Formation of hierarchical supramolecular microstructures from 6-O-alkylated α-cyclodextrin and their application to the selective extraction of long-chain unsaturated fatty acid esters.

We successfully fabricated rhombic plate-like microstructures composed of layered assemblies of head-to-head supramolecular dimers of 6-O-methylated and 6-O-ethylated α-cyclodextrins (6-Me-α-CD and 6-Et-α-CD, respectively). 6-Me-α-CD selectively extracted methyl elaidate (trans) over methyl oleate (cis) in methanol via microstructure formation driven by inclusion complexation between the 6-Me-α-CD dimer and fatty acid esters, whereas 6-Et-α-CD exhibited the opposite selectivity. These results demonstrate that subtle modulation of the alkyl chain length at the 6-O position of α-CD enables reversal of cis/trans selectivity in supramolecular extraction behavior. The origin of this selectivity was further elucidated by theoretical calculations based on density functional theory (DFT) and fragment molecular orbital (FMO) interaction energy analysis.