Mixtures of dimyristoylphosphatidylcholine (DMPC) and dicaproylphosphatidylcholine (DCPC) were
investigated by solid-state 31P and 2H NMR. By variation of the mole fraction, X, of DMPC in DCPC, the
temperature, and the water content, the conditions at which small discoidal particles, the so-called “bicelles”,
self-orient in the magnetic field were determined. The bicellar region has an ellipsoidal shape and is
delineated by compositions and temperatures ranging from X = 65−87% and T = 25−45 °C, at 80%
hydration in the presence of 100 mM KCl. In the absence of salt, the bicelles still orient in the field but
for a narrower range of composition (X ≈ 72−87%). The degree of macroscopic orientation increases in the
presence of salt. Reducing hydration to 40% increases the breadth of the bicelle domain. On the contrary,
above 95% water content, bicelles are no longer detected by NMR. In the bicelle domain, water shows
residual ordering which linearly increases with the decrease in water content. Analysis of the water
behavior in terms of bound and free water suggests that water bound to bicelles has the same surface
properties as in pure lipid membranes and that it promotes swelling. Perdeuteration of the DMPC lipid
chains indicates a reduction in local ordering in the bicelle core, relative to pure lipid dispersions, for
corresponding temperatures. As a consequence, the bilayer would be slightly thinner in the bicelle.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.