Replacing amine by azide: dopamine azide polymerization triggered by sodium periodate

Polydopamine (PDA) has been widely described for a range of biomedical and surface engineering applications. However the structure of PDA remains elusive owing to the insoluble nature of the polymer. Furthermore, the influence of the amine group present in the polydopamine and related functional polycatchols on the character and the structure of resulting functional materials remains vague. Here we perform polymerization of the dopamine analogue 4-(2-azidoethyl)benzene-1,2-diol (dopamine azide), where the amine group is switched to azide, using sodium periodate, which gives rise to particles with a diameter of up to one micrometer. The obtained particles are stable in water but, in contrast to other polycatcechol-based polymers, are soluble in organic solvents. The detailed structural investigations using various liquid and solid-state nuclear magnetic resonance (NMR) spectroscopy methods, X-ray photoelectron spectroscopy (XPS) and mass spectrometry (ESI/MALD) prove that the obtained polymeric material consists mainly of repeating monomers linked by C–C bonds of aromatic units bearing open-azidoethyl chains. Moreover, the resulting polymer shows a different morphology from polydopamine (PDA) obtained under the same polymerization conditions. Therefore, our results are an important step towards understanding the relationships between the structures of the starting catechol monomers and shed new light on the influence of the amine group on the nature of the resulting poly(catechols).