Hsueh Chung-Chuan, Chen Bor-Yann, Yen Chia-Yi
Department of Chemical and Materials Engineering, National I-Lan University, I-Lan 260, Taiwan.
J Hazard Mater. 2009 Aug 15;167(1-3):995-1001. doi: 10.1016/j.jhazmat.2009.01.077. Epub 2009 Jan 30.
This novel comparative study tended to disclose how the molecular structures present in seven azo dyes including two types of azo dyes (i.e., naphthol type azo dyes--Reactive Black 5 (RB 5), Reactive Blue 171 (RB 171), Reactive Green 19 (RG19), Reactive Red 198 (RR198), Reactive Red 141 (RR141), and non-naphthol type azo dyes--Direct Yellow 86 (DY86), Reactive Yellow 84 (RY84)) affected color removal capability of Aeromonas hydrophila. Generally speaking, the decolorization rate of naphthol type azo dye with hydroxyl group at ortho to azo bond was faster than that of non-naphthol type azo dye without hydroxyl group, except of RG19. The azo dyes with electron-withdrawing groups (e.g., sulfo group in RR198, RB5 and RR141) would be easier to be decolorized than the azo dyes with the electron-releasing groups (e.g., -NH-triazine in RB171 and RG19). In addition, the azo dyes containing more electron-withdrawing groups (e.g., RR198, RB5 and RR141) showed significantly faster rate of decolorization. The azo dyes with electron-withdrawing groups (e.g., sulfo group) at para and ortho to azo bond (e.g., RR198, RB5 and RR141) could be more preferred for color removal than those at meta (e.g., DY86 and RY84). The former azo dyes with para and ortho sulfo group provided more effective resonance effects to withdraw electrons from azo bond, causing azo dyes to be highly electrophilic for faster rates of reductive biodecolorization. However, since the ortho substituent caused steric hindrance near azo linkage(s), azo dyes with para substituent could be more favorable (e.g., SO(2)(CH(2))(2)SO(4)(-) in RR198 and RB5) than those with ortho substituent (e.g., sulfo group at RR141) for decolorization. Thus, the ranking of the position for the electron-withdrawing substituent in azo dyes to escalate decolorization was para>ortho>meta. This study suggested that both the positions of substituents on the aromatic ring and the electronic characteristics of substituents in azo dyes all significantly affected the performance of biodecolorization of A. hydrophila.
这项新颖的比较研究旨在揭示七种偶氮染料（包括两种类型的偶氮染料，即萘酚型偶氮染料——活性黑5（RB 5）、活性蓝171（RB 171）、活性绿19（RG19）、活性红198（RR198）、活性红141（RR141），以及非萘酚型偶氮染料——直接黄86（DY86）、活性黄84（RY84））中的分子结构如何影响嗜水气单胞菌的脱色能力。一般来说，除RG19外，偶氮键邻位带有羟基的萘酚型偶氮染料的脱色率比没有羟基的非萘酚型偶氮染料更快。带有吸电子基团（如RR198、RB5和RR141中的磺酸基）的偶氮染料比带有供电子基团（如RB171和RG19中的-NH-三嗪）的偶氮染料更容易脱色。此外，含有更多吸电子基团（如RR198、RB5和RR141）的偶氮染料显示出明显更快的脱色速率。偶氮键对位和邻位带有吸电子基团（如磺酸基）的偶氮染料（如RR198、RB5和RR141）比间位的偶氮染料（如DY86和RY84）更有利于脱色。前者带有对位和邻位磺酸基的偶氮染料提供了更有效的共振效应，从偶氮键上吸电子，使偶氮染料具有更高的亲电性，从而实现更快的还原性生物脱色速率。然而，由于邻位取代基在偶氮键附近造成空间位阻，带有对位取代基的偶氮染料（如RR198和RB5中的SO(₂)(CH₂)₂SO₄⁻）比带有邻位取代基的偶氮染料（如RR141中的磺酸基）更有利于脱色。因此，偶氮染料中吸电子取代基促进脱色的位置排序为对位>邻位>间位。这项研究表明，偶氮染料芳香环上取代基的位置和取代基的电子特性均显著影响嗜水气单胞菌的生物脱色性能。
