Stereochemical Effect
Revealed in Self-Assemblies
Based on Archaeal Lipid Analogues Bearing a Central Five-Membered
Carbocycle: A SAXS Study
- Publication date
- Publisher
Abstract
The relative stereochemistry (cis or trans) of a 1,3-disubstituted
cyclopentane unit in the middle of tetraether archaeal bipolar lipid
analogues was found to have a dramatic influence on their supramolecular
self-assembly properties. SAXS studies of two synthetic diastereomeric
archaeal lipids bearing two lactosyl polar head groups at opposite
ends revealed different lyotropic behaviors. The cis isomer led to
L<sub>c</sub>–L<sub>α</sub>–Q<sub>II</sub> transitions
whereas the trans isomer retained an L<sub>α</sub> phase from
20 to 100 °C. These main differences originate from the conformational
equilibrium (pseudorotation) of 1,3-disubstituted cyclopentanes. Indeed,
this pseudorotation exhibits quite similar orientations of the two
substituents in a trans isomer whereas several orientations of the
two alkyl chains are expected in a <i>cis</i>-1,3-dialkyl
cyclopentane, thus authorizing more conformational flexibility in
the lipid packing