Guanidinium-appended γ-cyclodextrin: efficient fullerene solubiliser for enhanced photodynamic therapy†

Efficient solubilisation of fullerenes in aqueous media is crucial for their photodynamic therapy (PDT) applications. We demonstrated the efficacy of guanidinium-appended γ-cyclodextrin (CD^Gu) as a novel solubiliser for C₆₀ and C₇₀ fullerenes, achieving exceptionally high aqueous concentrations of 3.1 mM and 0.37 mM, respectively, through simple mechanical mixing in the presence of Na⁺ ions. The resulting complexes, CD^Gu⊃C₆₀ and CD^Gu⊃C₇₀, enabled efficient fullerene transfer to cell membranes, a critical factor for PDT efficacy. Notably, CD^Gu⊃C₇₀ exhibited excellent singlet oxygen (¹0₂) generation (quantum yield Φ_Δ = 0.77 at 630 nm) and induced >90% cell death with only 5 min of white light exposure in vitro. This research highlights the importance of molecular dispersion in enhancing fullerenes’ photosensitising activity and membrane transfer, potentially advancing fullerene-based PDT approaches.