Spatial variation in the molecular tilt orientational order within the solid domains of phase-separated, mixed dialkylphosphatidylcholine monolayers.
The miscibility of the solid-phase-forming distearoylphosphatidylcholine (DSPC) and the fluid-phase-forming dilauroylphosphatidylcholine (DLPC) at the air/water interface was investigated by the Langmuir film balance. Surface pressure-area isotherms suggest that mixtures containing 25.0-62.5-mol% DLPC (range of composition investigated) are phase-separated. The lateral structure of the DSPC/DLPC monolayers was imaged by Brewster angle microscopy (BAM) as a function of the surface pressure. Quasi-circular condensed domains appeared at pressures between 0 and 0.5mN m(-1), and these structures were already fully developed at approximately 1mN m(-1). Further compression of the monolayers above 1mN m(-1) merely brought the domains closer together. The mixed monolayers consisted of solid domains of DSPC, approximately 3-20 micro in size, in a fluid matrix of DLPC. BAM and the phase contrast mode of intermittent-contact atomic force microscopy (AFM) revealed that the quasi-circular DSPC domains are divided into segments of different reflectivities (BAM) or phase shift (AFM) that arise from abrupt changes in the long-range orientational order of the tilted hydrocarbon chains. The DSPC domains in DSPC/DLPC internally exhibited star and cardioid textures that were heretofore only reported for single-component lipid monolayers in the phase coexistence region.
Sanchez
Jacqueline
J
FQRNT Center for Self-Assembled Chemical Structures and Department of Chemistry, Université de Montréal, C.P. 6128 succursale Centre-ville, Montréal, QC, Canada H3C 3J7.
Badia
Antonella
A
D016880:Anisotropy; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D008858:Microscopy, Phase-Contrast; D008968:Molecular Conformation; D010713:Phosphatidylcholines / Q000737:chemistry*
D008567:Membranes, Artificial; D010713:Phosphatidylcholines; C015153:1,2-dilauroylphosphatidylcholine; C010942:1,2-distearoyllecithin