Hanbin Mao

8‐oxoguanines (8‐oxoG) in cells form compromised G‐quadruplexes (GQs), which may vary GQ mediated gene regulations. By mimicking molecularly crowded cellular environment using 40% DMSO or sucrose, here it is found that oxidized human telomeric GQs have stabilities close to the wild‐type (WT) GQs. Surprisingly, while WT GQs show negative formation cooperativity between a Pt(II) binder and molecularly crowded environment, positive cooperativity is observed for oxidized GQ formation. Single‐molecule mechanical unfolding reveals that 8‐oxoG sequence formed more diverse and flexible structures with faster folding/unfolding transition kinetics, which facilitates the Pt(II) ligand to bind the best‐fit structures with positive cooperativity. These findings offer new understanding on structures and properties of oxidized G‐rich species in crowded environments. They also provide insights into the design of better ligands to target oxidized G‐rich structures formed under oxidative cell stress.