23Na NMR Study of the Interaction between Hyaluronan and the bications Ca++, Mg++ and Cu++

The relaxation rate R = pi Deltav(1/2) of the quadrupolar Na-23 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.