Liquid Crystalline Assembly of Rod–Coil Molecules - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 74

columns, with the polypeptide segments oriented perpendicularly to the di-
rector of the columns. The subsequent supramolecular columns are packed in
a superlattice with hexagonal periodicity parallel to the α -helical polypeptide

segments, with a lattice constant of 43 A .
In addition, the authors reported that two series of peptide rod-coil block
copolymers based on

-benzyloxycarbonyl-l-lysine
as a rod building block and a short oligo(styrene) (DP = 10) coil self-assembled
into well-ordered structures, and that the conformation of the

γ -benzyl-l-glutamate or ε

-helical pep-
tide rod is sensitive to temperature [63]. Under ambient conditions, the peptide
segments of the diblock oligomers largely possess an

α

-helical secondary
structure, indicating the rod-coil architecture of the molecules as confirmed
by FT-IR spectra. For all molecules, increasing the length of the peptide
segment results in a stabilization of the

α

-helical secondary structure and
ultimately allows a regular organization of the rod-like peptide blocks. The
small-angle X-ray diffraction pattern of peptide block copolymers based on
short

α

-benzyl-l-glutamate also indicates a columnar hexagonal arrangement,
except for one composed of the shortest peptide segments ( n = 10). However, in
case of the long

γ

-benzyl-l-glutamate peptide segments ( n = 20, 40), increas-
ing temperature transforms the organized structure from hexagonal columnar
intolamellarstructureduetothechangeofthepeptideconformationfrom

γ

Fig. 7 -sheet organization of the (styrene) 10 - b -

( γ -benzyl-l-glutamate) n diblock oligomers (PS 10 - b -PBLG n ). Reprinted with permission
from [63].

a Columnar hexagonal and b lamellar β

© 2001 American Chemical Society