The pH behavior of a 2-aminoethyl dihydrogen phosphate zwitterion studied with NMR-titrations

In this study a bifunctional 2-aminoethyl dihydrogen phosphate (AEPH2) was 1H and 31P NMR characterized in a pH range of 1–12 in order to determine the zwitterion properties in different pH regions in H2O and D2O solutions. NMR was also used to determine the pH range where AEPH2 exists as a zwitterion. The phosphate group has two deprotonation points, around pH 1 and 6, while the amino group deprotonates at pH 11. The zwitterion form of AEPH2 (NH3+CH2CH2OPO3H-) exists as the main ion between pH 1 and 6 in water solutions and also in the solid state.

► 2-Aminoethyl dihydrogen phosphate (AEPH2) exists as zwitterion in water solutions.
► AEPH2 has the zwitterionic form in the pH range of between 1 and 5.
► Phosphate group of AEPH2 deprotonates at pH 1.0 and 5.9.
► Amino group of AEPH2 deprotonates at pH 11.0.
► AEPH2 exists in the zwitterionic structure in solid state.