Hi!

My compound, Tacrolimus, has 3 pKa (2.94, 9.95 and 14.07). Even based on the structure, I am not entirely sure if it is acidic or basic (though I am leaning towards acidic as it has ketone groups). I am not sure how to use the Henderson-Hasselbalch equation to calculate the percentage unionised at pH 4.5 considering that it has 3 pKa. Does anyone know how to calculate?

Thank you!