Different chemical shifts of protons of C-8 in xanthine based on the DFT calculations.
| Sample | Xanthine | Xanthine ion | FCST | Xanthine solution at pH = 7.4a | FCST and xanthineb |
|---|---|---|---|---|---|
| Chemical shift of H(8) in xanthine | 7.510 | 7.380 | 7.530 | 7.449 | 7.519 |
a
A solution consisting of 46.8% xanthine ion and 53.2% un-ionized xanthine molecule (xanthine molecule and xanthine ion content based on calculations of pKa1 values of xanthine at pH = 7.4).
b
A solution consisting of 46.8% FAST and 53.2% un-ionized xanthine molecule based on the assumption that all urate ions are docked by xanthine ions (xanthine molecule and xanthine ion content based on calculations of pKa1 values of xanthine at pH = 7.4).