Separation of enantiomers of chiral fullerene derivatives through enantioselective encapsulation within an adaptable helical cavity of syndiotactic poly(methyl methacrylate) with helicity memory

Abstract

AbstractOptically active left (M)‐ and right (P)‐handed helical syndiotactic poly(methyl methacrylate)s (M‐ and P‐st‐PMMAs) with a helicity memory enantioselectively encapsulated the racemic C60 derivatives, such as 3,4‐fulleroproline tert‐butyl ester (rac‐1) and tetraallylated C60 (rac‐2), as well as the C60‐bound racemic 310‐helical peptides (rac‐3) within their helical cavities to form peapod‐like inclusion complexes and a unique “helix‐in‐helix” superstructure, respectively. The enantiomeric excess (ee) and separation factor (enantioselectivity) (α) of the analyte 1 (ee = 23%–25% and α = 2.35–2.50) encapsulated within the helical cavities of the M‐ and P‐st‐PMMAs were higher than those of the analytes 2 and 3 (ee = 4.3%–6.0% and α = 1.28–1.50). The optically pure (S)‐ and (R)‐1 were found to more efficiently induce an excess one‐handed helical conformation in the st‐PMMA backbone than the optically pure (S)‐ and (R)‐1‐phenylethylamine, resulting in intense mirror‐image vibrational circular dichroism (VCD) spectra in the PMMA IR regions. The excess one‐handed helices induced in the st‐PMMAs complexed with (S)‐ and (R)‐1 were memorized after replacement with the achiral C60, and the complexes exhibited induced electric CDs in the achiral C60 chromophore regions.