Farrugia Kristina N, Makuc Damjan, Podborska Agnieszka, Szaciłowski Konrad, Plavec Janez, Magri David C
Department of Chemistry, Faculty of Science, University of Malta, Msida, MSD 2080, Malta.
Org Biomol Chem. 2015 Feb 14;13(6):1662-72. doi: 10.1039/c4ob02091j.
Four model thiosemicarbazide anion chemosensors containing three N-H bonds, substituted with phenyl and/or 4-nitrophenyl units, were synthesised and studied for their anion binding abilities with hydroxide, fluoride, acetate, dihydrogen phosphate and chloride. The anion binding properties were studied in DMSO and 9 : 1 DMSO-H2O by UV-visible absorption and (1)H/(13)C/(15)N NMR spectroscopic techniques and corroborated with DFT studies. Significant changes were observed in the UV-visible absorption spectra with all anions, except for chloride, accompanied by dramatic colour changes visible to the naked eye. These changes were determined to be due to the deprotonation of the central N-H proton and not due to hydrogen bonding based on (1)H/(15)N NMR titration studies with acetate in DMSO-d6-0.5% water. Direct evidence for deprotonation was confirmed by the disappearance of the central thiourea proton and the formation of acetic acid. DFT and charge distribution calculations suggest that for all four compounds the central N-H proton is the most acidic. Hence, the anion chemosensors operate by a deprotonation mechanism of the central N-H proton rather than by hydrogen bonding as is often reported.
合成了四种含有三个N-H键、被苯基和/或4-硝基苯基单元取代的硫代氨基脲阴离子化学传感器，并研究了它们与氢氧根、氟离子、醋酸根、磷酸二氢根和氯离子的阴离子结合能力。通过紫外可见吸收光谱和（1）H/（13）C/（15）N核磁共振光谱技术在二甲基亚砜（DMSO）和9:1的DMSO-H2O中研究了阴离子结合特性，并通过密度泛函理论（DFT）研究进行了佐证。除氯离子外，所有阴离子的紫外可见吸收光谱均观察到显著变化，同时伴有肉眼可见的剧烈颜色变化。基于在DMSO-d6-0.5%水中用醋酸根进行的（1）H/（15）N核磁共振滴定研究，确定这些变化是由于中心N-H质子的去质子化，而不是由于氢键作用。中心硫脲质子的消失和醋酸的形成证实了去质子化的直接证据。DFT和电荷分布计算表明，对于所有四种化合物，中心N-H质子是最酸性的。因此，阴离子化学传感器通过中心N-H质子的去质子化机制运行，而不是像通常报道的那样通过氢键作用。
