Ion-Exchange Kinetics of Alpha-Zirconium Phosphate Nanoplatelets for Application in Targeted Alpha Therapy

The loading and kinetics of uptake for the inorganic ion-exchange material, α-zirconium phosphate, Zr(HPO₄)₂•H₂O, were investigated with ions relevant to targeted alpha therapy including natural Cs⁺ (as a surrogate for ²²¹Fr), natural Bi³⁺ (as a surrogate for ²¹³Bi), and natural La³⁺ (as a surrogate for ²²⁵Ac). The narrow interlayer spacing of the α-phase (d = 7.6 Å) was found not to be advantageous with respect to rapid ion exchange, while converting the material to the hydrated Na-phase (d = 12.2 Å) allowed ion exchange to proceed more quickly, reaching equilibrium in under an hour. High loading was achieved for all three ions, at 72 ± 4% for Cs⁺ and 95 ± 5% for La³⁺ at pH 3 and 108 ± 10% for Bi³⁺ at pH 0.5. Leaching profiles of the loaded materials in a simulated human plasma environment of 10 mM carbonate buffer at pH 7.4 and 37°C, showed negligible release, with less than 1% in all cases. The ion-exchange properties and overall benign nature of zirconium phosphate highlight these materials as a promising platform for a targeted alpha therapy drug-delivery vehicle.