4.4. LogP measurements

LogP values were determined using a standard method [46]. Briefly, [¹⁸F]1, [¹⁸F]4, or [¹⁸F]9 (10 μL, 1 μCi) in ethanol was added to a mixture of 1-octanol (1.0 mL) and water (1.0 mL) in test tubes in triplicate. The mixtures in the test tubes were subjected to vortexing for 5 min, which was repeated four times; the mixtures were then subjected to centrifugation (2×5 min, 4000 rpm at 4°C). From each test tube, three aliquots of the 1-octanol layer (50 μL each) were transferred into three gamma-counting tubes (nine tubes total). Similarly, 50-μL aliquots of the aqueous layer were transferred into nine separate test tubes. The amount of radioactivity in each tube was counted using a gamma counter. The partition coefficient (P) was calculated as the ratio of activity in octanol to activity in water. The LogD value was also measured in octanol/PBS (pH 7.4) using the same methodology. In addition, Cheminformatics software (Molinspiration, Slovak Republic) was used to calculate theoretical LogP values for [¹⁸F]1 (4.81), [¹⁸F]4 (6.01), and [¹⁸F]9 (6.94).