Transient chirality inversion during racemization of a helical cobalt(III) complex.

Sakata, Yoko; Chiba, Shunsuke; Akine, Shigehisa · Proc Natl Acad Sci U S A · 2022

basic_science · Level V

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Abstract

SignificanceWe first observed a transient chirality inversion on a simple unimolecular platform during the racemization of a chiral helical complex [LCo<sub>3</sub><b>A</b><sub>6</sub>]<sup>3+</sup>, i.e., the helicity changed from <i>P</i>-rich (right-handed) to <i>M</i>-rich (left-handed), which then racemized to a <i>P</i>/<i>M</i> equimolar mixture in spite of the absence of a reagent that could induce the <i>M</i> helix. This transient chirality inversion was observed only in the forward reaction, whereas the reverse reaction showed a simple monotonic change with an induction time. Consequently, the <i>M</i> helicity appeared only in the forward reaction. These forward and reverse reactions constitute a hysteretic cycle. Compounds showing such unique time responses would be useful for developing time-programmable switchable materials that can control the physical/chemical properties in a time-dependent manner.