Kinetics of Reduction of Thionine with Ribose and the Structural Properties of the Dye at Different pH Using DFT Method  

作　　者：Ahmed, Khalid Azmat, Rafia Uddin, Fahim Fatmi, M. Qaiser 

机构地区：[1]Department of Chemistry, University of Karachi, Karachi 752 70, Pakistan [2]Department of Chemistry, Jinnah University for Women, Nazimabad, Karachi, Pakistan [3]Department of Chemistry, University of California at Riverside, California 92521, USA

出　　处：《Chinese Journal of Chemistry》2011年第4期643-649,共7页中国化学（英文版）

摘　　要：The reaction between the thionine （Th） and the ribose was observed spectrophotometrically and changes in absorbance of Th were recorded at variable concentration of dye, reductant and pH. A pseudo first order rate of reaction was found to establish the reduction kinetics of the dye, studied at a pH range of 0.34 to 12.8. Absorption spectrum of Th at different pH, with ribose showed a pH （12.8） dependent introversion. The reduction most probably took place with enediol intermediate of the sugar at high pH. A full geometry optimization of predominant species of Th namely, mono-deprotonated, di-deprotonated Th, and LTh （leuco thionine） respectively, at low and high pH, was performed at B3LYP level of theory. The data obtained from the energy minimization were in excellent agreement with other experimental and theoretical observations. The calculated enthalpies of formation for both reduction reactions （mono-deprotonated Th＋H＋→leucothionine and di-deprotonated Th＋2H＋→leucothionine） provided evidences for maximum reduction of the dye at high pH.The reaction between the thionine （Th） and the ribose was observed spectrophotometrically and changes in absorbance of Th were recorded at variable concentration of dye, reductant and pH. A pseudo first order rate of reaction was found to establish the reduction kinetics of the dye, studied at a pH range of 0.34 to 12.8. Absorption spectrum of Th at different pH, with ribose showed a pH （12.8） dependent introversion. The reduction most probably took place with enediol intermediate of the sugar at high pH. A full geometry optimization of predominant species of Th namely, mono-deprotonated, di-deprotonated Th, and LTh （leuco thionine） respectively, at low and high pH, was performed at B3LYP level of theory. The data obtained from the energy minimization were in excellent agreement with other experimental and theoretical observations. The calculated enthalpies of formation for both reduction reactions （mono-deprotonated Th＋H＋→leucothionine and di-deprotonated Th＋2H＋→leucothionine） provided evidences for maximum reduction of the dye at high pH.

关 键 词：THIONINE RIBOSE PH enediol geometry optimization REDUCTION 

分 类 号：O641.1[理学—物理化学] TF046.6[理学—化学]