Domain formation in lipid bilayers probed by two-dimensional infrared spectroscopy

Two-dimensional infrared (2D-IR) spectroscopy has been used to probe structure and dynamics in binary sphingomyelin/phospholipid liposomes. The liposomes consist of 1-palmitoyl-2-linoleyl phosphatidylcholine (PLPC) and sphingomyelin (SPM) in the ratio 1:1. The diagonal part of the 2D-IR spectra shows two bands which are due to amide I of SPM and to the carbonyl moieties of PLPC. The diagonal components of the 2D-IR spectra reveal a difference in the molecular dynamics. The presence of off-diagonal cross-peaks indicates the occurrence of intermolecular structural correlation. The intensity of the cross-peaks is consistent with segregation of two lipid components into PLPC and SPM molecular domains.