Chromenoquinoline-based thiol probes: a study on the quencher position for controlling fluorescent Off–On characteristics
作者:Dnyaneshwar Kand、Arunasree Marasanapalli Kalle、Pinaki Talukdar
DOI:10.1039/c2ob27192c
日期:——
The design, synthesis and thiol sensing ability of chromenoquinoline-based fluorescent probes 4, 5 and 6 are reported here. The relative position of the maleimide moiety was varied along the chromenoquinoline fluorophore to decrease the background fluorescence. Lower background fluorescence in probes 4 and 6 was rationalized by the smaller kr/knr values compared to that of probe 5. An intramolecular charge transfer (ICT) mechanism was proposed for quenching and the extent was dependent on the position of the maleimide quencher. Fluorescent OffâOn characteristics were evaluated by theoretical calculations. All probes were selective only towards thiol containing amino acids. Thiol sensing by probes 4 and 6 were much better compared to 5. Probe 4 displayed a better fluorescence response for less hindered thiol (185-, 223- and 156-fold for Hcy, Cys and GSH, respectively), while for probe 6, a higher enhancement in fluorescence was observed with more hindered thiols (180-, 205- and 245-fold for Hcy, Cys and GSH, respectively). The better response to bulkier thiol, GSH by probe 6 was attributed to the steric crowding at the C-4 position and bulkiness of the GSH group which force the succinimide unit to be in a nearly orthogonal conformation. This spatial arrangement was important in reducing the fluorescence quenching ability of the succinimide moiety. The application of probes 4, 5 and 6 was demonstrated by naked eye detection thiols using a 96-well plate system as well as by live-cell imaging.
本研究报道了基于色烯并喹啉的荧光探针4、5和6的设计、合成及其对硫醇的检测能力。通过改变马来酰亚胺基团在色烯并喹啉荧光团中的相对位置,减少了背景荧光。与探针5相比,探针4和6的较低背景荧光可以通过其较小的kr/knr值来解释。提出了一种分子内电荷转移(ICT)机制来解释荧光淬灭的现象,且其程度依赖于马来酰亚胺淬灭剂的位置。通过理论计算评估了荧光的关-开特性。所有探针仅对含硫醇的氨基酸具有选择性。探针4和6对硫醇的检测能力显著优于探针5。探针4对不太受阻的硫醇(分别为Hcy、Cys和GSH时荧光增强185倍、223倍和156倍)表现出更好的荧光响应,而探针6则在对更加受阻的硫醇时(分别为Hcy、Cys和GSH时荧光增强180倍、205倍和245倍)显示出更高的荧光增强。探针6对体积更大的硫醇GSH的更好响应归因于C-4位置的空间拥挤和GSH基团的体积,这迫使琥珀酰亚胺单元呈现近乎正交的构象。这种空间排列对于降低琥珀酰亚胺基团的荧光淬灭能力至关重要。探针4、5和6的应用通过使用96孔板系统和活细胞成像进行了裸眼检测硫醇的验证。