The effect of protonation in a family of peptide based gemini amphiphiles on the interaction in Langmuir films

Abstract

The behavior and properties of four new gemini amphiphilic pseudopeptides (GAPs) were studied in monomolecular films formed at the air-water interface using surface pressure measurements, polarization-modulation infrared reflection-absorption spectroscopy as well as computational modeling. The molecules used differed in the structure of the polar heads containing amino and amide groups and in the number of apolar hydrocarbon chains. To better understand the role of the polar heads in the intra- and intermolecular interaction, the experiments were performed at different pH values of the water subphase.The experimental and theoretical results show that the interaction between the molecules forming monolayers change in function of pH; these changes depend on the pseudopeptide used. We propose that the effects observed are due to the differences in the protonation state of the polar heads in the four molecules. This outcome may give a handle on preparation of pH-dependent supramolecular structures based on tailor-made GAPs.