Conformational state diagram of DOPC/DPPCd62/cholesterol mixtures

Raman spectra of aqueous suspensions of vesicles composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), deuterated 1,2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (DPPCd62), and cholesterol (Chol) were studied at room temperature to determine the conformational states of the phospholipid hydrocarbon chains. Deuteration of DPPCd62 allowed us to characterize the conformational states of DOPC and DPPCd62 independently. The parameters of Raman peaks, which are sensitive to the conformational order, were studied in a wide range of compositions. It was found that the DOPC molecules are conformationally disordered for all compositions. The conformational state of the DPPCd62 molecules changes with composition. Their conformational state is influenced by cholesterol-induced partial disordering and DOPC solvation, transforming the DPPC molecules into the disordered state. The conformational state diagram from the Raman experiment was compared with outcomes from the differential scanning calorimetry (DSC) experiment. The Raman spectra also revealed that the DPPC molecules coexist in the disordered and all-trans ordered states for the DOPC/DPPCd62/Chol mixtures except for the pure liquid-disordered phase. [Display omitted] •Ternary mixtures of DOPC/DPPC/Chol are studied by Raman spectroscopy.•DOPC molecules are conformationally disordered for all compositions.•Conformational state of the DPPCd62 molecules changes with mixture composition.•Conformational state diagram for the DPPCd62 molecules is determined.•DPPC molecules coexist in the disordered and all-trans ordered states.