Table 8.
Solubilities and calculated pKa for compounds analyzed in rats.
| Compound | λmax EtOH (nm) | εEtOH ([mol/L]−1·cm−1) | λmax 10% EtOH/Water (nm) | ε10% EtOH/Water ([mol/L]−1·cm−1) | Water solubility at 20°C (μmol/L) | pKa[1] Calc'd |
|---|---|---|---|---|---|---|
| 1 | 260 | 17,000 | 260 | 14,000 | 0.28 ± 0.02 | 3.5 |
| 2 | 246 | 17,000 | 243 | 15,000 | 58 ± 1 | −0.4 |
| 4 | 284 | 24,000 | 283 | 18,000 | 7.6 ± 0.1 | 3.9 |
| 7 | 252 | 20,000 | 243 | 19,000 | 49 ± 1 | 1.8 |
| 9 | 221 (sh) | 19,000 | 220 | 25,000 | 67 ± 1 | 1.7 |
| 14 | 252 | 17,000 | 244 | 17,000 | 15 ± 1 | 1.1 |
A 2.0 mmol/L stock solution in ethanol of each compound was made from which ε was determined from a Beer's law plot of dilutions. A 10 μmol/L solution in 10% ethanol/water of each compound was also made by dissolving 0.020 mmol of each compound in 200 mL of ethanol and then diluting to 2 L with water. Dilutions of the 10 μmol/L solution in 10% ethanol/water were made to determine an equation for the Beer's law plot by linear regression. The water solubility of each compound was estimated by solving the linear regression equation from the Beer's law plot for the 10% ethanol/water solutions with the observed absorbance of saturated aqueous solutions of each compound. Water solubility estimates from measured absorbances are shown as the mean ± standard deviation or the last significant digit, whichever is greater.
Calculated pKa values, performed in Gaussian 9.0, using the thermodynamic cycle in Figure1.