Vibrational spectroscopy of synthetic and natural eumelanin

Abstract

We report vibrational spectra of two types of eumelanin samples: a synthetic one, produced by oxidation of tyrosine with hydrogen peroxide, and a natural one, extracted from Sepia officinalis, with the aim to point out the differences between the main vibrational properties of such two pigments. Fourier Transform Infrared (FTIR), Raman and Surface Enhanced Raman Scattering (SERS) spectra allow to identify several vibrational modes involving specific monomeric units. The main differences between the spectra of the two types of eumelanin are related to i) a larger amount of carboxylic acid in synthetic than in natural sample; ii) a shift of spectral position of corresponding peaks; iii) a contribution of residual proteins to the signal from natural sample. Such results suggest that vibrational techniques may be helpful to nondestructively determine the composition of different eumelanin pigments, with potential applications in biomedical, electronic and cultural heritage fields. This article is

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