Analysis of Biomolecules in Cochineal Dyed Archaeological Textiles by Surface-Enhanced Raman Spectroscopy.

Abstract

SERS spectroscopy is successfully employed in this work to reveal different components integrating the cochineal colorant employed for dying archaeological textile samples from the Arica region in North Chile. This analysis was done by in-situ experiments that does not imply the material (colorant and biomolecules) extraction. The spectroscopic analysis of the archaeological textiles by SERS reveals the presence of bands attributed to carminic acid and nucleobases, mainly adenine and guanine. The identification of these biomolecules was also verified in raw cochineal extract and in cochineal dyed replica wool fibers fabricated by us following ancient receipts. The effect of Al on the complexation of carminic acid and other biomolecules was also tested in order to understand the changes induced by the metal interaction on the colorant structure. This study revealed that Al can also complex biomolecules existing in the cochineal extract. In particular, guanine residue seems to interact strongly with the metal, since SERS bands of this residue are enhanced. Furthermore, a theoretical analysis on the interaction of carminic acid and a silver surface was also performed in order to better understand the interaction mechanism between carminic acid and a metal surface that leads to the final SERS spectrum. The results of the present work will be very useful in the identification of different molecules and metal complexes that may be forming part of the cochineal colorant found in archaeological materials.

Colors and dyes of archaeological textiles from Tarapacá in the Atacama Desert (South Central Andes)

“…When comparing our results with previous molecular identification of red dyes in neighboring regions, we found that in the north in southern Peru purpurin from a plant from Relbunium species and carminic acid from cochineal were reported for the Late Intermediate period (1000-1450 A.D.) [54]. The use of cochineal (carminic acid) was also recently reported in Formative textiles from Arica locality to the north of Tarapacá region studied, but without more precision to archaeological context [73]; while only purpurin was identified at San Pedro de Atacama to the eastern south, for the Middle (600-1000 A.D.) and Late Intermediate periods (1000-1450 A.D.) [63]. In the case of the Tarapacá region, only alizarin and carminic acid have been continuously used for a long time.…”

“…From an analytical perspective, they applied chromatographic or spectrometric techniques including gas chromatography-mass spectrometry (GC-MS), high-performance liquid chromatography with diode array detectors (HPLC-DAD) and/or mass spectrometry (HPLC-MS), direct analysis in real time mass spectrometry (DART-MS), which albeit sensitive are destructive methods [3, 48-50, 53, 54, 56-60, 62-64, 66, 70]. Analysis by surface-enhanced Raman spectroscopy (SERS) was applied in just five publications to analyze archaeological textiles from Peru and northern Chile [55,61,65,69,73]. Finally, the available literature shows a particular emphasis on the analysis of polychrome textiles from the Paracas and Nazca cultures (700 BC-800AD), on South-Central Perú [51-53, 59-61, 66, 67, 70].…”

“…Finally, the available literature shows a particular emphasis on the analysis of polychrome textiles from the Paracas and Nazca cultures (700 BC-800AD), on South-Central Perú [51-53, 59-61, 66, 67, 70]. For northern Chile, only three studies have been published addressing the physicochemical analysis of textile dyes: one related to textiles from San Pedro de Atacama, almost 500 km to the south of our study region, and the others for Arica, 270 km to the north [63,69,73]. Other results were just announced at a conference and are still unpublished [55].…”