A one‐handed 310‐helical hexapeptide is efficiently encapsulated within the helical cavity of st‐PMMA when a fullerene (C60) derivative is introduced at the C‐terminal end of the peptide. The encapsulation is accompanied by induction of a preferred‐handed helical conformation in the st‐PMMA backbone with the same‐handedness as that of the hexapeptide to form a crystalline st‐PMMA/peptide‐C60 inclusion complex with a unique optically active helix‐in‐helix structure. Although the st‐PMMA is unable to encapsulate the 310‐helical peptide without the terminal C60 unit, the helical hollow space of the st‐PMMA is almost filled by the C60‐bound peptides. This result suggests that the C60 moiety can serve as a versatile molecular carrier of specific molecules and polymers in the helical cavity of the st‐PMMA for the formation of an inclusion complex, thus producing unique supramolecular soft materials that cannot be prepared by other methods.
We report a highly enantio- and helix-sense-selective
encapsulation
of helical poly(lactic acid)s (PLAs) through a unique “helix-in-helix”
superstructure formation within the helical cavity of syndiotactic
poly(methyl methacrylate) (st-PMMA) with a one-handed helicity memory,
which enables the separation of the enantiomeric helices of the left
(M)- and right (P)-handed-PLAs.
The M- and P-helical PLAs with different
molar masses and a narrow molar mass distribution were prepared by
the ring-opening living polymerization of the optically pure l- and d-lactides, respectively, followed by end-capping
of the terminal residues of the PLAs with a 4-halobenzoate and then
a C60 unit, giving the C60-free and C60-bound M- and P-PLAs. The C60-free and C60-bound M- and P-PLAs formed crystalline inclusion complexes with achiral
st-PMMA accompanied by a preferred-handed helix induction in the st-PMMA
backbone, thereby producing helix-in-helix superstructures with the
same-handedness to each other. The induced helical st-PMMAs were retained
after replacement with the achiral C60, indicating the
memory of the induced helicity of the st-PMMAs. Both the C60-free and C60-bound helical PLAs were enantio- and helix-sense
selectively encapsulated into the helical hollow space of the optically
active M- and P-st-PMMAs with the
helicity memory prepared using chiral amines. The M- and P-PLAs are preferentially encapsulated within
the M- and P-st-PMMA helical cavity
with the same-handedness to each other, respectively, independent
of the terminal units. The C60-bound PLAs were more efficiently
and enantioselectively trapped in the st-PMMA compared to the C60-free PLAs. The enantioselectivities were highly dependent
on the molar mass of the C60-bound and C60-free
PLAs and significantly increased as the molar mass of the PLAs increased.
A preferred-handed helicity induced in an optically-inactive poly(phenyleneethynylene)-based foldamer bearing carboxylic acid pendants upon complexation with a single enantiomeric diamine was subsequently inverted into the opposite helix upon further addition of the diamine, accompanied by a remarkable change in the stability of the helices.
Ao ne-handed 3 10 -helical hexapeptide is efficiently encapsulated within the helical cavity of st-PMMA when afullerene (C 60 )derivative is introduced at the C-terminal end of the peptide.The encapsulation is accompanied by induction of ap referred-handed helical conformation in the st-PMMA backbone with the same-handedness as that of the hexapeptide to form acrystalline st-PMMA/peptide-C 60 inclusion complex with aunique optically active helix-in-helix structure.Although the st-PMMA is unable to encapsulate the 3 10 -helical peptide without the terminal C 60 unit, the helical hollowspace of the st-PMMA is almost filled by the C 60 -bound peptides.T his result suggests that the C 60 moiety can serve as av ersatile molecular carrier of specific molecules and polymers in the helical cavity of the st-PMMA for the formation of an inclusion complex, thus producing unique supramolecular soft materials that cannot be prepared by other methods.
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