title: Flexibility of phospholipids with saturated and unsaturated chains studied by Raman scattering: the effect of cholesterol on dynamical and phase transitions.
abstract: Raman scattering spectra were obtained at 25-320 K for bilayers prepared from saturated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and mono-unsaturated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) phospholipids, with and without cholesterol. Raman intensities were measured at modes sensitive to lipid inter-chain interactions and/or intra-chain torsional motion (asymmetric CH2 stretching at 2880 cm(-1)) and to the conformational state of lipids (C-C stretching at 1130 cm(-1)). These intensities decreased with temperature, which could be ascribed to increased lipid flexibility. For cholesterol-free and cholesterol-containing DPPC bilayers, the decrease of Raman intensities observed above ∼200 K could be related to the phenomenon of dynamical transition known for biological systems near these temperatures. For a cholesterol-free POPC bilayer, the decrease of intensity for the asymmetric CH2 stretching mode started at a lower temperature, above 100 K, while the addition of cholesterol shifted this starting temperature to a more normal ∼200 K value. The low-temperature lipid flexibility in the case of POPC was related to the abundance of free-volume holes, which disappeared in presence of cholesterol. Near gel-fluid phase transitions, Raman intensities for cholesterol-free bilayers dropped sharply, while for cholesterol-containing bilayers, they changed smoothly.
authors: Institute of Automation and Electrometry, Russian Academy of Sciences, Novosibirsk 630090, Russia.
authors: N V
authors: NV
authors: Surovtsev
authors: Department of Physics, Novosibirsk State University, Novosibirsk 630090, Russia.
authors: S A
authors: SA
authors: Dzuba
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D003080:Cold Temperature; D005782:Gels / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008968:Molecular Conformation; D044367:Phase Transition; D010743:Phospholipids / Q000737:chemistry*; D055585:Physical Phenomena; D013059:Spectrum Analysis, Raman
chemical_list: D005782:Gels; D008051:Lipid Bilayers; D010743:Phospholipids; D002784:Cholesterol