Protonation States of Glufosinate in Aqueous Solution

Glufosinate, an analogue of glutamic acid (also known as phosphinothricin), is an important herbicide. The protonation constants of glufosinate were determined by means of potentiometric titrations at variable temperatures with ionic strength 0.5 mol·L −1 (NaCl solution). The heat effects of the protonation reactions of glufosinate were measured by direct calorimetry. NMR spectroscopies have demonstrated that the first protonation site occurs on the nitrogen atom in the amino group, followed by one of the oxygen atoms in the phosphono group, and finally the carboxyl oxygen atom. This trend is in good agreement with the enthalpy of protonation and crystal structure results. These data will help to predict the speciation of glufosinate in physiological systems.