Figure 6.

Schematic images showing the transition from a weakly hydrogen-bonded network of hyaluronan at pH < 2.5 (top left) to a strongly hydrogen-bonded network at pH = 2.5 (right), to isolated single chains at pH > 2.5 (bottom left). At pH = 2.5, the balance between hydrogen-bond and Coulomb repulsion interactions is optimal, and allows the formation of hydrogen bonds between the carboxyl acid and amide groups observed as the fast time component in the cross-peak dynamics in 2D-IR. Green shaded squares indicate the formation of hydrogen bonds between amide and protonated carboxyl groups, whereas orange shaded squares depict the formation of hydrogen bonds between amide and deprotonated carboxyl groups.