Figure 2.

²³Na NMR spectral changes of sodium heparin caused by the addition of Ca²⁺ ions and the consequent release of sodium ions from heparin. (a) Upon titration of sodium heparin with 0 to 100 mM CaCl₂, the ²³Na chemical shift gets narrower and moves downfield towards the chemical shift of the reference NaCl sample (see Figure 1). (b) Changes in the ²³Na signal linewidth in dependence of added Ca²⁺ ion concentration, showing a monotonic decrease approaching a value slightly larger than the linewidth of the reference NaCl sample (represented by the dashed line). The spectra shown in (a) are re-scaled according to their peak intensities. The error bars in (b) are comparable in size to the symbols and, therefore, barely visible.