Publications

@article{torriani2009low,
title = {Low resolution structure of synthetic melanin aggregates in aqueous solutions and organic solvents},
author = {Torriani, IL and Silva, JC and Autreto, PAS and Galvao, DS and Caldas, MJ and Graeff, CFO},
url = {http://journals.iucr.org/a/issues/2008/a1/00/a39972/a39972.pdf},
year = {2009},
date = {2009-01-01},
journal = {Acta Crystalographica A},
volume = {64},
pages = {C552},
abstract = {In an effort to find out details of the melanin fundamental structural
unit, a great amount of information has been gathered using
several techniques. The local short range order of the melanin
molecular clusters has been described as consisting of five to seven
5,6-indolequinone units, arranged in planes which are pi-stacked
with a spacing of 0.34 nm. Typical cluster size is 1.5-2.0 nm in
lateral dimensions and 1.0 nm; in height. Nonetheless, structural
details and dimensions of the aggregates are still not clearly defined
and experiments did not answer the key question concerning the
identification of the fundamental melanin protomolecule. More
recently, small angle scattering of X-rays (SAXS) and neutrons
(SANS) were performed. Several authors used these techniques,
which are well designed to study macromolecules in solution to
find details of melanin-copper ions interaction as well as chemical
bleaching effects. A diversity of aggregated structures were proposed
for these nanoscaled particles based on size and apparent shape.
In this presentation we report the results of SAXS experiments
performed with melanin synthetized from L-dopa and L-tyrosine in
organic solvents, which were reported to be very effective for thin
film formation. Water-based synthetic melanin was also studied
for comparison purposes, since molecular aggregation behavior is
known to vary with the route used for the synthesis. Reliable data
was obtained for the water-based and DMSO dispersions. Data
analysis was performed by conventional IFT methods and the overall
shape and dimensional parameters of the melanin particles were
obtained. Using ab-initio calculations, a low resolution 3D model is
proposed for the basic melanin particle in aqueous media and DMSO.},
keywords = {Melanin, Structure},
pubstate = {published},
tppubtype = {article}
}

@article{lorite2006synthetic,
title = {Synthetic melanin films: Assembling mechanisms, scaling behavior, and structural properties},
author = {Lorite, Gabriela S and Coluci, Vitor R and da Silva, Maria Ivonete N and Deziderio, Shirlei N and Graeff, Carlos Frederico O and Galvao, Douglas S and Cotta, Monica A},
url = {http://scitation.aip.org/content/aip/journal/jap/99/11/10.1063/1.2200401},
year = {2006},
date = {2006-01-01},
journal = {Journal of Applied Physics},
volume = {99},
number = {11},
pages = {113511},
publisher = {AIP Publishing},
abstract = {In this work we report on the surface characterization of melanin thin films prepared using both water-based and organic solvent-based melanin syntheses. Atomic force microscopy(AFM) analysis of these films suggests that the organic solvent synthesis provides relatively planar basic melanin structures; these basic structures generate surface steps with height in the range of 2–3nm and small tendency to form larger aggregates. The scaling properties obtained from the AFM data were used to infer the assembling mechanisms of these thin films which depend on the solvent used for melanin synthesis. The behavior observed in organic solvent-based melanin suggests a diffusion-limited aggregation process. Thus films with good adhesion to the substrate and smoother morphologies than water-prepared melanin films are obtained. Electronic structure calculations using a conductorlike screening model were also performed in order to elucidate the microscopic processes of thin film formation. Our results suggest that the agglomerates observed in hydrated samples originate from reaction with water at specific locations on the surface most likely defects on the planar structure.},
keywords = {Electronic Structure, Melanin, Structure},
pubstate = {published},
tppubtype = {article}
}