Dopamine‐Based Coatings and Hydrogels: Toward Substitution‐Related Structure–Property Relationships

Abstract

The influence of 6-chloro and 6-nitro substituents on the thickness, homogeneity, and general properties of coatings produced by controlled oxidative polymerization of dopamine and its beta-hydroxy derivative, norepinephrine, is investigated. Substitution at the catecholamine 6-position affects the deposition kinetics due to modification of the oxidation potential of the catechol groups. Increasing the hydroxyl group acidity results likewise in changes in pH response and water uptake. A similar trend with pH is also observed in covalently crosslinked catechol-functionalized PEG-hydrogels, while an opposite behavior is measured in metal crosslinked films. These results pave the way toward the definition of structure-property relationships based on dopamine substitution effects in polycatecholamine layers and derived polymers

Chemistry of polydopamine analogues

“…The deposition kinetics, thickness, swelling properties and pH responsivity of films and hydrogels obtained by polymerization of DA, norepinephrine and their 6‐substituted nitro and chloro derivatives (Scheme ) were investigated in order to reveal the effect of electron withdrawing substituents in position 6 of the DA skeleton …”

“…6‐substituted derivatives of dopamine and norepinephrine, suggested intermediates in the oxidative polymerization of 6‐nitrodopamine, 5‐aminoethylpyrogallol …”

“…Furthermore, it was found that 6‐nitrodopamine under working pH formed zwitterionic forms of poly(6‐nitrodopamine). It was believed that the lower reactivity of chloro and nitro derivatives of PDA was due to electronic and steric factors since electron withdrawing substituents could decrease the π‐electron delocalization and lower the oxidation potential of monomers . In addition, blocking of the 6‐position could also inhibit nucleophilic addition and coupling reactivity as well as intramolecular cyclization of the quinones with side chain amine resulting in DHIs .…”

“…It was believed that the lower reactivity of chloro and nitro derivatives of PDA was due to electronic and steric factors since electron withdrawing substituents could decrease the π‐electron delocalization and lower the oxidation potential of monomers . In addition, blocking of the 6‐position could also inhibit nucleophilic addition and coupling reactivity as well as intramolecular cyclization of the quinones with side chain amine resulting in DHIs . Reaction pathways were proposed for such 6‐substituted derivatives wherein a cyclization to indole moieties does not occur via position 6 but via position 2 and several units were linked by O‐bridges (Scheme ) .…”

Smart Polymers for Biomedical Applications

“…Differences in the behavior of polymers containing oligo(ω-pentadecalactone) segments only, in contrast to PDLCL, are discussed and mainly attributed to the higher polarity and abundance of hydrogen bonds in the case of the oligo(ε-caprolactone) segments, of methyl groups, meaning the replacement of glycolide units by lactide units in poly(glycolide -colactide)s (PLGA) changes the thermal, mechanical, swelling, and degradation properties of these copolyesters. This strategy of replacement has been followed by Cui et al [ 7 ] in their paper "Dopamine-Based Coatings and Hydrogels: Towards Substitution-Related Structure-Property Relationships". Herein, the authors describe an active hydrogel system on the basis of poly(catecholamine)s, which is able to respond to pH changes by uptaking/releasing water (swelling/deswelling).…”