title: Structure and thermal history dependent phase behavior of hydrated synthetic sphingomyelin analogue: 1,2-dimyristamido-1,2-deoxyphosphatidylcholine.
abstract: The physical properties of hydrated multilamellar sample of 1,2-dimyristamido-1,2-deoxyphosphatidylcholine (DDPC) were investigated by means of differential scanning calorimetry (DSC), static X-ray diffraction, and simultaneous DSC and X-ray diffraction. The DDPC is a synthetic sphingomyelin analogue and has two amide bonds in its hydrophobic parts. This paper reports on metastable phase behavior of the hydrated DDPC sample. By cooling from a chain-melted state at the rates of greater than 4 degrees C min(-1), hydrated DDPC bilayers form a metastable gel phase. In the gel phase, the hydrophobic chains are tilted with respect to the bilayer normal, as like the gel phase of glycero-phosphatidylcholines. By heating, the metastable gel phase is transformed in to a stable phase associated with an exothermic heat event at 18.3 degrees C (DeltaH=14.6 kJ mol(-1)) and then the stable phase is transformed into a liquid-crystalline phase at 25.6 degrees C (DeltaH=42 kJ mol(-1)). The incubation at 17 degrees C for more than 1 h also induces the formation of the stable phase. In the stable phase, the hydrophobic chains are packed into highly ordered crystal-like structure. However, the X-ray diffraction pattern of the stable phase suggested that the entire DDPC molecules do not form a two-dimensional molecular ordered lattice, differing from normal subgel phase of glycero-phosphatidylcholines. The structure and phase behavior of DDPC revealed by the present study are discussed from the viewpoint of hydrogen bonds.
authors.affiliation: Department of Physics, Gunma University, 4-2 Aramaki, Maebashi 371-8510, Japan. htakahas@fs.aramaki.gunma-u.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Okumura
authors.forename: Junzo
authors.initials: J
authors.lastname: Sunamoto
mesh_terms: D002152:Calorimetry, Differential Scanning; D015394:Molecular Structure; D010713:Phosphatidylcholines / Q000737:chemistry*; D013109:Sphingomyelins / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D010713:Phosphatidylcholines; D013109:Sphingomyelins; C064611:1,2-dimyristoylamido-1,2-deoxyphosphatidylcholine