Shape and Size Tuning of Bi<sup>III</sup>-Centered Polyoxopalladates: High Resolution <sup>209</sup>Bi NMR and <sup>205/206</sup>Bi Radiolabeling for Potential Pharmaceutical Applications
Paulami Manna, Dániel Szücs, Tibor Csupász, Anikó Fekete, Dezső Szikra, Zhengguo Lin, Attila Gáspár, Saurav Bhattacharya, Alexandra Zulaica, Imre Tóth, Ulrich Kortz
Abstract
We have discovered five bismuth(III)-containing polyoxopalladates (POPs) which were fully characterized by solution and solid-state physicochemical techniques: the cube-shaped [BiPd12O32(AsPh)8]5– (BiPd12AsL), [BiPd12O32(AsC6H4N3)8]5– (BiPd12AsLN), and [BiPd12O32(AsC6H4COO)8]13– (BiPd12AsLC) as well as the star-shaped [BiPd15O40(PO)10H6]11– (BiPd15P) and [BiPd15O40(PPh)10]7– (BiPd15PL), respectively. The organically modified capping groups phenylarsonate, p-azidophenylarsonate, and p-carboxyphenylarsonate were chosen as the azido (−N3) and carboxyl (−COOH) groups open up opportunities to covalently conjugate (via click reaction, amide coupling, etc.) with targeting vectors. The synthesis of p-azidophenylarsonate is reported here for the first time. The effects of the BiIII template and the organoarsonate vs −posphonate capping groups on the resulting POP shape (cube vs star) are discussed. The 209Bi NMR (I = 9/2) spectra of BiPd12AsL, BiPd12AsLN, and BiPd12AsLC revealed narrow peaks (ν1/2 ∼ 200 Hz) at 5470 ppm with a longitudinal relaxation time in the millisecond range (at 8.46 T). The absence of a quadrupolar relaxation contribution could be attributed to the allocation of BiIII in the highly symmetrical cuboid POP host cage. Similar peaks were absent in the 209Bi-NMR spectra of the star-shaped POPs BiPd15P and BiPd15PL due to the less symmetric coordination environment around the central BiIII ion. Further, 205/206Bi-radiolabeled POPs have been synthesized by incorporating a 205/206BiIII ion in the center of the POP structures. Carrier-free 205/206Bi radioisotopes (as surrogates of α-emitting 213Bi) were incorporated into the POP host-cage for the preparation of 205/206BiPd12AsL, 205/206BiPd12AsLN, 205/206BiPd12AsLC, and 205/206BiPd15PL, respectively. The radiometal incorporation was complete (>99% radiochemical yield) in 10 min according to radio-thin-layer chromatography. The 205/206BiPd12AsL polyanion was purified by solid-phase extraction. The incubation in rat serum showed the formation of a 205/206BiPd12AsL–protein aggregate.