Highly efficient stabilisation of meta-ethynylpyridine polymers with amide side chains in water by coordination of rare-earth metals.

Hiroki Makida,Masahiko Inouye,Hajime Abe

doi:10.1039/c4ob02129k

Hiroki Makida, Masahiko Inouye + Show 1 more

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https://doi.org/10.1039/c4ob02129k

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Abstract

An amphiphilic meta-ethynylpyridine polymer with chiral amide side chains was developed. The polymer was prepared by sequential Sonogashira reactions, and the product was soluble in polar and apolar solvents. The additive effects of metal salts on the polymer were examined in water and aqueous EtOH on the basis of UV-vis and CD spectra. The enhancement of the positive Cotton effect and hypochromism around 360 nm occurred by the addition of various metal salts, indicating the coordination of the cations to the amide side chains of the polymer to stabilise the helical structure. Among them, rare-earth metal salts, especially Sc(OTf)3 showed more efficient additive effects probably because of its strong coordination ability even in water. Positive cooperativity was observed for the coordination of Sc(OTf)3 to the polymer in aqueous EtOH.

Highlights

Chiral helical structures are seen in many kinds of biomacromolecules such as proteins, nucleic acids, and polysaccharides
Since Moore and coworkers reported the sophisticated example of meta-phenylene ethynylenes in 1997, solvophobic interactions have been widely used as a driving force for the construction of helical structures of artificial foldamers.[2,3,4]
We have developed meta-ethynylpyridine polymers and oligomers, in which a number of pyridine rings are linked with acetylene bonds at their 2 and 6 positions.[5,6]

Summary

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Efficient stabilisation of metaethynylpyridine polymers with amide side chains. The additive effects of metal salts on the polymer were examined in water and aqueous EtOH on the basis of UV-vis and CD spectra. The enhancement of the positive Cotton effect and hypochromism around 360 nm occurred by the addition of various metal salts, indicating the coordination of the cations to the amide side chains of the polymer to stabilise the helical structure. Rare-earth metal salts, especially Sc(OTf )[3] showed more efficient additive effects probably because of its strong coordination ability even in water. Positive cooperativity was observed for the coordination of Sc(OTf )[3] to the polymer in aqueous EtOH

Introduction

Results and discussion

The spectral change of IR absorption caused by the addition of

Conclusions