Small- and wide-angle x-ray-diffraction measurements on the ${\mathrm{P}}_{\mathrm{\beta }\prime }$ phase of fully hydrated DL-β,γ-dipalmitoyl-α-phosphatidylcholine were performed in highly oriented lipid-water multibilayer samples. The data extend previous results on the ripple structure of this phase, as obtained by x-ray diffraction and scanning tunneling microscopy, and for the first time provide evidence that ${\mathrm{theL}}_{\mathrm{\beta }\prime }$→${\mathrm{P}}_{\mathrm{\beta }\prime }$ phase transition is characterized by a change in hydrocarbon-chain tilt direction, from the ortorhombic binto the a direction.© 1991 The American Physical Society

• Received 19 September 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.903