K + -Selectivity Due to Coordination with a D 4 d -Symmetric Homochiral Proline Octamer Verified by Mass Spectrometry and Infrared Photodissociation Spectroscopy.

Both phenomena of homochirality and sodium-potassium ion selectivity in cells have been regarded as important issues in the process of the origin of life. However, whether K + /Na + selectivity was involved in homochirogenesis has never been considered. Herein, we report that a homochiral proline octamer shows high K + -selectivity. Coordination of K + results in formation of a stable, noncovalent, D 4 d -symmetric complex, as demonstrated by mass spectrometry, infrared photodissociation spectroscopy, and calculations. A cooperative relationship between an eight-coordinated metal cation and a homochirality-restricted topological hydrogen-bonded proline network is the key for the K + /Na + selectivity. As the complex comprises merely the basic chiral amino acid, it provides a possible linkage between K + /Na + selectivity and the origin of chirality on the prebiotic Earth.