Fluorescein and sulfonefluorescein dyes are stable in solution within a wide pH range. Nucleophilic addition of the hydroxide (HO^–) group to the nodal carbon atom is not typical of these compounds. They are also not prone to rupture of the pyran cycle under the action of alkali. However, the last-named heterocycle readily opens at high pH values in the case of derivatives containing nitro groups in the xanthene moiety. Moreover, while in the case of nitrofluoresceins, for example, 4,5-dinitrofluorescein, this reaction is irreversible, with 4,5-dinitrosulfonefluorescein acidification of the alkaline solution immediately returns the visible absorption spectrum to that of the original hydroxyxanthene dye. We present a quantitative study of the kinetics of the pyran cycle rupture in aqueous alkali without and with micelles of a cationic surfactant. Also, both initial dye and reaction product were studied via the matrix-assisted laser desorption/ionisation time-of-flight (MALDI-ToF) technique. The second part of the article is devoted to the interaction of 4,5-dinitrosulfonefluorescein and other dyes of similar structure with lysozyme basing on the MALDI-ToF mass spectrometry. This made it possible to arrange the dyes according to their affinity for the protein and draw some conclusions about the nature of the association of the dye with lysozyme.

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4,5-二硝基砜荧光素和相关染料：吡喃环可逆断裂的动力学及其与溶菌酶的相互作用

荧光素和砜荧光素染料在较宽的 pH 范围内在溶液中稳定。亲核加成氢氧化物（HO的^-) 连接到节点碳原子的基团不是这些化合物的典型特征。它们在碱的作用下也不容易破裂吡喃循环。然而，在呫吨部分含有硝基的衍生物的情况下，最后命名的杂环很容易在高 pH 值下打开。此外，在硝基荧光素的情况下，例如 4,5-二硝基荧光素，该反应是不可逆的，碱性溶液的 4,5-二硝基砜荧光素酸化立即使可见吸收光谱恢复到原始羟基呫吨染料的可见吸收光谱。我们对没有和有阳离子表面活性剂胶束的碱水溶液中吡喃循环破裂的动力学进行了定量研究。还，通过基质辅助激光解吸/电离飞行时间 (MALDI-ToF) 技术研究初始染料和反应产物。文章的第二部分致力于基于 MALDI-ToF 质谱分析 4,5-二硝基砜荧光素和其他类似结构的染料与溶菌酶的相互作用。这使得根据染料对蛋白质的亲和力排列染料成为可能，并得出一些关于染料与溶菌酶结合性质的结论。