Left- and right-handed helical tubule intermediates from a pure chiral phospholipid

Differential phase contrast microscopy under conditions of very slow cooling reveals the dominant self-assembly mechanism of a chiral diacetylenic phospholipid into multilamellar tubules to be the rapid growth of helical ribbons from spherical multilamellar vesicles. Surprisingly, in the first seconds of tubule formation, a pure enantiomer of 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine [DC(8,9)PC] yields roughly equal numbers of left- and right-handed helices, inconsistent with the heretofore observed relationship between tubule helix handedness on phospholipid chirality. A much slower process follows by which tubules become multilamellar with a prominent helical ridge upon the exterior. Interestingly, these exterior helical ridges are of only a single handedness.