The best-known theory accounting for metal-alginate complexation is the so-called "Egg Box" model. In order to gain greater insight into the metal-saccharide interactions that underpin this model, the coordination chemistry of the corresponding monomeric units of alginate, L-guluronate (GulA) and D-mannuronate (ManA) have been studied herein.GulA andManA were exposed to solutions of different s-block cations and then analysed by¹H and¹³C NMR spectroscopy. It was found that theα/β ratio of the pyranose anomeric equilibria ofGulA showed large pertubations from the starting value (α/β = 0.21 ± 0.01) upon contact with 1.0 M Ca²⁺, Sr²⁺, and Ba²⁺ (α/β = 1.50 ± 0.03, 1.20 ± 0.02, and 0.58 ± 0.02, respectively) at pD 7.9, but remained almost constant in the presence of Na⁺, K⁺, and Mg²⁺ (α/β = 0.24 ± 0.01, 0.19 ± 0.01, and 0.26 ± 0.01, respectively). By comparison, no significant changes were observed in theα/β ratios ofManA and related mono-uronates D-glucuronate (GlcA) and D-galacturonate (GalA) in the presence of all of the metal ions surveyed. Analysis of the¹H and¹³C coordination chemical shift patterns indicate that the affinity of α-GulA for larger divalent cations is a consequence of the unique ax-eq-ax arrangement of hydroxyl groups found for this uronate anomer.