Two-dimensional polymerization of a polydiacetylene functionalized amphiphilic peptide at the air–water interface

An amphiphilic peptide comprising alternating hydrophilic and hydrophobic amino acid residues has been designed to form β-sheet assemblies as monolayers at the air–water interface. End group modification has been used to introduce a crosslinkable UV active group in the peptide sequence, and a diacetylenic group is present at the N-terminal of the functionalized peptide. Surface pressure–area isotherms as well as compression–expansion cycles of the un-functionalized and functionalized peptides reveal an enhancement in surface activity when the peptide is functionalized. The UV induced crosslinking of the diacetylenic peptide at the air–water interface has also been investigated qualitatively by observing changes in molecular area under constant surface pressure conditions. We have found that there are two steps involved in the photopolymerization reaction: an initial molecular reorientation followed by the crosslinking reaction. Network formation was confirmed as a significant increase in dynamic elasticity was observed after exposure to the UV light. The kinetics and extent of the reaction has been shown to be dependent on initial film organization, where a closer molecular packing leads to faster kinetics and more extensive network formation.