The structure activity relationship of non-dissolved redox mediators during azo dye bio-decolorization processes

Abstract Structure activity relationships were elucidated by applying chemical structure, electrochemistry and quantum chemical calculations for non-dissolved redox mediators (RM, quinones) with similar chemical structure. The decolorization efficiencies of acid red B by a Halomonas sp. GYW were enhanced 2.68, 2.58, 1.91 and 1.49 times with 1,5-dichloroanthraquinone, 1,8-dichloroanthraquinone, anthraquinone, and 1,4,5,8-tetrachloroanthraquinone, respectively. The order of oxidation reduction potential (ORP) during the decolorization process with four redox mediators agreed with their order of reduction potential ( Ea ) from cyclic voltammetry. The decolorization rate ( k ) with four redox mediators has a linear relation with their Ea values ( k  = 269.05 Ea  + 85.782, R 2  = 0.9226). The calculated ρ ( r c ) at the Ring Critical Point (RCP) based on Atoms in Molecules (AIM) and the inductive/resonance effects of the four redox mediators were also consistent with the accelerating effects on the decolorization. These established relationships might to be predictive models and mechanistic explanations for the accelerating decolorization with redox mediator.