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

Optically 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.

Self-Assembling Peptide-Appended Metallomacrocycle Pores for Selective Water Translocation.

Artificial water channels selectively transport water, excluding all ions. Unimolecular channels have been synthesized via complex synthetic steps. Ideally, simpler compounds requesting less synthetic steps should efficiently lead to selective channels by self-assembly. Herein, we report a self-assembled peptide-bound Ni2+ metallomacrocycle, 1, in which rim-peptide-bound units are connected to a central macrocycle obtained via condensation in the presence of Ni2+ ions. Compound 1 achieves a single-channel permeability up to 107-108 water/s/channel and insignificant ion transport, which is 1 order of magnitude lower than those for aquaporins. Molecular simulations probe that spongelike aggregates can form to generate transient cluster water pathways through the bilayer. Altogether, adaptive metallosupramolecular self-assembly is an efficient and simple way to construct selective channel superstructures.

Helix-Sense-Selective Encapsulation of Helical Poly(lactic acid)s within a Helical Cavity of Syndiotactic Poly(methyl methacrylate) with Helicity Memory.

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.

"Helix-in-Helix" Superstructure Formation through Encapsulation of Fullerene-Bound Helical Peptides within a Helical Poly(methyl methacrylate) Cavity.

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.

Helix-helix inversion of an optically-inactive π-conjugated foldamer triggered by concentration changes of a single enantiomeric guest leading to a change in the helical stability.

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.

Remote Control of the Planar Chirality in Peptide-Bound Metallomacrocycles and Dynamic-to-Static Planar Chirality Control Triggered by Solvent-Induced 3(10)-to-α-Helix Transitions.

The dynamic planar chirality in a peptide-bound Ni(II)-salphen-based macrocycle can be remotely controlled. First, a right-handed (P)-3(10)-helix is induced in the dynamic helical oligopeptides by a chiral amino acid residue far from the macrocyclic framework. The induced planar chirality remains dynamic in chloroform and acetonitrile, but is almost completely locked in fluoroalcohols as a result of the solvent-induced transition of the peptide chains from a 3(10)-helix to a wider α-helix, which freezes the rotation of the pendant peptide units around the macrocycle.