Hammett Relationship in Oxidase‐Mimicking Metal–Organic Frameworks Revealed through a Protein‐Engineering‐Inspired Strategy

Abstract

While the unique physicochemical properties of nanomaterials that enable regulation of nanozyme activities are demonstrated in many systems, quantitative relationships between the nanomaterials structure and their enzymatic activities remain poorly understood, due to the heterogeneity of compositions and active sites in these nanomaterials. Here, inspired by metalloenzymes with well‐defined metal–ligand coordination, a set of substituted metal–organic frameworks (MOFs) with similar coordination is employed to investigate the relationship between structure and oxidase‐mimicking activity. Both experimental results and density functional theory calculations reveal a Hammett‐type structure–activity linear free energy relationship (H‐SALR) of MIL‐53(Fe) (MIL = Materials of Institute Lavoisier) nanozymes, in which increasing the Hammett σm value with electron‐withdrawing ligands increases the oxidase‐mimicking activity. As a result, MIL‐53(Fe) NO2 with the strongest electron‐withdrawing NO2 substituent shows a tenfold higher activity than the unsubstituted MIL‐53(Fe). Furthermore, the generality of H‐SALR is demonstrated for a range of substrates, one other metal (Cr), and even one other MOF type (MIL‐101). Such biologically inspired quantitative studies demonstrate that it is possible to identify quantitative structure–activity relationships of nanozymes, and to provide detailed insight into the catalytic mechanisms as those in native enzymes, making it possible to use these relationships to develop high‐performance nanomaterials.

Accelerated discovery of superoxide-dismutase nanozymes via high-throughput computational screening

“…4b plots the measured reduction potentials as a function of σ m . The reduction potentials and the σ m values have similar variation tendencies, which is in agreement with the knowledge that a stronger electron-withdrawing substituent leads to a high electron affinity of the material 42 . Importantly, the reduction potentials vary from 0.28 V (for X = NH 2 ) to 0.31 V (for X = NO 2 ), which are exactly located in the range from −0.16 V to 0.94 V. Therefore, all the eight MOFs satisfy the energy level criterion.…”

“…To determine whether these MOFs satisfy the energy level criterion (Eq. ( 1 )), their reduction potentials were measured using the cyclic voltammetry technique 42 . Fig.…”

“…The synthesis and characterization of the MIL-53(Fe)-X (X = NH 2 , CH 3 , H, OH, F, Cl, Br, and NO 2 ) compounds have been reported in our recent study 42 . The reduction potential values of the MIL-53(Fe)-X discussed in this work were also taken from the previous study 42 .…”

“…The synthesis and characterization of the MIL-53(Fe)-X (X = NH 2 , CH 3 , H, OH, F, Cl, Br, and NO 2 ) compounds have been reported in our recent study 42 . The reduction potential values of the MIL-53(Fe)-X discussed in this work were also taken from the previous study 42 . Because the values were measured using a saturated calomel electrode (SCE) and in a buffer solution with pH = 4.5, the values were converted to those with respect to HE and at pH = 7 using the following equation: where ∆pH is the difference between the target pH and the pH of the measurement, namely ∆pH = 7 − 4.5 = 2.5.…”

Ligand Functionalized Iron‐Based Metal‐Organic Frameworks for Efficient Electrocatalytic Oxygen Evolution

“…[14] Materials of Institute Lavoisier (MIL) is a common MOFs material (such as MIL-53, MIL-88B, and MIL-101). [15] With the development of MOFs research, there are more and more MIL series derivatives with different functional groups (e.g: À NH 2 , À NHCHO, À F, À Cl, À NO 2 , À CH 3 , À OH, and, À Br) and the same framework structure. [15,16] The functional groups of the benzene rings in ligand can induce rotating of the À COOÀ groups due to the steric hindrance of groups.…”