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@ARTICLE{Arzillo:22273,
      author       = {Arzillo, M. and Mangiapia, G. and Pezzella, A. and Heenan,
                      R.K. and Radulescu, A. and Paduano, L. and $d\\'Ischia,$ M.},
      title        = {{E}umelanin {B}uildup on the {N}anoscale: {A}ggregate
                      {G}rowth/{A}ssembly and {V}isible {A}bsorption {D}evelopment
                      in {B}iomimetic 5,6-{D}ihydroxyindole {P}olymerization},
      journal      = {Biomacromolecules},
      volume       = {13},
      issn         = {1525-7797},
      address      = {Columbus, Ohio},
      publisher    = {American Chemical Soc.},
      reportid     = {PreJuSER-22273},
      pages        = {2379 - 2390},
      year         = {2012},
      note         = {This work was carried out in the frame of the EuMelaNet
                      project (http://www.esper.org/eumelanet/). Financial support
                      by MIUR, PRIN 2008 project, is gratefully acknowledged. We
                      thank the Julich Centre for Neutron Science and the
                      Rutherford Appleton Laboratory for provision of beam time.
                      SANS experiments were supported by the European Commission,
                      NMI3 contract RII3-CT-2003-505925.},
      abstract     = {Establishing structure-property relationships in the black
                      insoluble eumelanins, the key determinants of human
                      pigmentation and skin photoprotective system, is a
                      considerable conceptual and experimental challenge in the
                      current drive for elucidation of the biological roles of
                      these biopolymers and their application as advanced
                      materials for organoelectronics. Herein, we report a new
                      breakthrough toward this goal by the first detailed
                      investigation on the nanoscale level of the oxidative
                      polymerization of 5,6-dihydroxyindole (DHI), a model process
                      of eumelanin synthesis. On the basis of a combined use of
                      spectrophotometry, dynamic light scattering (DLS), and
                      small-angle neutron scattering (SANS) investigations, it was
                      possible to unveil the dynamics of the aggregation process
                      before precipitation, the key relationships with visible
                      light absorption and the shape of fundamental aggregates.
                      The results indicated a polymerization mechanism of the
                      type: Polymer(n) + DHI(x) = Polymer(n+x), where DHI(x)
                      indicates monomer, dimer, or low oligomers (x ≤ 5). During
                      polymerization, visible absorption increases rapidly,
                      reaching a plateau. Particle growth proceeds slowly, with
                      formation of 2-D structures ~55 nm thick, until
                      precipitation occurs, that is, when large aggregates with a
                      maximum hydrodynamic radius (R(h)) of ~1200 nm are formed.
                      Notably, markedly smaller R(h) values, up to ~110 nm, were
                      determined in the presence of poly(vinyl alcohol) (PVA) that
                      was shown to be an efficient aggregation-preventing agent
                      for polymerizing DHI ensuring water solubilization. Finally,
                      it is shown that DHI monomer can be efficiently and
                      partially irreversibly depleted from aqueous solutions by
                      the addition of eumelanin suspensions. This behavior is
                      suggested to reflect oxidant-independent competing pathways
                      of polymer synthesis and buildup via monomer conversion on
                      the active aggregate surface contributing to particle
                      growth. Besides filling crucial gaps in DHI polymerization,
                      these results support the attractive hypothesis that
                      eumelanins may behave as a peculiar example of living
                      biopolymers. The potential of PVA as a powerful tool for
                      solution chemistry-based investigations of eumelanin
                      supramolecular organization and for technological
                      manipulation purposes is underscored.},
      keywords     = {J (WoSType)},
      cin          = {ICS-1 / JCNS (München) ; Jülich Centre for Neutron
                      Science JCNS (München) ; JCNS-FRM-II / JCNS-1},
      ddc          = {540},
      cid          = {I:(DE-Juel1)ICS-1-20110106 /
                      I:(DE-Juel1)JCNS-FRM-II-20110218 /
                      I:(DE-Juel1)JCNS-1-20110106},
      pnm          = {BioSoft: Makromolekulare Systeme und biologische
                      Informationsverarbeitung (FUEK505) / 544 - In-house Research
                      with PNI (POF2-544)},
      pid          = {G:(DE-Juel1)FUEK505 / G:(DE-HGF)POF2-544},
      experiment   = {EXP:(DE-MLZ)KWS2-20140101},
      shelfmark    = {Biochemistry $\&$ Molecular Biology / Chemistry, Organic /
                      Polymer Science},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:22651227},
      UT           = {WOS:000307422300020},
      doi          = {10.1021/bm3006159},
      url          = {https://juser.fz-juelich.de/record/22273},
}