An algorithm to find the optimal oriented external electrostatic field for annihilating a reaction barrier in a polarizable molecular system

Abstract

The use of oriented external electric fields (OEEFs) to promote and control chemical reactivity has motivated many theoretical and computational studies in the last decade to model the action of OEEFs on a molecular system and its effects on chemical processes. Given a reaction, a central goal in this research area is to predict the optimal OEEF (oOEEF) required to annihilate the reaction energy barrier with the smallest possible field strength. Here, we present a model rooted in catastrophe and optimum control theories that allows us to find the oOEEF for a given reaction valley in the potential energy surface (PES). In this model, the effective (or perturbed) PES of a polarizable molecular system is constructed by adding to the original, non-perturbed, PES a term accounting for the interaction of the OEEF with the intrinsic electric dipole and polarizability of the molecular system, so called the polarizable molecular electric dipole (PMED) model. We demonstrate that the oOEEF can be established by locating a point in the original PES with unique topological properties: the optimal barrier breakdown or bond-breaking point (oBBP). The essential feature of the oBBP structure is the fact that this point maintains its topological properties for all the applied OEEFs, also for the unperturbed PES, thus becoming much more relevant than the commonly used minima and transition state structures. The PMED model proposed here has been implemented in an open access package and is shown to successfully predict the oOEEF for two processes: an isomerization reaction of a cumulene derivative and the Huisgen cycloaddition reaction.

My Vision of Electric-Field-Aided Chemistry in 2050

“…As we shall see next, locating the reaction axis is simple and extremely intuitive. At the same time, it is optional to use one of the computational methods, which have been developed to locate the OEEF direction which will optimize the barrier-lowering effect. − Similarly, there are methods which calculate electric fields from charge distributions. ,, Application of the F Z OEEF along the reaction axis of a given reaction will polarize the TS and increase its dipole moment (μ Z ), as shown in Figure b and Figure a. Flipping the direction of the OEEF along the same axis will decrease the dipole moment of the TS (e.g., see Figure a). The interaction energy of the OEEF, with the polarized dipole moment of the TS or of any species along the reaction axis, is given by eq , as a direct product of the OEEF vector (F Z in units of V/Å) and the corresponding molecular dipole moment vector (μ Z in Debye (D) units) which in turn, involves the due polarization by the OEEF. E int ⁣ false( kcal/mol false) = 4.8 F Z · m Z …”

“…As we shall see next, locating the reaction axis is simple and extremely intuitive. At the same time, it is optional to use one of the computational methods, which have been developed to locate the OEEF direction which will optimize the barrier-lowering effect. − Similarly, there are methods which calculate electric fields from charge distributions. ,, …”

“…In retrospect, the acquired VB thinking turned out to be essential for the developments of the current notions of OEEF and formulating the “reaction axis rule”, which defines the best action of OEEFs on structure and reactivity. − The “reaction axis” is the essential direction along which the OEEF should be applied in order to enhance (or inhibit, if so desired) reaction rates. This rule has served as a conceptual guide and proved to be useful and easily applicable. , As reviewed by Siddiki et al, by now, the task of locating the directions of OEEFs that will minimize the energy barrier for a given reaction system have also been implemented in computational procedures, for example, in refs − . My primary goal in the present Perspective is to outline key principles of using OEEF and to note a few recent experimental studies, which may impact the future of mainstream chemistry and, hence, also my vision for 2050.…”

Using oriented external electric fields to manipulate rupture forces of mechanophores

“…They have recently been used for determining optimal OEEFs for the purpose of lowering reaction barriers. 32,33 Modelling the bond rupture of a mechanophore requires including mechanical force in the calculation, which can be done using a multitude of different approaches, 34,35 but to the best of our knowledge, a thorough computational investigation of the behaviour of mechanophores in OEEFs using a combination of electric field and mechanical force models has not been done until now.…”

Local Electric Fields Drives the Proton-Coupled Electron Transfer within Cytochrome P450 Reductase

“…Extensive experiments and theories have shown that externally applied electric fields or internal electric fields intrinsically present in certain catalysts can be used to effectively control chemical activity and selectivity. − Specifically, the significant role of electric fields has been extensively researched in both natural and synthetic enzymes. − Protonation of His180, adding a positive charge to the imidazole ring of its side chain, notably alters the electrostatic environment in which the PCET reaction takes place. We examined the electrostatic impact of the positively charged HIP180 by using Mulliken charges from QM/MM calculations to assess the interaction energy between His180’s charged side chain and the PCET reaction complex, including FADH – , FMN, Glu142, and the bridging water molecules.…”