Xu Yu, Jiang Zheng, Xiao Yu, Bi Fu-Zhen, Miao Jun-Ying, Zhao Bao-Xiang
School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China; Taishan College, Shandong University, Jinan 250100, PR China.
School of Life Science, Shandong University, Jinan 250100, PR China; Taishan College, Shandong University, Jinan 250100, PR China.
Anal Chim Acta. 2014 Apr 11;820:146-51. doi: 10.1016/j.aca.2014.02.029. Epub 2014 Feb 22.
A novel turn-off fluorescent probe based on coumarin and imidazole moiety for extremely acidic conditions was designed and developed. The probe with pKa=2.1 is able to respond to very low pH value (below 3.5) with high sensitivity relying on fluorescence quenching at 460 nm in fluorescence spectra or the ratios of absorbance maximum at 380 nm to that at 450 nm in UV-vis spectra. It can quantitatively detect pH value based on equilibrium equation, pH=pKa-log[(Ix-Ib)/(Ia-Ix)]. It had very short response time that was less than 1 min, good reversibility and nearly no interference from common metal ions. Moreover, using (1)H NMR analysis and theoretical calculation of molecular orbital, we verified that a two-step protonation process of two N atoms of the probe leaded to photoinduced electron transfer (PET), which was actually the mechanism of the fluorescence quenching phenomenon under strongly acidic conditions. Furthermore, the probe was also applied to imaging strong acidity in bacteria, E.coli and had good effect. This work illustrates that the new probe could be a practical and ideal pH indicator for strongly acidic conditions with good biological significance.
设计并开发了一种基于香豆素和咪唑部分的新型用于极端酸性条件的猝灭型荧光探针。该探针的pKa = 2.1，能够依靠荧光光谱中460 nm处的荧光猝灭或紫外可见光谱中380 nm处最大吸光度与450 nm处最大吸光度之比，对非常低的pH值（低于3.5）做出高灵敏度响应。它可以基于平衡方程pH = pKa - log[(Ix - Ib)/(Ia - Ix)]定量检测pH值。其响应时间非常短，小于1分钟，具有良好的可逆性，并且几乎不受常见金属离子的干扰。此外，通过核磁共振氢谱（¹H NMR）分析和分子轨道理论计算，我们验证了探针两个氮原子的两步质子化过程导致了光诱导电子转移（PET），这实际上是强酸性条件下荧光猝灭现象的机理。此外，该探针还应用于大肠杆菌中强酸度的成像，效果良好。这项工作表明，这种新型探针对于具有良好生物学意义的强酸性条件可能是一种实用且理想的pH指示剂。
