Utilize este identificador para referenciar este registo: http://hdl.handle.net/10362/50266
Autor: Sousa, Micaela Margarida Ferreira de
Orientador: Melo, Maria João
Almeida, Joaquim
Data de Defesa: 2008
Resumo: A characterization at the molecular level of three important historic dyes was undertaken: the most popular blue in the history of humankind, indigo, one the most ancient red resins, dragon’s blood, and the first synthetic dye with high commercial value, mauve. The molecular studies evolved along two axes: the characterization of relevant chromophores for mauve and dragon's blood resins and the study of indigo photochemistry. Natural flavylium compounds were rediscovered as the chromophores responsible for the red colour in dragon's blood resins. 7,4’-dihydroxy-5-methoxyflavylium (dracoflavylium) was for the first time identified in samples of the resin dragon’s blood, extracted from the tree Dracaena draco. Also, 7,4’-dihydroxyflavylium was identified for the first time as the red natural flavylium in Dracaena cinnabari species. Following these results, the use of flavylium compounds as markers to identify the species source of dragon’s blood resins is proposed. This method was built-up on the analyses of more than 50 resin samples from different trees, and further successfully tested on 19th century Kew Gardens collection (in a collaboration with Kew Gardens, Kew). Moreover, the complex network of reversible chemical reactions, at acidic or slightly basic conditions, that dracoflavylium undergoes in aqueous solution is described, and it is concluded that the red colour of these resins is due to the stable quinoid base, which is the major species in the pH range 4-6. The photodegradation of indigo and its water-soluble derivative indigo carmine was carried out in liquid and organized media. Photodegradation quantum yields were obtained for monochromatic irradiation at 335 nm and 610 nm; the main photodegradation product was identified by HPLC-DAD-MS as being isatin for indigo. The stability of indigo and the mechanisms of degradation are discussed and compared to what was observed in millenary Paracas textiles (in a collaboration with Museum of Fine Arts, Boston). The characterization of mauve revealed that, contrarily to what is reported in the literature, the dye is a complex mixture of at least 13 chromophores with the 7-amino-5-phenyl-3- (phenylamino)phenazin-5-ium core. From the analysis of historic mauve samples it was possible to verify that the “original mauve”, made in the early years of 1856-7 by Perkin, exists in historic textile samples. The historic salt samples analysed, including the one displayed in the Science Museum of London as the “original mauve performed by William Perkin in 1856”, were found to be later than 1862 (in a collaboration with Science Museum, London).
URI: http://hdl.handle.net/10362/50266
Designação: Doutor em Conservação e Restauro, especialidade Ciências da Conservação
Aparece nas colecções:FCT: DCR - Teses de Doutoramento

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