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Biomimetics 2018, 3(3), 26;

The Chemistry of Polydopamine Film Formation: The Amine-Quinone Interplay

Department of Chemical Sciences, University of Naples Federico II, Via Cinthia 4, I-80126 Naples, Italy
Department of Physics “Ettore Pancini”, University of Naples Federico II, Via Cinthia 4, I-80126 Naples, Italy
Institute for Polymers, Composites and Biomaterials, National Council of Research of Italy (IPCB-CNR), via Campi Flegrei 34, I-80078 Pozzuoli, Italy
Author to whom correspondence should be addressed.
Received: 31 July 2018 / Revised: 5 September 2018 / Accepted: 5 September 2018 / Published: 13 September 2018
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Despite extensive investigations over the past decade, the chemical basis of the extraordinary underwater adhesion properties of polydopamine (PDA) has remained not entirely understood. The bulk of evidence points to PDA wet adhesion as a complex process based on film deposition, and growth in which primary amine groups, besides catechol moieties, play a central role. However, the detailed interplay of chemical interactions underlying the dynamics of film formation has not yet been elucidated. Herein, we report the results of a series of experiments showing that coating formation from dopamine at pH 9.0 in carbonate buffer: (a) Requires high dopamine concentrations (>1 mM); (b) is due to species produced in the early stages of dopamine autoxidation; (c) is accelerated by equimolar amounts of periodate causing fast conversion to the o-quinone; and (d) is enhanced by the addition of hexamethylenediamine (HMDA) and other long chain aliphatic amines even at low dopamine concentrations (<1 mM). It is proposed that concentration-dependent PDA film formation reflects the competition between intermolecular amine-quinone condensation processes, leading to adhesive cross-linked oligomer structures, and the intramolecular cyclization route forming little adhesive 5,6-dihydroxyindole (DHI) units. Film growth would then be sustained by dopamine and other soluble species that can be adsorbed on the surface. View Full-Text
Keywords: polydopamine; polymerization; film; quinone; periodate; amines polydopamine; polymerization; film; quinone; periodate; amines

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Alfieri, M.L.; Panzella, L.; Oscurato, S.L.; Salvatore, M.; Avolio, R.; Errico, M.E.; Maddalena, P.; Napolitano, A.; D’Ischia, M. The Chemistry of Polydopamine Film Formation: The Amine-Quinone Interplay. Biomimetics 2018, 3, 26.

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