Effect of External Electric Fields on the C−H Bond Activation Reactivity of Nonheme Iron−Oxo Reagents

Dinitrogen Activation within Frustrated Lewis Pairs Is Promoted by Adding External Electric Fields

This study uses computational means to explore the feasibility of N2 cleavage by frustrated Lewis pair (FLPs) species. The employed FLP systems are phosphane/borane (1) and carbene/borane (2). Previous studies show that 1 and 2 react with H2 and CO2 but do not activate N2. The present study demonstrates that N2 is indeed inert, and its activation requires augmentation of the FLPs by an external tool. As we demonstrate here, FLP-mediated N2 activation can be achieved by an external electric field oriented along the reaction axis of the FLP. Additionally, the study demonstrates that FLP -N2 activation generates useful nitrogen compound, e.g., hydrazine (H2N-NH2). In summary, we conclude that FLP effectively activates N2 in tandem with oriented external electric fields (OEEFs), which play a crucial role. This FLP/OEEF combination may serve as a general activator of inert molecules.

Ligand effect on Ru-centered species toward methane activation

Ligands have been known to profoundly affect the chemical transformations of methane, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we demonstrate that the conversion of methane can be regulated by Ru centered cations with a series of ligands (C, CH, CNH, CHCNH). Gas-phase experiments complemented by theoretical dynamic analysis were performed to explore the essences and principles governing the ligand effect. In contrast to the inert Ru+, [RuC]+, and [RuCNH]+ toward CH4, the dehydrogenation dominates the reaction of ligand-regulated systems [RuCH]+/CH4 and [RuCHCNH]+/CH4. In active cases, CH acts as active sites, and regulates the activation of CH4 assisted by the "seemingly inert" CNH ligand.

Optimal Oriented External Electric Fields to Trigger a Barrierless Oxaphosphetane Ring Opening Step of the Wittig Reaction

The Wittig reaction is one of the most important processes in organic chemistry for the asymmetric synthesis of olefinic compounds. In view of the increasingly acknowledged potentiality of the electric fields in promoting reactions, here we will consider the effect of the oriented external electric field (OEEF) on the second step of Wittig reaction (i. e. the ring opening oxaphosphetane) in a model system for non-stabilized ylides. In particular, we have determined the optimal direction and strength of the electric field that should be applied to annihilate the reaction barrier of the ring opening through the polarizable molecular electric dipole (PMED) model that we have recently developed. We conclude that the application of the optimal external electric field for the oxaphosphetane ring opening favours a Bestmann-like mechanism.

One Stone, Two Birds: Using High Electric Fields to Enhance the Mobility and the Concentration of Point Defects in Ion-Conducting Solids

Improving the ionic conductivity of outstanding, composition-optimized crystalline electrolytes is a major challenge. Achieving increases of orders of magnitude requires, conceivably, highly nonlinear effects. One known possibility is the use of high electric fields to increase point-defect mobility. In this study, we investigate quantitatively a second possibility that high electric fields can increase substantially point-defect concentrations. As a model system, we take a pyrochlore oxide (La2Zr2O7) for its combination of structural vacancies and dominant anti-Frenkel disorder; we perform molecular-dynamics simulations with many-body potentials as a function of temperature and applied electric field. Results within the linear regime yield the activation enthalpies and entropies of oxygen-vacancy and oxygen-interstitial migration, and from three independent methods, the enthalpy and entropy of anti-Frenkel disorder. Transport data for the nonlinear regime are consistent with field-enhanced defect concentrations and defect mobilities. A route for separating the two effects is shown, and an analytical expression for the quantitative prediction of the field-dependent anti-Frenkel equilibrium constant is derived. In summary, we demonstrate that the one stone of a nonlinear driving force can be used to hit two birds of defect behavior.

Harnessing the High Interfacial Electric Fields on Water Microdroplets to Accelerate Menshutkin Reactions

Even though it is still an emerging field, the application of a high external electric field (EEF) as a green and efficient catalyst in synthetic chemistry has recently received significant attention for the ability to deliver remarkable control of reaction selectivity and acceleration of reaction rates. Here, we extend the application of the EEF to Menshutkin reactions by taking advantage of the spontaneous high electric field at the air-water interfaces of sprayed water microdroplets. Experimentally, a series of Menshutkin reactions were accelerated by 7 orders of magnitude. Theoretically, both density functional theory calculations and ab initio molecular dynamics simulations predict that the reaction barrier decreases significantly in the presence of oriented external electric fields, thereby supporting the notion that the electric fields in the water droplets are responsible for the catalysis. In addition, the ordered solvent and reactant molecules oriented by the electric field alleviate the steric effect of solvents and increase the successful collision rates, thus facilitating faster nucleophilic attack. The success of Menshutkin reactions in this study showcases the great potential of microdroplet chemistry for green synthesis.

Methane Activation by [AlFeO3 ]+ : the Hidden Spin Selectivity

The performance of heteronuclear cluster [AlFeO3 ]+ in activating methane has been explored by a combination of high-level quantum chemical calculations with gas-phase experiments. At room temperature, [AlFeO3 ]+ is a mixture of 7 [AlFeO3 ]+ and 5 [AlFeO3 ]+ , in which two states lead to different reactivity and chemoselectivity for methane activation. While hydrogen extracted from methane is the only product channel for the 7 [AlFeO3 ]+ /CH4 couple, 5 [AlFeO3 ]+ is able to convert this substrate to formaldehyde. In addition, the introduction of an external electric field may regulate the reactivity and product selectivity. The interesting doping effect of Fe and the associated electronic origins are discussed, which may guide one on the design of Fe-involved catalyst for methane conversion.

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

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.

Theoretical Investigation of the X-ray Stark Effect in Small Molecules

We have studied the Stark effect in the soft x-ray region for various small molecules by calculating the field-dependent x-ray absorption spectra. This effect is explained in terms of the response of molecular orbitals (core and valence), the molecular dipole moment, and the molecular geometry to the applied electric field. A number of consistent trends are observed linking the computed shifts in absorption energies and intensities with specific features of the molecular electronic structure. We find that both the virtual molecular orbitals (valence and/or Rydberg) as well as the core orbitals contribute to observed trends in a complementary fashion. This initial study highlights the potential impact of x-ray Stark spectroscopy as a tool to study electronic structure and environmental perturbations at a submolecular scale.

Quantum Tunneling in Reactions Modulated by External Electric Fields: Reactivity and Selectivity

Quantum tunneling and external electric fields (EEFs) can promote some reactions. However, the synergetic effect of an EEF on a tunneling-involving reaction and its temperature-dependence is not very clear. In this study, we extensively investigated how EEFs affect three reactions that involve hydrogen- or (ground- and excited-state) carbon-tunneling using reliable DFT, DLPNO-CCSD(T1), and variational transition-state theory methods. Our study revealed that oriented EEFs can significantly reduce the barrier and corresponding barrier width (and vice versa) through more electrostatic stabilization in transition states. These EEF effects enhance the nontunneling and tunneling-involving rates. Such EEF effects also decrease the crossover temperatures and quantum tunneling contribution, albeit with lower and thinner barriers. Moreover, EEFs can modulate and switch on/off the tunneling-driven 1,2-H migration of hydroxycarbenes under cryogenic conditions. Furthermore, our study predicts for the first time that EEF/tunneling synergy can control the chemo- or site-selectivity of one molecule bearing two similar/same reactive sites.

A catastrophe theory-based model for optimal control of chemical reactions by means of oriented electric fields

The effect of oriented external electric fields (OEEF) on chemical reactivity has been studied theoretically and computationally in the last decades. A central goal in this research area is to predict the orientation and the smallest amplitude electric field that renders a barrierless chemical process with the smallest possible strength. Recently, a model to find the optimal electric field has been proposed and described (Bofill JM et al., J. Chem. Theory Comput. 18:935, 2022). We here proof that this model is based on catastrophe and optimum control theories. Based on both theories a technical treatment of the model is given and applied to a two-dimensional generic example that provides insight into its nature and capability. Finally, the model is applied to determine the optimal OEEF for the trans-to-cis isomerization of a [3]cumulene derivative.

Effects and Influence of External Electric Fields on the Equilibrium Properties of Tautomeric Molecules

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an oriented external electric field (OEEF) on excited-state intramolecular proton transfer (ESIPT) from the studies available to date. The possibilities provided by OEEF for regulating several processes and studying physicochemical processes in tautomers have turned this direction into an attractive area of research due to its numerous applications.

Oriented External Electric Fields Regurating the Reaction Mechanism of CH4 Oxidation Catalyzed by Fe(IV)-Oxo-Corrolazine: Insight from Density Functional Calculations

Methane is the simplest alkane and can be used as an alternative energy source for oil and coal, but the greenhouse effect caused by its leakage into the air is not negligible, and its conversion into liquid methanol not only facilitates transportation, but also contributes to carbon neutrality. In order to find an efficient method for converting methane to methanol, CH₄ oxidation catalyzed by Fe(IV)-Oxo-corrolazine (Fe(IV)-Oxo-Cz) and its reaction mechanism regulation by oriented external electric fields (OEEFs) are systematically studied by density functional calculations. The calculations show that Fe(IV)-Oxo-Cz can abstract one H atom from CH₄ to form the intermediate with OH group connecting on the corrolazine ring, with the energy barrier of 25.44 kcal mol⁻¹. And then the product methanol is formed through the following rebound reaction. Moreover, the energy barrier can be reduced to 20.72 kcal mol⁻¹ through a two-state reaction pathway. Furthermore, the effect of OEEFs on the reaction is investigated. We found that OEEFs can effectively regulate the reaction by adjusting the stability of the reactant and the transition state through the interaction of electric field-molecular dipole moment. When the electric field is negative, the energy barrier of the reaction decreases with the increase of electric intensity. Moreover, the OEEF aligned along the intrinsic Fe‒O reaction axis can effectively regulate the ability of forming the OH on the corrolazine ring by adjusting the charges of O and H atoms. When the electric field intensity is −0.010 a.u., the OH can be directly rebounded to the CH₃· before it is connecting on the corrolazine ring, thus forming the product directly from the transition state without passing through the intermediate with only an energy barrier of 17.34 kcal mol⁻¹, which greatly improves the selectivity of the reaction.

Boosting the performance of single-atom catalysts via external electric field polarization

Single-atom catalysts represent a unique catalytic system with high atomic utilization and tunable reaction pathway. Despite current successes in their optimization and tailoring through structural and synthetic innovations, there is a lack of dynamic modulation approach for the single-atom catalysis. Inspired by the electrostatic interaction within specific natural enzymes, here we show the performance of model single-atom catalysts anchored on two-dimensional atomic crystals can be systematically and efficiently tuned by oriented external electric fields. Superior electrocatalytic performance have been achieved in single-atom catalysts under electrostatic modulations. Theoretical investigations suggest a universal “onsite electrostatic polarization” mechanism, in which electrostatic fields significantly polarize charge distributions at the single-atom sites and alter the kinetics of the rate determining steps, leading to boosted reaction performances. Such field-induced on-site polarization offers a unique strategy for simulating the catalytic processes in natural enzyme systems with quantitative, precise and dynamic external electric fields.

While single-atom catalysts offer high atomic utilization and tunable reaction pathways, there are still challenges in controlling reactivity. Here, authors use oriented external electric fields to induce electrostatic polarization in metal single-atoms and to boost water-splitting performances.

Oriented internal electrostatic fields: an emerging design element in coordination chemistry and catalysis

The power of oriented electrostatic fields (ESFs) to influence chemical bonding and reactivity is a phenomenon of rapidly growing interest. The presence of strong ESFs has recently been implicated as one of the most significant contributors to the activity of select enzymes, wherein alignment of a substrate's changing dipole moment with a strong, local electrostatic field has been shown to be responsible for the majority of the enzymatic rate enhancement. Outside of enzymology, researchers have studied the impacts of "internal" electrostatic fields via the addition of ionic salts to reactions and the incorporation of charged functional groups into organic molecules (both experimentally and computationally), and "externally" via the implementation of bulk fields between electrode plates. Incorporation of charged moieties into homogeneous inorganic complexes to generate internal ESFs represents an area of high potential for novel catalyst design. This field has only begun to materialize within the past 10 years but could be an area of significant impact moving forward, since it provides a means for tuning the properties of molecular complexes via a method that is orthogonal to traditional strategies, thereby providing possibilities for improved catalytic conditions and novel reactivity. In this perspective, we highlight recent developments in this area and offer insights, obtained from our own research, on the challenges and future directions of this emerging field of research.

Controlling Chemical Reactivity with Optimally Oriented Electric Fields: A Generalization of the Newton Trajectory Method

The use of oriented external electric fields (OEEF) as a tool to accelerate chemical reactions has recently attracted much interest. A new model to calculate the optimal OEEF of the least intensity to induce a barrierless chemical reaction path is presented. A suitable ansatz is provided by defining an effective potential energy surface (PES), which considers the unperturbed or original PES of the molecular reactive system and the action of a constant OEEF on the overall dipole moment of system. Based on a generalization of the Newton Trajectories (NT) method, it is demonstrated that the optimal OEEF can be determined upon locating a special point of the potential energy surface (PES), the so-called "optimal bond-breaking point" (optimal BBP), for which two different algorithms are proposed. At this point, the gradient of the original or unperturbed PES is an eigenvector of zero eigenvalue of the Hessian matrix of the effective PES. A thorough discussion of the geometrical aspects of the optimal BBP and the optimal OEEF is provided using a two-dimensional model, and numerical calculations of the optimal OEEF for a S_N2 reaction and the 1,3-dipolar retrocycloaddition of isoxazole to fulminic acid plus acetylene reaction serve as a proof of concept. The knowledge of the orientation of optimal OEEF provides a practical way to reduce the effective barrier of a given chemical process.

On the Precise and Continuous Regulation of the Superatomic and Spectroscopic Behaviors of the Quasi-Cubic W4C4 Cluster by the Oriented External Electric Field

Designing and realizing novel superatoms with controllable and tunable electronic properties is vital for their potential applications in cluster-assembly nanomaterials. Here, we investigated the effect of the oriented external electric field (OEEF) on the geometric and electronic structures as well as the spectroscopic properties of the quasi-cubic W₄C₄ cluster by utilizing the density functional theory (DFT) calculations. Compared with traditional models, the OEEF was observed to hold the special capability in continuously and precisely modulating the electronic properties of W₄C₄, that is, remarkably increasing its electron affinity (EA) (1.58 eV) to 5.61 eV under the 0.040 au OEEF (larger than any halogen atoms in the periodic table), which possesses the superhalogen behavior. Furthermore, the downward movement of the lowest unoccupied molecular orbital level of the cluster accompanied by the enhancement of the OEEF intensity was demonstrated to be the origin of the EA increment. Additionally, the photoelectron spectra (PES) of W₄C₄^- were also simulated under different OEEF intensities, where the PES peaks move to a higher energy area following the enhancement of the OEEF strength, exhibiting the blue-shift behavior. These findings observed here open a new avenue in conveniently and precisely adjusting the electronic properties of clusters, which will be beneficial for the rational design of superatoms or superatom-assembled nanomaterials under the external field.

An electrostatic duel: subtle differences in the catalytic performance of monoamine oxidase A and B isoenzymes elucidated at the residue level using quantum computations

The origin of the immense catalytic power of enzymes remains one of the biggest unresolved questions in biochemistry, with electrostatics being one of the main contenders. Herein, we report results that not only confirm that electrostatics is the driving force behind enzyme catalysis, but also that it is capable of tuning subtle differences in the catalytic performance between structurally similar enzymes, as demonstrated using the example of isoenzymes, monoamine oxidases A and B. Using our own computationally efficient multiscale model [A. Prah, et al., ACS Catal., 2019, 9, 1231] we analyzed the rate-limiting step of the reaction between phenylethylamine and both isoenzymes and deduced that the electrostatic environment provided by isoenzyme B has a perceivably higher catalytic influence on all the considered parameters of the reaction (energy barrier, charge transfer, dipole moment, and HOMO-LUMO gap). This is in full agreement with the available experimental kinetic data and with our own simulations of the reaction in question. In-depth analysis of individual amino acid contributions of both isoenzymes to the barrier (based on the interaction between the electric field provided by the enzyme and the dipole moment of the reacting moiety) shows that the majority of the difference between the isoenzymes can be attributed to a small number of sizable differences between the aligned amino acid pairs, whereas in most of the pairs the difference in contribution to the barrier is vanishingly small. These results suggest that electrostatics largely controls the substrate selectivity of enzymes and validates our approach as being capable of discerning fine nuances in the selectivity of structurally related isoenzymes.

Hydrogen and Halogen Bonding in Homogeneous External Electric Fields: Modulating the Bond Strengths

Recent years have witnessed various fascinating phenomena arising from the interactions of noncovalent bonds with homogeneous external electric fields (EEFs). Here we performed a computational study to interpret the sensitivity of intrinsic bond strengths to EEFs in terms of steric effect and orbital interactions. The block-localized wavefunction (BLW) method, which combines the advantages of both ab initio valence bond (VB) theory and molecular orbital (MO) theory, and the subsequent energy decomposition (BLW-ED) approach were adopted. The sensitivity was monitored and analyzed using the induced energy term, which is the variation in each energy component along the EEF strength. Systems with single or multiple hydrogen (H) or halogen (X) bond(s) were also examined. It was found that the X-bond strength change to EEFs mainly stems from the covalency change, while generally the steric effect rules the response of H-bonds to EEFs. Furthermore, X-bonds are more sensitive to EEFs, with the key difference between H- and X-bonds lying in the charge transfer interaction. Since phenylboronic acid has been experimentally used as a smart linker in EEFs, switchable sensitivity was scrutinized with the example of the phenylboronic acid dimer, which exhibits two conformations with either antiparallel or parallel H-bonds, thereby, opposite or consistent responses to EEFs. Among the studied systems, the quadruple X-bonds in molecular capsules exhibit remarkable sensitivity, with its interaction energy increased by -95.2 kJ mol^-1 at the EEF strength 0.005 a.u.

How Oriented External Electric Fields Modulate Reactivity

A judiciously oriented external electric field (OEEF) can catalyze a wide range of reactions and can even induce endo/exo stereoselectivity of cycloaddition reactions. The Diels-Alder reaction between cyclopentadiene and maleic anhydride is studied by using quantitative activation strain and Kohn-Sham molecular orbital theory to pinpoint the origin of these catalytic and stereoselective effects. Our quantitative model reveals that an OEEF along the reaction axis induces an enhanced electrostatic and orbital interaction between the reactants, which in turn lowers the reaction barrier. The stronger electrostatic interaction originates from an increased electron density difference between the reactants at the reactive center, and the enhanced orbital interaction arises from the promoted normal electron demand donor-acceptor interaction driven by the OEEF. An OEEF perpendicular to the plane of the reaction axis solely stabilizes the exo pathway of this reaction, whereas the endo pathway remains unaltered and efficiently steers the endo/exo stereoselectivity. The influence of the OEEF on the inverse electron demand Diels-Alder reaction is also investigated; unexpectedly, it inhibits the reaction, as the electric field now suppresses the critical inverse electron demand donor-acceptor interaction.

External electric field: a new catalytic strategy for the anti-Markovnikov hydrohydrazination of parent hydrazine

The anti-Markovnikov hydroamination reaction is considered to be a particular challenge, and one of the reactants, parent hydrazine, is also regarded as a troubling reagent. In this study, we first studied the hydrohydrazination of parent hydrazine via an effective and green catalyst—external electric field (EEF). The calculation results demonstrated that the anti-Markovnikov and Markovnikov pathways are competitive when there was no catalyst. EEF oriented along the negative direction of the X axis (F_x) accelerated the anti-Markovnikov addition reaction. Moreover, it lowered the barrier height of the first step by 16.0 kcal mol⁻¹ (from 27.8 to 11.8 kcal mol⁻¹) when the field strength was 180 (×10⁻⁴) au. Under the same conditions, the Markovnikov reaction pathway was inhibited, which means that EEF achieved the specificity of hydrohydrazination. The solvents are favorable for the first step addition reaction, particularly the synergy between solvents and F_x lowered the barrier heights by 8.3 (C₆H₆) and 10.7 (DMSO) kcal mol⁻¹ for an F_x = −60 (×10⁻⁴) au. Besides, the introduction of the electron-withdrawing substituent (trifluoromethyl) is also a good strategy to catalyze hydrohydrazination, while the electron-donating group (methoxy) is unfavorable.

The anti-Markovnikov hydrohydrazination of parent hydrazine were catalyzed by external electric field (EEF) to a large extent. Furthermore, the solvent effects and the substituent effects of the hydrohydrazination were enhanced in the presence of EEF.

Switch chemistry at cryogenic conditions: quantum tunnelling under electric fields

While the influence of intramolecular electric fields is a known feature in enzymes, the use of oriented external electric fields (EEF) to enhance or inhibit molecular reactivity is a promising topic still in its infancy. Herein we will explore computationally the effects that EEF can provoke in simple molecules close to the absolute zero, where quantum tunnelling (QT) is the sole mechanistic option. We studied three exemplary systems, each one with different reactivity features and known QT kinetics: π bond-shifting in pentalene, Cope rearrangement in semibullvalene, and cycloreversion of diazabicyclohexadiene. The kinetics of these cases depend both on the field strength and its direction, usually giving subtle but remarkable changes. However, for the cycloreversion, which suffers large changes on the dipole through the reaction, we also observed striking results. Between the effects caused by the EEF on the QT we observed an inversion of the Arrhenius equation, deactivation of the molecular fluxionality, and stabilization or instantaneous decomposition of the system. All these effects may well be achieved, literally, at the flick of a switch.

Adding an external electric field to reactions driven by quantum mechanical tunneling brings a whole new dimension to the idea of switch chemistry.

DFT-based reactivity and QSPR studies of platinum (IV) anticancer drugs

In the present work the influence of different axial ligands on reactivity of some selected Pt(IV) complexes with anticancer activities are investigated in both gas and solvent phases using Density Functional Theory (DFT) calculations. Calculated geometries of the complexes are in good agreement with their available X-ray data. The reactivity descriptors such as hardness, chemical potential and electrophilicity are calculated to measure stability and reactive nature of the complexes. It has been interesting to observe that the increase in the number of carbon chain of carboxylato axial ligand has no influence on reactivity of Pt(IV) complexes. Multiple linear regression analyses are performed to build Quantitative Structure Property Relationship (QSPR) models using DFT and molecular mechanics (MM+) based descriptors in gas and solvent phases. Chemical potential is found to be the most significant single descriptor to measure reduction potential of Pt(IV) complexes giving 87% correlation with experimental data. While gas phase derived descriptors are not statistically significant, inclusion of solvent medium increases the correlation of each descriptor with reduction potential and hydrophobicity of the complexes.

Manipulation of Diatomic Molecules with Oriented External Electric Fields: Linear Correlations in Atomic Properties Lead to Nonlinear Molecular Responses

Oriented external electric fields (OEEFs) have been shown to have great potential in being able to provide unprecedented control of chemical reactions, catalysis, and selectivity with applications ranging from H₂ storage to molecular machines. We report a theoretical study of the atomic origins of molecular changes because of OEEFs since understanding the characteristics of OEEF-induced couplings between atomic and molecular properties is an important step toward comprehensive understanding of the effects of strong external fields on the molecular structure, stability, and reactivity. We focus on the atomic and molecular (bond) properties of a set of homo- (H₂, N₂, O₂, F₂, and Cl₂) and heterodiatomic (HF, HCl, CO, and NO) molecules under intense external electric fields in the context of quantum theory of atoms in molecules (QTAIM). It is shown that the atomic properties (atomic charges, energies, and localization indices) correlate linearly with the field strengths, but molecular properties (bond length, electron density at the bond critical point, and electron delocalization index) exhibit nonlinear responses to the imposed fields. In particular, the changes in the electron density distribution alter the shapes and locations of the zero-flux surfaces, atomic volumes, atomic electron population, and localization/delocalization indices. The topography and topology of the molecular electrostatic potential undergo dramatic changes. External fields also perturb the covalent-polar-ionic characteristic of the studied chemical bonds, hallmarking the impact of electric fields on the stability and reactivity of chemical compounds. The findings are well-rationalized within the framework of the QTAIM and form a coherent conceptual understanding of these effects in prototypical diatomic molecules.

Rotatory Response of Molecular Electron Momentum Densities in Linear, Homogeneous Weak Electric Fields: A Topographical Analysis

One-electron properties for molecules such as electron density, electrostatic potential (ESP), and electron momentum density (EMD) are experimentally tractable quantities, useful in understanding chemical characteristics. In this work, effects of a uniform homogeneous external electric field on some characteristic one-electron properties of simple molecules are analyzed. EMDs and ESPs were used to understand the response of water, hydrogen fluoride, carbon monoxide, chloroacetylene, and ammonia in an electric field. Remarkably, the EMD maxima for these molecules get rotated as the electric field strength is varied. A greater order of change in EMD than in ESP with increasing electric field strength brings out the sensitivity of the EMDs, especially for the valence electronic region, which in the momentum space is mapped onto the vicinity of its origin. The eigenvectors of the EMD Hessian maxima at the momentum-space origin are seen to rotate as a function of increasing field strength, with the extra angular momentum imparted by the field manifesting itself as reconfiguration of the EMD distribution. In the presence of the field, valence states may couple with higher electronic states, leading to a mixing of the states resulting in avoided crossings as a function of the field strength. The avoided crossings legitimately estimate maximal field strength limits for the calculation, prior to ionization.

Tuning the Electronic Properties and Performance of Low-Temperature CO Oxidation of the Gold Cluster by Oriented External Electronic Field

Conventional electronic rules, including Jellium and Wade-Mingos rules and so on, have long been successfully dedicated to design superatoms. These rules, however, rely on altering the intrinsic properties, for example, the compositions or the number of valence electrons, of clusters, which is relatively complicated and inconvenient to manipulate, especially in experiments. Herein, by employing density functional theory calculations, the oriented external electric field (OEEF) was demonstrated to possess the capability of precisely and continuously regulating the electronic properties of clusters at will, representing a novel and noninvasive methodology in constructing stable superatoms because it hardly changes the geometries of clusters. More interestingly, the active sites formed by the charge redistribution upon the introduction of an OEEF could significantly promote the catalytic performance of the low-temperature CO oxidation over clusters. Considering the convenient source of the OEEF, the findings highlighted here may boost the potential applications of superatom-assembly nanomaterials in catalysis and materials science.

Theoretical study of methane adsorption and C─H bond activation over Fe-embedded graphene: Effect of external electric field

The effect of an external electric field (EF) on the methane adsorption and its activation on iron-embedded graphene (Fe-GPs) are investigated by using the M06-L density functional method. The EF is applied in the perpendicular direction to the graphene in the range of -0.015 to +0.015 a.u. with the interval of 0.005 a.u. The effects of EF on the adsorption, transition state and product complexes of the methane activation reaction are revealed. The binding energies of methane on Fe site in Fe-GPs are increased from -12.9 to -15.3, -18.1 and -21.5 kcal/mol for the negative EF of -0.005, -0.010 and -0.015, respectively. By applying positive EF, the activation barriers for methane activation are reduced in range of 3-8 kcal/mol (around 12-31%) and the reaction energies are more exothermic. The positive EF kinetically favors the reaction compared to the system without EF. The adsorption and activation of methane on Fe-GPs can be easily tuned by adjusting the external electric field for various applications. © 2019 Wiley Periodicals, Inc.

Insights into the activation process of CO2 through Dihydrogenation reaction

Based on first principle calculation, activation of CO₂ has been analyzed thoroughly by using different conceptual density functional theory based descriptors like reaction force, reaction force constant, reaction electronic flux, dual descriptor, etc. via dihydrogenation reaction of B₃N₃, H₂ and CO₂. The total reaction is a two-step reaction where initially B₃N₃H₂ is formed from the reaction between B₃N₃ and H₂ and in the second step HCOOH is form due to the reaction of CO₂ by B₃N₃H₂. It has been found that the di-hydrogen reaction for the CO₂ activation is endothermic in nature, which can be changed to exothermic reaction by applying proper external electric field. Movement of H₂ plays an important role in the CO₂ activation process. The reaction force constant, Wiberg bond index and its derivative reveal that the reaction is slightly asynchronous and concerted in nature.

A dynamic and electrostatic potential prediction of the prototropic tautomerism between imidazole 3-oxide and 1-hydroxyimidazole in external electric field

In order to obtain an optimum scheme for separating the proton-transfer tautomer, a dynamic investigation into the effect of the external electric field on the proton-transfer tautomeric conversion in imidazole 3-oxide and 1-hydroxyimidazole was carried out at the M06-2X/6-311++G** and CCSD(T)/6-311++G(2d,p) level, accompanied by the analysis of the surface electrostatic potentials. The results show that, for both the forward reaction "imidazole 3-oxide → N-hydroxyimidazole free radical → 1-hydroxyimidazole" and its reverse reaction processes, the fields parallel to the N→O or N-OH bond axis affect the barrier heights and rate constants considerably more than those parallel to the other orientations. As the field strength is increased along the orientation from the O to N atom, the chemical equilibrium moves toward the direction for the formation of 1-hydroxyimidazole, while the amount of imidazole 3-oxide is increased with the increased field strength along the opposite orientation. In the fields along the orientation consistent with the dipole moment, the electrostatic potentials and their variances "abnormally" increase for the transition states with the N→O bond in comparison with those in no field (they decrease generally), which enhances the nucleophilicity of the coordination O atom and the electrophilicity of the activated H atom. The analyses of the AIM (atoms in molecules) and NICS (nucleus-independent chemical shift) were used to explain the above anomaly. Graphical Abstract Electrostatic potentials and their variances "abnormally" increase in the external electric field, which greatly affects tautomeric conversion.

A greener catalyst for hydroboration of imines-external electric field modify the reaction mechanism

Usually, an extra catalyst (for example, the transition metal complexes) need to be used in catalyzing hydroboration, which involved the cost, environment, and so forth. Here, a greener and controllable catalyst-external electric field (EEF) was used to study its effect on hydroboration of N-(4-methylbenzyl)aniline (PhN═CHPhMe) with pinacolboane (HBPin). The results demonstrated that EEF could affect the barrier heights of both two pathways of this reaction. More significantly, flipping the direction of EEF could modify the reaction mechanism to induce a dominant inverse hydroboration at some field strength. That is to say, oriented EEF is a controlling switch for the anti- or Markovnikov hydroboration reaction of imines. This investigation is meaningful for the exploration of greener catalyst for chemistry reaction and guide a new method for the Markovnikov hydroboration addition. © 2019 Wiley Periodicals, Inc.

Dynamic Electric Field Complicates Chemical Reactions in Solutions

Chemical reactions can be strongly influenced by an external electric field (EEF), but because the EEF is often time-dependent and in case it does not adapt quickly enough to the reaction progress, especially during fast barrier crossing processes, dynamic effects could be important. Here we find that electrostatic interactions can reduce the height of the reaction barrier for a Claissen rearrangement reaction and accelerate the key motions for bonding. Meanwhile, strong electrostatic interactions can modify the barrier into an effective potential well, confining the system into the barrier until solvents adjust themselves to provide an appropriate EEF for charge redistribution. In this case, the otherwise concerted mechanism becomes a stepwise one. Consequently, the motion of solvents modulates the reaction dynamics and leads to heterogeneous reaction paths, even in a seemingly homogeneous aqueous solution. In addition, an excessive stabilization of transition state retards the barrier crossing process, making the thermodynamically favorable pathway less favored dynamically.

Electric field-induced selective catalysis of single-molecule reaction

Oriented external electric fields (OEEFs) offer a unique chance to tune catalytic selectivity by orienting the alignment of the electric field along the axis of the activated bond for a specific chemical reaction; however, they remain a key experimental challenge. Here, we experimentally and theoretically investigated the OEEF-induced selective catalysis in a two-step cascade reaction of the Diels-Alder addition followed by an aromatization process. Characterized by the mechanically controllable break junction (MCBJ) technique in the nanogap and confirmed by nuclear magnetic resonance (NMR) in bottles, OEEFs are found to selectively catalyze the aromatization reaction by one order of magnitude owing to the alignment of the electric field on the reaction axis. Meanwhile, the Diels-Alder reaction remained unchanged since its reaction axis is orthogonal to the electric fields. This orientation-selective catalytic effect of OEEFs reveals that chemical reactions can be selectively manipulated through the elegant alignment between the electric fields and the reaction axis.

A valence bond study of the activation of methyl halides bonds by electric fields

In the present work, the activation of methyl halides bonds under experience of an external electric field (EEF) is explained from the Valence Bond theory perspective. The dissociation mechanism of C–X bonds (X [Formula: see text] Cl, Br, I) influenced by a homogeneous and a heterogeneous field placed parallel to the bond axis is presented. For all examples, an increase in the electric field strength have similar consequences: (i) the decrease of the energy depth along the dissociation path, (ii) an increase of the equilibrium interatomic distance (at high EEFs), and (iii) the transition from a homolytic to a heterolytic dissociation after some field magnitude. These general behaviors are explained through the curve crossing between the ionic and the covalent structure at some field strength.

A noncovalent interaction insight onto the concerted metallation deprotonation mechanism

The CMD/AMLA mechanisms of cyclopalladation and the parent fictitious cyclonickelation of N,N-dimethylbenzylamine have been investigated by joint DFT-D and DLPNO-CCSD(T) methods assisted by QTAIM.

Metal-free catalysis for the Markovnikov hydrosilylation of styrene

Both the directions of the external electric field oriented along the “bond axis” (FX) and the “reaction axis” (FY) influenced the Markovnikov hydrosilylation of styrene, where the negative FY direction induced the largest effect.

Electric field influence on the helical structure of peptides: insights from DFT/PCM computations

The switching of the electric field with a particular directionality could be used for the healing of misfolded proteins.

Possible B–C bonding in the hydroboration of benzonitrile by an external electric field

Generally, the hydroboration of benzonitrile produces B–N containing compound. An unprecedented B–C bond may be formed in the presence of suitable external electric field (EEF), which could influence hydroboration and control selectivity by changing its magnitude and directions.

The directions of an external electric field control the catalysis of the hydroboration of C–O unsaturated compounds

EEF facilitates hydroboration by reducing its barrier in a specific direction; as illustrated in the image, the monkey easily picks the peach on the lower branch.