Relation of Phospholipid Conformations to Longitudinal Acoustic Mode and the C‐C Stretching Raman Bands

ABSTRACT The longitudinal acoustic mode (LAM) band, which is a characteristic feature of the Raman spectrum of methylene chains, is very sensitive to the conformational state of the chain. However, in the case of phospholipids, the potential of the LAM band for characterizing the conformational states of hydrocarbon chains remains unrealized. Here, we investigated the Raman scattering spectra of the saturated phospholipid 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC) in a wide temperature range, focusing on the LAM band and the C‐C stretching peak, which is also an indicator of long sequences of all‐trans rotamers. The conformational sensitivity of the LAM and C‐C stretching peaks was also tested by DFT modeling. The analysis of the results showed that the LAM band allows one to unambiguously determine the fraction of the all‐trans conformation in phospholipid chains, while some non‐all‐trans conformations contribute to the C‐C stretching peak. A model describing the phospholipid conformations and the temperature dependences of the LAM and C‐C stretching peaks is proposed.