Ahmad Iqbal, Bano Raheela, Musharraf Syed Ghulam, Ahmed Sofia, Sheraz Muhammad Ali, ul Arfeen Qamar, Bhatti Muhammad Salman, Shad Zufi
Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super highway, Gadap Road, Karachi, 74600, Pakistan.
AAPS PharmSciTech. 2014 Dec;15(6):1588-97. doi: 10.1208/s12249-014-0184-x. Epub 2014 Aug 20.
The kinetics of photodegradation of moxifloxacin (MF) in aqueous solution (pH 2.0-12.0), and organic solvents has been studied. MF photodegradation is a specific acid-base catalyzed reaction and follows first-order kinetics. The apparent first-order rate constants (kobs) for the photodegradation of MF range from 0.69 × 10(-4) (pH 7.5) to 19.50 × 10(-4) min(-1) (pH 12.0), and in organic solvents from 1.24 × 10(-4) (1-butanol) to 2.04 × 10(-4) min(-1) (acetonitrile). The second-order rate constant (k2) for the [H(+)]-catalyzed and [OH(-)]-catalyzed reactions are 6.61 × 10(-2) and 19.20 × 10(-2) M(-1) min(-1), respectively. This indicates that the specific base-catalyzed reaction is about three-fold faster than that of the specific acid-catalyzed reaction probably as a result of the rapid cleavage of diazabicyclononane side chain in the molecule. The kobs-pH profile for the degradation reactions is a V-shaped curve indicating specific acid-base catalysis. The minimum rate of photodegradation at pH 7-8 is due to the presence of zwitterionic species. There is a linear relation between kobs and the dielectric constant and an inverse relation between kobs and the viscosity of the solvent. Some photodegraded products of MF have been identified and pathways proposed for their formation in acid and alkaline solutions.
研究了莫西沙星（MF）在水溶液（pH 2.0 - 12.0）和有机溶剂中的光降解动力学。MF光降解是一种特定的酸碱催化反应，遵循一级动力学。MF光降解的表观一级速率常数（kobs）范围为0.69×10⁻⁴（pH 7.5）至19.50×10⁻⁴ min⁻¹（pH 12.0），在有机溶剂中为1.24×10⁻⁴（1 - 丁醇）至2.04×10⁻⁴ min⁻¹（乙腈）。[H⁺]催化和[OH⁻]催化反应的二级速率常数（k2）分别为6.61×10⁻²和19.20×10⁻² M⁻¹ min⁻¹。这表明特定的碱催化反应比特定的酸催化反应快约三倍，这可能是由于分子中重氮双环壬烷侧链的快速裂解所致。降解反应的kobs - pH曲线是一条V形曲线，表明存在特定的酸碱催化。pH 7 - 8时光降解速率最低是由于两性离子物种的存在。kobs与介电常数之间存在线性关系，与溶剂粘度之间存在反比关系。已鉴定出MF的一些光降解产物，并提出了它们在酸性和碱性溶液中的形成途径。
