氧氟沙星的荧光光谱与质子化作用研究

研究了氧氟沙星(Ofloxacin，OFL)在不同pH条件下的荧光光谱、紫外光谱和质子化作用。在强酸性溶液中，OFL分子可以结合两个质子而以三元酸H₃L2+的形式存在，最大荧光发射波长(λ_max)为505 nm。随着pH值升高，OFL的荧光光谱发生变化，在激发光谱中352 nm 形成一等荧光点，同时在紫外吸收光谱中出现等色点，这一光谱特征表明H₃L2+逐渐失去4位C羰基氧结合的质子。在pH 2.5～4范围内，OFL以H₂L+形式存在，λ_max为499 nm。当pH＞4时，随pH值升高，位于499 nm 的荧光发射峰逐渐蓝移至455 nm，在484 nm形成一等荧光发射点，表明C-3位羧基质子的离解。在pH 7左右，OFL以双极离子HL形式存在，λ_max为455 nm，是最强的荧光型体。当pH＞8时，随pH值升高，λ_max由455 nm红移至约475 nm，同时荧光强度下降，表明HL失去哌嗪环N-4上结合的质子。当pH＞10时，OFL以阴离子L-形式存在, 荧光强度随pH值升高而降低，但λmax基本不变，表明介质环境对OFL的荧光性质有一定影响。

Fluorescence Spectra and Protonation of Ofloxacin

Fluorescence spectra, ultraviolet spectra and protonation of Ofloxacin (OFL) at different pH values have been studied. In strong acidic solutions, OFL molecule might accept two protons to exist as ternary acid H3L2+ with a maximum emission wavelength (lambdamax) at 505 nm. Along with the increase in pH value, fluorescence spectrum of OFL changed, an iso-fluorescence point at 352 nm was found in the fluorescence excitation spectra, and at the same time, isosbestic points were found in its UV absorption spectra. This spectral feature reveals that H3L2+ gradually lost hydrogen ion combined on C-4 keto oxygen. In the range of pH 2.5 to pH 4, OFL exists as H2L+ with lambdamax at 499 nm. When pH>4, the fluorescence emission peak at 499 nm gradually blue-shifted to 455 nm as pH was increasing, and an iso-fluorescence emission point was formed at 484 nm, indicating the dissociation of hydrogen ion of carboxylic acid at C-3. At about pH 7.0, OFL exists in the dipole ion form HL with lambdamax at 455 nm, which is the strongest fluorescence form. When pH>8, lambdamax red-shift from 455 to 475 nm as pH increases, meanwhile, fluorescence intensity decreases, indicating that HL lost hydrogen ion combined on N-4 of piperazinyl group. When pH>10, OFL exists in anion ion form L-, and fluorescence intensity decreases with pH increasing, but lambdamax remains essentially constant, indicating that medium environment influences the fluorescence property of OFL.