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Molecules 2016, 21(11), 1583; doi:10.3390/molecules21111583

Temperature-Triggered Switchable Helix-Helix Inversion of Poly(phenylacetylene) Bearing l-Valine Ethyl Ester Pendants and Its Chiral Recognition Ability

1
Polymer Materials Research Center, Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China
2
Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan
3
Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
*
Authors to whom correspondence should be addressed.
Academic Editor: Derek J. McPhee
Received: 10 October 2016 / Revised: 15 November 2016 / Accepted: 16 November 2016 / Published: 21 November 2016
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Abstract

A phenylacetylene containing the l-valine ethyl ester pendant (PAA-Val) was synthesized and polymerized by an organorhodium catalyst (Rh(nbd)BPh4) to produce the corresponding one-handed helical cis-poly(phenylacetylene) (PPAA-Val). PPAA-Val showed a unique temperature-triggered switchable helix-sense in chloroform, while it was not observed in highly polar solvents, such as N,N′-dimethylformamide (DMF). By heating the solution of PPAA-Val in chloroform, the sign of the CD absorption became reversed, but recovered after cooling the solution to room temperature. Even after six cycles of the heating-cooling treatment, the helix sense of the PPAA-Val’s backbone was still switchable without loss of the CD intensity. The PPAA-Val was then coated on silica gel particles to produce novel chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). These novel PPAA-Val based CSPs showed a high chiral recognition ability for racemic mandelonitrile (α = 2.18) and racemic trans-N,N′-diphenylcyclohexane-1,2-dicarboxamide (α = 2.60). Additionally, the one-handed helical cis-polyene backbone of PPAA-Val was irreversibly destroyed to afford PPAA-Val-H by heating in dimethyl sulfoxide (DMSO) accompanied by the complete disappearance of the Cotton effect. Although PPAA-Val-H had the same l-valine ethyl ester pendants as its cis-isomer PPAA-Val, it showed no chiral recognition. It was concluded that the one-handed helical cis-polyene backbone of PPAA-Val plays an important role in the chiral recognition ability. View Full-Text
Keywords: helical poly(phenylacetylene); temperature-triggered; helix-helix inversion; chiral stationary phases; cis-to-trans isomerization helical poly(phenylacetylene); temperature-triggered; helix-helix inversion; chiral stationary phases; cis-to-trans isomerization
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Zhou, Y.; Zhang, C.; Qiu, Y.; Liu, L.; Yang, T.; Dong, H.; Satoh, T.; Okamoto, Y. Temperature-Triggered Switchable Helix-Helix Inversion of Poly(phenylacetylene) Bearing l-Valine Ethyl Ester Pendants and Its Chiral Recognition Ability. Molecules 2016, 21, 1583.

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