Which structure forms when phospholipids with large head groups pack together in water?
Self-assembly morphology of amphipathic lipids follows thermodynamic principle minimizing hydrocarbon water contact and elastic bending energy described by Helfrich Hamiltonian. Large headgroup relative to single alkyl tail gives packing parameter p equals v divided by a times l less than one third, molecule conical inverted shape promotes aggregation into spherical micelles about thirty to hundred monomers core of tails shielded from water exterior heads highly hydrated dynamic surface curvature positive. Examples lysophosphatidylcholine detergent, bile salts, single-chain phospholipids. Double-chain phospholipids with p approximately one cylindrical shape bilayers favor planar lamellar phase that closes into vesicles liposomes eliminating edge energy line tension about ten piconewtons by forming sealed sphere enclosing aqueous core through sonication extrusion detergent dialysis providing energy overcoming bending rigidity kappa about twenty kBT. Intermediate p half to one cylindrical micelles wormlike. Monolayer forms at air water interface Langmuir film surface pressure. Hence phospholipids with very large headgroups would behave micelle forming rather than bilayer due to geometric mismatch explaining why lysolipids solubilize membranes into mixed micelles above CMC enabling detergent mediated protein purification and reconstitution protocols.
Ref: Israelachvili et al., Theory of Self-Assembly and Packing Parameter, Q Rev Biophys.