Figure 5.

Translational diffusion of sodium ions measured in heparin samples through ²³Na or ¹H-based pulse field gradient NMR diffusion experiments. (a,b) Gradient-dependent decrease in the intensity of ²³Na NMR signals in sodium heparin samples in the presence of 100 mM CaCl₂ or MgCl₂, as well as in the reference NaCl sample. Due to the fast relaxation of ²³Na signals in the sodium heparin sample without added ions and the severe loss of ²³Na signal intensity, no ²³Na NMR diffusion experiment could be conducted for this sample. Instead, as shown in (b), the diffusion coefficient of sodium ions in the heparin-bound form was estimated through a ¹H-based NMR diffusion experiment, assuming that the heparin molecules and sodium ions are rigidly bound and diffuse together. (c) The obtained translational diffusion coefficients (D_tr) of sodium ions in the measured samples. The diffusion data are consistent with the partial release of sodium ions from heparin after the addition of Mg²⁺ and especially Ca²⁺ ions.