Abstract：Metal-organic supramolecular with well-defined nanosized molecular cavity is able to encapsulate some special guest substrates so that they have been widely applied in molecular recognition and molecular separations. In this work, a highly sensitive recognition of biological molecular γ-glutamyl-cysteinyl-glycine (GSH) was achieved with a trinuclear zinc-based metal-organic cyclohelicate fluorescence probe M-1, which was assembled with zinc ion and two tridentate (N2O) ligand with dansyl sulfonamide group and hydrogen bond site. The recognition process for GSH with M-1 was determined with 1H NMR, ESI-MS, UV-Vis and fluorescence spectra. To establish the recognition mechanism of GSH, its component amino acids (Cys，Glu，Gly) were investigated by spectroscopic titrations. The results show that the M-1 with trinuclear structure exhibits high stability in a water/DMF 1∶9 solution. UV-Vis adsorption titration revealed that a significant absorbance increase at 303 nm with the addition of GSH to the M-1 solution, but an absorbance decrease was observed at 380 nm. A sharp isobestic point was obtained at 330 nm. In addition, based on the UV-Vis adsorption titration results, ESI-MS analysis of M-1 confirmed that 1∶1 complexation stoichiometry of the host-guest behavior was obtained for GSH and the association constant (log KGSH) was calculated as 4.62±0.15. Moreover, 1H NMR titrations of M-1 upon the above amino acids revealed that the Glu residue of GSH was sent into M-1 cavity through the static interactions between the COO- groups and metal ions. In addition, it was found that the fluorescence intensity exhibits a two-fold enhancement, with the emission wavelength red-shifted from 510 to 540 nm upon the addition of GSH into M-1. Upon the addition of Cys and Glu in the solution of M-1, the luminescence intensity exhibits 0.4 times and 0.2 times enhancement, respectively, with the emission wavelength not being shifted. On the contrary, no change of the luminescence intensity was observed after adding the Gly to the solution of M-1. Based on the above analysis, it is confirmed that the joint effects of size limitation of the M-1 cavity and the hydrogen bonding interactions between Cys moiety of GSH and the amide groups sited in M-1 molecuar will generate measurable spectral changes, which lead to visualizing the highly sensitive recognition for GSH. The low detection limit was up to 3.0×10-6 mol·L-1.
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