Chirality responsive helical poly(phenylacetylene) bearing L-proline pendants.

A novel, optically active, cis-transoidal poly(phenylacetylene) bearing an L-proline residue as the pendant group (poly-1) was prepared by the polymerization of the corresponding monomer using a rhodium catalyst in water, and its chiroptical property was investigated using circular dichroism spectroscopy. Poly-1 showed intense Cotton effects in the UV-visible region of the polymer backbone in water, resulting from the prevailing one-handed helical conformation induced by the covalent-bonded chiral L-proline pendants and exhibited a unique helix-sense inversion in response to external, achiral, and chiral stimuli, such as the solvent and interactions with chiral small molecules. We found that poly-1 could enantioselectively trap 1,1'-2-binaphthol within its hydrophobic helical cavity inside the polymer in aqueous media and underwent an inversion of its helical sense in the presence of one of the enantiomers.

Polymerization of phenylacetylene by rhodium complexes within a discrete space of apo-ferritin.

Polymerization reactions of phenylacetylene derivatives are promoted by rhodium complexes within the discrete space of apo-ferritin in aqueous media. The catalytic reaction provides polymers with restricted molecular weight and a narrow molecular weight distribution. These results suggest that protein nanocages have potential for use as various reaction spaces through immobilization of metal catalysts on the interior surfaces of the protein cages.

Polymerization of an optically active phenylacetylene derivative bearing an azide residue by click reaction and reaction with a rhodium catalyst.

A facile method for synthesizing diverse optically active polymers with different backbone structures was developed by the polymerization of an optically active aromatic azide bearing an acetylene unit with a rhodium catalyst followed by the click reaction of the pendant azides or by the click polymerization of the monomer.

Macromolecular helicity inversion of an optically active helical poly(phenylacetylene) by chemical modification of the side groups.

An optically active helical poly(phenylacetylene) was synthesized by the copolymerization of phenylacetylenes bearing optically active hydroxy or ester groups obtained by the kinetic resolution of a racemic phenylacetylene with lipase; the helix-sense was inverted from one helix to another by the further chemical modification of the hydroxy groups with achiral bulky isocyanates or an acid chloride.

Synthesis and chiroptical properties of a helical poly(phenylacetylene) bearing optically active pyrene pendants.

A novel poly(phenylacetylene) derivative bearing optically active pyrene moieties as the pendant groups (poly-(R)-1) was prepared by the polymerization of the corresponding monomer (R)-1 in the presence of a rhodium catalyst, and its chiroptical property was investigated. Poly-(R)-1 exhibited an induced circular dichroism (ICD) in the polymer backbone region due to the predominantly one-handed helical conformation. The ICD pattern dramatically changed and was accompanied by inversion of the Cotton effect sign in response to a change in the temperature and solvent, indicating that poly-(R)-1 underwent a helix-helix transition in response to the external stimuli.

Detection of the chirality of C alpha-methylated alpha-amino acids with a dynamic helical poly(phenylacetylene) bearing aza-18-crown-6 ether pendants.

A stereoregular poly(phenylacetylene) bearing the aza-18-crown-6 ether pendants (poly-1) was found to form a predominantly one-handed helix upon complexation with optically active C(alpha)-methylated alpha-amino acids and their amide derivatives including typical meteoritic C(alpha)-methylated alpha-amino acids such as C(alpha)-methyl norvaline and C(alpha)-methyl valine. The complexes exhibited an induced circular dichroism (ICD) in the UV-visible region of the polymer backbone. Therefore, poly-1 can be used as a novel probe for detection of the chirality of C(alpha)-methylated alpha-amino acids.

Chiral amplification in macromolecular helicity assisted by noncovalent interaction with achiral amines and memory of the helical chirality.

Poly[(4-carboxyphenyl)acetylene] (poly-1) exhibits an intense induced circular dichroism (ICD) in the UV-visible region upon complexation with excess (R)-1-(1-naphthyl)ethylamine ((R)-2), owing to the formation of a predominantly single-handed helical conformation of the polymer backbone. In the presence of a small amount of (R)-2, poly-1 showed a very weak ICD due to the lack of a single-handed helical conformation. However, we have found that the co-addition of the excess bulky, achiral 1-naphthylmethylamine (5) with a small amount of (R)-2 caused a dramatic increase in the ICD magnitude, comparable to the full ICD induced by excess (R)-2.

Mechanism of helix induction on a stereoregular Poly((4-carboxyphenyl)acetylene) with chiral amines and memory of the macromolecular helicity assisted by interaction with achiral amines.

Cis-transoidal poly((4-carboxyphenyl)acetylene) (poly-1) is an optically inactive polymer but forms an induced one-handed helical structure upon complexation with optically active amines such as (R)-(1-(1-naphthyl)ethyl)amine ((R)-2) in DMSO. The complexes show a characteristic induced circular dichroism (ICD) in the UV-visible region of the polymer backbone. Moreover, the macromolecular helicity of poly-1 induced by (R)-2 can be "memorized" even after complete replacement of (R)-2 by various achiral amines.

Temperature dependence of helical structures of poly(phenylacetylene) derivatives bearing an optically active substituent.

The temperature dependence of the helical conformations for the homopolymers of phenylacetylene derivatives bearing an optically active substituent, such as the (R)-((1-phenylethyl)carbamoyl)oxy and (R)-((1-(1-naphthyl)ethyl)carbamoyl)oxy groups at the phenyl group, and their copolymers with achiral phenylacetylenes were investigated in solution using circular dichroism (CD) and absorption spectroscopies. The magnitude of the induced CD (ICD) of the optically active homopolymers increased with decreasing temperature and was accompanied by a blueshift in their absorption maxima. On the other hand, the copolymers with achiral phenylacetylenes exhibited interesting ICD changes with temperature, depending on the bulkiness of the achiral comonomers.