Biomimetic system for removal of fungal melanin staining on paper

Fungal melanin staining is a problem on many cultural objects, ranging from the French Palaeolithic cave at Lascaux to books and papers in museum collections. Melanin, because it is insoluble and resistant to bleaching, may leave behind undesirable stains long after the fungal infestation has been controlled. Research into removal of melanin stains from paper and other sensitive substrates using industrial biomimetic oxidizing systems has shown considerable success. We studied relative concentration of the bleaching reagents and the reaction kinetics both in liquid suspensions of melanin and on melanized paper samples. Liquid suspension samples were tested for changes in their chemical composition (appearance and relative representation of functional groups and chemical bonds) with FTIR spectrometry. Changes in color of melanized paper samples were investigated with a CIE L*a*b system, where the effectiveness of the treatment (bleaching) was determined as a change in lightness (ΔL). Melanin was oxidized in the liquid suspensions, and the intensity of modification depended on the procedure employed. Bleaching of melanin with the biomimetic copper–pyridine complex proved to be far superior to the effect of white-rot fungal oxidizing enzymes, previously reported on by this group.