Exploring the Linear Energy Relationships between Activation Energy and Reaction Energy under an Electric Field

Electric-field (EF)-mediated chemistry has recently garnered increasing attention partly owing to its capability to catalyze a broad range of chemical reactions. How the EF affects the kinetics and thermodynamics of target reactions is a critical question. Herein, both density functional theory (DFT) and MP2 calculations suggest that the change of activation energy ΔΔE‡ and the change of reaction energy ΔΔErxn under an EF display a linear energy relationship (LER) ΔΔE‡ = mΔΔErxn. This has been tested against several reactions such as SN2 and proton transfer reactions, including neutral and charged systems and endothermic and exothermic processes. The linear coefficient m approximates to the ratio of the dipole moment change, i.e., Δμ‡/Δμrxn, of the studied reactions. The LER holds well at EF strengths up to ≈1 V/nm but deviates from the DFT-calculated results at larger EFs. Such deviations are mainly caused by the molecular geometry changes under an EF. Systems with larger polarizability experience greater geometry changes under an EF, thus leading to larger deviations. In addition, we propose that the reaction barrier can be predicted by -Δμ‡F - 0.5Δα‡F2, while it is well approximated by -Δμ‡F for small EF strengths. The proposed LER and the field-dependent barrier estimation promise broad applicability in EF-mediated chemical reactions.

Space Charge, Modulating the Catalytic Activity of Single-Atom Metal Catalysts

Potential-induced electrode charging is a prerequisite to initiate electrochemical reactions at the electrode-electrolyte interface. The 'interface space charge' could dramatically alter the reaction environment and the charge density of the active site, both of which potentially affect the electrochemical activity. However, our understanding of the electrocatalytic role of space charge has been limited. Here, we separately modulate the amount of space charge (characterized by the areal density, σ) with maintaining the electrochemical potential for the oxygen reduction reaction (ORR) at the same level, by exploiting the unique structural feature of MeNC. We reveal that changes in σ control the ORR activity, which is computationally explained by the inductive polarization of the charge density at the active sites, affecting their turnover rates. To guide catalyst design including the space charge effect, we develop a new descriptor, explaining the activity trend in various metal centers and pH conditions using a single volcano. These findings offer fresh insights into the role of space charge in electrocatalysis, providing a new framework for optimizing catalyst design and performance.

Control of Reversible Oxidative Addition/Reductive Elimination of Surface-Attached Catalysts by External Electric Fields

We demonstrate that applied electric fields at interfaces can control the oxidative addition/reductive elimination equilibria of surface-attached molecular catalysts without any synthetic modification. Density functional theory (DFT) calculations show that the oxidative addition of HCl to a Co complex is "field switchable", being favorable under negative fields but unfavorable under sufficiently positive fields. Extending the analysis to different substrates (O2, H2) and metal centers (Rh, Ir) reveals consistent trends in the magnitude of the electric field effect: Co > Rh ≈ Ir and HCl > O2 > H2. Our analysis indicates that these field-dependent effects are driven by changes in the permanent dipole moment, offering key insights for the design of field-controllable catalytic systems. This framework presents a novel strategy to overcome the "Goldilocks problem" of balancing competing catalytic steps by leveraging applied electric fields to dynamically tune catalytic reactivity in situ.

Putting Charge Transfer Degree as a Bridge Connecting Surface-Enhanced Raman Spectroscopy and Photocatalysis

To date, few systematic approach has been established for predicting catalytic performance by analyzing the spectral information of molecules adsorbed on photocatalyst surfaces. Effective charge transfer (CT) between the semiconductor photocatalysts and surface-absorbed molecules is essential for enhancing catalytic activity and optimizing light energy utilization. This study aimed to validate the surface-enhanced Raman spectroscopy (SERS) based on the CT enhancement mechanism in investigating the CT process during semiconductor photocatalytic C-C coupling model reactions. A copper ion doping strategy was employed to simultaneously enhance the SERS effect and catalytic activity of zinc oxide (ZnO) derived from metal-organic framework (MOF). By analyzing molecular fingerprint SERS spectra, we calculated the degree of CT (ρCT), revealing that SERS enhancement is attributed to the CT mechanism. In situ SERS spectra confirmed a high correlation between the catalytic activity and ρCT of ZnO with varying copper ion doping levels. A range of photoelectric and spectroscopic tests validated the effectiveness of SERS in linking CT to photocatalytic performance, consistent with first-principles density functional theory (DFT) simulations. This finding is also validated in other semiconductor materials and catalytic reactions, demonstrating the broad applicability of ρCT for predicting and evaluating SERS and catalytic activity.

The Impact of Electric Fields on Processes at Electrode Interfaces

The application of external electric fields to influence chemical reactions at electrode interfaces has attracted considerable interest in recent years. However, the design of electric fields to achieve highly efficient and selective catalytic systems, akin to the optimized fields found at enzyme active sites, remains a significant challenge. Consequently, there has been substantial effort in probing and understanding the interfacial electric fields at electrode/electrolyte interfaces and their effect on adsorbates. In this review, we examine recent advances in experimental, computational, and theoretical studies of the interfacial electric field, the origin of the vibrational Stark effect of adsorbates on electrode surfaces, and the effects of electric fields on reactions at electrode/electrolyte interfaces. We also discuss recent advances in control of charge transfer and chemical reactions using magnetic fields. Finally, we outline perspectives on key areas for future studies.

Supramolecularly Built Local Electric Field Microenvironment around Cobalt Phthalocyanine in Covalent Organic Frameworks for Enhanced Photocatalysis

The local electric field (LEF) plays an important role in the catalytic process; however, the precise construction and manipulation of the electric field microenvironment around the active site remains a significant challenge. Here, we have developed a supramolecular strategy for the implementation of a LEF by introducing the host macrocycle 18-crown-6 (18C6) into a cobalt phthalocyanine (CoPc)-containing covalent organic framework (COF). Utilizing the supramolecular interaction between 18C6 and potassium ion (K+), a locally enhanced K+ concentration around CoPc can be built to generate a LEF microenvironment around the catalytically active Co site. The COF with this supramolecularly built LEF realizes an activity of up to 7.79 mmol mmolCo-1 h-1 in the photocatalytic CO2 reduction reaction (CO2RR), which is a 180% improvement compared to its counterpart without 18C6 units. The effect of LEF can be subtly controlled by fully harnessing the K+@18C6 interaction by changing the potassium salts with different counterions. In situ spectroscopy and density functional theory calculations show that the complexation of K+ by 18C6 creates a positive electric field that stabilizes the critical intermediate *COOH involved in CO2RR, which can be tuned by the halide ion-mediated K+@18C6 interaction and hydrogen-bonding interaction, consequently leading to improved catalytic performance to varying degrees.

Modulating the Band Structure of Two-Dimensional Black Phosphorus via Electronic Effects of Organic Functional Groups for Enhanced Hydrogen Production Activity

Electronic effects of organic functional groups play a fundamental role in determining the rate and/or direction of organic chemical reactions. The implementation of this concept in selective organic catalysis is achieved by tuning the electronic effects of organic functional groups to alter the corresponding reactivity. However, this approach has hardly been applied to modulate the band structure of inorganic materials. Here, we show that modulating the electronic band structure of two-dimensional black phosphorus (BP) is possible via the electronic effects of organic functional groups covalently modified on its surface. Organic functional group can either donate or withdraw charge density from BP surface, which will alter the bonding/anti-binding orbitals occupancy and thus shift the band-edge positions of functionalized BP downward/upward. Therefore, the valence-band maxima and the conduction-band minima of functionalized BP can be continuously tuned by changing the binding group with different Hammett parameters. Finally, unexpectedly high hydrogen evolution reaction rates under visible light are achieved using functionalized BP heterojunctions as photocatalysts. This work underscores the significant role of electronic effects in chemically controlling BP's band structure, offering greater flexibility and affordability beyond physical method limits.

Utilization of Electric Fields to Modulate Molecular Activities on the Nanoscale: From Physical Properties to Chemical Reactions

As a primary energy source, electricity drives broad fields from everyday electronic circuits to industrial chemical catalysis. From a chemistry viewpoint, studying electric field effects on chemical reactivity is highly important for revealing the intrinsic mechanisms of molecular behaviors and mastering chemical reactions. Recently, manipulating the molecular activity using electric fields has emerged as a new research field. In addition, because integration of molecules into electronic devices has the natural complementary metal-oxide-semiconductor compatibility, electric field-driven molecular devices meet the requirements for both electronic device miniaturization and precise regulation of chemical reactions. This Review provides a timely and comprehensive overview of recent state-of-the-art advances, including theoretical models and prototype devices for electric field-based manipulation of molecular activities. First, we summarize the main approaches to providing electric fields for molecules. Then, we introduce several methods to measure their strengths in different systems quantitatively. Subsequently, we provide detailed discussions of electric field-regulated photophysics, electron transport, molecular movements, and chemical reactions. This review intends to provide a technical manual for precise molecular control in devices via electric fields. This could lead to development of new optoelectronic functions, more efficient logic processing units, more precise bond-selective control, new catalytic paradigms, and new chemical reactions.

Screening of F-containing electrolyte additives and clarifying their decomposition routes for stable Li metal anodes

Constructing a LiF-rich solid electrolyte interphase (SEI) is a feasible strategy for inhibiting lithium (Li) dendrites of Li metal anodes (LMAs). However, selecting appropriate F-containing additives with efficient LiF contribution is still under active research. Herein, a series of fluorinated additives with diverse F/C molar ratios are investigated, and we demonstrate that the hexafluoroglutaric anhydride (F6-0) holds the best capability to derive the LiF-rich SEI in regular carbonate electrolytes (RCEs). To ameliorate the decomposition kinetics of the F6-0, LiNO3 (LNO) as an adjuvant is further introduced in the system. As a result, the reduction efficiency of F6-0 is increased to 91% under the F6-0/LNO synergistic effect, enabling the LMA with a uniform LiF-rich SEI in the RCE with merely 4 vol. % F6-0/LNO (F6L) addition. The LiNi0.8Co0.1Mn0.1O2||Li-20μm full-cell with the F6L also showcases better cycling and rate performances than the cases with other F-containing additives.

Electro-inductive Effects and Molecular Polarizability for Vibrational Probes on Electrode Surfaces

A microscopic understanding of electric fields and molecular polarization at interfaces will aid in the design of electrocatalytic systems. Herein, variants of 4-mercaptobenzonitrile are designed to test different schemes for breaking the continuous conjugation between a gold electrode surface and a nitrile group. Periodic density functional theory calculations predict applied potential dependencies of the CN vibrational frequencies similar to those observed experimentally. The CN frequency response decreased more when the conjugation was broken between the benzene ring and the nitrile group than between the electrode and the benzene ring, highlighting molecular polarizability effects. The systems with continuous or broken conjugation are dominated by electro-inductive effects or through-space electrostatic effects, respectively. Analysis of the fractional charge transfer between the electrode and the molecule as well as the occupancy of the CN antibonding orbital provides further insights. Balancing the effects of molecular polarizability, electro-induction, and through-space electrostatics has broad implications for electrocatalyst design.

Interfacial Electrochemistry of Catalyst-Coordinated Graphene Nanoribbons

The immobilization of molecular electrocatalysts on conductive electrodes is an appealing strategy for enhancing their overall activity relative to those of analogous molecular compounds. In this study, we report on the interfacial electrochemistry of self-assembled two-dimensional nanosheets of graphene nanoribbons (GNR-2DNS) and analogs containing a Rh-based hydrogen evolution reaction (HER) catalyst (RhGNR-2DNS) immobilized on conductive electrodes. Proton-coupled electron transfer (PCET) taking place at N-centers of the nanoribbons was utilized as an indirect reporter of the interfacial electric fields experienced by the monolayer nanosheet located within the electric double layer. The experimental Pourbaix diagrams were compared with a theoretical model, which derives the experimental Pourbaix slopes as a function of parameter f, a fraction of the interfacial potential drop experienced by the redox-active group. Interestingly, our study revealed that GNR-2DNS was strongly coupled to glassy carbon electrodes (f = 1), while RhGNR-2DNS was not (f = 0.15). We further investigated the HER mechanism by RhGNR-2DNS using electrochemical and X-ray absorption spectroelectrochemical methods and compared it to homogeneous molecular model compounds. RhGNR-2DNS was found to be an active HER electrocatalyst over a broader set of aqueous pH conditions than its molecular analogs. We find that the improved HER performance in the immobilized catalyst arises due to two factors. First, redox-active bipyrimidine-based ligands were shown to dramatically alter the activity of Rh sites by increasing the electron density at the active Rh center and providing RhGNR-2DNS with improved catalysis. Second, catalyst immobilization was found to prevent catalyst aggregation that was found to occur for the molecular analog in the basic pH. Overall, this study provides valuable insights into the mechanism by which catalyst immobilization can affect the overall electrocatalytic performance.

Local electric field in nanocavities dictates the vibrational relaxation dynamics of interfacial molecules

Plasmonic nanocavities enable the generation of strong light-matter coupling and exhibit great potential in plasmon-mediated chemical reactions (PMCRs). Although an electric field generated by nanocavities (E n) has recently been reported, its effect on the vibrational energy relaxation (VER) of the molecules in the nanocavities has not been explored. In this study, we reveal the impact of an electric field sensed by molecules (para-substituted thiophenol derivatives) in a nanocavity (E f) on VER processes by employing advanced time-resolved femtosecond sum frequency generation vibrational spectroscopy (SFG-VS) supplemented by electrochemical measurements. The magnitude of E n is almost identical (1.0 ± 0.2 V nm-1) beyond the experimental deviation while E f varies from 0.3 V nm-1 to 1.7 V nm-1 depending on the substituent. An exponential correlation between E f and the complete recovery time of the ground vibrational C[double bond, length as m-dash]C state (T 2) of the phenyl ring is observed. Substances with a smaller T 2 are strongly correlated with the reported macroscopic chemical reactivity. This finding may aid in enriching the current understanding of PMCRs and highlights the possibility of regulating vibrational energy flow into desired reaction coordinates by using a local electric field.

Insight from Boric Acid into Bioskeleton Formation: Inscribed Circle Effect on the Edge-Base Plate Growth

Complex morphologies in nature often arise from the assembly of elemental building blocks, leading to diverse and intricate structures. Understanding the mechanisms that govern the formation of these complex morphologies remains a significant challenge. In particular, the edge-base plate growth of biogenic crystals plays a crucial role in directing the development of intricate bioskeleton morphologies. However, the factors and regulatory processes that govern edge-base plate growth remain insufficiently understood. Inspired by biological skeletons and based on the soluble property of boric acid (BA) in both water and alcohols, we obtained a series of novel BA morphologies, including coccolith, and anemone biological skeletons. Here, we unveil the "inscribed circle effect", a concise mathematical model that reveals the underlying causative factors and regulatory mechanisms driving edge-base plate growth. Our findings illuminate how variations in solvent environments can exert control over the edge-base plate growth pathways, thereby resulting in the formation of diverse and complex morphologies. This understanding holds significant potential for guiding the chemical synthesis of bioskeleton materials.

Raman Monitoring of the Electro-Optical Synergy-Induced Enhancements in Carbon-Bromine Bond Cleavage, Reaction Rate, and Product Selectivity of p-Bromothiophenol

Electro-optical synergy has recently been targeted to improve the separation of hot carriers and thereby further improve the efficiency of plasmon-mediated chemical reactions (PMCRs). However, the electro-optical synergy in PMCRs needs to be more deeply understood, and its contribution to bond dissociation and product selectivity needs to be clarified. Herein, the electro-optical synergy in plasmon-mediated reduction of p-bromothiophenol (PBTP) was studied on a plasmonic nanostructured silver electrode using in situ Raman spectroscopy and theoretical calculations. It was found that the electro-optical synergy-induced enhancements in the cleavage of carbon-bromine bonds, reaction rate, and product selectivity (4,4'-biphenyl dithiol vs thiophenol) were largely affected by the applied bias, laser wavelength, and laser power. The theoretical simulation further clarified that the strong electro-optical synergy is attributed to the matching of energy band diagrams of the plasmonic silver with those of the adsorbed PBTP molecules. A deep understanding of the electro-optical synergy in PBTP reduction and the clarification of the mechanism will be highly beneficial for the development of other highly efficient PMCRs.

Spectroelectrochemical determination of thiolate self-assembled monolayer adsorptive stability in aqueous and non-aqueous electrolytes

Self-assembled monolayers (SAM) are ubiquitous in studies of modified electrodes for sensing, electrocatalysis, and environmental and energy applications. However, determining their adsorptive stability is crucial to ensure robust experiments. In this work, the stable potential window (SPW) in which a SAM-covered electrode can function without inducing SAM desorption was determined for aromatic SAMs on gold electrodes in aqueous and non-aqueous solvents. The SPWs were determined by employing cyclic voltammetry, attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and surface plasmon resonance (SPR). The electrochemical and spectroscopic findings concluded that all the aromatic SAMs used displayed similar trends and SPWs. In aqueous systems, the SPW lies between the reductive desorption and oxidative desorption, with pH being the decisive factor affecting the range of the SPW, with the widest SPW observed at pH 1. In the non-aqueous electrolytes, the desorption of SAMs was observed to be slow and progressive. The polarity of the solvent was the main factor in determining the SPW. The lower the polarity of the solvent, the larger the SPW, with 1-butanol displaying the widest SPW. This work showcases the power of spectroelectrochemical analysis and provides ample future directions for the use of non-polar solvents to increase SAM stability in electrochemical applications.

Mechanistic Studies of Stimulus-Response Integrated Catalysis of Single-Atom Alloys under Electric Fields for Electrochemical Nitrogen Reduction

The present work introduces a novel catalytic strategy to promote the nitrogen reduction reaction (NRR) by employing a cooperative Cu-based single-atom alloy (SAA) and oriented external electric fields (OEEFs) as catalysts. The field strength (F)-dependent reaction pathways are investigated by means of first-principles calculations. Different dipole-induced responses of intermediates to electric fields break the original scaling relationships and effectively tune not only the activity but also the product selectivity of the NRR. When the most active Os1Cu SAA is taken as an example, in the absence of an OEEF, the overpotential (η) of the NRR is 0.62 V, which is even larger than that of the competitive hydrogen evolution reaction (HER). A negative field not only reduces η but switches the preference to the NRR over the HER. In particular, η at F = -1.14 V/Å reaches the bottom of 0.18 V, which is 70% lower than that in the field-free state.

Exploring Chemical Reaction Space with Machine Learning Models: Representation and Feature Perspective

Chemical reactions serve as foundational building blocks for organic chemistry and drug design. In the era of large AI models, data-driven approaches have emerged to innovate the design of novel reactions, optimize existing ones for higher yields, and discover new pathways for synthesizing chemical structures comprehensively. To effectively address these challenges with machine learning models, it is imperative to derive robust and informative representations or engage in feature engineering using extensive data sets of reactions. This work aims to provide a comprehensive review of established reaction featurization approaches, offering insights into the selection of representations and the design of features for a wide array of tasks. The advantages and limitations of employing SMILES, molecular fingerprints, molecular graphs, and physics-based properties are meticulously elaborated. Solutions to bridge the gap between different representations will also be critically evaluated. Additionally, we introduce a new frontier in chemical reaction pretraining, holding promise as an innovative yet unexplored avenue.

Electrically driven proton transfer promotes Brønsted acid catalysis by orders of magnitude

Electric fields play a key role in enzymatic catalysis and can enhance reaction rates by 100,000-fold, but the same rate enhancements have yet to be achieved in thermochemical heterogeneous catalysis. In this work, we probe the influence of catalyst potential and interfacial electric fields on heterogeneous Brønsted acid catalysis. We observed that variations in applied potential of ~380 mV led to a 100,000-fold rate enhancement for 1-methylcyclopentanol dehydration, which was catalyzed by carbon-supported phosphotungstic acid. Mechanistic studies support a model in which the interfacial electrostatic potential drop drives quasi-equilibrated proton transfer to the adsorbed substrate prior to rate-limiting C-O bond cleavage. Large increases in rate with potential were also observed for the same reaction catalyzed by Ti/TiOyHx and for the Friedel Crafts acylation of anisole with acetic anhydride by carbon-supported phosphotungstic acid.

Tailoring Interfaces for Enhanced Methanol Production from Photoelectrochemical CO2 Reduction

Efficient and stable photoelectrochemical reduction of CO2 into highly reduced liquid fuels remains a formidable challenge, which requires an innovative semiconductor/catalyst interface to tackle. In this study, we introduce a strategy involving the fabrication of a silicon micropillar array structure coated with a superhydrophobic fluorinated carbon layer for the photoelectrochemical conversion of CO2 into methanol. The pillars increase the electrode surface area, improve catalyst loading and adhesion without compromising light absorption, and help confine gaseous intermediates near the catalyst surface. The superhydrophobic coating passivates parasitic side reactions and further enhances local accumulation of reaction intermediates. Upon one-electron reduction of the molecular catalyst, the semiconductor-catalyst interface changes from adaptive to buried junctions, providing a sufficient thermodynamic driving force for CO2 reduction. These structures together create a unique microenvironment for effective reduction of CO2 to methanol, leading to a remarkable Faradaic efficiency reaching 20% together with a partial current density of 3.4 mA cm-2, surpassing the previous record based on planar silicon photoelectrodes by a notable factor of 17. This work demonstrates a new pathway for enhancing photoelectrocatalytic CO2 reduction through meticulous interface and microenvironment tailoring and sets a benchmark for both Faradaic efficiency and current density in solar liquid fuel production.

Multiplexed immunosensing of cancer biomarkers on a split-float-gate graphene transistor microfluidic biochip

This work reports the development of a novel microfluidic biosensor using a graphene field-effect transistor (GFET) design for the parallel label-free analysis of multiple biomarkers. Overcoming the persistent challenge of constructing μm2-sized FET sensitive interfaces that incorporate multiple receptors, we implement a split-float-gate structure that enables the manipulation of multiplexed biochemical functionalization using microfluidic channels. Immunoaffinity biosensing experiments are conducted using the mixture samples containing three liver cancer biomarkers, carcinoembryonic antigen (CEA), α-fetoprotein (AFP), and parathyroid hormone (PTH). The results demonstrate the capability of our label-free biochip to quantitatively detect multiple target biomarkers simultaneously by observing the kinetics in 10 minutes, with the detection limit levels in the nanomolar range. This microfluidic biosensor provides a valuable analytical tool for rapid multi-target biosensing, which can be potentially utilized for domiciliary tests of cancer screening and prognosis, obviating the need for sophisticated instruments and professional operations in hospitals.

Electro-inductive Effect Dominates Vibrational Frequency Shifts of Conjugated Probes on Gold Electrodes

Interfacial electric fields play a critical role in electrocatalysis and are often characterized by using vibrational probes attached to an electrode surface. Understanding the physical principles dictating the impact of the applied electrode potential on the vibrational probe frequency is important. Herein, a comparative study is performed for two molecular probes attached to a gold electrode. Both probes contain a nitrile (CN) group, but 4-mercaptobenzonitrile (4-MBN) exhibits continuous conjugation from the electrode through the nitrile group, whereas this conjugation is interrupted for 2-(4-mercaptophenyl)acetonitrile (4-MPCN). Periodic density functional theory calculations predict that the CN vibrational frequency shift of the 4-MBN system is dominated by induction, which is a through-bond polarization effect, leading to a strong potential dependence that does not depend significantly on the orientation of the CN bond relative to the surface. In contrast, the CN vibrational frequency shift of the 4-MPCN system is influenced less by induction and more by through-space electric field effects, leading to a weaker potential dependence and a greater orientation dependence. These theoretical predictions were confirmed by surface-enhanced Raman spectroscopy experiments. Balancing through-bond and through-space electrostatic effects may assist in the fundamental understanding and design of electrocatalytic systems.

Mechanism and Selectivity of Copper-Catalyzed Bromination of Distal C(sp3)-H Bonds

Unactivated C(sp3)-H bonds are the most challenging substrate class for transition metal-catalyzed C-H halogenation. Recently, the Yu group [Liu, T.; Myers, M. C.; Yu, J. Q. Angew. Chem., Int. Ed.2017, 56 (1), 306-309] has demonstrated that a CuII/phenanthroline catalyst and BrN3, generated in situ from NBS and TMSN3 precursors, can achieve selective C-H bromination distal to a directing group. The current understanding of the mechanism of this reaction has left numerous questions unanswered. Here, we investigated the mechanism of Cu-catalyzed C(sp3)-H bromination with distal site selectivity using density functional theory calculations. We found that this reaction starts with the Br-atom transfer from BrN3 to the Cu center that occurs via a small energy barrier at the singlet-triplet state seam of crossing. In the course of this reaction, the presence of the N-H bond in the substrate is critically important and acts as a directing group for enhancing the stability of the catalyst-substrate interaction and for the recruitment of the substrate to the catalyst. The required C-centered radical substrate formation occurs via direct C-H dehydrogenation by the Cu-coordinated N3 radical, rather than via the previously proposed N-H bond dehydrogenation and then the 1,5-H transfer from the γ-(C-H) bond to the N-radical center pathway. The C-H bond activation by the azide radical is a regioselectivity-controlling step. The following bromination of the C-centered radical by the Cu-coordinated bromine completes the product formation. This reaction step is the rate-limiting step, occurs at the singlet-to-triplet state seam of the crossing point, and is exergonic.

A closed-loop catalytic nanoreactor system on a transistor

Precision chemistry demands miniaturized catalytic systems for sophisticated reactions with well-defined pathways. An ideal solution is to construct a nanoreactor system functioning as a chemistry laboratory to execute a full chemical process with molecular precision. However, existing nanoscale catalytic systems fail to in situ control reaction kinetics in a closed-loop manner, lacking the precision toward ultimate reaction efficiency. We find an inter-electrochemical gating effect when operating DNA framework-constructed enzyme cascade nanoreactors on a transistor, enabling in situ closed-loop reaction monitoring and modulation electrically. Therefore, a comprehensive system is developed, encapsulating nanoreactors, analyzers, and modulators, where the gate potential modulates enzyme activity and switches cascade reaction "ON" or "OFF." Such electric field-effect property enhances catalytic efficiency of enzyme by 343.4-fold and enables sensitive sarcosine assay for prostate cancer diagnoses, with a limit of detection five orders of magnitude lower than methodologies in clinical laboratory. By coupling with solid-state electronics, this work provides a perspective to construct intelligent nano-systems for precision chemistry.

Two-Way Catalysis in a Diels-Alder Reaction Limits Inhibition Induced by an External Electric Field

Oriented external electric fields (EEFs) act as catalysts that can induce selectivity in chemical reactions. The responses of the Diels-Alder (DA) reaction between butadiene and ethylene (BDE-DA) as well as cyclopentadiene and ethylene (CPDE-DA) towards EEF stimuli are investigated here using density functional theory (B3LYP) calculations. EEF is a vector that catalyzes the reaction in one direction while inhibiting it in the opposite direction. Here we report that the inhibitive direction becomes rate-enhancing after some increase in the EEF. The EEF value that brings about the maximum possible inhibition for the reaction is defined as the electrostatic resistance point (ERP). The possibility of both normal and inverse electron-demand DA reactions causes catalytic activity in both directions of the EEF starting at a unique ERP value. The C5 substituents of cyclopentadiene control the ERP values depending upon the resistance power that the functional group provides against the EEF. The endo and exo diastereomeric transition states of the DA reaction have distinct ERP values and the difference (ΔERP) provides the through-space electrostatic contribution to the stereoselectivity on a relative scale. Thus, the ERP values can be used as a gauge for the electrostatic interactions between substituent groups and external stimuli.

A highly selective and sensitive sensor for promethazine based on molecularly imprinted interface coated Au/Sn bimetal nanoclusters functionalized acupuncture needle microelectrode

Promethazine (PMZ) is an effective antihistamine that is used as a nerve tranquilizer to treat mental disorders. However, drug abuse causes harm to the human body and also pollutes the environment to a certain extent. Therefore, it is crucial to develop a highly selective and sensitive biosensor for PMZ determination. An acupuncture needle (AN) was used as an electrode in 2015, and further research on the electrode's essence in electrochemistry is needed. In this work, a sensor based on a surface imprinted film coordinated Au/Sn biometal was first fabricated on AN via electrochemistry. The obtained cavities showed complementary and suitable sites for "N atom" electron transfer through the phenyl ring structure in promethazine, which is rigorous for the configuration near the interface. Under the optimal conditions, MIP/Au/Sn/ANE exhibits a good linear relationship in the range of 0.5 μM-500 μM, and the detection limit (LOD) is 0.14 μM (S/N = 3). The sensor exhibits good repeatability, stability, and selectivity and can be successfully used to analyze and detect PMZ in human serum and environmental water. The findings are scientifically significant for AN electrochemistry and the sensors have potential for in vivo medicamentosus monitoring in the future.

Fractional Charge Density Functional Theory and Its Application to the Electro-inductive Effect

We employed the chemical potential equalization principle to demonstrate that fractional electrons are involved in the electro-inductive effect as well as the vibrational Stark effect. By the chemical potential model, we were able to deduce that the frontier molecular orbitals of immobilized molecules can provide valuable insight into these effects. To further understand and quantify these findings, we introduced fractional charge density functional theory (FC-DFT), a canonical ensemble approach for open systems. This method allows for the calculation of electronic energies, nuclear gradients, and the Hessian matrix of fractional electronic systems. To correct the spurious delocalization error commonly found in approximate density functionals for small systems, we imposed the Perdew-Parr-Levy-Balduz (PPLB) condition through linear interpolation of two adjacent integer points (LI-FC-DFT). Although this approach is relatively simple in terms of molecular modeling, the results obtained through LI-FC-DFT calculations predict the same trend seen in experimental reactivity and the frequency change of immobilized molecules.

Inductive Effect Alone Cannot Explain Lewis Adduct Formation and Dissociation at Electrode Interfaces

Understanding breaking and formation of Lewis bonds at an electrified interface is relevant to a large range of phenomena, including electrocatalysis and electroadsorption. The complexities of interfacial environments and associated reactions often impede a systematic understanding of this type of bond at interfaces. To address this challenge, we report the creation of a main group classic Lewis acid-base adduct on an electrode surface and its behavior under varying electrode potentials. The Lewis base is a self-assembled monolayer of mercaptopyridine and the Lewis acid is BF₃, forming a Lewis bond between nitrogen and boron. The bond is stable at positive potentials but cleaves at potentials more negative of approximately -0.3 V vs Ag/AgCl without an associated current. We also show that if the Lewis acid BF₃ is supplied from a reservoir of Li⁺BF₄^- electrolyte, the cleavage is completely reversible. We propose that the N-B Lewis bond is affected both by the field-induced intramolecular polarization (electroinduction) and by the ionic structures and ionic equilibria near the electrode. Our results indicate that the second effect is responsible for the Lewis bond cleavage at negative potentials. This work is relevant to understanding the fundamentals of electrocatalytic and electroadsorption processes.

Ultraminiaturized Microfluidic Electrochemical Surface-Enhanced Raman Scattering Chip for Analysis of Neurotransmitters Fabricated by Ship-in-a-Bottle Integration

Electrochemical surface-enhanced Raman scattering (EC-SERS) is a promising technique for the diagnosis of trace amounts of neurotransmitters, because it can elucidate neurotransmitters' behavior on electrodes to deduce their functions in the human body. However, the current EC-SERS devices need several tens of milliliters of analyte solution to collect enough signal for analysis. Miniaturization of EC-SERS devices is crucial for the early diagnosis of disease and point-of-care testing. Herein, a new type of EC-SERS sensor based on 3D microfluidic chips for the analysis of neurotransmitters in ultrasmall volumes is proposed. The microfluidic EC-SERS chip is fabricated by a ship-in-a-bottle technique based on hybrid laser processing. The working electrode is modified using silver/zinc oxide materials, enabling the formation of a unique "candy apple" structure. To assess the fabricated microfluidic EC-SERS chips, ascorbic acid is analyzed using the ingenious microfluidic EC-SERS chips to elucidate its redox reaction by EC-SERS spectroscopy. Significantly, a sub-10 μL volume of analyte solution is sufficient for EC-SERS analysis, which is several orders smaller in volume than the requirements of current EC-SERS devices. The unprecedented microfluidic EC-SERS chips fabricated by the ship-in-a-bottle integration technique can be used in portable and smart analyzers for next-generation biomedicines and catalysts.

VSe2-x O x @Pd Sensor for Operando Self-Monitoring of Palladium-Catalyzed Reactions

Operando monitoring of catalytic reaction kinetics plays a key role in investigating the reaction pathways and revealing the reaction mechanisms. Surface-enhanced Raman scattering (SERS) has been demonstrated as an innovative tool in tracking molecular dynamics in heterogeneous reactions. However, the SERS performance of most catalytic metals is inadequate. In this work, we propose hybridized VSe2-x O x @Pd sensors to track the molecular dynamics in Pd-catalyzed reactions. Benefiting from metal-support interactions (MSI), the VSe2-x O x @Pd realizes strong charge transfer and enriched density of states near the Fermi level, thereby strongly intensifying the photoinduced charge transfer (PICT) to the adsorbed molecules and consequently enhancing the SERS signals. The excellent SERS performance of the VSe2-x O x @Pd offers the possibility for self-monitoring the Pd-catalyzed reaction. Taking the Suzuki-Miyaura coupling reaction as an example, operando investigations of Pd-catalyzed reactions were demonstrated on the VSe2-x O x @Pd, and the contributions from PICT resonance were illustrated by wavelength-dependent studies. Our work demonstrates the feasibility of improved SERS performance of catalytic metals by modulating the MSI and offers a valid means to investigate the mechanisms of Pd-catalyzed reactions based on VSe2-x O x @Pd sensors.

Precise electrical gating of the single-molecule Mizoroki-Heck reaction

Precise tuning of chemical reactions with predictable and controllable manners, an ultimate goal chemists desire to achieve, is valuable in the scientific community. This tunability is necessary to understand and regulate chemical transformations at both macroscopic and single-molecule levels to meet demands in potential application scenarios. Herein, we realise accurate tuning of a single-molecule Mizoroki-Heck reaction via applying gate voltages as well as complete deciphering of its detailed intrinsic mechanism by employing an in-situ electrical single-molecule detection, which possesses the capability of single-event tracking. The Mizoroki-Heck reaction can be regulated in different dimensions with a constant catalyst molecule, including the molecular orbital gating of Pd(0) catalyst, the on/off switching of the Mizoroki-Heck reaction, the promotion of its turnover frequency, and the regulation of each elementary reaction within the Mizoroki-Heck catalytic cycle. These results extend the tuning scope of chemical reactions from the macroscopic view to the single-molecule approach, inspiring new insights into designing different strategies or devices to unveil reaction mechanisms and discover novel phenomena.

Sub-Nanometer Mapping of the Interfacial Electric Field Profile Using a Vibrational Stark Shift Ruler

The characterization of electrical double layers is important since the interfacial electric field and electrolyte environment directly affect the reaction mechanisms and catalytic rates of electrochemical processes. In this work, we introduce a spectroscopic method based on a Stark shift ruler that enables mapping the electric field strength across the electric double layer of electrode/electrolyte interfaces. We use the tungsten-pentacarbonyl(1,4-phenelenediisocyanide) complex attached to the gold surface as a molecular ruler. The carbonyl (CO) and isocyanide (NC) groups of the self-assembled monolayer (SAM) provide multiple vibrational reporters situated at different distances from the electrode. Measurements of Stark shifts under operando electrochemical conditions and direct comparisons to density functional theory (DFT) simulations reveal distance-dependent electric field strength from the electrode surface. This electric field profile can be described by the Gouy-Chapman-Stern model with Stern layer thickness of ∼4.5 Å, indicating substantial solvent and electrolyte penetration within the SAM. Significant electro-induction effect is observed on the W center that is ∼1.2 nm away from the surface despite rapid decay of the electric field (∼90%) within 1 nm. The applied methodology and reported findings should be particularly valuable for the characterization of a wide range of microenvironments surrounding molecular electrocatalysts at electrode interfaces and the positioning of electrocatalysts at specific distances from the electrode surface for optimal functionality.

Breaking the nanoparticle's dispersible limit via rotatable surface ligands

Achieving versatile dispersion of nanoparticles in a broad range of solvents (e.g., water, oil, and biofluids) without repeatedly recourse to chemical modifications are desirable in optoelectronic devices, self-assembly, sensing, and biomedical fields. However, such a target is limited by the strategies used to decorate nanoparticle's surface properties, leading to a narrow range of solvents for existing nanoparticles. Here we report a concept to break the nanoparticle's dispersible limit via electrochemically anchoring surface ligands capable of sensing the surrounding liquid medium and rotating to adapt to it, immediately forming stable dispersions in a wide range of solvents (polar and nonpolar, biofluids, etc.). Moreover, the smart nanoparticles can be continuously electrodeposited in the electrolyte, overcoming the electrode surface-confined low throughput limitation of conventional electrodeposition methods. The anomalous dispersive property of the smart Ag nanoparticles enables them to resist bacteria secreted species-induced aggregation and the structural similarity of the surface ligands to that of the bacterial membrane assists them to enter the bacteria, leading to high antibacterial activity. The simple but massive fabrication process and the enhanced dispersion properties offer great application opportunities to the smart nanoparticles in diverse fields.

Quantifying Hot Electron Energy Contributions in Plasmonic Photocatalysis Using Electrochemical Surface-Enhanced Raman Spectroscopy

Due to the challenge in measuring hot electron energy under reaction conditions, very few studies focus on experimental determination of hot carrier energy. Here, we adjust the energy state of free electrons in Au nanoparticles to quantify the hot electron energy in plasmonic photocatalysis. Reactant molecules with different reduction potentials such as 4-nitrothiophenol (4-NTP), 4-iodothiophenol (4-ITP), etc. are chosen as molecular probes to investigate the reducing ability of hot electrons. By comparing the voltage required to achieve the same conversion of photo- and electro-reaction pathways, we calibrate the maximum energy efficiency of hot electrons in 4-NTP reduction to be 0.32 eV, which is much lower than the excitation photon energy of 1.96 eV. Our work provides insight into the energy distribution of hot electrons and will be helpful for rational design of highly efficient plasmon-mediated chemical reactions.

Vibrational Stark Effects: Ionic Influence on Local Fields

Molecules containing vibrational Stark shift reporters provide a useful tool for measuring DC electric fields in situ. To quantify this effect theoretically, density functional theory (DFT) calculations are usually utilized in a uniform electric field. However, using a combined theoretical and experimental study, we demonstrate here that uniform field DFT cannot simultaneously model the behavior of the three strongest vibrational modes in molecules forming a monolayer on an electrode. We show, by directly modeling ionic movement, that the measured Stark shifts are explained by partial electrical double-layer penetration into the molecular layer. This effect is sensitive to the local environment, and the Stark shifts can be fully suppressed experimentally by introducing a mixed molecular layer that prevents ionic double-layer penetration.

Dual External Field-Engineered Hyperhalogen

Hyperhalogens, a superatom featuring the highest known electron affinity (EA), have promising applications in the synthesis of superoxidizers. Contributions regarding the identified numbers and corresponding design strategies of hyperhalogens, however, are scarce. Herein, a novel and noninvasive dual external field (DEF) strategy, including the ligand field and oriented external electric field (OEEF), is proposed to construct hyperhalogens. The DEF strategy was shown to possess the power to increase Au₈'s EA, forming the hyperhalogen. Strikingly, the ligation process can increase the cluster's stability, while OEEF can realize the precise and continuous regulation of the cluster's EA. Moreover, besides the model Au₈ system, an experimentally synthesized Ag₁₇ nanocluster was also investigated, further demonstrating the reliability of the proposed strategy. Considering the crucial role of ligands in the liquid synthesis of clusters and the convenient source of OEEF, such a DEF strategy may greatly increase the synthesis and applications of hyperhalogens in the condensed phase.

Electrostatic vs. inductive effects in phosphine ligand donor properties and reactivity

Enhanced rates and selectivity in enzymes are enabled in part by precisely tuned electric fields within active sites. Analogously, the use of charged groups to leverage electrostatics in molecular systems is a promising strategy to tune reactivity. However, separation of the through space and through bond effects of charged functional groups is a long standing challenge that limits the rational application of electric fields in molecular systems. To address this challenge we developed a method using the phosphorus selenium coupling value (J _P-Se) of anionic phosphine selenides to quantify the electrostatic contribution of the borate moiety to donor strength. In this analysis we report the synthesis of a novel anionic phosphine, PPh₂CH₂BF₃K, the corresponding tetraphenyl phosphonium and tetraethyl ammonium selenides [PPh₄][SePPh₂CH₂BF₃] and [TEA][SePPh₂CH₂BF₃], and the Rh carbonyl complex [PPh₄][Rh(acac)(CO)(PPh₂(CH₂BF₃))]. Solvent-dependent changes in J _P-Se were fit using Coulomb's law and support up to an 80% electrostatic contribution to the increase in donor strength of [PPh₄][SePPh₂CH₂BF₃] relative to SePPh₂Et, while controls with [TEA][SePPh₂CH₂BF₃] exclude convoluting ion pairing effects. Calculations using explicit solvation or point charges effectively replicate the experimental data. This J _P-Se method was extended to [PPh₄][SePPh₂(2-BF₃Ph)] and likewise estimates up to a 70% electrostatic contribution to the increase in donor strength relative to SePPh₃. The use of PPh₂CH₂BF₃K also accelerates C-F oxidative addition reactivity with Ni(COD)₂ by an order of magnitude in comparison to the comparatively donating neutral phosphines PEt₃ and PCy₃. This enhanced reactivity prompted the investigation of catalytic fluoroarene C-F borylation, with improved yields observed for less fluorinated arenes. These results demonstrate that covalently bound charged functionalities can exert a significant electrostatic influence under common solution phase reaction conditions and experimentally validate theoretical predictions regarding electrostatic effects in reactivity.

Electrochemically activated carbon-halogen bond cleavage and C-C coupling monitored by in situ shell-isolated nanoparticle-enhanced Raman spectroscopy

The electroreductive cleavage of carbon-halogen bonds has attracted increasing attention in both electrosynthesis and pollution remediation. Herein, by employing the in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) technique, we have successfully investigated the electroreductive dehalogenation process of aryl halides with the thiol group on a smooth Au electrode in aqueous solution at different pH values. The obtained potential-dependent Raman spectra directly reveal a mixture of the reduction products 4,4'-biphenyldithiol (BPDT) and thiophenol (TP). The conversion ratios of the C-Cl and C-Br bonds at pH = 7 are 37% and 55%, respectively. Furthermore, quantitative analysis of the intensity variations of ν(C-Cl), ν(C-Br) and aromatic ν(CC) stretching modes suggests electroreductive dehalogenation via both direct electron transfer reduction and electrocatalytic hydrodehalogenation. Molecular evidence for the C-C cross coupling process through TP reaction with benzene free radical intermediates is found at negative potentials, which leads to the increasing selectivity of biphenyl products.

Effect of Electric Fields on Silicon-Based Monolayers

Electric fields can induce bond breaking and bond forming, catalyze chemical reactions on surfaces, and change the structure of self-assembled monolayers on electrode surfaces. Here, we study the effect of electric fields supplied either by an electrochemical potential or by conducting atomic force microscopy (C-AFM) on Si-based monolayers. We report that typical monolayers on silicon undergo partial desorption followed by the oxidation of the underneath silicon at +1.5 V vs Ag/AgCl. The monolayer loses 28% of its surface coverage and 55% of its electron transfer rate constant (k_et) when +1.5 V electrochemical potential is applied on the Si surface for 10 min. Similarly, a bias voltage of +5 V applied by C-AFM induces complete desorption of the monolayer at specific sites accompanied by an average oxide growth of 2.6 nm when the duration of the bias applied is 8 min. Current-voltage plots progressively change from rectifying, typical of metal-semiconductor junctions, to insulating as the oxide grows. These results define the stability of Si-based organic monolayers toward electric fields and have implication in the design of silicon-based monolayers, molecular electronics devices, and on the interpretation of charge-transfer kinetics across them.

Lessons from an Array: Using an Electrode Surface to Control the Selectivity of a Solution-Phase Chemical Reaction

Electrochemistry offers a variety of novel means by which selectivity can be introduced into synthetic organic transformations. In the work reported, it is shown how methods used to confine chemical reactions to specific sites on a microelectrode array can also be used to confine a preparative reaction to the surface of an electrode inserted into a bulk reaction solution. In so doing, the surface of a modified electrode can be used to introduce new selectivity into a preparative reaction that is not observed in the absence of either the modified electrode surface or the effort to confine the reaction to that surface. The observed selectivity can be optimized in the same way that confinement is optimized on an array and is dependent on the nature of the functionalized surface.

Observing Mesoscopic Nucleic Acid Capacitance Effect and Mismatch Impact via Graphene Transistors

This work reports a molecular-scale capacitance effect of the double helical nucleic acid duplex structure for the first time. By quantitatively conducting large sample measurements of the electrostatic field effect using a type of high-accuracy graphene transistor biosensor, an unusual charge-transport behavior is observed in which the end-immobilized nucleic acid duplexes can store a part of ionization electrons like molecular capacitors, other than electric conductors. To elucidate this discovery, a cascaded capacitive network model is proposed as a novel equivalent circuit of nucleic acid duplexes, expanding the point-charge approximation model, by which the partial charge-transport observation is reasonably attributed to an electron-redistribution behavior within the capacitive network. Furthermore, it is experimentally confirmed that base-pair mismatches hinder the charge transport in double helical duplexes, and lead to directly identifiable alterations in electrostatic field effects. The bioelectronic principle of mismatch impact is also self-consistently explained by the newly proposed capacitive network model. The mesoscopic nucleic acid capacitance effect may enable a new kind of label-free nucleic acid analysis tool based on electronic transistor devices. The in situ and real-time nucleic acid detections for virus biomarkers, somatic mutations, and genome editing off-target may thus be predictable.

Computational Study of Key Mechanistic Details for a Proposed Copper (I)-Mediated Deconstructive Fluorination of N-Protected Cyclic Amines

Using calculations, we show that a proposed Cu(I)-mediated deconstructive fluorination of N-benzoylated cyclic amines with Selectfluor^® is feasible and may proceed through: (a) substrate coordination to a Cu(I) salt, (b) iminium ion formation followed by conversion to a hemiaminal, and (c) fluorination involving C-C cleavage of the hemiaminal. The iminium ion formation is calculated to proceed via a F-atom coupled electron transfer (FCET) mechanism to form, formally, a product arising from oxidative addition coupled with electron transfer (OA + ET). The subsequent β-C-C cleavage/fluorination of the hemiaminal intermediate may proceed via either ring-opening or deformylative fluorination pathways. The latter pathway is initiated by opening of the hemiaminal to give an aldehyde, followed by formyl H-atom abstraction by a TEDA²⁺ radical dication, decarbonylation, and fluorination of the C3-radical center by another equivalent of Selectfluor^®. In general, the mechanism for the proposed Cu(I)- mediated deconstructive C-H fluorination of N-benzoylated cyclic amines (LH) by Selectfluor^® was calculated to proceed analogously to our previously reported Ag(I)-mediated reaction. In comparison to the Ag(I)-mediated process, in the Cu(I)-mediated reaction the iminium ion formation and hemiaminal fluorination have lower associated energy barriers, whereas the product release and catalyst re-generation steps have higher barriers.

Tribo-electrochemistry induced artificial solid electrolyte interface by self-catalysis

Potassium (K) metal is a promising alkali metal anode for its high abundance. However, dendrite on K anode is a serious problem which is even worse than Li. Artificial SEI (ASEI) is one of effective routes for suppressing dendrite. However, there are still some issues of the ASEI made by the traditional methods, e.g. weak adhesion, insufficient/uneven reaction, which deeply affects the ionic diffusion kinetics and the effect of inhibiting dendrites. Herein, through a unique self-catalysis tribo-electrochemistry reaction, a continuous and compact protective layer is successfully constructed on K metal anode in seconds. Such a continuous and compact protective layer can not only improve the K⁺ diffusion kinetics, but also strongly suppress K dendrite formation by its hard mechanical properties derived from rigid carbon system, as well as the improved K⁺ conductivity and lowered electronic conductivity from the amorphous KF. As a result, the potassium symmetric cells exhibit stable cycles last more than 1000 h, which is almost 500 times that of pristine K.