Figure 1From: Crystal structure and characterization of pyrroloquinoline quinone disodium trihydrateChemical structure of PQQ. Sodium interacts with the oxygen present at the underlined position . (a) PQQ disodium trihydrate. 2- and 7-COOH groups take anion forms (2- and 7-COO-). (b) PQQ disodium pentahydrate. Two crystallographically independent conformation PQQ.Back to article page