Structure/Redox potential relationship of simple organic compounds as potential precursors of dyes for laccase‐mediated transformation

Abstract

The aim of this study was to examine the ability of an extracellular fungal laccase (LAC) to form colored products from simple non-colored organic precursors. Thirty different phenolic and non-phenolic precursors (o-, m-, and p-methoxy-, hydroxy-, sulfonic-, and amino-substituted) were tested as single and coupled substrates in a LAC-catalyzed oxidation. The findings show that LAC catalyzes the formation of colored products (from yellow/brown to red and blue) by oxidation of single substrates that are benzene derivatives containing at least two substituents comprised of amino, hydroxy, and methoxy groups. All precursors were tested by cyclic voltammetry and the correlation between their structure and redox potential, and the possibility of their transformation into colored products by fungal LAC was found. Colored products were yielded from single substrates possessing a value of the oxidation peak (E(o)) lower than 1,150 mV vs. normal hydrogen electrode (NHE). Substrates with an oxidation peak higher than 1,150 mV vs. NHE were transformed by LAC into colored compounds only in the presence of an additional precursor characterized by a low value of E(o) and the presence of reactive substituents such as methoxy, hydroxy, and amino groups. Therefore, additional hydroxylation, methoxylation, and amination of phenolic and non-phenolic substrates may represent a strategy to increase the range of these compounds as potential dyes precursors.

Toxicity and dyeing properties of dyes obtained through laccase-mediated synthesis

“…In this context, new chemical structures with good dyeing properties, which can be enzymatically created, represent a promising alternative to chemical synthesis (Polak and Jarosz-Wilkolazka, 2012a). Different kinds of color compounds are synthesized by different laccases; among them, very important are phenolic dyes (Jeon et al, 2012;Mustafa et al, 2005;Polak and Jarosz-Wilkolazka, 2012b), phenoxazinone dyes (Bruyneel et al, 2008;Forte et al, 2010;Sousa et al, 2014), and azo dyes (Enaud et al, 2010;Setti et al, 1999). Therefore, the interest in the use of laccase as a biocatalyst in colorant synthesis has increased in recent years.…”

“…4; Tables 1a,b). All products synthesized via the homomolecular transformations had the main peak in the spectrum in a wavelength range from 430 to 495 nm (Table 1a), which is characteristic for the orangeered color (Polak and Jarosz-Wilkolazka, 2012b). Orange dyes with a wavelength at a maximum from 436 to 450 nm were products denoted with acronyms A1, A22, and A3, obtained during the homotransformations of precursors 3A4HBA, 3A4HBSA, and 2A3MeBA, respectively.…”

“…They can undergo spontaneous coupling reactions to many various coupled products, including colorful dimers, oligomers, and polymers, whose color can be used as dyes (Bruyneel et al, 2008;Forte et al, 2010;Ganachaud et al, 2008). These colored products are results of laccase-mediated oxidation of simple aromatic compounds containing reactive substituents such as methoxy, amino, hydroxy, and sulfonic groups (Polak and Jarosz-Wilkolazka, 2012b).…”

Role of Laccase and Low Molecular Weight Metabolites fromTrametes versicolorin Dye Decolorization

“…Some reports concerning the use of fungal laccases for the bioconversion of simple organic compounds into active compounds imply the suitability of these enzymes as regioselective reagents [26]. Actually, some roles of the organic acids have been described: Mn 3+ stabilization after its production by manganese peroxidases [27], avoiding compound III (inactive enzyme) formation in lignin peroxidase redox cycle [28], hydroxyl radicals generation from oxalate [29] or from malonate oxidation by Mn 3+ [30], electron source for Fe 3+ reduction producing superoxide radicals [31].…”

Laccase Properties, Physiological Functions, and Evolution

“…Laccase secretion is considered as one of the basic fungal responses to the presence of antagonistic conditions: other microorganisms, xenobiotics, metals, toxins, and biologically active compounds. Fungal laccases oxidize not only phenolic compounds but also non-phenolic substrates such as aromatic amines, polycyclic aromatic hydrocarbons, synthetic dyes, antibiotics, and other non-obvious laccase substrates [35,167]. In this way, laccase is a very useful enzymatic "tool" for elimination of natural or synthetic toxins occurring in the environment and is therefore involved in fungal active defense.…”