Michael Addition Reactions in Dyeing of Protein Fibers with Quercetin

The Michael reaction typically refers to the base catalyzed addition of a nucleophile (Michaeldonor) to an activated α,ß-unsaturated carbonyl-containing compound (Michael acceptor).Base catalysts are often unnecessary in the case of amines, because of the strong nucleophilicityof the nitrogen atom, whereas weak bases aid in deprotonation of thiols [1]. Laccases areable to initiate nucleophilic amination of poly phenolic compounds with primary aromaticamines, resulting in the formation of the corresponding mono-aminated and di-aminated quinones[2]. The enzyme-generated quinones could react with proteins fibers [3]. Natural colorantsare composed of polyphenolic compounds, so, they are good substrates for laccase to beconverted to related quinones. Quercetin, a plant flavonol from the flavonoid group of polyphenols,is found in many fruits, vegetables and leaves. In this study a new idea was studiedfor making a covalent bond between quinones formed by laccase from quercetin, as a naturaldye, and nucleophilic side chains. (Fig. 1). FTIR results and dye fixation measurements showthe possibility of using this method to obtain colored wool with high wash fastness.