Determination of partition coefficients (log P)

The partition coefficient (log P) for each complex was determined by adding 5 μL of each ⁸⁹Zr-labeled complex (5 μCi; 0.19 MBq) to a mixture of 500 μL of octanol and 500 μL of water [41]. The resulting solutions (n = 8) were vigorously vortexed for 5 min at room temperature and then centrifuged for 5 min to ensure complete layer separation. From each sample, a 50 μL aliquot was removed from each phase. Radioactivity in each phase was counted separately in a gamma counter. Each organic phase was washed with water before gamma counting. The partition coefficient was calculated as a ratio of counts in the octanol fraction to counts in the water fraction. The log P values were reported as an average of four measurements (S2 Table).