Reversed Cation Selectivity of G 8 ‐Octamer and G 16 ‐Hexadecamer towards Monovalent and Divalent Cations

A reverse‐binding‐selectivity between monovalent and divalent cations was observed for two different self‐assembly G 16 ‐hexadecamer and G 8 ‐octamer systems. The dissociation constant between G 4 ‐quadruplex and monomer was calculated via VT‐ 1 H NMR experiments. Quantitative energy profiles revealed entropy as the key factor for the weaker binding toward Ba 2+ compared with K + in the G 8 ‐octamer system despite stronger ion‐dipole interactions. This study is the first direct comparison of the G 4 ‐quartet binding affinity between mono and divalent cations and will benefit future applications of G‐quadruplex‐related research. Further competition experiments between the G 8 ‐octamer and 18‐crown‐6 with K + demonstrated the potential of this G 8 system as a new potassium receptor.