Interaction of polyelectrolyte complex between sodium alginate and chitosan dimers with a single glyphosate molecule: A DFT and NBO study.

The formation of a polyelectrolyte complex through dimers of alginate and chitosan in the presence of sodium cations (SA/CS), and its interaction with the glyphosate herbicide, has been investigated at the DFT level (B3LYP/6‒311+G(d,p)). The lowest energy structure for SA/CS presents one Na+ cation coordinated to both dimers and formation of two H-bonds involving COO- and NH3+. The coordination energy of Na+ contributes with about 40% of the total complex stabilization energy. LMOEDA method indicates important contribution of covalent nature to stabilization of SA/CS. This result is corroborated by NBO analysis which shows high contribution of lp(O)→σ*(NH) overlapping, with average energy of 30 kcal mol-1 for the formed H-bonds. Two water molecules neighboring the complex increases its stability and promotes an octahedral coordination arrangement around Na+. The glyphosate interacts with SA/CS coordinating to Na+ and bonding to the chitosan dimer by H-bond, in agreement to performed fluorescence microscopy measurements.