated samples. Wide-angle x-
ray scattering (WAXS) experiments indicated that the α-helical peptide blocks
were assembled in a hexagonal array. For a number of block copolymer samples
it was found that the calculated length of the peptide helix was larger than the
thickness of the polypeptide layer. To accommodate this difference, it was
proposed that the peptide helices were folded in the peptide layer. The lamellar
structure consists of planar, parallel equidistant sheets. Each sheet is obtained by
superposition of two layers; (i) the PB chains in a more or less random coil
conformation and (ii) the α-helical polypeptide blocks in a hexagonal array of
folded chains. The hexagonal-in-lamellar structure was also found for
polybutadiene- block -poly( ō -benzyloxycarbonyl L -lysine) (PB- b -PZLLys) and
polybutadiene- block -poly( L -lysine) (PB- b -PLLys) block copolymers by the same
authors [12-15].
More recently, the solid-state nanoscale structure of polyisoprene- block -
poly( ō -benzyloxycarbonyl L -lysine) (PI- b -PZLLys) diblock copolymers was
reported [16]. Diblock copolymers composed of a PI block with a number-
average degree of polymerization of 49 and a PZLLys block containing 61-178
amino acid residues were investigated with dynamic mechanical analysis (DMA)
and x-ray scattering (SAXS and WAXS). For the PI 49 - b -PZLLys 35 , PI 49 - b -