Interaction between G-Quadruplex and Zinc Cationic Porphyrin: The Role of the Axial Water.

The interaction of ligands with G-quadruplexes has attracted considerable attention due to its importance in molecular recognition and anticancer drugs design. Here, we utilize triplet excited state as a sensitive reporter to study the binding interaction of zinc cationic porphyrin (ZnTMPyP4) with three G-quadruplexes, AG(TAG), (GTG)2, and (TGT)4. By monitoring the triplet decay dynamics of ZnTMPyP4 with transient absorption spectroscopy, the coexisted binding modes via π-π stacking of porphyrin macrocycle and the G-quartets are allowed to be identified quantitatively, which involve intercalation (25% and 36%) versus end-stacking (75% and 64%) for AG(TAG) and (GTG)2, and end-stacking (23%) versus partial intercalation (77%) for (TGT)4.