I am working with a lipid and I have firm reasons to believe that its pKa is around 8. This lipid is a cationic lipid where the nitrogen is a quaternary amine with two lipid chains and two methyl groups.
Now, my question is that at a pH above the pKa of this lipid, the quaternary ammonium ion should get deprotonated, or basically act as an acid. But the quaternary ammonium cation doesn't have any protons to lose, so what would happen to it? My guess would be it accepts a lone pair and becomes negatively charged.