3.4.1. Distribution Coefficient (logD)

To determine the hydrophilicity the distribution of the <sup>68</sup>Ga-labeled conjugates between an organic (octanol) and aqueous (PBS) layer was assessed. Aliquots (50 µL) of the <sup>68</sup>Ga-labeled tracers (~5 µM) were diluted in 1 mL of octanol/PBS (1:1, *v*/*v*) and the mixture was vortexed at 1400 rpm (MS 3 basic vortexer, IKA, Staufen, Germany) for 15 min at RT. Subsequently the mixture was centrifuged for 2 min at 4500 rpm followed by measuring aliquots (50 µL) of both layers in the gamma counter (Wizard<sup>2</sup> 3", Perkin Elmer, Waltham, MA, USA). LogD was calculated using Microsoft Excel (*n* = 3, six replicates).
