Raman and optical spectroscopy of eumelanin films

Vibrational characterization of pheomelanin and trichochrome F by Raman spectroscopy

“…It is important to note that the high Raman intensity in the region around 1750-2500 cm À1 (Fig. 1) is very charactistic of pheomelanin, as the Raman spectrum of eumelanin is flat at this region ( [4,18,19] and see below).…”

“…The shape of the Raman spectrum of pheomelanin is very different to that of eumelanin [4,18,19], showing three 'humps' (Fig. 1).…”

“…2). Indeed, the Raman spectrum of trichochrome F showed the D and G bands characteristic of eumelanin and disordered graphite [4,18,19] and absence of signal in the 1750-2500 cm À1 region. From four measurements at different sites of the trichochrome powder sample, we detected the D band at 1323, 1323, 1337 and 1360 cm À1 , and the G band at 1480, 1494, 1502 and 1502 cm À1 (Fig.…”

“…The vibrational characterization of eumelanin through Raman spectroscopy has been made in different studies [4,[18][19][20], showing that its most outstanding features are two bands at about 1380 and 1580 cm À1 similar to D and G bands, respectively, observed in the Raman spectrum of disordered graphite (the Raman spectrum of black fungal pigments may exhibit an additional band about 1250 cm À1 because it is synthesized from the polymerization of phenols instead of 5,6-dihydroxyindole as in animals; [20]). These bands have thus been attributed to the stretching vibration of the hexagonal carbon rings, the stretching vibration of the C-C bonds within the rings and the C-H vibrations in the methyl and methylene groups in the eumelanin polymers [4].…”

Raman microspectroscopy of melanosomes: the effect of long term light irradiation

“…In the higher frequency region, the two peaks at 1562 and 1598 cm À1 are attributed to the stretching mode of sp 2 hybridized carbon of C¼C and E 2g mode of C--C vibrations, respectively, of an aromatic compound present in the indole structure of eumelanin [25]. Also a contribution due to stretching C¼O vibration is probable at this wavelength [26]. The main contribution to the peak at 1390 cm À1 comes from the disorder activated Raman mode similar to the A 1g mode in graphitic domains ( Figure 3) [27].…”