Characterization of the Changes in Secondary Structure and Architecture of Elastin−Mimetic Triblock Polypeptides during Thermal Gelation

Vibrational spectroscopy and light scattering studies identify the conformational changes associated with gelation of elastin−mimetic triblock (EMT) copolymers. The EMT polypeptide is based on the VPGVG repeat of elastin and is constructed as a BAB triblock copolymer with relatively hydrophobic B-blocks. Laser Raman and ATR-FTIR spectroscopies probed changes in secondary structure associated with gelation in H 2 O and D 2 O. The amide I regions of these spectra suggest that the network-stabilizing interactions are intermolecular β-sheets with a significant fraction of the network containing β-turns and disordered structures. Peak frequency shifts in the ATR-FTIR spectra showed a conversion of extended hydrogen-bonded structures (polyproline II-like structures) to β-sheets during gelation. Molecular weights extrapolated through static light scattering at temperatures below the thermal transition were greater than for a single EMT chain. This suggests that some molecular organization exists prior to gelation, thus requiring relatively modest changes for molecular assembly to occur.