Cardona Maria A, Makuc Damjan, Szaciłowski Konrad, Plavec Janez, Magri David C
Department of Chemistry, Faculty of Science, University of Malta, Msida MSD 2080, Malta.
Slovenian NMR Centre, National Institute of Chemistry, Hajdrihova 19, SI-1000 Ljubljana, Slovenia.
ACS Omega. 2017 Sep 26;2(9):6159-6166. doi: 10.1021/acsomega.7b00887. eCollection 2017 Sep 30.
Water-soluble azobenzene derivatives containing amino[(ethanesulfonate)] groups are demonstrated as colorful pH indicators in water and on filter paper. Vibrant color changes were observed from yellow/orange to pink between pH 1 and 4, which are attributed to an intramolecular charge-transfer mechanism. The p s of the indicators range from 2.1 to 2.6. H/H-N NMR studies in deuterium oxide reveal that the protonation of the azobenzene pH indicators occurs predominantly at the β-azo nitrogen atom, in agreement with the density functional theory calculations. Excellent selectivity for protons was confirmed in water over common biologically relevant metal ions. Studies in methanol, however, indicate that the pH indicator with a methoxy group to the amino[(ethanesulfonate)] group facilitates the selective coordination of Cu with a binding constant pβ of 4.6 ± 0.1. The indicators complement the existing library of azobenzene indicator dyes and may be useful for measuring the environmental pH at higher proton concentrations.
含有氨基[(乙磺酸盐)]基团的水溶性偶氮苯衍生物被证明是水中和滤纸上的彩色pH指示剂。在pH 1至4之间观察到从黄色/橙色到粉红色的鲜明颜色变化，这归因于分子内电荷转移机制。这些指示剂的pKa范围为2.1至2.6。在重水中进行的1H/15N NMR研究表明，偶氮苯pH指示剂的质子化主要发生在β-偶氮氮原子上，这与密度泛函理论计算结果一致。在水中，相对于常见的生物相关金属离子，已证实这些指示剂对质子具有出色的选择性。然而，在甲醇中的研究表明，氨基[(乙磺酸盐)]基团带有甲氧基的pH指示剂促进了Cu的选择性配位，结合常数pβ为4.6±0.1。这些指示剂补充了现有的偶氮苯指示剂染料库，可能有助于在较高质子浓度下测量环境pH值。
