Polymerization of diacetylene in casting parallel and anti-parallel β-sheet

In the β sheet structure of the peptide, the distance among the β-strands are 5 Å. This distance corresponds with distance among the monomer units of diacetylene and diene. Therefore the β-sheet will be able to be cross-linked by introducing these monomer units into the diacetylene and diene into peptide that formed β-sheet by using this. In this work, we synthesized peptide 1-4. Peptide 1 and 2 were design to form anti-parallel β-sheet alone. On the other hand, peptide 3 and 4 were design to form parallel β-sheet by mixing them. Polymerization of 1 and 2 was conducted by UV irradiation. After the polymerization, UV-vis spectra of 1 and 2 in dichloroacetic acid had an absorbance at 573 nm that originates in poly diacetylene. The result of FT-IR measurement of them showed disappearance of a peak at 2250 cm-1 that originates in diacetylene. Amide I region suggested that the peptides formed anti-parallel β-sheet and random coil. Therefore, it seemed that polymerization occurred in the β-sheet formed part.