BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 9

based peptide-synthetic hybrid block copolymers has been studied for a series of
low-molecular weight PS- b -PBLG and PS- b -PZLLys [23,24]. These diblock
copolymers, consisting of a short PS block with P n ~ 10 and a polypeptide block
containing ~10 to 80 amino acid repeat units were characterized by means of
variable temperature Fourier transform infrared (FTIR) spectroscopy and x-ray
scattering. These experiments allowed the construction of “phase diagrams”,
which are shown in Figure 5. The phase diagrams reveal a number of interesting
features. At temperatures below 200 °C and for sufficiently long polypeptide
blocks, a hexagonal arrangement of the diblock copolymers was found,
analogous to the hexagonal-in-lamellar morphology of the high-molecular weight
analogues. Upon decreasing the length of the peptide block, however, several
novel solid-state structures were discovered. For very short peptide block lengths
(PS 10 - b -PBLG 10 , PS 10 - b -PZLLys 20 , PS 10 - b -PZLLys 40 and PS 10 - b -PZLLys 60 ) a
lamellar supramolecular structure was found. This is due to the fact that, for such
short peptide block lengths, a substantial fraction of the peptide blocks adopts a
β-strand secondary structure.

(a) (b)

(c)

Fig. 5. Phase diagrams describing the solid-state nanoscale structure of (a) PS- b -PBLG and (b) PS-
b -PZLLys diblock copolymers; (c) Illustration of the lamellar, double hexagonal and hexagonal
morphologies found for the low molecular-weight hybrid block copolymers. Adapted from [23,24].