Binding of Glyphosate by Open-chain Polyammonium Cations

Interaction of glyphosate (N-(phosphonomethyl)-glycine) with six polyamines (ethylendiamine, cadaverine, putrescine, triethylenetetramine, spermine, and tetraethylenepentamine) was studied potentiometrically. Several species of different stoichiometry are formed in the various systems, according to the general formation reaction i1 (j 2 3) (i 1 j 2 3) AH 1 H (glp) 5 A(glp)H i j i 1 j (where A 5 amine and glp 5 glyphosate). The complex species formed are always A(glp)Hr 2 3) with r 5 1 . . . (n 1 2) (n 5 maximum degree of protonation of amines). The stability of various complexes is a linear function of charges involved in the formation reaction, and can be expressed as logKij 5 0.9(60.2)z (where z 5 i[3 2 j]). From the temperature dependence of formation constants, DH0 (and TDS0) values have been obtained. Formation percentages of mixed glyphosate–polyammonium cation complexes are relevant also in low concentration conditions, and this means that these species may play a significant role in the speciation of natural fluids containing the reactants. Keywords—Amine–glyphosate complexes Pesticides Amines Anion coordination chemistry Glyphosate speciation