Acceleration and deceleration of chirality inversion speeds in a dynamic helical metallocryptand by alkali metal ion binding.
basic_science · Level V
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- Record sourced from PubMed, PMID 37922347.
- Also identified by DOI 10.1126/sciadv.adj5536 and PMC identifier 10624348.
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Abstract
We report that the chirality inversion kinetics of a trinickel(II) cryptand can be controlled by guest recognition in the cryptand cavity. When the guest was absent, the nickel(II) cryptand underwent a dynamic interconversion between the <i>P</i> and <i>M</i> forms in solution, preferring the <i>M</i> form, with a half-life of <i>t</i><sub>1/2</sub> = 4.99 min. The <i>P</i>/<i>M</i> equilibrium is reversed to <i>P</i>-favored by binding with an alkali metal ion in the cryptand cavity. The timescale of this <i>M→P</i> inversion kinetics was both notably accelerated and decelerated by the guest binding (<i>t</i><sub>1/2</sub> = 0.182 min for K<sup>+</sup> complex; 186 min for Cs<sup>+</sup> complex); thus, the equilibration rate constants differed by up to 1000-fold depending on the guest metal ions. This acceleration/deceleration can be explained in terms of the virtual binding constants at the transition state of the <i>P</i>/<i>M</i> chirality inversion; K<sup>+</sup> binding more stabilizes the transition state rather than the <i>P</i> and <i>M</i> forms to result in the acceleration.