Reaction Equilibrium Research Articles

Sorption-enhanced chemical looping steam reforming coupled with water splitting for syngas and H2 coproduction using waste plastic as fuel

Chemical looping is a promising technology for hydrogen production. Achieving both high purity and yield is an ongoing challenge, due to low fuel conversion and carbon deposition. In this study, a sorption-enhanced chemical looping reforming coupled with water splitting (SE-CLSR-WS) process was proposed to co-produce syngas and H2 by using waste plastic as the fuel. The Ni-doped Ca2Fe2O5 brownmillerites were designed and employed as oxygen carriers (OCs) and CO2 sorbent. The introduction of Ni leaded to lattice distortion of brownmillerite, thereby enhancing the redox activity of lattice oxygen. In fuel reactor (FR), CaO in-situ captured CO2 and shifted reaction equilibrium towards PET pyrolysis gas reforming, enhancing both syngas yield and PET conversion rates. Adhere to the surface of OCs, CaO improved cyclic performance by inhibiting agglomeration of active metals. Calcination reactor (CR) was set between FR and steam rector (SR) to in-situ desorb CO2 and remove carbon deposition, enhancing hydrogen purity in SR. When Ca2Ni0.75Fe1.25O5-0.25CaO was applied to SE-CLSR-WS process, it exhibited synergistically strengthened performance in reaction activity, sorption capacity and cyclic stability, with a syngas purity of 82.71 % and H2 yield of 8.01 mmol/g OC with 93.26 % purity.

Preparation of high-performance Bi-YG ferrite based on LTCC technology and theoretical analysis of its sintering mechanism

In the preparation process of Microwave Multi-Chip Module (MMCM), it is necessary to simultaneously sinter both microwave medium (ferrite) and silver electrodes. Hence, this necessitates keeping the sintering temperature below the melting point of silver (961 °C). An excessively low sintering temperature would significantly impair the electromagnetic properties of the ferrite material. To address this concern, this study synthesizes Bi-YIG (Y3-xBixFe5O12, x = 0–1.0) ferrites with optimized characteristics, including low ferromagnetic resonance line-width (ΔH) and high saturation magnetization (Ms), at 945 °C using Low Temperature Co-fired Ceramic (LTCC) technology. The mechanism of low-temperature liquid phase sintering, facilitated by a fluxing agent, was investigated using a theoretical model. The addition of Bi2O3 fluxing agent was found to reduce the reaction activation energy, disrupt the chemical reaction equilibrium, and promote low-temperature liquid phase sintering, thus lowering the critical sintering temperature below the melting point of silver. Furthermore, optimal bismuth content was identified to regulate the dynamic balance between grain growth and boundary diffusion, suppressing abnormal grain growth and enhancing the electromagnetic properties of the ferrite. This exploration, leveraging LTCC technology, may offer valuable insights for enhancing the overall performance of MMCMs.

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium.

Fabricating nanoscale metal carbides is a great challenge due to them having higher Gibbs free energy of formation (ΔG°) values than other metal compounds; additionally, these carbides have harsh calcination conditions, in which metal oxidation is preferred in the atmosphere. Herein, we report oxocarbon-mediated calcination for the predictive synthesis of nanoscale metal carbides. The thermochemical oxocarbon equilibrium of CO-CO2 reactions was utilized to control the selective redox reactions in multiatomic systems of Mo-C-O, contributing to the phase-forming and structuring of Mo compounds. By harnessing the thermodynamically predicted processing window, we controlled a wide range of Mo phases (MoO2, α-MoC1-x, and β-Mo2C) and nanostructures (nanoparticle, spike, stain, and core/shell) in the Mo compounds/C nanofibers. By inducing simultaneous reactions of C-O (selective C combustion) and Mo-C (Mo carbide formation) in the nanofibers, Mo diffusion was controlled in C nanofibers, acting as a template for the nucleation and growth of Mo carbides and resulting in precise control of the phases and structures of Mo compounds. The formation mechanism of nanostructured Mo carbides was elucidated according to the CO fractions of CO-CO2 calcination. Moreover, tungsten (W) and niobium (Nb) carbides/C nanofibers have been successfully synthesized by CO-CO2 calcination. We constructed the thermodynamic map for the predictive synthesis of transition metal carbides to provide universal guideline via thermochemical oxocarbon equilibrium. We revealed that our thermochemical oxocarbon-mediated gas-solid reaction enabled the structure and phase control of nanoscale transition metal compounds to optimize the material-property relationship accordingly.

Biosensor-assisted evolution of RhaD for enhancing the biosynthetic yield of d-allulose

d-Allulose, is an improtant rare sugar, having health-promoting properties and applications in the food, pharmaceutical and nutrition sectors. White the aldol reaction-based method shows promise as an alternative to the “Izumori” strategy for ᴅ-allulose bioproduction, its industrial exploitability is hindered by the low product yield in reaction equilibrium and the high costs associated with the use of purified enzymes. To address these limitations, this study explored cell-based biosynthesis of ᴅ-allulose from low-cost glycerol by overexpression the enzymes involved in the ᴅ-allulose aldol condensation (AC) biosynthesis pathway, namely fructose-1-phosphatase (YqaB), alditol oxidase (AldO), and l-rhamnulose-1-phosphate aldolase (RhaD), in Escherichia coli. Results indicated that RhaD is a rate-limiting step of the ᴅ-allulose biosynthetic pathway. Then, biosensor-based high throughput screening was employed for the directed evolution of RhaD. In this way, two RhaD mutants, namely RhaDN156D and RhaDP184S, were successfully screened from 40,129 individual colonies, which exhibited respectively achieved a ᴅ-allulose titer of 3.1 g/L and 2.9 g/L, respectively in shake flasks, representing a more than 20% improvement compared to the wildtype strain. Overall, the ᴅ-allulose biosensor-assisted key enzyme evolution strategy and the high throughput screening method presented in this work provide a paradigm for improving rare sugars’ high-valued productions from cheap substrates.

Poly(aniline‐co‐pyrrole) as Adsorbent for Removal of Pharmaceuticals: Preparation, Characterization, Kinetics, Isotherms and Application on Sample Preparation

AbstractHerein, poly(aniline‐co‐pyrrole) has been synthetized and investigated to adsorb phenylbutazone (PBZ), ceftiofur (CEF) and prednisolone (PRD) in aqueous medium as proof of concept. After proper adsorbent characterization, some studies were carried out in batch process, i. e., contact time, pH, and concentration. The adsorption mechanism has been conducted using kinetic and isothermal models. It was found that the reaction equilibrium was reached in 20 min for all analytes. The best fit for the experimental data were obtained employing the models of dual‐site Langmuir–Freundlich, Fritz–Schlunder and Langmuir, with R2=0.999, 0.952 and 0.974, for PBZ, CEF and PRD, respectively. For PBZ, CEF and PRD, poly(aniline‐co‐pyrrole) provided a Qmax=238.8 mg g−1 and Kmax=0.086 L g−1, Q=0.028 mg g−1 and Kmax=3.258 L g−1, Q=13.66 mg g−1 and KL=0.005 L g−1, respectively. Finally, the copolymer was evaluated in solid phase extraction, which showed recovery around 70 % for PBZ, offering also exciting opportunities for further application in the separation process.

Thermodynamic simulation of hydrogen production from the nano-CaO reactive sorption enhanced biomass steam reforming

Based on the principles of thermodynamic reaction equilibrium, a simulation method enhanced by the nano-CaO reactive sorption CO2 for hydrogen production from biomass steam reforming has been established. MATLAB R2022b software has been utilized to calculate the composition concentration of the product gas. Detailed simulations have been conducted to understand the changes in gas component concentration and yield under various reaction conditions, includes temperatures, steam to biomass (S/B) molar ratios, and CaO to carbon (CaO/C) molar ratios. The result demonstrated that temperature plays a significant role in both the concentration and yield of hydrogen. At an optimal reaction temperature of 650 °C, the concentration of H2 in the product reaches 77% (S/B = 2 and CaO/C = 0.5). S/B molar ratio over 2 is necessary to increase the H2 concentration. The study also reveals CaO/C molar ratio 0.5 enable successful removal of CO2 generated by reaction. The application of nano-CaO notably enhanced the efficiency of hydrogen production from biomass steam reforming, leading to a 25% increase in H2 concentration and a boost in H2 yield to 50 mL/gBiomass, and reaction temperature decrease 200 °C compared to the case without CaO.

Absorption characteristics and molecular mechanism of a low viscosity iron-based ionic liquid for removing H2S

Aiming at the problem of by-product salt and volatile solvent component in industrial liquid redox process of H2S removal. A new absorbent, a 1-butyl-3-methylpyridine iron-based ionic liquid (rFeCl3/[BMP]Cl) with three iron-pyridine ratios (r=0.6, 0.8, and 1.0), was synthesized. The physicochemical properties and H2S solubility of rFeCl3/[BMP]Cl were measured and modeled. The molecular mechanism of chemical absorption of H2S by iron-based ionic liquids was explained from the interaction energy, reduced density gradient (RDG) and atoms in molecules (AIM) topology analysis, and standard reaction equilibrium constant by quantum chemical calculation. It was found that rFeCl3/[BMP]Cl have low viscosity, high solubility, and good thermal stability. Its Bronsted acidity avoids by-product salts produced in the absorption of H2S. The hydrophobicity makes the ionic liquid not diluted by the generated water during the absorption. The results of quantum chemical calculations show that rFeCl3/[BMP]Cl-H2S has moderate intermolecular interaction and large reactivity, which is consistent with the experimental results of the Henry's coefficient and reaction equilibrium constant.

ThermoBounce: Visualizing Chemical Kinetics via a Gravitational Potential Analogy

ThermoBounce is an interactive online visualization designed to help students understand how enthalpy, entropy, and temperature contribute to the reaction rate and equilibrium of a unimolecular chemical change between reactant and product states, for example, molecular isomerizations or phase transitions. At the start of the animation, reactant molecules are represented by spheres bouncing around in a reactant room, with an average kinetic energy proportional to the temperature. This room is connected to an adjacent product room by a window. When the user triggers the animation, spheres may convert to the product state by passing through the window into the product room, changing color as they do so. The difference between the floor heights of the reactant and product rooms represents the enthalpy change of the reaction, and the floor areas of the two rooms represent the entropies of the reactant and product states. The height of the bottom of the window above the floor of the reactant room represents the enthalpy of activation, and the width of the window represents the entropy of activation. Users can change the geometry of the rooms and window to adjust all these quantities and can modify the temperature before or during the reaction. They can then observe the resulting changes in the reaction rate and in the accumulation of product molecules, as shown on a reaction progress graph. The visualization and instructions for interacting with it are freely available on the Internet.

Development of a consistent geochemical model of the Mg(OH)2–MgCl2–H2O system from 25°C to 120°C

The formation of magnesium chloride-hydroxide salts (magnesium hydroxychlorides) has implications for many geochemical processes and technical applications. For this reason, a thermodynamic database for evaluating the Mg(OH)2–MgCl2–H2O ternary system from 0 °C–120 °C has been developed based on extensive experimental solubility data. Internally consistent sets of standard thermodynamic parameters (ΔGf°, ΔHf°, S°, and CP) were derived for several solid phases: 3 Mg(OH)2:MgCl2:8H2O, 9 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2: 2H2O(s), brucite (Mg(OH)2), bischofite (MgCl2:6H2O), and MgCl2:4H2O. First, estimated values for the thermodynamic parameters were derived using a component addition method. These parameters were combined with standard thermodynamic data for Mg2+(aq) consistent with CODATA (Cox et al., 1989) to generate temperature-dependent Gibbs energies for the dissolution reactions of the solid phases. These data, in combination with values for MgOH+(aq) updated to be consistent with Mg2+-CODATA, were used to compute equilibrium constants and incorporated into a Pitzer thermodynamic database for concentrated electrolyte solutions. Phase solubility diagrams were constructed as a function of temperature and magnesium chloride concentration for comparisons with available experimental data. To improve the fits to the experimental data, reaction equilibrium constants for the Mg-bearing mineral phases, the binary Pitzer parameters for the MgOH+ — Cl− interaction, and the temperature-dependent coefficients for those Pitzer parameters were constrained by experimental phase boundaries and to match phase solubilities. These parameter adjustments resulted in an updated set of standard thermodynamic data and associated temperature-dependent functions. The resulting database has direct applications to investigations of magnesia cement formation and leaching, chemical barrier interactions related to disposition of heat-generating nuclear waste, and evaluation of magnesium-rich salt and brine stabilities at elevated temperatures.

Binding Curve Viewer: Visualizing the Equilibrium and Kinetics of Protein-Ligand Binding and Competitive Binding.

Understanding the thermodynamics and kinetics of the protein-ligand interaction is essential for biologists and pharmacologists. To visualize the equilibrium and kinetics of the binding reaction with 1:1 stoichiometry and no cooperativity, we obtained the exact relationship of the concentration of the protein-ligand complex and the time in the second-order binding process and numerically simulated the process of competitive binding. First, two common concerns in measuring protein-ligand interactions were focused on how to avoid the titration regime and how to establish the appropriate incubation time. Then, we gave examples of how the commonly used experimental conditions of [L]0 ≫ [P]0 and [I]0 ≫ [P]0 affected the estimation of the kinetic and thermodynamic properties. Theoretical inhibition curves were calculated, and the apparent IC50 and IC50 were estimated accordingly under predefined conditions. Using the estimated apparent IC50, we compared the apparent Ki and Ki calculated by using the Cheng-Prusoff equation, Lin-Riggs equation, and Wang's group equation. We also applied our tools to simulate high-throughput screening and compare the results of real experiments. The visualization tool for simulating the saturation experiment, kinetic experiments of binding and competitive binding, and inhibition curve, "Binding Curve Viewer," is available at www.eplatton.net/binding-curve-viewer.

Identification and structure-based engineering of a dipeptidase CpPepD from Clostridium perfringens for the synthesis of l-carnosine

l-Carnosine (l-Car), an endogenous dipeptide presents in muscle and brain tissues of various vertebrates, has a wide range of application values. The enzymatic preparation of l-Car is a promising synthetic method because it avoids the protection and deprotection steps. In the present study, a dipeptidase gene (CpPepD) from Clostridium perfringens with high l-Car synthetic activity was cloned and characterized. In an effort to improve the performance of this enzyme, we carried out site saturation mutagenesis using CpPepD as the template. By the o-phthalaldehyde (OPA)-derived high throughput screening method, mutant A171S was obtained with 2.2-fold enhanced synthetic activity. The enzymatic properties of CpPepD and mutant A171S were investigated. Under the optimized conditions, 63.94 mM (14.46 g L−1) or 67.02 mM (15.16 g L−1) l-Car was produced at the substrate concentrations of 6 M β-Ala and 0.2 M l-His using wild-type or mutant A171S enzyme, respectively. Although the mutation enhanced the enzyme activity, the reaction equilibrium was barely affected.

Space confinement effect of carbon nanotube-alumina strip support on the Cu-Co catalysts for CO2 methanation

The present work reported the space confinement effect of carbon nanotube-alumina strip (CAS) support on the Cu-Co bimetallic catalyst or the single Cu, Co catalysts for the CO2 methanation. CAS, made by extrusion of nanotubes and Al-based sol and high temperature calcination, was a macroscopic support with sufficient mesopores and hydrophobic property. Cu-Co/CAS catalysts exhibited high catalytic activity for methanation of CO2 (H2/CO2=3:1), where CO2 conversion was 49.62% and CH4 selectivity was 95.98% at temperature as low as 250 ℃ and 1.5 MPa, and showed advantage significantly over those with the supports of individual nanotube or pure Alumina support. The comparison suggested the hydrophobicity of carbon nanotubes can effectively remove water from the metal active sites, enhancing the equilibrium of reverse water gas shift and CO methanation reactions, as compared to alumina support. Additionally, CAS support had a spatial confinement effect that increased the contact time of CO2 or intermediates with the active sites, compared with individual nanotube support. XPS and Raman spectroscopy validated the presence of oxygen vacancies of CAS, promoting the CO2 methanation. H2-TPR results, in combination with DFT calculations, confirmed that the CAS supports enabled the Cu-Co active phase by changing their electronic structures, to possess a strong adsorption activation capacity for H2 at low temperatures with high performance for CO2 methanation.

Highly efficient nitric oxide absorption by low viscosity superbase/amide deep eutectic solvents through mutual promotion effect

A series of low-viscous deep eutectic solvents (DESs) with superbase as HBA and amide as HBD were designed and prepared for NO absorption. Impressively, both a comparably low viscosity of 8.07 mPa∙s and a high absorption capacity of 6.43 mol∙kg−1 (∼0.19 kg/kg) at 293.2 K were achieved, which was superior to that of other reported absorbents. Through a combination of absorption experiments, FT-IR characterization, and thermodynamic modelling, the results indicated that such a high solubility for NO was originated from the mutual promotion effect between the superbase and the amide. Considering that chemical absorption occurred accompanied with physical one, a reaction equilibrium thermodynamic model (RETM) equation was derived to correlate the experiment solubility data, so that the thermodynamic parameters were obtained to evaluate the absorption process. The absorption-desorption cycle experiment revealed that the regeneration efficiency of the superbase/amide DESs could be high up to 90 %. Given the low viscosity, high absorption capacity and excellent recycle efficiency, the superbase/amide DES was considered as a promising candidate for NO capture and utilization.

Modeling phase or chemical reaction equilibrium with an equation of state, an unrealistic modeling

The traditional chemical thermodynamics considered the chemical potential then fugacity of a component in a single-phase, open system is just the one of the component in a co-existing phase of an equilibrium, multi-component, multi-phase system or in an equilibrium, chemical reaction system and the fugacity can be calculated with the equation of state of the single-phase, open system. Therefore, the most common method to model phase or chemical reaction equilibrium is with an equation of state. Obviously, modeling phase or chemical reaction equilibrium with an equation of state requires to the single-phase, open system is equivalent to the co-existing phase or the equilibrium, chemical reaction system. However, there are significant differences in the thermodynamics properties between the single-phase, open system and the co-existing phase or the equilibrium, chemical reaction system. Therefore, the chemical potential then fugacity of a component in the single-phase, open system is impossible the one of the component in the co-existing phase or in the equilibrium, chemical reaction system. That is, the calculated fugacity of a component in a single-phase, open system with the equation of state of the single-phase, open system is impossibly the fugacity of the component in a co-existing phase of an equilibrium, multi-component, multi-phase system or in an equilibrium, chemical reaction system. Therefore, it is unrealistic to model phase or chemical reaction equilibrium with an equation of state. For this, we establish the chemical potential differential formula of a component in a co-existing phase and in an equilibrium, chemical reaction system to calculate phase or chemical reaction equilibrium. The calculated values of solubility in molar concentration within the framework of the present theory equals exactly the measured values of solubility in molar concentration by the experiments.

A flow equilibrium of zinc in cells of Cupriavidus metallidurans.

Understanding the biochemical action of a single enzyme or transport protein is the pre-requisite to obtain insight into its cellular function but this is only one half of the coin. The other side concerns the question of how central metabolic functions of a cell emerge from the interplay of different proteins and other macromolecules. This paper demonstrates that a flow equilibrium of zinc uptake and efflux reactions is at the core of cellular zinc homeostasis and identifies the most important contributors to this flow equilibrium: the uptake and efflux systems and metal-binding components of the cytoplasm.

Highly efficient La/Ni co-doped strontium titanate catalyst for co-production of propylene and hydrogen from propane in protonic ceramic electrochemical cells

A highly efficient La/Ni co-doped strontium titanate (LSNT) perovskite catalyst is developed and integrated in a protonic ceramic electrochemical cell for co-production of propylene and high-purity hydrogen from commercial propane feedstock. Propane conversion and hydrogen production rate can be effectively enhanced under an applied current due to the electrochemical promotion effect and/or shifted reaction equilibrium induced by rapid separation of hydrogen product. Water vapor in the feed gas could significantly improve the catalyst stability by suppressing the coke formation. The propane conversion could reach up to 53% at 600 °C under a current density of 90 mA cm−2. The LSNT catalyst also shows excellent tolerance for the sulfur contaminant in commercial propane gas. The excellent performance of the LSNT catalyst is attributed to the highly active and selective Ni species at the interface with the perovskite substrate, which are formed in situ via reduction-induced exsolution under reaction conditions.

Diallyl Trisulfide Acts as a Soil Disinfestation Against the Ilyonectria destructans through Inducing the Burst of Reactive Oxygen Species.

Soil-borne diseases represent an impediment to the sustainable development of agriculture. A soil-borne disease caused by Ilyonectria destructans severely impacts Panax species, and soil disinfestation has proven to be an effective management approach. Here, diallyl trisulfide (DATS), derived from garlic, exhibited pronounced inhibitory effects on the growth of I. destructans in vitro tests and contributed to the alleviation of soil-borne diseases in the field. A comprehensive analysis demonstrated that DATS inhibits the growth of I. destructans by activating detoxifying enzymes, such as GSTs, disrupting the equilibrium of redox reactions. A series of antioxidant amino acids were suppressed by DATS. Particularly noteworthy is the substantial depletion of glutathione by DATS, resulting in the accumulation of ROS, ultimately culminating in the inhibition of I. destructans growth. Briefly, DATS could effectively suppress soil-borne diseases by inhibiting pathogen growth through the activation of ROS, and it holds promise as a potential environmentally friendly soil disinfestation.

Thermochemistry of Gas-Phase Thermal Oxidation of C2 to C8 Perfluorinated Sulfonic Acids with Extrapolation to C16.

New ideal-gas thermochemistry Cp°(T), H°(T), S°(T), and G°(T) are predicted for 53 species involved in the thermal destruction of perfluorinated sulfonic acids (PFSAs) ranging from C2 to C8 in perfluorinated alkyl chain length. Species were selected by considering both the pyrolytic and oxidative pathways of PFSA destruction. After the sulfur-containing moieties are removed, subsequent reactions largely involve species from a prior set of thermochemistry for the thermal destruction of perfluorinated carboxylic acids (Ram et al., J. Phys. Chem. A, 2024, 128, 7, 1313-1326). Enthalpies of formation at 0 K are computed using a new isogyric reaction scheme. Rigid-rotor harmonic-oscillator partition functions were calculated over a 200-2500 K temperature range using rovibrational properties at G4 (≤C3S1 species) and M06-2X-D3(0)/def2-QZVPP (≥C4S1 species), employing the 1D hindered rotor approximation to correct for torsional modes. Seven-coefficient NASA polynomial fits are reported in standardized formats. Bond dissociation energies and important reaction equilibria are examined to provide insights into the reactivity of potentially persistent species. Extrapolated NASA polynomials are also systematically predicted for 126 species larger than C8/C8S1 in size, allowing reasonably accurate estimates of thermochemistry without the need for expensive electronic structure calculations.

Investigation of effective CO2 capture by ternary deep eutectic solvents based on superbase

The absorption and separation of CO2 is one of the main strategies to reduce carbon emissions and mitigate global climate change. In this context, a series of ternary superbase/betaine-based deep eutectic solvents (DESs) were synthesized to capture CO2, and their density, viscosity and thermal stability were investigated. The effects of temperature, pressure, different hydrogen bond donors (HBDs) and alkalinity of the superbase on their CO2 affinity were evaluated by the isovolumetric saturation method. The uptake of CO2 by the DES synthesized from betaine, 1,2-propanediol and 1,8-diazabicyclo(5.4.0)undec-7-ene reached a maximum of 1.5071 mol·kg−1 at 303.15 K and a pressure of 0.187 MPa. The simultaneous chemical and physical adsorption of CO2 by the ternary DESs was verified by FTIR spectroscopy, and the absorption mechanism was also proposed. The reaction equilibrium thermodynamic model (RETM) was improved to obtain the “Active DES” model, which was correlated with the experimentally determined CO2 solubility. The reaction equilibrium constants and Henry's law constants were obtained for each ternary system. The ternary superbase/betaine DESs proposed in this paper are green, economical and high-performance absorbers for capturing CO2.

Glycerol 3-Phosphate Dehydrogenase: Role of the Protein Conformational Change in Activation of a Readily Reversible Enzyme-Catalyzed Hydride Transfer Reaction.

Kinetic parameters are reported for glycerol 3-phosphate dehydrogenase (GPDH)-catalyzed hydride transfer from the whole substrate glycerol 3-phosphate (G3P) or truncated substrate ethylene glycol (EtG) to NAD, and for activation of the hydride transfer reaction of EtG by phosphite dianion. These kinetic parameters were combined with parameters for enzyme-catalyzed hydride transfer in the microscopic reverse direction to give the reaction equilibrium constants Keq. Hydride transfer from G3P is favored in comparison to EtG because the carbonyl product of the former reaction is stabilized by hyperconjugative electron donation from the -CH2R keto substituent. The kinetic data show that the phosphite dianion provides the same 7.6 ± 0.1 kcal/mol stabilization of the transition states for enzyme-catalyzed reactions in the forward [reduction of NAD by EtG] and reverse [oxidation of NADH by glycolaldehyde] directions. The experimental evidence that supports a role for phosphite dianion in stabilizing the active closed form of the GPDH (EC) relative to the ca. 6 kcal/mol more unstable open form (EO) is summarized.