Artículo de revista
Identification of coexisting indigo species in an ancient green thread using direct plasmon-enhanced raman spectroscopy
Fecha
2020Registro en:
J. Chil. Chem. Soc., 65, N°2 (2020)
0717-9707
Autor
Celis, Freddy
Tirapegui, Cristian
García, Macarena
Aracena, Andrés
Aliaga, Álvaro E.
Campos Vallette, Marcelo
Institución
Resumen
A green ancient thread sample from a Chilean mummy turban was analyzed by plasmon-enhanced Raman scattering spectroscopy using a direct drop-colloidal method. The enhanced-Raman signals in the sample are associated with biomolecules from the thread and two coexisting dyes, indigo and leuco-indigo. The presence of indigo (blue colour) was identified from its most characteristic vibrational bands. Leuco-indigo (yellow colour) was identified for the first time in an ancient textile; its SERS signals are coincident with the SERS bands of a synthesized leuco-indigo. The interconversion leuco-indigo to indigo was followed by UV-visible spectroscopy. Based on theoretical calculations it is proposed that the interconversion involves a it electron delocalization mainly around the NC-CN bridge. The mixture of both dyes (indigo and leuco-indigo) is the responsible for the green colour observed.