A structural DFT study of MM, GG, MG, and GM alginic acid disaccharides and reactivity of the MG metallic complexes.

The density functional theory method using the B3LYP/6-31G(d,p) level of theory was used to perform isoenergetic maps in order to determine the lower energy conformers of four disaccharides constituting alginic acids, which are based on β-D-mannuronic (M) and α-L-guluronic acid (G), called MM, GG, MG, and GM. The preferred structures are combined to monovalent (Li, Na, and K) cations and further fully optimized, and an isoenergetic map corresponding to the complex (MG, 2Na) was performed. Then, the reactivity of MG complexes with mono- and bivalent cations was studied using the global nucleophilic index. The position selectivity was also predicted using the local nucleophilic indices. It was demonstrated that experimental trends of relative reactivity and regioselectivity of the complexes are correctly predicted using these empirical indices of reactivity. Graphical abstract MM, GG, MG, and GM alginic acid disaccharides and reactivity of the MG metallic complexes.