Zhang Jingtuo, Yang Mu, Mazi Wafa, Adhikari Kapil, Fang Mingxi, Xie Fei, Valenzano Loredana, Tiwari Ashutosh, Luo Fen-Tair, Liu Haiying
Department of Chemistry, Michigan Technological University, Houghton, MI 49931.
Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China.
ACS Sens. 2016 Feb 26;1(2):158-165. doi: 10.1021/acssensors.5b00065. Epub 2015 Nov 27.
Three uncommon morpholine-based fluorescent probes (, and ) for pH were prepared by introducing morpholine residues to BODIPY dyes at 4,4'- and 2,6-positions, respectively. In contrast to morpholine-based fluorescent probes for pH reported in literature, these fluorescent probes display high fluorescence in a basic condition while they exhibit very weak fluorescence in an acidic condition. The theoretical calculation confirmed that morpholine is unable to function as either an electron donor or an electron acceptor to quench the BODIPY fluorescence in the neutral and basic condition via photo-induced electron transfer (PET) mechanism because the LUMO energy of morpholine is higher than those of the BODIPY dyes while its HOMO energy is lower than those of the BODIPY dyes. However, the protonation of tertiary amines of the morpholine residues in an acidic environment leads to fluorescence quenching of the BODIPY dyes d-PET mechanism. The fluorescence quenching is because the protonation effectively decreases the LUMO energy which locates between the HOMO and LUMO energies of the BODIPY dyes. Fluorescent probe with deep-red emission has been successfully used to detect pH changes in mammalian cells.
通过分别在4,4'-位和2,6-位将吗啉残基引入到BODIPY染料中，制备了三种用于检测pH值的罕见的基于吗啉的荧光探针（、和）。与文献中报道的用于检测pH值的基于吗啉的荧光探针不同，这些荧光探针在碱性条件下显示出高荧光，而在酸性条件下则表现出非常弱的荧光。理论计算证实，吗啉在中性和碱性条件下不能通过光诱导电子转移（PET）机制作为电子供体或电子受体来淬灭BODIPY荧光，因为吗啉的最低未占分子轨道（LUMO）能量高于BODIPY染料的LUMO能量，而其最高已占分子轨道（HOMO）能量低于BODIPY染料的HOMO能量。然而，在酸性环境中吗啉残基的叔胺质子化会导致BODIPY染料通过d-PET机制发生荧光淬灭。荧光淬灭是因为质子化有效地降低了位于BODIPY染料的HOMO和LUMO能量之间的LUMO能量。具有深红色发射的荧光探针已成功用于检测哺乳动物细胞中的pH变化。
