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Open AccessArticle

Citric Acid Tunes the Formation of Antimicrobial Melanin-Like Nanostructures

Department of Chemical, Materials and Production Engineering, University of Naples “Federico II”, p.le V. Tecchio 80, 80125 Naples, Italy
CSGI, Center for Colloid and Surface Science, via della Lastruccia 3, 50019 Sesto Fiorentino (FI), Italy
Department of Biology, University of Naples “Federico II” Via Cintia 4, I-80126 Naples, Italy
Nanofaber Spin-Off at Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA), Casaccia Research Centre, Via Anguillarese 301, 00123 Rome, Italy
Department of Chemical Sciences, University of Naples “Federico II” Via Cintia 4, I-80126 Naples, Italy
Authors to whom correspondence should be addressed.
Biomimetics 2019, 4(2), 40;
Received: 12 February 2019 / Revised: 25 May 2019 / Accepted: 28 May 2019 / Published: 30 May 2019
(This article belongs to the Special Issue Selected Papers from N.I.C.E. 2018)
Nature has provided a valuable source of inspiration for developing high performance multifunctional materials. Particularly, catechol-containing amino acid l-3,4-dihydroxyphenylalanine (l-DOPA) has aroused the interest to design hybrid multifunctional materials with superior adhesive ability. DOPA oxidative polymerization mediated by either melanogenic enzymes or an alkaline environment involving catechol intermolecular cross-linking, ultimately leads to melanin oligomers. Recently, relevant studies disclosed the ability of Ti-based nanostructures to tune melanin’s supramolecular structure during its formation, starting from melanogenic precursors, thus improving both antioxidant and antimicrobial properties. In this work, we propose a novel biomimetic approach to design hybrid DOPA melanin-like nanostructures through a hydrothermal synthesis opportunely modified by using citric acid to control hydrolysis and condensation reactions of titanium alkoxide precursors. UV-Vis and Electron paramagnetic resonance (EPR) spectroscopic evidences highlighted the key role of citrate–Ti(IV) and DOPA–Ti(IV) complexes in controlling DOPA polymerization, which specifically occurred during the hydrothermal step, mediating and tuning its conversion to melanin-like oligomers. Trasmission electron microscopy (TEM) images proved the efficacy of the proposed synthesis approach in tuning the formation of nanosized globular nanostructures, with high biocide performances. The obtained findings could provide strategic guidelines to set up biomimetic processes, exploiting the catechol-metal complex to obtain hybrid melanin-like nanosystems with optimized multifunctional behavior. View Full-Text
Keywords: hybrid nanostructure; melanin-like; citrate–Ti complex; antimicrobial; biomimicry hybrid nanostructure; melanin-like; citrate–Ti complex; antimicrobial; biomimicry
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MDPI and ACS Style

Melone, P.; Vitiello, G.; Di Napoli, M.; Zanfardino, A.; Caso, M.F.; Silvestri, B.; Varcamonti, M.; D’Errico, G.; Luciani, G. Citric Acid Tunes the Formation of Antimicrobial Melanin-Like Nanostructures. Biomimetics 2019, 4, 40.

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