强酸性环境中氧氟沙星的质子化模型研究

利用核磁共振波谱技术研究了不同浓度硫酸溶液中氧氟沙星(OFL)的1H,19F和13C核磁共振谱,对不同硫酸浓度引起的δH,δF,δC和JFC耦合常数的变化进行比较分析,由此推测其结构状态.综合1H,19F和13C核磁共振谱特点及其变化,提出OFL分子在强酸性环境中N1'被进一步质子化的结构模型.在浓硫酸溶液中,N1'被进一步质子化,并与F9形成氢键(N1'—H+┈F9),该结构使分子的共轭程度大幅降低,导致其荧光发射波长、荧光激发波长及紫外吸收波长均发生蓝移.硫酸溶液中氧氟酸和甲基氧氟沙星的荧光光谱行为进一步证明了OFL分子在浓硫酸溶液中质子化模型的合理性.

Studies on the Protonation Structure of Ofloxacin in Concentrated Sulfuric Acid Solutions

Systematic NMR spectroscopic investigation on ofloxacin(OFL) in concentrated sulfuric acid solution was carried out via 19F NMR, 1H NMR and 13C NMR experiments. Complete assignment on 19F NMR, 1H NMR and 13C NMR of ofloxacin in sulfuric acid solutions were obtained. The chemical shift of H, F, C, and the JFC of OFL molecule in sulfuric acid solutions of different concentrations were found to be very helpful for the identification the protonation structure of OFL molecule. According to the variation of the chemical shift of H, F, C, and the JFC of OFL molecule in sulfuric acid solutions of different concentrations, we propose that the N1′ is further protonated in concentrated sulfuric acid solutions. Additionally, a new hydrogen bond(N1′—H+┈F9) forms and the structure can be stabilized by a five-member ring and the conjugate system is distorted by the five-member ring. As a result, the emission peak, excitation peak in fluorescent spectra and absorption peak in UV spectra of OFL exhibit blue-shifted significantly. In addition, the proposed protonation structure was further supported by spectroscopic behavior of oxygen-fluorine acid and methyl-ofloxacin.