สำนักราชบัณฑิตยสภา

211 สมศั กดิ์ ด� ำรงค์เลิ ศ และคณะ วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๑ ม.ค.-มี.ค. ๒๕๕๕ cultured-filtrates containing known concentration of AH 2 QDS (≈ 0.25 mM) demonstrated that the chemical reduction of orange and violet dye required two moles of AH 2 QDS to produce the corresponding aromatic amines and by four moles of AH 2 QDS to produce the corresponding aromatic amines of black dye. The stoichiometry suggested a complete reduc- tion of sulfonated azo dyes to the corresponding aromatic amines. Characterization of products formed from chemical reduction of various sul- fonated azo dyes The reduction products of sulfonated azo dyes present in the reaction mixtures were analyzed by HPLC as described in Materials and Methods. HPLC chromatogram of reduction products of individual azo dyes by AH 2 QDS was compared with the HPLC chromatogram of completely reduction products of each azo dye obtained by reduction the dye with sodium dithionite, a strong chemical reducing agent (2). Form comparison results, the complete re- duction of each azo dye to its corresponding amines by AH 2 QDS was proposed in this study (data not shown). DISCUSSION Several different mechanisms have been proposed for reduction or degradation of azo dyes and similar compounds. A description of a nonspecific azo reductase sys- tem involved in azo dye reduction has been provided for selected bacterial species, and it has been shown that the relevant gene is relatively conserved in various anaerobic and facultative bacteria (29, 41). In this research it was also hypothesized that coenzyme reducing equivalents (e.g., NADH) involved in normal electron transport through oxi- dation of organic substrates may act as electron donors for reduction of azo dyes. This would likely explain the observation that azo dye reduction occurs more readily as a co- metabolic event when additional readily degradable substrates (glucose) are provided (Fig. 2). There were at least two possible ways for glucose to enhance reduction of sulfonated azo dyes. It could act as a donor of reducing equivalents [e.g., via NADH or FADH 2 ], or its addition could result in more actively respiring cells, thus rapidly removing the oxygen