Thermodynamics of the Protonation of an Analogue of Glyphosate, N -(phosphonomethyl)- l -proline, in Aqueous Solutions

N -(phosphonomethyl)- l -proline is an analogue of glyphosate. The protonation for N -(phosphonomethyl)- l -proline was studied by potentiometry, calorimetry, 31 P NMR spectroscopy and quantum chemical calculations to further understand the protonation process of glyphosate. The results confirmed that the order of successive protonation sites of totally deprotonated N -(phosphonomethyl)- l -proline are a phosphonate oxygen, amino nitrogen, and finally the carboxylate oxygen. The results can improve the understanding of the biological activity of these types of molecules in solution.