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Fungal stains on paper: Melanins produced by fungi
Publication . Melo, Daniela Correia de; Macedo, Maria Filomena; Sequeira, Sílvia; Lopes, João
Books, prints, drawings, watercolours, engravings as well as all other works of art based on paper comprise a great portion of our cultural heritage. Therefore, its preservation is a matter of great concern.
Paper can be deteriorated due to physical, chemical and biological agents. Fungi are among the most common biodeteriogens affecting paper-based collections, causing severe material and information losses.
This work focused on fungal stains on paper which are often coloured. These interfere with the readability of the artefacts diminishing their artistic and monetary value. Up to now, there is still no definitive answer for this problem. The successful cleaning of fungal stains from paper is a mandatory conservation task, considered a priority by paper conservators. However, most of the authors refer the stain colour and patterns but they do not indicate the colourant or colourants (or chemical compound) responsible for the stain.
Black stains on paper are of major concern because, not only they are very frequent, as well as its dark colour leads to a great loss of visibility. Therefore, this work focused primarily in the extraction and characterization of fungal melanins from three different species: Aspergillus niger, Chaetomium globosum and Cladosporium cladosporioides, known to be responsible for black staining on paper and melanin production.
UV-Vis, μ-FTIR and μ-Raman analyses were carried out for all three fungi melanin extracts.
UV-Vis, μ-FTIR and μ-Raman results show that, after extraction and purification, purified melanin samples were obtained from the three-fungal species. Moreover, SSNMR allowed to characterize A. niger’s melanin as a L-DOPA type melanin, and Cl. cladosporioides as a DHN type melanin, by comparison with the synthetic L-DOPA melanin (Sigma-Aldrich) and the literature.
This will allow for a colourant-specific testing of newly developed cleaning methods,
considering the base structure of the polymer (melanin) to be removed from the paper.
Characterization of Fungal Melanins from Black Stains on Paper Artefacts
Publication . Melo, Daniela; Paiva, Tiago G.; Lopes, João A.; Corvo, Marta C.; Sequeira, Sílvia O.; DCR - Departamento de Conservação e Restauro; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; LAQV@REQUIMTE; MDPI - Multidisciplinary Digital Publishing Institute
Melanins play a fundamental role in the biology and ecology of several fungal species. Unfortunately, this group of amorphous macromolecules also severely (and most times irreversibly) stains cultural heritage objects. Despite efforts made throughout the years, knowledge of the chemical composition and structure of melanins is still insufficient, which hampers the task of safely cleaning these colourants from cultural heritage materials in a targeted way without causing further deterioration. This work aimed therefore to contribute towards enlightening the characteristics of fungal melanins from three fungi that are common paper colonizers: Aspergillus niger, Chaetomium globosum and Cladosporium cladosporioides. The extracted melanins were characterized by FTIR, Raman, UV-vis, Solid-State NMR and MALDI-TOF MS spectroscopies and the effect of inhibitors of DHN-melanin and DOPA-melanin pathways on colony pigmentation and growth was evaluated. Although all the extracted colourants show a predominantly aromatic structure with carbonyl and phenolic groups, some differences between the melanins can be highlighted. Melanins obtained from Ch. globosum and Cl. cladosporioides exhibited similar structures and composition and both presented DHN-melanin characteristics, while A. niger’s melanins revealed a more complex and ordered structure, with a higher prevalence of highly conjugated carbonyls than the others, besides the additional presence of a yellow/green component. These conclusions cannot be overlooked while selecting targeted cleaning methodologies for melanin stains on cultural heritage materials.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/EPH-PAT/0224/2014