Degradation of lucidin: New insights into the fate of this natural pigment present in Dyer's madder ( Rubia tinctorum L.) during the extraction of textile artefacts

Abstract

The complex mixtures of colorants present in different madder species can provide significant information about which plant species or technique was used to dye the fibres of historical textile artefacts, hence, when extracting and analysing colorants from textile artefacts as much of this information as possible should be preserved. Historical textiles are most commonly extracted with 37% hydrochloric acid: methanol: water (2:1:1, v/v/v), but this solvent system hydrolyses dye glycosides and may also induce chemical reactions. One of the primary components in Dyers' madder (Rubia tinctorum L.) is lucidin primeveroside, but it is rarely seen in artefacts, nor is the corresponding aglycon lucidin. It has been demonstrated that the hydrochloric acid method causes hydrolysis of anthraquinone glycosides to their aglycon counterpart. Herein it is demonstrated that lucidin is not stable in such acidic conditions and degrades rapidly to xanthopurpurin. This is confirmed by HPLC, LC-MS and 1 H NMR, which also provide evidence of the mechanism of degradation being a retro-aldol process.

Combined, sequential dye analysis and radiocarbon dating of single ancient textile yarns from a Nazca tunic

“…However, minor anthraquinones reported by Armitage et al were not observed in the extract even with selected ion monitoring; namely, 1-methoxy-2-methylanthraquinone (m/z 251), 2-methoxy-2-methylanthraquinone (m/z 237), and the primeverosides of xanthopurpurin (m/z 533), rubiadin (m/z 547), and pseudopurpurin (m/z 593) [11]. Lucidin was also not detected, but its glycoside, lucidin primeveroside was observed due to the mild extraction procedure [59].…”

Quantitative 1H NMR Spectroscopy Method for Determination of Anthraquinone Derivatives in Extracts from Rubia tinctorum L. Roots and Rhizomes

“…The extractants used for the separation of biologically active substances from the roots of Rubia tinctorum L. include ethanol, water and their combination at various ratios [12,28]. The most common procedure described for extracting anthraquinone derivatives from Rubia tinctorum L. roots and rhizomes is performed with the 37% hydrochloric acid/methanol/water (2:1:1, v/v/v) mixture [30]. But the presence of water in extractant solutions leads to the degradation of the primary anthraquinone derivatives such as RA [12], which makes analyzing the primary anthraquinone derivatives impossible.…”

Examining Safety of Biocolourants from Fungal and Plant Sources-Examples from Cortinarius and Tapinella, Salix and Tanacetum spp. and Dyed Woollen Fabrics

“…Those reactions may also affect the dyeing potential, as the products of hydrolysis, i.e., aglycone structures, differ in their properties and affinities to various materials compared to their derivatives [9,13]. The historical background does not necessarily give any guarantee of safeness as even widely-used dye sources can contain toxic secondary metabolites: madder root extracts (R. tinctorum) having alizarin (1) as the main anthraquinone aglycone, also contained toxic lucidin (2), rubiadin (3) and xanthopurpurin (4) (Table 1) [26][27][28][29][30], of which lucidin and xanthopurpurin were hydrolysis and decarboxylation products of lucidin primeveroside and munjistin. Furthermore, it has been proposed that lucidin is converted into other compounds, such as nordamnacanthal or quinone methide [26,28,31] or degrade to xanthopurpurin.…”