Power-law solvation dynamics in G-quadruplex DNA: Role of hydration dynamics on ligand solvation inside DNA

G-quadruplex DNA (GqDNA) structures act as promising anticancer targets for small-molecules (ligands). Solvation dynamics of a ligand (DAPI: 4′,6-diamidino-2-phenylindole) inside antiparallel-GqDNA is studied through direct comparison of time-resolved experiments to molecular dynamics (MD) simulation. Dynamic Stokes shifts of DAPI in GqDNA prepared in H₂O buffer and D₂O are compared to find the effect of water on ligand solvation. Experimental dynamics (in H₂O) is then directly compared with the dynamics computed from 65 ns simulation on the same DAPI-GqDNA complex. Ligand solvation follows power-law relaxation (summed with fast exponential relaxation) from ∼100 fs to 10 ns. Simulation results show relaxation below ∼5 ps is dominated by water motion, while both water and DNA contribute comparably to dictate long-time power-law dynamics. Ion contribution is, however, found to be negligible. Simulation results also suggest that anomalous solvation dynamics may have origin in subdiffusive motion of perturbed water near GqDNA.