Understanding the Interaction of Polypeptides at the Air/Water Interface

Research into the behavior of polypeptides at the air/water interface reveals intriguing dynamics influenced by polymer concentration and structure. When branched polypeptides are introduced into an aqueous subphase, their ability to increase surface pressure over time varies significantly. Observations indicate that higher polymer concentrations lead to greater surface pressure, with the maximum effects typically noted after an extended period of 60 minutes. Interestingly, some polypeptides, such as OAK and Ac-EAK, showed immediate incorporation at the interface, while others like AK, SAK, and EAK needed a distinct induction period—particularly at lower concentrations.

The surface pressure of these branched polypeptides is sensitive to their structural characteristics. For instance, SAK demonstrated the highest surface activity, contrasting sharply with polylysine, which exhibited negligible changes in surface pressure even at increased concentrations. This finding suggests that the terminal amino acid residues of the polypeptides play a crucial role in their surface activity, leading to a hierarchy of effectiveness: SAK > AK > EAK > Ac-EAK > OAK > polylysine.

Further investigation into the penetration of these polypeptides into phospholipid monolayers offers valuable insights. These monolayers, which mimic biological membranes, serve as an effective model to assess how macromolecules interact with lipid interfaces. The studies highlight that as polymers are introduced into pre-established lipid monolayers, surface pressure increases can be recorded, providing a clear indication of penetration.

Among the polypeptides tested, SAK consistently resulted in the highest surface pressure increase when interacting with a DPPC monolayer. Notably, this increase in surface pressure was lesser with other polypeptides, indicating that specific structural features enhance interaction with phospholipids. Interestingly, the presence of additional phospholipids, such as PG, appeared to diminish the surface activity of polycationic polypeptides like SAK and AK due to increased packing density in the monolayer.

This nuanced understanding of how branched polypeptides interact with lipid monolayers and the air/water interface opens the door to potential applications in drug delivery and biomaterials. By tailoring polymer structures, researchers can enhance or inhibit interactions with biological membranes, providing greater control in the development of pharmaceutical formulations.