AAAA–DDDD Quadruple H‑Bond-Assisted Ionic Interactions: Robust Bis(guanidinium)/Dicarboxylate Heteroduplexes in Water

The use of geminal di­(guanidinium) and acridin-9­(10H)-one-derived di­(carboxylate) derivatives (1a–c and 2a–e, respectively) allows stabilization of heterodimers characterized by high binding affinities in water (maximum ΔG < −7 kcal mol^–1, K_a > 10⁵ M^–1) as inferred from UV–vis spectroscopic titrations and ITC measurements, therefore rivaling or surpassing the interaction energy between the strongest DNA or RNA triplet pairs. These duplexes are readily accessible and are structurally modifiable, rendering them attractive as building blocks for creating heteroduplex constructs. Incorporating poly­(ethylene glycol)-decorated benzyl groups into the dicarboxylate, allows formation of hydrogels in the case of 1b–2c.