Phosphonate Lipid Tubules II

Abstract

We describe a new chiral tubule-forming lipid in which the C-O-P phosphoryl linkage of the archetypal tubule-forming molecule, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine, "DC(8,9)PC", is replaced by a C-P linkage. Tubule formation with this phosphonate analogue proceeds under the same mild conditions as with DC(8,9)PC and produces similar yields, but synchrotron small-angle X-ray scattering, atomic force microscopy, and optical microscopy show the new tubules to have diameters 1.94 times as great, to be significantly shorter, and to be thinner-walled. A significant portion of the enantiomerically pure chiral phosphonate precipitate is in the form of stable open helices, and these helices are divided almost evenly between left- and right-handed members.

Chiral Molecular Self‐Assembly

“…The small-angle X-ray scattering data in Figure 5.34 shows that the interlamellar spacings of the tubules from the three compounds are quite similar despite the difference in diameter. 146 However, the broader peaks observed for the phosphonate tubules indicates the correlation length is about half that for DC 8,9 PC tubules due to their thinner walls.…”

“…145,146 Tubule formation with these phosphonate lipids (41, 42) was determined using the ethanol-water preparation conditions described above. X-ray diffraction and microscopy revealed these tubules have diameters of about 1 µm, twice that of DC 8,9 PC tubules, in ethanol-water solutions.…”

“…17 Atomic force microscopy showed that the phosphonate tubules were more deformable than those of DC 8,9 PC and flattened upon drying. 146 A small portion of the phosphonate is in the form of stable open helices which were imaged using liquid mode AFM. Surprisingly, Thomas et al found helices with both senses of handedness in an enantiomerically pure sample.…”

“…However, the differences in bond lengths and bond angles associated with this chemical change can modify the packing of neighboring molecules. 146 This modification is small enough that tubules can still form but large enough to increase the tubule diameter by a factor of 2. This connection between chemical structure and tubule-forming properties is a great benefit derived from synthetic effort in this area.…”

“…As discussed in Sections 2-5, in most experiments on chiral materials, tubules and helical ribbons are observed with only one sense of handedness. However, there are a few exceptions in experiments on diacetylenic phospholipids, 144 diacetylenic phosphonate lipids, 145,146 and bile. 162 In these exceptional cases, some helices are observed with the opposite sense of handedness from the majority.…”