Peptidic Hydrogels - In-Situ Gelling Polymers: For Biomedical Applications - page 131

Fig. 5 A diagram of a beta-hairpin molecule, showing the hydrogen bonds ( dotted lines ) that
stabilize the folded conformation between carboxyl and amide groups [ 28 ]. On folding, the
hydrophobic, valine side chain-rich face collapses together with a neighbor to form a bilayered
fibril cross-section. The hairpins also hydrogen bond with neighbors to form fibrils that branch
and entangle with physical crosslinks as indicated by the arrows in the Cryo-TEM image [ 49 ]
Fig. 6 AFM micrographs on negatively charged mica of freshly prepared a ʱ -helix forming
AEAKAEAK solution and b ʲ -sheet forming FEFEFKFK. Alanine based peptide sequence to
phenylalanine changes folding properties. Both form secondary structures that go on to create
fibrils into a higher order structures [ 44 ]
A benefit of peptide synthesis is that one can easily fine tune amino acid con-
tent (i.e. primary structure) of peptides to customize final molecular conformations,
gelation times, or other molecular interactions. This allows the creation of an array
of peptides with minute differences in sequences but vast differences in final proper-
ties. Characterization is important to understanding the secondary structures formed
by individual peptides and, consequently, the higher order structures that are formed
during gelation. To confirm and characterize second order structure, two spectro-
scopic methods, circular dichroism spectroscopy (CD) and Fourier-transform infra-
red spectroscopy (FTIR) are frequently used. Both methods examine light absorption