Characterization of Fungal Melanins from Black Stains on Paper Artefacts

Author:

Melo Daniela,Paiva Tiago G.ORCID,Lopes João A.,Corvo Marta C.ORCID,Sequeira Sílvia O.ORCID

Abstract

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.

Funder

Portuguese funds

Associate Laboratory for Green Chemistry—LAQV

i3N Associate Laboratory and PTNMR

iMed.ULisboa

Publisher

MDPI AG

Subject

Materials Science (miscellaneous),Archeology,Conservation

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