The relaxation rate R = πΔν_1/2 of the quadrupolar ²³Na nucleus was measured at pH ≊ 7 using a 200 MHz NMR spectrometer with a view to observe the interaction between hyaluronan and its natural counterion Na⁺ and the bications Ca⁺⁺, Mg⁺⁺ and Cu⁺⁺.

An interpretation of our results, by means of the ?entropy of fluctuations? concept of Na⁺, is presented.

We show that Cu⁺⁺ ions are more effective than Ca⁺⁺ and Mg⁺⁺. A possible model of complexation of Cu⁺⁺ in a cage formed by the 1-4 glycosidic bond, the carboxylate side-chain and the acetoamide side-chain is proposed, according to electrostatic potential computations using the ZINDO1 quantum semi empirical method.