Studies of the Binding of Calcium and Lanthanum Ions to D-Lyxose and D-Ribose in Aqueous Solutions Using Proton Magnetic Resonance

Aldoses having a cis arrangement of three consecutive hydroxyl groups in one of their tautomeric species form weak complexes with metal ions in aqueous solution. Procedures are outlined for the analysis of proton NMR data obtained for solutions containing aldoses and metal ions in two particular systems: the case in which the aldose exists primarily in two anomeric forms, one of which binds to metal ions, and the system in which the aldose exists in all four anomers of which only one does not interact with metal ions. The first method was used in the analysis of data obtained for the interactions of D-lyxose with LaCl₃, La(ClO₄)₃, and CaCl₂. The second method was applied to data obtained for the interaction of D-ribose with LaCl₃ and CaCl₂. From these analyses it is found that predominantly 1:1 metal-sugar complexes are formed in aqueous solution. The results presented confirm the suggestion that metal complexation occurs with the pyranose in a conformation which has an axeq-ax arrangement of the three consecutive cis-hydroxyl groups.