Free Energy Of Transition State Research Articles

Revealing operando surface defect–dependent electrocatalytic performance of Pt at the subparticle level

Understanding the operando defect-tuning performance of catalysts is critical to establish an accurate structure-activity relationship of a catalyst. Here, with the tool of single-molecule super-resolution fluorescence microscopy, by imaging intermediate CO formation/oxidation during the methanol oxidation reaction process on individual defective Pt nanotubes, we reveal that the fresh Pt ends with more defects are more active and anti-CO poisoning than fresh center areas with less defects, while such difference could be reversed after catalysis-induced step-by-step creation of more defects on the Pt surface. Further experimental results reveal an operando volcano relationship between the catalytic performance (activity and anti-CO ability) and the fine-tuned defect density. Systematic DFT calculations indicate that such an operando volcano relationship could be attributed to the defect-dependent transition state free energy and the accelerated surface reconstructing of defects or Pt-atom moving driven by the adsorption of the CO intermediate. These insights deepen our understanding to the operando defect-driven catalysis at single-molecule and subparticle level, which is able to help the design of highly efficient defect-based catalysts.

Perturbative diffraction methods resolve a conformational switch that facilitates a two-step enzymatic mechanism

Enzymes catalyze biochemical reactions through precise positioning of substrates, cofactors, and amino acids to modulate the transition-state free energy. However, the role of conformational dynamics remains poorly understood due to poor experimental access. This shortcoming is evident with Escherichia coli dihydrofolate reductase (DHFR), a model system for the role of protein dynamics in catalysis, for which it is unknown how the enzyme regulates the different active site environments required to facilitate proton and hydride transfer. Here, we describe ligand-, temperature-, and electric-field-based perturbations during X-ray diffraction experiments to map the conformational dynamics of the Michaelis complex of DHFR. We resolve coupled global and local motions and find that these motions are engaged by the protonated substrate to promote efficient catalysis. This result suggests a fundamental design principle for multistep enzymes in which pre-existing dynamics enable intermediates to drive rapid electrostatic reorganization to facilitate subsequent chemical steps.

Temperature‐dependent kinetics of the reactions of CH2OO with acetone, biacetyl, and acetylacetone

AbstractTemperature‐dependent rate constants for the reactions of CH2OO with acetone (Ac), biacetyl (BiAc), and acetylacetone (AcAc) have been measured over the range 275–335 K using a flash photolysis, transient absorption spectroscopy technique. The measurements were performed at a total pressure of ∼80 Torr in N2 bath gas, which corresponds to the high‐pressure limit for these reactions. All three reactions show linear Arrhenius plots with negative temperature dependences. Rate constants increase in the order Ac < AcAc « BiAc across the temperature range; at 295 K the rate constants are kAc = (4.8 ± 0.4) × 10–13 cm3 s–1, kAcAc = (8.0 ± 0.7) × 10–13 cm3 s–1, and kBiAc = (1.10 ± 0.09) × 10–11 cm3 s–1. Sensitivity to temperature, characterized by the magnitude of the negative activation energy, increases in the order AcAc < BiAc < Ac (Ea/R values of –1830 ± 170 K, –1260 ± 170 K, and –460 ± 180 K, respectively). CBS‐QB3 calculations show that the Ac and BiAc reactions proceed via formation of an entrance channel complex followed by 1,3‐dipolar cycloaddition to form secondary ozonide products via a submerged transition state. For the BiAc reaction, the rate limiting step appears to be rearrangement of a long‐range van der Waals complex into the short‐range complex that subsequently leads directly to the cycloaddition transition state with a very low energy barrier. The calculations show that two reaction pathways are competitive for AcAc with nearly identical transition state free energies (ΔG° = +10.1 kcal mol–1 at 298 K) found for cycloaddition at the C=O and at the C=C site of the dominant enolone tautomer. The weak temperature dependence observed is likely due to competition between these pathways.

The role of water and acid catalysis in the reaction of acetone with hydrogen peroxide: A DFT study

The proposed first step in the synthesis of peroxide explosives such as triacetone triperoxide (TATP) is investigated computationally at the M06-2X/6-311+G(2d,p) level in SMD water. The reaction between acetone and hydrogen peroxide is thought to produce 2-hydroperoxy-2-isopropanol (HPP) as the first intermediate. The conformers of HPP are optimized and described structurally and thermodynamically. A nucleophilic mechanism for the formation of HPP, with and without a strong Bronsted acid catalyst, is considered. The thermodynamic properties associated with each step of the mechanism, and for the overall reaction, are determined; overall, ΔG* = +6.3 kJ/mol. Without an acid catalyst, the transition state free energy ranges from 167 kJ/mol without any assisting water molecules, to 84 kJ/mol with the assistance of catalytic water. With an acid catalyst, the free energy reaction barrier drops to 22 kJ/mol. This pathway consists of a network of three water molecules facilitating proton transfer from H2O2 to acetone.

Comprehensive theoretical study of nickel‐NHC‐catalyzed enantioselective intramolecular indole C—H cyclization: Reaction mechanism, reactivity, regioselectivity, and electronic processes

Density functional theory was used to illuminate the reaction mechanism of Ni(0)‐NHC‐catalyzed enantioselective intramolecular CH cyclization of indoles. The ωB97XD functional with 6‐31G(d,p) basis set (SDD for nickel) was employed to optimize all intermediates and transition states. The computations revealed that the reactivity of C1H bond was the best among all CH bonds of indole catalyzed by the Ni‐NHC complex, and in the C1H bond activation, the concerted oxidative addition was more dominant than the ligand‐to‐ligand H transfer reaction, due to the lower free energy barrier. The most favorable channels predicted theoretically went through the ligand‐to‐ligand H transfer reaction and reductive elimination, and two chiral products ((R)‐ and (S)‐tetrahydroindolizines) were coexisted as a result of similar transition states and little difference in free energy barrier. Hence, the model ligandL1was not good for the regioselectivity. Nevertheless, another ligandL2, a chiral N‐heterocyclic carbene ligand, gave good regioselectivity, and it changed the rate‐determining step and generally decreased the free energies of transition states and intermediates.

Kinetics-Based Approach to Developing Electrocatalytic Variants of Slow Oxidations: Application to Hydride Abstraction-Initiated Cyclization Reactions.

Electrochemical oxidant regeneration is challenging in reactions that have a slow redox step because the steady-state concentration of the reduced oxidant is low, causing difficulties in maintaining sufficient current or preventing potential spikes. This work shows that applying an understanding of the relationship between intermediate cation stability, oxidant strength, overpotential, and concentration on reaction kinetics delivers a method for electrochemical oxoammonium ion regeneration in hydride abstraction-initiated cyclization reactions, resulting in the development of an electrocatalytic variant of a process that has a high oxidation transition state free energy. This approach should be applicable to expanding the scope of electrocatalysis to include additional slow redox processes.

Aldol Condensation and Esterification over Ti-Substituted *BEA Zeolite: Mechanisms and Effects of Pore Hydrophobicity

Aldol condensation and esterification reactions provide paths to upgrade ethanol and acetaldehyde to higher-value molecules useful as fuels or intermediates for the synthesis of polymers. Transition-metal-substituted BEA zeolites (M-BEA) catalyze these reactions; however, the mechanisms for these processes in M-BEA and the effects of incidental or purposefully included silanol groups are not reported. Here, we combine kinetic and spectroscopic measurements obtained during catalytic reactions of acetaldehyde (CH3CHO), ethanol (C2H5OH), and hydrogen (H2) mixtures over a series of Ti-BEA catalysts that possess a known range of silanol group densities to examine the kinetic relevance of intervening steps and the impact of silanol groups on catalytic rates. Across all Ti-BEA, rates for aldol condensation and esterification increase with the pressure of CH3CHO; however, C2H5OH and H2O weakly inhibit the rates of these reactions. The substitution of CD3CDO for CH3CHO decreases aldol condensation rates slightly (∼10%) but leads to greater esterification rates (2- to 5-fold). The kinetic isotope effects together with the measured dependence of rates on reactant pressures suggest that aldol condensation and esterification occur on unoccupied Ti sites and involve multiple kinetically relevant steps. CH3CHO deprotonates irreversibly, and the kinetically relevant nucleophilic attack of the enolate to CH3CHO* (i.e., adsorbed CH3CHO on Ti sites) leads to aldol products, while the nucleophilic attack of the enolate to C2H5OH* gives esters. Selectivities toward aldol condensation increase with the ratio of CH3CHO to C2H5OH pressure and with increases in the silanol density of the as-synthesized Ti-BEA. During catalysis, in situ infrared spectroscopy demonstrates that these silanol groups react with C2H5OH to form ethoxysilane groups (i.e., SiOC2H5) that modify the polarity of the environment near Ti active sites. As initial silanol densities increase, steady-state turnover rates for aldol condensation and esterification increase by factors of 5 and 2, respectively. The changes in rates and selectivities among Ti-BEA catalysts likely reflect changes in excess free energies of transition states for enolization and nucleophilic attack of the enolate to adsorbed coreactants. The differences in excess stability report on the interactions among reactive intermediates at framework Ti atoms and the ethoxysilane and remaining silanol groups present. The in situ modification of these pore environments confers changes in the stability of reactive species in a manner that contradicts intuition when considering the initial state of the catalyst but can be reconciled after accounting for the formation of persistent alkoxy surface moieties in the pores.

Intrinsic Nucleophilicity of Inverting and Retaining Glycoside Hydrolases Revealed Using Carbasugar Glyco-Tools

Hydrolyses of cyclohexenyl-based carbasugars that mimic either α-d-glucose or α-d-galactose were explored with two Bacteroides thetaiotaomicron enzymes from glycoside hydrolase family 97: an inverting α-glucosidase (BtGH97a) and a retaining α-galactosidase (BtGH97b). Both enzymes yield nucleophilic substitutions at the pseudo-anomeric center of the carbasugar substrates, giving significantly different linear energy relationships for the catalytic rate constant as a function of the leaving group ability. Specifically, the kinetic data for the inverting α-glucosidase is consistent with the reaction giving a hydrolyzed inverted carbaglucose product by a mechanism that proceeds with little nucleophilic participation by the bound water molecule at the reaction transition state. In contrast, the reaction of carbagalactose substrates with the retaining GH97 enzyme involves a rate-limiting nonchemical step, likely a conformational change, followed by rapid substitution involving a nucleophilic amino acid residue to give a covalently bound intermediate. Considering the structural similarities between these two GH97 enzymes, the kinetic data nonetheless reveal a significant (>106) difference in the rates of nucleophilic attack between the unique enzymatic nucleophiles─with the less nucleophilic species being H2O in the inverting α-glucosidase and the better nucleophile being a carboxylate in the retaining α-galactosidase. The enzymatic rate constant ratio for the phenyl carbasugars contrasts with the corresponding kinetic data obtained using natural substrate phenyl glycopyranosides. Last, for the galactocarbasugar with a phenol leaving group, the second-order rate constant for alkylation of the GH97 α-galactosidase is only ∼10-fold lower than that for glycosylation of this enzyme by the parent carbohydrate phenyl α-d-galactopyranoside. This modest difference in rate constants underscores our conclusion that retaining glycoside hydrolases may not have optimized the nucleophilicity of their active site nucleophiles with the result that the transition state free energies for formation and hydrolysis of the covalent enzyme intermediate are matched.

A density functional theory study of the hydride shift in the Eschweiler–Clarke reaction

AbstractThe Eschweiler–Clarke (the amine methylation) reaction was investigated by density functional theory (DFT) calculations. First, a reaction model of H3CNH2 + HC(O)OH + CH2O + (H2O)3 → (H3C)2NH + CO2 + (H2O)4 was employed for geometry optimizations. Geometries and activation free energies of transition states (TSs) by eight DFTs, B2PLYP‐D3, B3LYP, B3LYP‐D, BP86‐D, PBE0‐D, M06‐2X, wB97X‐D, and APF‐D, along with MP2 were compared. Four elementary processes were obtained. The rate‐determining step is of the hydride‐transfer TS, H3CN+HCH2 + HCO2− → H3CNHCH3 + CO2. Whereas BP86‐D and APF‐D gave underestimated energies, M06‐2X was found to be a reasonable DFT to trace the present reaction. Second, by the use of M06‐2X/6‐311++G**, hydride‐shift TSs were examined for various sizes of the water cluster (H2O)n, and the controversial two mechanisms were evaluated. It was suggested that the first formic acid contributes to formation of the iminium ion H3CN+HCH2 and the second formic acid works for the hydride transfer. The Eschweiler–Clarke reaction was described by the scheme, R1R2NH + H2CO + (HCOOH)2 + (H2O)n → R1R2NCH3 + CO2 + HCO2− + H3O+(H2O)n.

The study of oxygen reduction reaction on Ge‐doped MoS 2 monolayer based on first principle

Rational design of electrocatalyst for air cathode with high oxygen reduction reaction (ORR) performance is highly demanded. However, current low performance of electrocatalyst remains a big challenge. Herein, the possibility of germanium (Ge)-doped molybdenum disulfide (MoS2) monolayer as a novel electrocatalyst for ORR in alkaline solution was studied based on first principle calculation. The results indicate that oxygen is strongly adsorbed on the surface of Ge-doped MoS2 monolayer. Moreover, a high barrier should be overcome during H2O molecular dissociation and the barrier of dissociation decreases with the number of doped Ge atoms increasing. Based on the calculation of transition state and Gibbs free energy, the triple Ge atoms-doped MoS2 monolayer shows the best activity toward ORR with the lowest rate-determine step barrier of 0.23 eV. Our study may provide a meaningful method for the design of novel MoS2-based electrocatalyst for ORR.

Accuracy of Molecular Simulation-Based Predictions of koff Values: A Metadynamics Study.

The koff values of ligands unbinding to proteins are key parameters for drug discovery. Their predictions based on molecular simulation may under- or overestimate experiment in a system- and/or technique-dependent way. Here we use an established method-infrequent metadynamics, based on the AMBER force field-to compute the koff of the ligand iperoxo (in clinical use) targeting the muscarinic receptor M2. The ligand charges are calculated by either (i) the Amber standard procedure or (ii) B3LYP-DFT. The calculations using (i) turn out not to provide a reasonable estimation of the transition-state free energy. Those using (ii) differ from experiment by 2 orders of magnitude. On the basis of B3LYP DFT QM/MM simulations, we suggest that the observed discrepancy in (ii) arises, at least in part, from the lack of electronic polarization and/or charge transfer in biomolecular force fields. These issues might be present in other systems, such as DNA-protein complexes.

Thermodynamically consistent forward and reverse degrees of rate control in reversible reactions

The net rate of a composite reaction is the difference between the forward and reverse reaction rates, which are kinetically distinct despite sharing elementary reaction steps and therefore have different rate-controlling transition states and species. Thus, degrees of rate control defined to identify rate-controlling transition states and species for the net rate confound contributions from the forward and reverse reactions. Herein, the forward and reverse degrees of rate control are defined to independently quantify the extent that species and transition states control the forward and reverse rates in reversible reactions. These degrees of rate control are defined as the relative change in the forward and reverse reaction rates per kBT decrease in the standard-state molecular free energies of transition states and species, and they are related to experimentally measurable quantities such as steady-state fractional coverages, reaction orders, and energies and entropies of activation of the forward and reverse reaction rates. The forward/reverse degrees of rate control represent stoichiometric coefficients for species and transition states in an equilibrium between the initial states and transition states of the apparent rate-controlling steps of forward and reverse overall reactions. At equilibrium, the apparent transition states for the forward reaction and reverse reaction converge, and thus the forward and reverse rate-controlling steps combine to form a single apparent rate-controlling step. This apparent rate-controlling step is comprised of an apparent initial state, transition state, and final state, where the apparent final state of the forward reaction is the apparent initial state of the reverse reaction. The apparent rate-controlling step behaves identically to an elementary step reaction at equilibrium with a pseudo-mass-action rate function given by the transition-state-theory (TST) form rate function (Foley and Bhan, 2020) with a stoichiometric number equal to the affinity-averaged stoichiometric number, σ¯. The ratio of the forward and reverse TST-form rate functions is identical to the overall thermodynamic equilibrium relation, consistent with the principles of microscopic reversibility and detailed balance at equilibrium.

5-Carboxylcytosine and Cytosine Protonation Distinctly Alter the Stability and Dehybridization Dynamics of the DNA Duplex.

Applications associated with nucleobase protonation events are grounded in their fundamental impact on DNA thermodynamics, structure, and hybridization dynamics. Of the canonical nucleobases, N3 protonation of cytosine (C) is the most widely utilized in both biology and nanotechnology. Naturally occurring C derivatives that shift the N3 pKa introduce an additional level of tunability. The epigenetic nucleobase 5-carboxylcytosine (caC) presents a particularly interesting example since this derivative forms Watson-Crick base pairs of similar stability and displays pH-dependent behavior over the same range as the canonical nucleobase. However, the titratable group in caC corresponds to the exocyclic carboxyl group rather than N3, and the implications of these divergent protonation events toward DNA hybridization thermodynamics, kinetics, and base pairing dynamics remain poorly understood. Here, we study the pH dependence of these physical properties using model oligonucleotides containing C and caC with FTIR and temperature-jump IR spectroscopy. We demonstrate that N3 protonation of C completely disrupts duplex stability, leading to large shifts in the duplex/single-strand equilibrium, a reduction in the cooperativity of melting, and an acceleration in the rate of duplex dissociation. In contrast, while increasing 5-carboxyl protonation in caC-containing duplexes induces an increase in base pair fluctuations, the DNA duplex can tolerate substantial protonation without significant perturbation to the duplex/single-strand equilibrium. However, 5-carboxyl protonation has a large impact on hybridization kinetics by reducing the transition state free energy. Our thermodynamic and kinetic analysis provides new insight on the impact of two divergent protonation mechanisms in naturally occurring nucleobases on the biophysical properties of DNA.

Nanoporous Zeolite-X as a new carrier for laccase immobilization and its application in dyes decolorization

Abstract Laccase enzyme from Polyporus durus ATCC 26726 was immobilized on nanoporous Zeolite-X (ZX), with 83% immobilization yield. The immobilization process protected laccase against pH and temperature changes. The activation energy was lowered after immobilization. Compared to the free enzyme the immobilized enzyme displayed higher Km value and lower Vmax. The immobilized laccase exhibited higher half-life values (t1/2), higher decimal reduction time (D-value) and lower deactivation rate constant (Kd) within the temperature range of 50–70 °C. The thermodynamic analysis for substrate oxidation indicated that the enthalpy (ΔH*), entropy (ΔS*), and free energy of transition state (ΔG*E–T) were lower for immobilized laccase. Furthermore, there was an increase in turnover number (kcat) after immobilization. The immobilized laccase could decolorize two dyes and two synthetic wastewater solutions. It retained 100% activity against AB 225 dye after 7 successive decolorization cycles and it could be reused for 11 times with 48% activity loss.

Origins of the Mechanochemical Coupling of Peptide Bond Formation to Protein Synthesis.

Mechanical forces acting on the ribosome can alter the speed of protein synthesis, indicating that mechanochemistry can contribute to translation control of gene expression. The naturally occurring sources of these mechanical forces, the mechanism by which they are transmitted 10 nm to the ribosome's catalytic core, and how they influence peptide bond formation rates are largely unknown. Here, we identify a new source of mechanical force acting on the ribosome by using in situ experimental measurements of changes in nascent-chain extension in the exit tunnel in conjunction with all-atom and coarse-grained computer simulations. We demonstrate that when the number of residues composing a nascent chain increases, its unstructured segments outside the ribosome exit tunnel generate piconewtons of force that are fully transmitted to the ribosome's P-site. The route of force transmission is shown to be through the nascent polypetide's backbone, not through the wall of the ribosome's exit tunnel. Utilizing quantum mechanical calculations we find that a consequence of such a pulling force is to decrease the transition state free energy barrier to peptide bond formation, indicating that the elongation of a nascent chain can accelerate translation. Since nascent protein segments can start out as largely unfolded structural ensembles, these results suggest a pulling force is present during protein synthesis that can modulate translation speed. The mechanism of force transmission we have identified and its consequences for peptide bond formation should be relevant regardless of the source of the pulling force.

Conformational study and stereodynamics of ortho-substituted ortho-terphenyl and its derivatives

Derivatives of 2,2″-dimethyl-ortho-terphenyl have been prepared and their conformational study was carried out by variable temperature NMR analysis. These molecules showed presence of atropisomers due to the restricted rotation about the aryl-aryl (ArAr) and aryl-CH2 (ArCH2) bonds. The barrier of their interconversion was determined as a function of ΔG‡, the transition state free energy at coalescence temperature.

Catalytic, kinetic and thermodynamic properties of stabilized Bacillus stearothermophilus alkaline protease

Bacillus stearothermophilus alkaline protease was conjugated to several oxidized polysaccharides of different chemical structure. The conjugates were evaluated for the kinetic and thermodynamic stability. The conjugated enzyme with oxidized pectin had the highest retained activity (79.5%) and the highest half-life (T1/2) at 50°C and pH 9.0. Compared to the native protease, the conjugated preparation exhibited lower activation energy (Ea), lower deactivation constant rate (kd), higher T1/2, and higher D values (decimal reduction time) within the temperature range of 50–60°C. The thermodynamic parameters for irreversible inactivation of native and conjugated protease indicated that conjugation significantly decreased entropy (ΔS*) and enthalpy (ΔH*) of deactivation. The calculated value of activation energy for thermal denaturation (Ead) for the conjugated enzyme was 20.4KJmole−1 higher over the native one. The results of thermodynamic analysis for substrate hydrolysis indicated that the enthalpy of activation (ΔH*) and free energy of activation (free energy of substrate binding) ΔG*E–S and (ΔG*), (free energy of transition state) ΔG*E–T values were lower for the modified protease. Similarly, there was significant improvement of kcat, kcat/Km values. The enzyme proved to be metalloprotease and significantly stimulated by Ca2+ and Mg2+ whereas Hg2+, Fe3+ Cu2+ and Zn2+ inhibited the enzyme activity. There was no pronounced effect on substrate specificity after conjugation.

Characterizing Active Site Conformational Heterogeneity along the Trajectory of an Enzymatic Phosphoryl Transfer Reaction.

States along the phosphoryl transfer reaction catalyzed by the nucleoside monophosphate kinase UmpK were captured and changes in the conformational heterogeneity of conserved active site arginine side‐chains were quantified by NMR spin‐relaxation methods. In addition to apo and ligand‐bound UmpK, a transition state analog (TSA) complex was utilized to evaluate the extent to which active site conformational entropy contributes to the transition state free energy. The catalytically essential arginine side‐chain guanidino groups were found to be remarkably rigid in the TSA complex, indicating that the enzyme has evolved to restrict the conformational freedom along its reaction path over the energy landscape, which in turn allows the phosphoryl transfer to occur selectively by avoiding side reactions.

Characterizing Active Site Conformational Heterogeneity along the Trajectory of an Enzymatic Phosphoryl Transfer Reaction

AbstractStates along the phosphoryl transfer reaction catalyzed by the nucleoside monophosphate kinase UmpK were captured and changes in the conformational heterogeneity of conserved active site arginine side‐chains were quantified by NMR spin‐relaxation methods. In addition to apo and ligand‐bound UmpK, a transition state analog (TSA) complex was utilized to evaluate the extent to which active site conformational entropy contributes to the transition state free energy. The catalytically essential arginine side‐chain guanidino groups were found to be remarkably rigid in the TSA complex, indicating that the enzyme has evolved to restrict the conformational freedom along its reaction path over the energy landscape, which in turn allows the phosphoryl transfer to occur selectively by avoiding side reactions.

Substituent effect and ligand exchange control the reactivity in ruthenium(II)-catalyzed hydroacylation of isoprenes and aldehydes ‖ A DFT study

Density functional theory (DFT) was used to investigate the reaction mechanisms of ruthenium(II)-catalyzed hydroacylation of isoprene with benzaldehyde, and o-methoxyl, m-methoxyl and p-methoxyl benzaldehyde. All intermediates and transition states were entirely optimized at the B3LYP/6-31G(d,p) level (LANL2DZ(f) for Ru). The results demonstrated that the hydroacylation had two different catalytic cycles (path I and II), path II was more favorable than path I. Ru(II)-catalyzed hydroacylation began from the first catalytic cycle, and the nucleophilic reaction was the rate-determining step. The activation barriers of hydrogen migration were the highest in two catalytic cycles, so the hydrogen migration was the rate-determining step. The activation barrier of hydrogen migration could be broken down to two parts: the free energy of exchange ([Formula: see text]) and the relative free energy of transition state ([Formula: see text]). The ligand exchange energy ([Formula: see text]) had more contribution to the activation barrier than the relative free energy of transition state ([Formula: see text]), so the ligand exchange would control these hydroacylation. Furthermore, our calculations also described the substituent effect, and the results indicated that four aldehydes showed different chemical reactivity, and benzaldehyde and m-methoxyl benzaldehyde were predicted to have the best reactivity in ruthenium hydride-catalyzed hydroacylation.