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PSA structure. (A) Chemical composition of one tetrasaccharide repeating unit of PSA, illustrating the chemical modifications to eliminate the negatively charged free amine (red) and the negatively charged carboxylate (blue) with acetic anhydride and carbodiimide reduction, respectively. (B) Stereo ball-and-stick average solution structure of PSA using coordinates determined by the NMR spectroscopy, showing the right-handed helical conformation (Wang et al. 2000).
