Directional Electric Fields at Designed MOF Sites: Implications for Electrostatic Preorganization and Catalysis
Year: 2026
Type: preprint
Abstract: Enzymes achieve their enormous catalytic power in part through electrostatic preorganization: non-covalent interactions arrange an electric field that is preorganized to stabilize the change in dipole moment between a reaction's ground and transition states. Thus, the catalytic relevance of an electric field depends not only on its magnitude but also on its orientation. Here we use the enforced rigidity of a metal–organic framework (MOF), PCN-521, to demonstrate this orientation dependence directly. We introduce an aldehyde carbonyl vibrational Stark probe in situ, first as a protected ketal, then deprotect it to reveal a carbonyl at the same node-capping site as a previously reported nitrile probe, extending field measurements to a field reporter of greater relevance to enzymatic catalysis. Electric field- vibrational frequency calibrated probes using the vibrational Stark effect report a trifluoroacetate field donor that projects nearly its full destabilizing field onto the collinear nitrile (sp, C≡N) but only a fraction onto the off-axis aldehyde (sp2, C=O) — a geometric effect. Because the framework's non-covalent contacts, unlike an enzyme active site's, cannot reorganize, this controlled, single-site comparison isolates alignment from magnitude. While electric fields are often invoked to explain observations near electrodes or droplet interfaces, these results show the importance of alignment which is often neglected.
Source: ChemRxiv
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214630420