Chemical Reaction Steps Research Articles

Investigation on the Necessity of Low Rates Activation toward Lithium‐Sulfur Batteries

AbstractLow rate activation process is always used in conventional transition metal oxide cathode and fully activates active substances/electrolyte to achieve stable electrochemical performance. However, the related working mechanism in lithium‐sulfur (Li‐ battery is unclear due to the multiple complex chemical reaction steps including the redox of sulfur and the dissolution of polysulfides intermediate. Hence, the influencing mechanism of activation process on Li‐S battery is explored by adopting different current densities of 0.05, 0.2, and 1 C in initial three cycles before long‐term cycling tests at 0.2 C (denoted by 0.05, 0.2, and 1‐battery). 0.05‐battery presents the highest initial capacity in activation process, while 0.2‐battery presents superior electrochemical performances after 150 cycles. The similar trend can be found in more long‐term cycling rates such as 0.02, 0.1, 0.5, and 1 C. Potentiostatically Li2S precipitation test demonstrates that rapid generation of Li2S is achieved at higher current density, and S8‐Li2Sn‐Li2S conversion is accelerated according to Tafel plots. However, interfacial electrochemical and physical characterizations suggest that serious lithium dendrite growth will be induced under high current density. Therefore, considering the reaction kinetics and interfacial properties, low rate activation process is unnecessary when cycling current lower than 1 C for Li‐S battery.

Amine-modified SiO2 aerogel for efficient adsorption of low-pressure CO2: Response surface methodology optimization and adsorption mechanism

Amine-modified SiO2 aerogel (AMSA) has shown tremendous potential in CO2 capture due to its unique three-dimensional network structure and excellent stability. However, it still faces many challenges in the preparation optimization, adsorption enhancement at low CO2 partial pressure, and mechanism elucidation. Hence, in this paper, the response surface methodology is employed for the first time and the optimal preparation conditions for AMSA are determined. A regression model is successfully established to accurately predict the CO2 adsorption capacity of AMSA under different synthesis conditions (with a relative error of only 0.98 %). Additionally, the AMSA prepared at optimal conditions exhibits high CO2 adsorption capacity of 2.11 mmol/g and excellent stability (only decreased by 1.44 % after 8 cycles) at 10 % CO2 partial pressure, indicating enormous application potential. Notably, the CO2 adsorption mechanism by AMSA at different temperatures and partial pressures are revealed in detail through fitting with the Freundlich isotherm and the double-exponential model, as well as thermodynamic parameter calculations. Firstly, the CO2 adsorption behavior belongs to the multi-layer adsorption behavior with uneven energy of active sites. Secondly, the CO2 adsorption capacity and rate are jointly controlled by molecular motion and chemical reaction equilibrium, diffusion and chemical reaction steps, respectively. Finally, the adsorption process is exothermic and spontaneous, and the level of disorder decreases at the gas-solid interface. This study not only achieves efficient adsorption of low-pressure CO2, but also deepens the understanding of gas-solid interface adsorption mechanisms, providing scientific basis and technological support for the development of novel efficient AMSA adsorbent materials.

A novel design of urea-assisted hydrogen production in electrochemical-chemical decoupled self-circulating systems.

In traditional water electrolysis processes, the oxidation and reduction reactions of water are coupled in both time and space, which presents significant challenges. Here, we propose an optimized design for an electrochemical-chemical self-circulating decoupled system. This system uses the continuous Ni2+/Ni3+ redox process on nickel hydroxide electrode sheets to stepwise couple the urea oxidation-assisted hydrogen production system, separating the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) into two distinct steps: electrochemical and chemical reactions. In the first electrochemical step, water is reduced at the cathode to produce hydrogen, while the single-electron electrochemical oxidation of Ni(OH)2 at the anode generates NiOOH. Then, in the second chemical reaction step, NiOOH spontaneously oxidizes urea, causing its decomposition and simultaneously reducing back to the Ni(OH)2 state. We concurrently investigated the effects of temperature and OH-concentration on the spontaneous oxidation of urea. At 80 °C and with a 1 M KOH concentration containing 50 mg of urea solution, the NiOOH electrode successfully catalyzed the spontaneous decomposition of urea, achieving conversion rate of 100% and faradaic efficiency of 98%.

Electrical power, energy efficiency, NO and CO emissions investigations of an ammonia/methane-fueled micro-thermal photovoltaic system with a reduced chemical reaction mechanism

Ammonia is an alternative renewable green fuel with significant potential for addressing climate change concerns. Blending ammonia with methane has emerged as a viable strategy to improve the laminar burning velocity of ammonia. In this study, we propose a mechanism for methane/ammonia combustion, comprising 31 species and 131 chemical reaction steps, and investigate the emissions of CO and NO, along with electrical power output and energy efficiency of a micro-thermal photovoltaic (MTPV) system fueled with premixed ammonia/methane/oxygen. Three key parameters are identified as: 1) the inlet mixture flow velocity, 2) the CH4 mole fraction blended ratio (ξCH4), and 3) the material of the micro-combustor. The MTPV system achieves its highest energy efficiency (5.8 %) at an inlet velocity (vin) of 2.3 m/s, and reaches its maximum electrical power output (6.9 W) at vin = 7.2 m/s. Further, increasing ξCH4 can enhance electrical power output (ξCH4 = 0.9 yields 1.37 W more than that at ξCH4 = 0.1). Finally, altering the micro-combustor material is shown to have little effects on electrical power output, NO emissions, and energy efficiency. However, the MTPV system made of quartz is found to reduce CO emissions by 15 % and 12 % in comparison with those systems made of Sic and steel, respectively.

Growing strings in a chemical reaction space for searching retrosynthesis pathways

Machine learning algorithms have shown great accuracy in predicting chemical reaction outcomes and retrosyntheses. However, designing synthesis pathways remains challenging for existing machine learning models which are trained for single-step prediction. In this manuscript, we propose to recast the retrosynthesis problem as a string optimization problem in a data-driven fingerprint space, leveraging the similarity between chemical reactions and embedding vectors. Based on this premise, multi-step complex synthesis can be conceptualized as sequences that link multidimensional vectors (fingerprints) representing individual chemical reaction steps. We extracted an extensive corpus of chemical synthesis from patents and converted them into multidimensional strings. While optimizing the retrosynthetic path, we use the Euclidean metric to minimize the distance between the expanded trajectory of the growing retrosynthesis string and the corpus of extracted strings. By doing so, we promote the assembly of synthetic pathways that, in the chemical reaction space, will be more similar to existing retrosyntheses, thereby inheriting the strategic guidelines designed by human experts. We integrated this approach into the RXN platform (https://rxn.res.ibm.com/) and present the method’s application to complex synthesis as well as its ability to produce better synthetic strategies than current methodologies.

Stereomutations in silicate oligomerization: the role of steric hindrance and intramolecular hydrogen bonding.

Stereomutation has previously been explored in the literature with regard to the different mechanisms and activation energy barriers between different forms. However, the forces which govern stereomutations within the intermediate steps in chemical reactions have not been explored previously, a topic addressed in this article. The process of silicate oligomerization has been chosen in this study and it is demonstrated that steric hindrance of molecules and intramolecular hydrogen bonding govern the stereomutation of intermediate pentacoordinate silicon compounds in the silicate oligomerization process. It could be observed that the combined effect of intramolecular hydrogen bonding and steric hindrance in the silicate oligomerization process facilitates the conventional berry pseudorotation mechanism rather than other pseudorotation mechanisms reported in the literature.

In Vitro and In Silico Evaluations of the Antileishmanial Activities of New Benzimidazole-Triazole Derivatives.

Benzimidazole and triazole rings are important pharmacophores, known to exhibit various pharmacological activities in drug discovery. In this study, it was purposed to synthesize new benzimidazole-triazole derivatives and evaluate their antileishmanial activities. The targeted compounds (5a-5h) were obtained after five chemical reaction steps. The structures of the compounds were confirmed by spectral data. The possible in vitro antileishmanial activities of the synthesized compounds were evaluated against the Leishmania tropica strain. Further, molecular docking and dynamics were performed to identify the probable mechanism of activity of the test compounds. The findings revealed that compounds 5a, 5d, 5e, 5f, and 5h inhibited the growth of Leishmania tropica to various extents and had significant anti-leishmanial activities, even if some orders were higher than the reference drug Amphotericin B. On the other hand, compounds 5b, 5c, and 5g were found to be ineffective. Additionally, the results of in silico studies have presented the existence of some interactions between the compounds and the active site of sterol 14-alpha-demethylase, a biosynthetic enzyme that plays a critical role in the growth of the parasite. Therefore, it can be suggested that if the results obtained from this study are confirmed with in vivo findings, it may be possible to obtain some new anti-leishmanial drug candidates.

Characterization, kinetics and thermodynamic evaluation of struvite produced using ferrochrome slag as a magnesium source

There is limited data on studies that have focused on the kinetics, thermodynamics, and characterization of struvite crystallization from alternative magnesium sources. This study focused on thermal analysis of struvite (produced using ferrochrome slag as a magnesium source) and the results indicated that the residual quantities of struvite were lower than the theoretical mass loss of struvite of 51.42%. When using ferrochrome slag (FCS) as the magnesium source, 47.9%, 47.4%, and 46.9% losses in mass were observed for heating rates of 5°C/min; 10°C/min and 15°C/min respectively. The mean activation energies for struvite produced using FCS were deduced using isoconversional kinetic methods and ranged from 49.81to 56.20 kJ/mol which is very similar to the activation energies deduced using MgCl2. The study also focused on the surface morphology, and particle size of the final product at different pH and N:P ratios. The final particle size distribution of the product was significantly influenced by the solution pH. To improve the crystal growth kinetics for both MgCl2 and FCS, a high ratio of N:P molar ratios should be adopted. The product's highest median particle size was obtained using FCS as the magnesium source at a low pH. Median particle size increased with decrease in pH, at a pH of 7.5 the recorded median particle size was 96 µm whilst, the lowest was 31 µm at a pH of 9.5. The highest percent of fines (<10 µm) was recorded at a pH of 9.5 using FCS as magnesium source in the metastable region of struvite precipitation whereas at a pH of 7.5 no fines (<10 µm) were recorded. SEM images confirmed that the struvite underwent morphological changes when prepared with FCS in comparison to that produced using MgCl2. The surface morphology of the finished product demonstrated the presence of irregular shaped particles, due to presence of impurities. The kinetic data showed that struvite precipitation was limited by the chemical reaction step. Model fitting was used to determine the reaction control mechanism and the average activation energies obtained by four model free methods were FWO (56.2), KAS (51.67) Starink (49.61) and Tang (49.81) kJ/mol, indicating that the FWO method was the least accurate method. The thermodynamic data indicated that the thermal degradation of struvite crystals has a high degree of disorder, and the process is endothermic, irreversible, and non-spontaneous.

The Dissolution Mechanism of Low-Molecular-Weight Organic Acids on the Sillimanite.

The interaction between low-molecular-weight organic acids (LMWOAs) and minerals in nature has been widely studied; however, limited research has been conducted on the dissolution mechanism of sillimanite in the presence of different organic acids. In this study, the interaction between the sillimanite sample and LMWOAs (citric acid, oxalic acid, and citric/oxalic mixture) at the same pH was investigated. The dissolution rate of Si and Al was high during the initial reaction time, then slowed down in the presence of LMWOAs. The dissolution data for Si and Al from sillimanite in the LMWOAs fit well with the first-order equation (Ct = a(1 - exp(-kt))) (R2 > 0.991). The dissolution process of sillimanite in the organic acids was controlled by the surface chemical reaction step. The dissolution concentration of Si in aqueous citric acid was higher than that in oxalic acid. In contrast, the dissolution concentration of Al in oxalic acid was more than that in citric acid. The maximum concentrations of Si and Al in the presence of composite organic acids were 1754 μmol/L and 3904 μmol/L. The sillimanite before and after treatment with LMWOAs were studied using X-ray diffraction (XRD) and scan electron microscopy (SEM). These results are explained by the characterization of the sillimanite. Under the single acid solution, the (210) crystal plane with a high areal density of Al in sillimanite was easily dissolved by the oxalic acid, while the (120) in sillimanite with a high areal density of Si was more easily dissolved by citric acid. In the composite organic acids, the Si-O bond and Al-O bond in sillimanite were attacked alternately, leading to the formation of some deeper corrosion pits on the surface of sillimanite. The results are of interest in the dissolution mechanisms of sillimanite in the low-molecular-weight organic acids and the environmentally friendly activation of sillimanite.

Excited State Dynamics of a Conformationally Fluxional Copper Coordination Complex.

The conversion of solar energy into chemical fuel represents a capstone goal of the 21st century and has the potential to supply terawatts of power in a globally distributed manner. However, the disparate time scales of photodriven charge separation (∼fs) and steps in chemical reactions (∼μs) represent an inherent bottleneck in solar-to-fuels technology. To address this discrepancy, we are developing earth-abundant coordination complexes that undergo light-induced conformational rearrangements such that charge separation (CS) is hastened, while charge recombination (CR) is slowed. To these ends, we report the preparation and characterization of a new series of conformationally fluxional copper coordination complexes that contain a twisted intramolecular charge transfer (TICT) fluorophore as part of their ligand scaffold. Structural and spectroscopic characterization of the Cu(I) and Cu(II) complexes formed with these ligands in their ground states establish oxidation state-dependent conformational dynamicity, while time-resolved emission and transient absorption spectroscopies define the photophysical parameters of photo-induced excited states. Building on initial reports with a related set of molecules, the improved ligand design presented here greatly simplifies the observed photophysics, effectively shutting down unwanted ligand-centered excited states previously observed. Time-dependent density functional theory (TDDFT) analyses reveal an unusual metal-to-TICT electronic transition only reported once before, and though the formation of a CS state is not observed directly through experiments, TDDFT geometry optimizations in the excited states support the formation of transient Cu(II) CS species, lending credence to the potential success of our approach. These studies establish a clear model for the excited state dynamics at play in proof-of-concept systems and clarify key design parameters for future optimizations toward achieving long-lived CS via photoinduced conformational gating.

Reaction Environment Impacts Charge Transfer but Not Chemical Reaction Steps in Hydrogen Evolution Catalysis

Heterogeneous electrocatalysis involves elementary chemical and charge transfer reaction steps, with the kinetics of each step contributing to the overpotential requirement at a given reaction rate. Typical experiments report on the aggregate rate-overpotential profile with no information about the relative contributions from charge transfer and chemical steps. For the hydrogen evolution reaction (HER), the applied overpotential can be partitioned into a charge transfer overpotential, the overpotential necessary to drive proton-coupled electron transfer (PCET) to and from the surface, and a chemical overpotential, corresponding to a change in surface H activity. Reaction conditions can affect either or both the charge transfer and chemical components. Herein, we employ a Pd membrane double cell to spatially separate the charge transfer and chemical reactions steps of HER catalysis, enabling quantification of the chemical and charge transfer overpotential. We further analyze how each depend on pH, and the introduction of HER poisons and promoters. We find that for a given rate of H2 release, the chemical overpotential is constant across diverse reaction environments whereas the charge transfer overpotential is strongly sensitive to reaction conditions. These findings suggest that reaction condition dependent-HER efficiencies are driven predominantly by changes to the kinetics of charge transfer rather than the chemical reactivity of surface H.

Studies on Water–Aluminum Scrap Reaction Kinetics in Two Steps and the Efficiency of Green Hydrogen Production

This work aims to explain aluminum hydrolysis reaction kinetics based on a properly chosen theoretical model with machined aluminum waste chips as well as alkali solutions up to 1M as a promoter and to estimate the overall reaction profit. The purpose of this work is to assess the optimal alkali concentration in the production of small- and medium-scale green hydrogen. To obtain results with better accuracy, we worked with flat Al waste chips, because a flat surface is preferable to maximally increase the time for the created hydrogen bubbles to reach the critical gas pressure. Describing the reaction kinetics, a flat shape allows for the use of a planar one-dimensional shrinking core model instead of a much more complicated polydisperse spheric shrinking core model. We analyzed the surface chemical reaction and mass transfer rate steps to obtain the first-order rate constant for the surface reaction and the diffusion coefficient of the aqueous reactant in the byproduct layer, respectively. We noted that measurements of the diffusion coefficient in the byproduct layer performed and discussed in this paper are rare to find in publications at alkali concentrations below 1M. With our reactor, we achieved a H2 yield of 1145 mL per 1 g of Al with 1M NaOH, which is 92% of the theoretical maximum. In the estimation of profit, the authors’ novelty is in paying great attention to the loss in alkali and finding a crucial dependence on its price. Nevertheless, in terms of consumed and originated materials for sale, the conversion of aluminum waste material into green hydrogen with properly chosen reaction parameters has positive profit even when consuming an alkali of a chemical grade.

Soft X-Ray-induced Dimerization of Methane

Carbon 1s excitation of methane, CH4, has been studied in the gas phase using the ion trap integrated with the photon–ion instrument at PETRA III/DESY and soft X-rays from the beamline P04. The created photoions are stored within the ion trap so that in further steps the photoions can undergo reactions with neutral methane molecules. The ionic photoproducts as well as reaction products created thereby are mass-over-charge analyzed by an ion time-of-flight spectrometer. Besides the photoions, product ions with up to three carbon atoms are found. In contrast to experiments using vacuum ultraviolet radiation, especially highly reactive product ions with a small number of hydrogen atoms such as and are found, which are important precursors for larger hydrocarbons such as C6H6. Possible production routes of the product ions are analyzed on the basis of a model that considers the probabilities for photofragmentation and the first subsequent chemical reaction step. The model indicates that the high degree of fragmentation by photons with energies around 280 eV is favoring these products. The results of the measurements show that the products like and can be generated by a single collision of the ionization product with neutral methane. The results suggest that soft X-rays might be important for chemical reactions in planetary atmospheres, which has usually not been taken into account. However, due to the high degree of fragmentation and large cross sections involved, they can have a large influence even when the corresponding photon flux is rather small.

Leaching of Waste Pharmaceutical Blister Package Aluminium in Sulphuric Acid Media

In this study, the leaching behaviour of aluminium from waste pharmaceutical blister packages (WPBs) is investigated in sulphuric acid media to build future strategies for aluminium recycling from this non-recycled waste fraction. The results suggest that in hydrometallurgical recycling, passivation of aluminium during leaching can be mitigated in dilute sulphuric acid solutions (0.25 M), at high temperatures (60–80 °C) and specifically with H2O2 addition. With this system, 100% extraction was achieved within five hours under optimized conditions (H2SO4 = 0.25 M, T = 80 °C, H2O2 = 1.25 vol.%). The leaching mechanism is suggested to be based on electrochemical dissolution of metallic aluminium oxidized by H+ or H2O2, followed by fast passivation by Al2O3 and consequent chemical dissolution of Al2O3 at slower kinetics. The calculated activation energy (~69 kJ/mol) suggests that the leaching reaction is controlled by the chemical or electrochemical reaction step rather than diffusion. By WPB leaching, an aluminium sulphate solution could be obtained, suitable for further aluminium sulphate crystallization. This may provide a potential route for the valorisation of aluminium from a currently overlooked waste fraction of pharmaceutical blister packages.

Hydrogen production using aluminum-water splitting: A combined experimental and theoretical approach

Hydrogen generation from aluminum hydrolysis with NaOH as an activator is investigated experimentally. A theoretical model is developed using the Density Functional Theory (DFT) and a one-dimensional transport model formalism. The effects of NaOH concentration and reaction temperature on hydrogen production rates are investigated. The kinetic parameters calculated by DFT are used in the COMSOL transport equations and compared. A transport model is implemented for a reaction-diffusion problem of water over the Al surface. The activation barrier increases as the reaction progresses and adsorption of H2O molecules is limited due to space constraints. The reaction rate constants depend on temperature, species convection, and vibrational frequency. The three chemical reaction steps have activation barriers ranging from 7.72 to 61.75 kJ/mol. The activation barrier of the first H2O dissociation step is Ea,1 = 7.72 kJ/mol, whereas the second and third steps have activation barriers of Ea,2 = 15.44 kJ/mol and Ea,3 = 61.75 kJ/mol, respectively. The estimated DFT harmonic vibrational frequency of H2O stretching mode is 3788 cm−1.

Reaction environment impacts charge transfer but not chemical reaction steps in hydrogen evolution catalysis

Reaction environment impacts charge transfer but not chemical reaction steps in hydrogen evolution catalysis

Single Turnover of Transient of Reactants Supports a Complex Interplay of Conformational States in the Mode of Action of Mycobacterium tuberculosis Enoyl Reductase

The enoyl reductase from Mycobacterium tuberculosis (MtInhA) was shown to be a major target for isoniazid, the most prescribed first-line anti-tuberculosis agent. The MtInhA (EC 1.3.1.9) protein catalyzes the hydride transfer from the 4S hydrogen of β-NADH to carbon-3 of long-chain 2-trans-enoyl thioester substrates (enoyl-ACP or enoyl-CoA) to yield NAD+ and acyl-ACP or acyl-CoA products. The latter are the long carbon chains of the meromycolate branch of mycolic acids, which are high-molecular-weight α-alkyl, β-hydroxy fatty acids of the mycobacterial cell wall. Here, stopped-flow measurements under single-turnover experimental conditions are presented for the study of the transient of reactants. Single-turnover experiments at various enzyme active sites were carried out. These studies suggested isomerization of the MtInhA:NADH binary complex in pre-incubation and positive cooperativity that depends on the number of enzyme active sites occupied by the 2-trans-dodecenoyl-CoA (DD-CoA) substrate. Stopped-flow results for burst analysis indicate that product release does not contribute to the rate-limiting step of the MtInhA-catalyzed chemical reaction. The bearings that the results presented herein have on function-based anti-tuberculosis drug design are discussed.

Debromination of Waste Circuit Boards by Reaction in Solid and Liquid Phases: Phenomenological Behavior and Kinetics

The debromination of waste circuit boards (WCBs) used in computer motherboards and components has been studied with two different pieces of equipment. Firstly, the reaction of small particles (around one millimeter in diameter) and larger pieces obtained from WCBs was carried out with several solutions of K2CO3 in small non-stirred batch reactors at 200-225 °C. The kinetics of this heterogeneous reaction has been studied considering both the mass transfer and chemical reaction steps, concluding that the chemical step is much slower than diffusion. Additionally, similar WCBs were debrominated using a planetary ball mill and solid reactants, namely calcined CaO, marble sludge, and calcined marble sludge. A kinetic model has been applied to this reaction, finding that an exponential model is able to explain the results quite satisfactorily. The activity of the marble sludge is about 13% of that of pure CaO and is increased to 29% when slightly calcinating its calcite at only 800 °C for 2 h.

A New Method of AFM‐Based Nanolithography Using Frequency Enhanced Electrochemical Pressure Solution Etching

AbstractA new method of direct‐write nanolithography that is able to rapidly etch silica surfaces under a scanning atomic force microscopy (AFM) probe in tapping mode (TM) is reported. In this lithography technique, silica surfaces are etched using a recently described electro‐chemo‐mechanical phenomenon of frequency enhanced electrochemical pressure solution (FEEPS). In FEEPS, the tapping of the AFM tip generates oscillations of the Stern potential at the silica‐water interface that can accelerate the silica dissolution kinetics by more than 5–6 orders of magnitude when surface resonance states are achieved; i.e., when the oscillation frequency is in phase with the dynamics of interfacial chemical reaction steps. By scanning silica surfaces in TM, silica is selectively dissolved below the tapping tip as it is scanned. The FEEPS accelerated silica dissolution rates can generate etched features with depths of more than 60 nm in a single AFM tip pass. The rate of etching can be controlled easily by varying the scanning rate or by modulating the tapping frequency. This fine control over the silica etching process and because material is removed (dissolved) rather than displaced as with nanoscratching, the FEEPS process lends itself to gray‐scale nanolithography which is demonstrated.

Mechanistic Basis for a Connection between the Catalytic Step and Slow Opening Dynamics of Adenylate Kinase.

Escherichia coli adenylate kinase (AdK) is a small, monomeric enzyme that synchronizes the catalytic step with the enzyme's conformational dynamics to optimize a phosphoryl transfer reaction and the subsequent release of the product. Guided by experimental measurements of low catalytic activity in seven single-point mutation AdK variants (K13Q, R36A, R88A, R123A, R156K, R167A, and D158A), we utilized classical mechanical simulations to probe mutant dynamics linked to product release, and quantum mechanical and molecular mechanical calculations to compute a free energy barrier for the catalytic event. The goal was to establish a mechanistic connection between the two activities. Our calculations of the free energy barriers in AdK variants were in line with those from experiments, and conformational dynamics consistently demonstrated an enhanced tendency toward enzyme opening. This indicates that the catalytic residues in the wild-type AdK serve a dual role in this enzyme's function─one to lower the energy barrier for the phosphoryl transfer reaction and another to delay enzyme opening, maintaining it in a catalytically active, closed conformation for long enough to enable the subsequent chemical step. Our study also discovers that while each catalytic residue individually contributes to facilitating the catalysis, R36, R123, R156, R167, and D158 are organized in a tightly coordinated interaction network and collectively modulate AdK's conformational transitions. Unlike the existing notion of product release being rate-limiting, our results suggest a mechanistic interconnection between the chemical step and the enzyme's conformational dynamics acting as the bottleneck of the catalytic process. Our results also suggest that the enzyme's active site has evolved to optimize the chemical reaction step while slowing down the overall opening dynamics of the enzyme.