Poly[3,4-dihydroxybenzhydrazide]: A Polydopamine Analogue?

3,4-Dihydroxybenzhydrazide (DHBH) could be considered a structural analogue of dopamine, forming polymers under oxidative conditions in a polydopamine (PDA) fashion. However, the former turns out to be more reluctant to oxidize and thus, more drastic conditions must be applied to achieve polymerization. Heating of DHBH in the presence of ammonium peroxydisulfate in Tris buffer yields a mixture of oligomers (average 9-10 monomer units). Although it looks black like PDA, its structure is very different. The polymer is not built up by CC bond formation but by replacement of hydroxyl groups resulting in acylhydrazine, acylhydrazone, and 1,3,4-oxadiazoline bridging. Since the catechol moiety of the starting material is destroyed, the polymer lacks the mussel-like anchoring property found in PDA.