Characterization of thin cast films of a trileucine-induced lipid by infrared multiple-angle incidence resolution spectrometry

Infrared multiple-angle incidence resolution spectrometry (MAIRS) has been employed to characterize a thin cast film of tripeptide-induced lipid (Leu3) prepared on a germanium substrate. Leu3 molecules are designed to spontaneously interact with each other by hydrogen bonding via amide groups and leucine fastener. The molecular aggregate of Leu3 is known to have a unique property that it forms a flexible polymer-like film, although the molecules are not covalently bonded. Infrared MAIRS has revealed that a Leu3 cast film forms the parallel β-sheet structure, and the amide groups have a specific molecular orientation, probably because the molecules would have strong interaction with the substrate. Further, it has experimentally been confirmed that the amide B band is a Fermi resonance band derived from the amide II mode powered by amide A mode by the analysis of the MAIRS spectra.