LAQV/REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, 4169-007, Porto, Portugal.
Centro de Investigação em Química (CIQUP), Departamento de, Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Rua Campo Alegre 687, 4169-007, Porto, Portugal.
Chemistry. 2019 Nov 27;25(66):15073-15082. doi: 10.1002/chem.201903313. Epub 2019 Sep 24.
A series of pyridyl analogues of rosamines was prepared by employing two methodologies: (i) the conventional-heating condensation of a pyridinecarboxaldehyde with 3-(diethylamino)phenol in propionic acid, and (ii) the novel ohmic-heating assisted condensation under "on water" conditions, followed by oxidation. The 4-pyridyl substituted rosamine was further converted into the N-methylpyridinium derivative through N-alkylation using methyl iodide. The influence of the position and cationization of the nitrogen atom of the pyridyl ring in the physicochemical properties of fluorophores was investigated by H, C, N NMR spectral analysis, UV/Vis and fluorescence spectroscopy, single-crystal X-ray diffraction (4-pyridyl and N-methylpyridinium derivatives) and thermal-behavior analysis. Curiously, for ethanolic solutions of 4-pyridyl and N-methylpyridinium derivatives an extinction of color and fluorescence over time was observed. This phenomenon was further studied and the data revealed that it is the result of nucleophilic addition of ethoxide ion to the central 9-position of the xanthene. The kinetics of the process is slower for the 4-pyridyl rosamine, which emphasizes the importance of the charge in the N-methylpyridinium analogue in the reactivity of the molecule towards a nucleophile agent. This phenomenon is reversible, meaning that the compounds can be rapidly recovered by decreasing the pH, opening new avenues in the sensing applications of this class of rosamines.
（i）在丙酸中，用吡啶甲醛与 3-（二乙氨基）苯酚进行常规加热缩合，和（ii）在“水相”条件下采用新颖的欧姆加热辅助缩合，然后进行氧化。4-吡啶取代的罗沙明通过用碘化甲烷进行 N-烷基化进一步转化为 N-甲基吡啶鎓衍生物。通过 1 H、13 C、15 N NMR 光谱分析、UV/Vis 和荧光光谱、单晶 X 射线衍射（4-吡啶和 N-甲基吡啶鎓衍生物）和热行为分析研究了吡啶环氮原子的位置和阳离子化对荧光团物理化学性质的影响。奇怪的是，对于 4-吡啶和 N-甲基吡啶鎓衍生物的乙醇溶液，观察到颜色和荧光随时间的消光。进一步研究了这一现象，数据表明这是由于乙氧基离子对呫吨的中心 9-位的亲核加成。4-吡啶罗沙明的过程动力学较慢，这强调了电荷在 N-甲基吡啶鎓类似物中对分子对亲核试剂反应性的重要性。这种现象是可逆的，这意味着通过降低 pH 值可以快速回收化合物，为这一类罗沙明的传感应用开辟了新途径。
