How acidic are monomeric structural units of heparin?

Density functional theory methods with the B3LYP functional have been used to study the acidity of carboxylate, O-sulfate and N-sulfate groups in six basic monomeric structural units of heparin (1-OMe ΔUA-2S, 1-OMe GlcN-S6S, 1,4-DiOMe GlcA, 1,4-DiOMe GlcN-S3S6S, 1,4-DiOMe IdoA-2S, and 1,4-DiOMe GlcN-S6S).