Chemical reactions necessitate the correct spatiotemporal meeting of reactants with sufficient energy. The reaction's occurrence is governed by charge (positive or negative), quantity, surrounding atoms, and molecular charge distribution. Reactions between like-charged molecules require extra energy to overcome Coulomb repulsions, potentially taking days or weeks in pure water. Biological systems typically accelerate these reactions using enzymes as catalysts, with electrostatic effects and charge stabilization playing a crucial catalytic role, as demonstrated by Warshel's work. While there's significant interest in synthetic enzymes or enzyme mimics (nanozymes), replicating the charge stabilization properties of enzyme active sites remains challenging and often highly reaction-specific. A previous study showed significant acceleration of reactions between negatively charged reactants with the addition of positively charged polymers, attributed to reactant sliding along molecular tracks (diffusive binding). This current work systematically investigates whether rate enhancement by 'counter-charged' species is a general phenomenon, exploring the theoretical basis of such electrostatic catalysis. The study examines how reaction kinetics of two independent experimental systems (covalent and non-covalent product formation) are affected by charge type and introduction method (salt ions, charged monomers/oligomers, micelles, polymers).

The literature extensively discusses the challenges of reactions between like-charged molecules due to strong electrostatic repulsion. Wolfenden and Snider highlighted the significant time scales involved in such reactions in the absence of catalysis. Warshel's work established the fundamental role of electrostatic effects and charge stabilization in enzyme catalysis. The development and application of nanozymes and artificial enzymes have been active research areas, aiming to mimic the catalytic efficiency of natural enzymes. However, achieving the same level of catalytic activity and specificity remains a significant hurdle. The authors' previous work on diffusive binding along polymer tracks provided inspiration for this study, suggesting that the interaction of like-charged reactants with oppositely charged species could be a general approach to accelerating such reactions. This current study builds upon this prior work to systematically investigate the phenomenon and its underlying mechanisms.

Two experimental systems were employed to investigate the influence of charge screening on reaction kinetics: a covalent reaction and a non-covalent interaction. **Covalent Reaction:** The model reaction involved the reaction between coenzyme A (CoA) and bromo-N-methylmaleimide substituted coenzyme A (CoA-M). The reaction product (CoA-M-CoA) formation was monitored through fluorescence increase. Reaction kinetics were analyzed using a second-order kinetic model. The rate constant (k) was determined by fitting experimental data. The influence of various catalysts (ions, zwitterions, charged monomers, oligomers, polymers, and micelles) on the reaction rate was examined. The catalyst concentrations were adjusted such that the concentration of positive charges introduced by the catalyst was equal to the concentration of negative charges on the reactants. Ionic strength was also considered in the analysis. Measurements were performed using a Nikon C1 inverted confocal microscope with a PicoQuant LSM module and a PicoHarp 300 Time-Correlated Single-Photon Counting setup. **Non-Covalent Interaction:** DNA hybridization served as the second model system. The kinetics of double-strand formation between two 13-base pair complementary DNA oligonucleotides (one labeled with ATTO488 and the other with ATTO647N) were monitored using Förster resonance energy transfer (FRET). Experiments were conducted in phosphate buffer and water, with the addition of various catalysts. The effect of different catalyst types and concentrations on the reaction rate was investigated. FRET data were analyzed using a second-order reaction model. Stopped-flow measurements complemented the confocal microscope analysis. **Data Analysis:** Reaction rate constants (k) were determined by fitting the experimental fluorescence data to appropriate kinetic models. Error analysis, including weighted mean errors, was performed. For the theoretical model, the electrostatic interactions between reactants and catalysts were considered, taking into account Debye length and surface charge density. The Smoluchowski equation was employed to calculate the reactant flux towards the catalyst surface. Materials used included CoA, CoA-M (synthesized in the lab), DNA oligonucleotides, MES buffer, phosphate buffer, various catalysts (arginine, arginine-9, poly-L-lysine, CTAC, BTC, CPC, SDS, Brij L23), and appropriate solvents. Detailed procedures for CoA-M and CoA-M-CoA synthesis are described in the Methods section. The critical micelle concentration (CMC) was calculated using a volume-based thermodynamics model. Stopped-flow experiments were performed using an Applied Photophysics Ltd. SX20 stopped-flow fluorometer.

The study yielded several key findings: 1. **Significant Rate Enhancement:** The reaction between negatively charged CoA molecules was accelerated by orders of magnitude in the presence of positively charged catalysts. The use of cationic micelles resulted in a ~5 million-fold increase in reaction rate compared to a 0.5 M NaCl solution. Other highly charged species like oligomers and polymers also showed significant catalytic effects (10⁴–10⁵-fold). 2. **Generalizability of the Effect:** The observed rate enhancement was not limited to the covalent CoA reaction. Similar acceleration was observed in the non-covalent DNA hybridization reaction, demonstrating the generality of the phenomenon. 3. **Influence of Charge Density:** The degree of reaction acceleration was found to correlate with the surface charge density of the catalysts. Higher charge density led to greater rate enhancements. 4. **Optimal Catalyst Concentration:** A non-monotonic relationship was observed between catalyst concentration and reaction rate. Maximum acceleration occurred at low micelle/reactant concentration ratios, where the concentration of reactants was higher than that of the micelles. 5. **Electrostatic Nature of the Effect:** The catalytic effect was confirmed to be primarily electrostatic, as evidenced by the lack of acceleration observed with neutral and negatively charged micelles. 6. **Theoretical Model:** A theoretical model was developed to explain the observed acceleration. The model considered electrostatic interactions between reactants and catalysts, taking into account Debye length and surface charge density. The model successfully predicted the relationship between catalyst properties and reaction rate. 7. **Controlled Reaction Rates:** The results demonstrated the possibility of controlling reaction rates within several orders of magnitude by carefully tuning the charge magnitude and spatial distribution of the catalysts.

The findings address the research question by demonstrating that the rate enhancement of reactions between like-charged molecules is a general phenomenon that can be achieved through effective screening of Coulomb repulsions using oppositely charged catalysts. The significant acceleration observed in both covalent and non-covalent systems validates the generality of this approach. The correlation between catalytic effect and surface charge density highlights the importance of electrostatic interactions in determining reaction rates. The theoretical model successfully explains the observed rate enhancements, providing a framework for predicting and controlling such reactions. The results are relevant to fields such as biochemistry, materials science, and nanotechnology, offering potential applications in areas such as biosensing, drug delivery, and catalysis. The observed non-monotonic relationship between catalyst concentration and reaction rate suggests the existence of an optimal catalyst concentration for maximum acceleration. Further research is needed to fully understand the dynamics of reactant interactions at the catalyst surface.

This study demonstrated that the reaction rates of like-charged molecules can be controlled by several orders of magnitude through the use of oppositely charged catalysts. This control is achieved by manipulating the charge density and spatial distribution of the catalyst. The findings provide a valuable tool for controlling and predicting the rates of reactions involving like-charged molecules. Future research could focus on exploring the optimal design of catalysts for specific reactions, investigating the effects of different catalyst geometries, and exploring applications of this method in various fields.

The study focused on specific model reactions and catalysts. The generality of the findings might be limited to systems with similar characteristics. The theoretical model used certain simplifying assumptions, such as the Debye-Hückel approximation, which might not be entirely accurate in all situations. Further research is needed to fully validate the model and explore its applicability to more complex systems.