Acid—Base Properties of the Reaction Product of Sialic Acid with Fluorogenic Reagent, 1,2‐Diamino‐4,5‐methylenedioxybenzene (DMB).

Abstract N-Acetylneuraminic acid (Neu5Ac) forms the highly fluorophoric quinoxalinone derivative (Q) when treated with 1,2-diamino-4,5-methylenedioxybenzene (DMB). Effects of protonation and deprotonation on the fluorescence of Q were examined at room temperature. The strong fluorescence was found to be caused by the neutral form Q but not the protonated form of its excited state [Q]* and at pH below 1 the emission was completely quenched. The deprotonated singlet form [Q−]* was a less efficient fluorescer than [Q]*.