Real-time Monitoring Excitation Dynamics of Human Telomeric Guanine Quadruplexes: Effect of Folding Topology, Metal Cation, and Confinement by Nanocavity Water Pool.

Guanine(G)-rich human telomeric (HT) DNA repeats, crucial to maintenance of genome stability, readily form G-quadruplexes (GQs) with various folding topologies. Research on excitation dynamics of HT-GQs is, however, scarce. Herein, we report a femtosecond time-resolved fluorescence coupled with transient absorption investigation on HT-GQ with the basket-type structure in Na+ solution. The result unveils an unusual multichannel nonradiative mechanism dominated by states with varying character of charge transfer lasting ten and hundreds of picoseconds, accounting altogether for an overwhelming ∼85% of the overall deactivation involving proton transfer. Our comparative study shows that encapsulating the GQ in nanocavity water pool or changing it into hydrid-type topologies with the presence of K+ ions alter differently energies and lifetimes of these states, yet without affecting the nature of the electronic excitation involved. The finding of this work underscores a leading role of structural rigidity in regulating the interplay with the microenvironment of photoexcited monomolecularly folded HT-GQs.