Asymmetric and symmetric stretching vibrational modes of the carboxylate group of sorbed glyphosate were subjected to downward shifts of 4 -24 cm -1 on Mn oxides and BSA-Mn oxide associations whereas interfacial δ(NH2 + ) vibrational modes were shifted to lower energies by 11 -29 cm -1 . Generally, hydrogen bonding lowers the frequency of stretching vibrations by reducing the restoring force, while increasing the frequency of bending vibrations by introducing an additional restoring force. Therefore, glyphosate's amine groups do not contribute to Hbonding in interfacial complexes (Figure ). Although downward shifts were observed to be greater at pH 7.2 and in the presence of BSA, No specific trend was observed in interfacial carboxylate-amine bands of glyphosate adsorbed on K-birnessite and hausmannite. This highlights the fact that H-bonds do not from between glyphosate's carboxylate and amine groups and Mn oxides' hydroxyl groups, and that H-bonds mainly occur in OS complexes (Figure ).