Carbohydrazide-based covalent organic framework as a novel peroxidase mimic.

Nanomaterials with enzymatic properties have attracted much attention in recent years for various reasons such as good catalytic efficiency, high stability, low cost and good biocompatibility. Here, we synthesized and characterized a covalent organic framework (COF) via the condensation reaction of 2,4,6-triformylphloroglucinol (Tp) and carbohydrazide (CR). The computational studies were done using DFT/B3LYP/6-311G(d,p). The optimized structure (confirmed as energy minimum) exhibits a 3.08 eV HOMO-LUMO gap, indicating Lewis acidic character (ω = 5.64). NBO analysis reveals strong charge transfer (E2 up to 223 kcal/mol), while NCI-RDG shows coexistance of hydrogen bonds, van der Waals interactions and steric hindrance. ELF (> 0.5) confirms covalent CN bonding of two linkers. These results validate the COF's successful formation and electronic properties. In the presence of hydrogen peroxide (H2O2), the TP-CR COF was able to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to a blue-colored oxidized product (ox-TMB), indicating its high peroxidase-like activity. Based on this phenomenon, the reported COF was used as a colorimetric probe for the sensitive and selective detection of H2O2 and glucose. The limit of detection (LOD) of H2O2 was calculated to be 5.5 μM in a linear range from 10 to 250 μM, while the LOD of glucose was evaluated to be 6.7 μM in the range of 10-265 μM. Therefore, the prepared TP-CR COF can be used as a highly sensitive and selective peroxidase mimic for the detection of hydrogen peroxide-related molecules, indicating their potential in biomedical applications.