Nanochannel-Based Heterometallic {Co^IITb^III}-Organic Framework for Fluorescence Recognition of Tryptophan and Catalytic Cycloaddition of Epoxides with CO₂

Abstract

To pave the way for the salient application of metal–organic frameworks (MOFs) as realistic sensors, it is critical to screen or design the customized functional structure with specified prominent synergistic effects provided by its constituents, voids, specific surfaces, functional sites, etc. This prompts us to study the sensing performance of a honeycomb nanochannel of heterometallic MOFs previously invented. This structure has excellent physical and chemical properties of high specific surface area, good chemical stability, and highly open coexistence of Lewis acid–base sites. In this work, the highly robust sky-blue [CoTb(CO2)6(OH2)]-based heterometallic framework of {[(CH3)2NH2][CoTb(TDP)(H2O)]·3H2O·4DMF} n (NUC-31; H6TDP = 2,4,6-tri(2′,4′-dicarboxyphenyl)pyridine) was synthesized. The results of the fluorescence recognition experiment show that, compared with other amino acids, NUC-31 has an ultrastrong fluorescence quenching for tryptophan with a detection limit as low as 0.11 mM, which means that NUC-31 can be used as a potential fluorescence probe for the targeted detection of tryptophan of ecosystems. In addition, the catalytic experiment results indicated that NUC-31 has high activity for catalyzing the cycloaddition reaction of epoxides with CO2 under 75 °C and 1 atm. It is precisely due to NUC-31 having extremely unsaturated tetracoordinated Co(II) and hepta-coordinated Tb(III) metal ions as well as a high pore volume (65.1%), which makes the catalytic reaction conditions relatively mild. Therefore, this work certificated that nanoporous MOFs assembled from a multifunctional ligand with the highly open coexistent Lewis acid–base sites had a potential application not only in monitoring tryptophan in clinical scenarios but also as an effective heterogeneous catalyst.

Nanoporous Lanthanide-Based MOFs for Catalyzing the Cycloaddition of CO2 and the Knoevenagel Condensation

“…The mechanism of Knoevenagel condensation facilitated by MOF-based catalysts has been hypothetically elaborated in most of published literatures and our previous studies. − Based on the structural characteristics of NUC-110Gd and obtained catalytic experimental data, the speculated reaction mechanism is shown in Figure . First, aldehyde is polarized via the formation of complex M···OCH-R between the Lewis acidic Gd 3+ ion and the oxygen atom of the formyl group, causing the carbon atoms of aldehyde groups to become positively charged centers.…”

Robust Nitro-Functionalized {Zn3}-Organic Framework for Excellent Catalytic Performance on Cycloaddition Reaction of CO2 with Epoxides and Knoevenagel Condensation

“…The yield results of BN product catalyzed by repeatedly used NUC-80a are shown in Figure S33, which exhibited that the yield of BN product had a slight downward trend with the increase of cycle time, which might be caused by the loss and contamination of the catalyst in the process of centrifugal separation, cleaning, drying, and transfer. 76,77 However, the very slow catalytic deactivation performance of NUC-80a during performed five-cycle experiments proved that it could be recovered and used repeatedly. In addition, the PXRD and the FTIR diagrams for recovered and assynthesized NUC-80a in Figures S34−S35 exhibited that the link mode between Zn 2+ and organic ligand in the host framework remained intact because of the consistence for main peaks.…”