Nonreducing terminal chimeric isomaltomegalosaccharide and its integration with azoreductase for the remediation of soil-contaminated lipophilic azo dyes.

Lipophilic azo dyes are practically water-insoluble, and their dissolution by organic solvents and surfactants is harmful to biological treatment with living cells and enzymes. This study aimed to evaluate the feasibility of a newly synthesized nonreducing terminal chimeric isomaltomegalosaccharide (N-IMS) as a nontoxic solubilizer of four simulated lipophilic azo dye wastes for enzymatic degradation. N-IMS bearing a helical α-(1 â†’ 4)-glucosidic segment derived from a donor substrate α-cyclodextrin was produced by a coupling reaction of cyclodextrin glucanotransferase. Inclusion complexing by N-IMS overcame the solubility issue with equilibrium constants of 1786-242 M-1 (methyl yellow > ethyl red > methyl red > azo violet). Circular dichroism spectra revealed the axial alignment of the aromatic rings in the N-IMS cavity, while UV-visible absorption quenching revealed that the azo bond of methyl yellow was particularly induced. Desorption of the dyes from acidic and neutral soils was specific to aqueous organic over alkali extraction. The dissolution kinetics of the incorporated dyes followed a sigmoid pattern facilitating the subsequent decolorization process with azoreductase. It was demonstrated that after soil extraction, the solid dyes dissolved with N-IMS assistance and spontaneously digested by coupled azoreductase/glucose dehydrogenase (for a cofactor regeneration system) with the liberation of the corresponding aromatic amine.

Physicochemical functionality of chimeric isomaltomegalosaccharides with α-(1 → 4)-glucosidic segments of various lengths.

Isomaltomegalosaccharide (IMS) is a long chimeric glucosaccharide composed of α-(1 â†’ 6)- and α-(1 â†’ 4)-linked segments at nonreducing and reducing ends, respectively; the hydrophilicity and hydrophobicity of these segments are expected to lead to bifunctionality. We enzymatically synthesized IMS with average degrees of polymerization (DPs) of 15.8, 19.3, and 23.5, where α-(1 â†’ 4)-segments had DPs of 3, 6, and 9, respectively. IMS exhibited considerably higher water solubility than maltodextrin because of the α-(1 â†’ 6)-segment and an identical resistance to thermal degradation as short dextran. Interaction of IMS with a fluorescent probe of 2-p-toluidinylnaphthalene-6-sulfonate demonstrated that IMS was more hydrophobic than maltodextrin, where the degree of hydrophobicity increased as DP of α-(1 â†’ 4)-segment increased (9 > 6 > 3). Fluorescent pyrene-estimating polarity of IMS was found to be similar to that of methanol or 1-butanol. The bifunctional IMS enhanced the water solubility of quercetin-3-O-glucoside and quercetin: the solubilization of less-soluble bioactive substances is beneficial in carbohydrate industry.