Two Co-Based Metal–Organic Framework Isomers with Similar Metal-Carboxylate Sheets: Turn-On Ratiometric Luminescence Sensing Activities toward Biomarker N-Acetylneuraminic Acid and Discrimination of Ga<sup>3+</sup> and In<sup>3+</sup>
Luyao Wang, Jiawei Cheng, Nana Liu, Huiqi Zou, Hui Yan, Jing Lü, Houting Liu, Yun‐Wu Li, Jianmin Dou, Suna Wang
Abstract
Two supramolecular Co-MOF isomers, namely, {[Co(L) 0.5 ( m -bimb)]·3H 2 O} n ( LCU-115 ) and {[Co(L) 0.5 ( p -bimb)]·3H 2 O} n ( LCU-116 ), were synthesized from an amide-containing carboxylic acid N, N ″-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide (H 4 L) and two flexible positional isostructural N-containing ligands m -bimb and p -bimb ( m -bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene; p -bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene). The carboxylate ligands connect Co(II) centers to form 2D metal-carboxylate sheets, which are extended further by m -bimb and p -bimb to form a 2D bilayer with parallel stacking ( LCU-115 ) and a 3D framework ( LCU-116 ), respectively. Luminescence measurements indicated that these two complexes exhibited interesting multiresponsive sensing activities toward pH, biomarker N-acetylneuraminic acid, and trivalent cations Ga 3+ /In 3+ . They show highly sensitive turn-on fluorescence responses in the acidic range and can also be regarded as on–off–on vapoluminescent sensors to typical acidic and basic gases HCl and Et 3 N. It is worth noting that these complexes have excellent turn-on ratiometric fluorescence sensing ability for N-acetylneuraminic acid (NANA) with detection limits as low as 7.39 and 8.06 μ M, respectively. Furthermore, they were successfully applied for the detection of NANA in simulated urine and serum samples with satisfactory results. For ion detection, LCU-116 could detect both Ga 3+ and In 3+, while LCU-115 could distinguish Ga 3+ from In 3+ with the latter showing luminescence quenching. The sensing mechanism was investigated in detail by XRD, UV–vis, EDS, XPS, SEM, and TEM. The results of interday and intraday precision studies gave low RSD values in the range of 1.19–3.53%, ascertaining the reproducibility of these sensors. The recoveries for the sensing analytes in simulated urine/serum or real water are satisfactory from 96.7 to 103.3% (toward NANA) and 96.6 to 115.0% (toward Ga 3+ and In 3+ ), indicating that these two complexes also possess acceptable reliability for monitoring in real samples. The results indicated that the supramolecular isomers LCU-115 and LCU-116 are promising material candidates for application in biological and environmental monitoring.