强酸性环境中氧氟沙星的荧光光谱与质子化作用研究

Fluorescence Spectra and Protonation of Ofloxacin in Strong Acidic Solutions

研究了氧氟沙星(ofloxacin,简称OFL)在不同浓度H2SO4溶液中的荧光光谱,紫外光谱和质子化作用。OFL分子上含3个N原子,4个O原子和1个F原子,当将其溶于适当的溶剂中时,OFL会随所处溶液的酸度不同获取或释放H离子,从而改变其质子化状态。质子化状态的不同会影响分子结构的共轭范围,进而对其荧光光谱和紫外可见光谱行为产生深刻影响。在高浓度H2SO4溶液中,OFL分子质子化程度较高,最大荧光发射波长为400nm。在低浓度H2SO4溶液中,OFL分子质子化程度较低,最大荧光发射波长为505nm。在中等浓度的H2SO4溶液中,OFL的荧光发射光谱则有400和500nm两个发射峰,且其强度随着H2SO4浓度的变化而变化,这说明至少有两种质子化结构状态共存,其浓度随着H2SO4浓度不同而彼消此长。随着H2SO4浓度的降低,OFL的荧光激发光谱和紫外吸收光谱均发生了红移,也表明H2SO4浓度直接影响OFL的质子化状态。基于此,有望开发出一种高酸度条件下的紫外和荧光探针。

Fluorescence and UV-Vis spectra of ofloxacin （OFL）in sulfuric acid were studied. In the present paper, a new promnation state of OFL was observed. In hydrochloric acid, OFL produced bright green fluorescence upon excitation by UV radiation. The maximal emission wavelength of OFL is about 505 nrn. However, OFL produces violet fluorescence when dissolved in concentrated sulfuric acid. The maximal emission wavelength changes into 400 nm. Further analysis demonstrated that the above changes arise from the variation of protonation states of OFL molecule. In dilute sulfuric acid, OFL accepted one proton, resulting in a protonation state that is similar to the OFL molecule dissolved HCI solution. The corresponding fluorescence band occurs at 505 nm. In concentrated sulfuric acid solution, OFL might accept additional protons. As a result, the size of the conjugated system is reduced and the fluorescence band exhibits a blue shift. In sulfuric acid of moderate concentrations, two bands at 505 and 400 nm respectively were found in the fluorescence emission spectra, indicating that OFL in two different protonation states coexists in the solution. In addition, both excitation band in excitation spectra and absorption bands in UV-Vis spectra exhibit red-shifted with the decrease in the concentration of sulfuric acid. Based on the above result, OFL can be used as a spectral probe to reflect the variation of H^＋ in strong acid environment.