H-phosphinic analogs of natural amino acids: a novel and efficient treatment for preventing biodeterioration of treasured painted artworks

Introduction: Microorganisms can destroy various materials that make up objects of cultural heritage. In particular, ancient tempera paintings are made with egg yolk, animal glue, and a number of other organic materials, which serve as a good breeding ground for the development of microorganisms. Recently, the range of traditional antiseptics used to protect tempera paintings from biodeterioration has been significantly reduced because of undesirable properties associated with their interaction with painting materials and toxicity. Therefore, it is necessary to develop a new generation of antiseptics that can effectively protect paintings from destructive microorganisms. Methods: To solve this challenging task and protect paintings from fungal damage, we used H-phosphinic analogs of natural amino acids. Twelve different H-phosphinic analogs of natural amino acids were screened on Czapek–Dox agar medium against 11 mold fungi belonging to the genera Aspergillus, Penicillium, Simplicillium, Microascus, Cladosporium, and Ulocladium. These mold fungi are responsible for the biodegradation of tempera paintings and are the dominant representatives of the microbiome of the State Tretyakov Gallery in Russia. Results: All the studied compounds at concentrations of 0.7–2.5 mM inhibited the mycelial growth of mold fungi. The supplementation of H-phosphinic analogs of alanine, aspartate, and valine resulted in the loss of characteristic pigmentation of Penicillium chrysogenum, which may be associated with inhibition of Ac-CoA and malonyl-CoA biosynthesis. The H-phosphinic analog of methionine protected mock layers with sturgeon glue more effectively than the other H-phosphinates and standard antiseptics, such as benzalkonium chloride or sodium pentachlorophenolate. The addition of H-phosphinic amino acid analogs to sturgeon glue did not significantly affect the spectral and surface properties of the glue applied on the layout but effectively inhibited the growth of the studied mold fungi on mock-up layers during long-term storage. Conclusion: Our data provide the first evidence of the successful use of nontoxic H-phosphinic analogs of natural amino acids for protecting paintings from biodeterioration.