Beyond the Active Site: Mechanistic Investigations of the Role of the Secondary Coordination Sphere and Beyond in Multi-electron Electrocatalytic Reactions

ACS Catalysis ◽  
2021 ◽  
pp. 8292-8303
Author(s):  
Vincent C.-C. Wang
Keyword(s):  
Coordination Sphere ◽  
Active Site ◽  
Secondary Coordination Sphere ◽  
Mechanistic Investigations ◽  
Electrocatalytic Reactions

scholarly journals Beyond the Active Site: Mechanistic Investigations of the Role of the Secondary Coordination Sphere and Beyond on Multi-Electron Electrocatalytic Reactions and Their Relations Between Kinetics and Thermodynamics

2020 ◽  
Author(s):  
Vincent Wang
Keyword(s):  
Thermodynamic Parameters ◽  
Coordination Sphere ◽  
Active Site ◽  
Rate Constants ◽  
Reduction Reaction ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secondary Coordination Sphere ◽  
Catalytic Rate ◽  
Rate Limiting

<p>The development of an electrocatalyst with a rapid turnover frequency, low overpotential and long-term stability is highly desired for fuel-forming reactions, such as water splitting and CO<sub>2</sub> reduction. The findings of the scaling relationships between the catalytic rate and thermodynamic parameters over a wide range of electrocatalysts in homogeneous and heterogeneous systems provide useful guidelines and predictions for designing better catalysts for those redox reactions. However, such relationships also suggest that a catalyst with a high catalytic rate is typically associated with a high overpotential for a given reaction. Inspired by enzymes, the introduction of additional interactions through the secondary coordination sphere beyond the active site, such as hydrogen-bonding or electrostatic interactions, have been shown to offer a promising avenue to disrupt these unfavorable relationships. Herein, we further investigate the influence of these cooperative interactions on the faster chemical steps, in addition to the rate-limiting step widely examined before, for molecular electrocatalysts with the structural and electronic modifications designed to facilitate the dioxygen reduction reaction, CO<sub>2</sub> reduction reaction and hydrogen evolving reaction. Based on the electrocatalytic kinetic analysis, the rate constants for faster chemical steps and their correlation with the corresponding thermodynamic parameters are evaluated. The results suggest that the effects of the secondary coordination sphere and beyond on these fuel-forming reactions are not necessarily beneficial for promoting all chemical steps and no apparent relation between rate constants and thermodynamic parameters are found in some cases studied here, which may implicate the design of electrocatalysts in the future. Finally, these analyses demonstrate that the characteristic features for voltammograms and foot-of-the-wave-analysis plots are associated with the specific kinetic phenomenon among these multi-electron electrocatalytic reactions, which provides a useful framework to probe the insights of chemical and electronic modifications on the catalytic steps quantitatively (i.e. kinetic rate constants) and to optimize some of critical steps beyond the rate-limiting step.</p>

scholarly journals Kinetic Study of CO2 Hydration by Small-Molecule Catalysts with A Second Coordination Sphere that Mimic the Effect of the Thr-199 Residue of Carbonic Anhydrase

Biomimetics ◽  
2019 ◽  
Vol 4 (4) ◽  
pp. 66
Author(s):  
Park ◽  
Lee
Keyword(s):  
Hydrogen Bonding ◽  
Carbonic Anhydrase ◽  
Coordination Sphere ◽  
Active Site ◽  
Hydration Reaction ◽  
Ph Titration ◽  
Hydration Rate ◽  
Pka Value ◽  
Secondary Coordination Sphere ◽  
Hydrogen Bonding Network

Zinc complexes were synthesized as catalysts that mimic the ability of carbonic anhydrase (CA) for the CO2 hydration reaction (H2O + CO2 → H+ + HCO3-). For these complexes, a tris(2-pyridylmethyl)amine (TPA) ligand mimicking only the active site, and a 6-((bis(pyridin-2-ylmethyl)amino)methyl)pyridin-2-ol (TPA-OH) ligand mimicking the hydrogen-bonding network of the secondary coordination sphere of CA were used. Potentiometric pH titration was used to determine the deprotonation ability of the Zn complexes, and their pKa values were found to be 8.0 and 6.8, respectively. Stopped-flow spectrophotometry was used to confirm the CO2 hydration rate. The rate constants were measured to be 648.4 and 730.6 M-1s-1, respectively. The low pKa value was attributed to the hydrogen-bonding network of the secondary coordination sphere of the catalyst that mimics the behavior of CA, and this was found to increase the CO2 hydration rate of the catalyst.

Secondary Coordination Sphere Effects in Ruthenium(III) Tetraammine Complexes: Role of the Coordinated Water Molecule

2015 ◽  
Vol 54 (4) ◽  
pp. 2067-2080 ◽  
Author(s):  
Maykon L. Souza ◽  
Eduardo E. Castellano ◽  
Joshua Telser ◽  
Douglas W. Franco
Keyword(s):  
Water Molecule ◽  
Coordination Sphere ◽  
Secondary Coordination Sphere ◽  
Coordinated Water

scholarly journals The Role of the Secondary Coordination Sphere in a Fungal Polysaccharide Monooxygenase

2017 ◽  
Vol 12 (4) ◽  
pp. 1095-1103 ◽  
Author(s):  
Elise A. Span ◽  
Daniel L. M. Suess ◽  
Marc C. Deller ◽  
R. David Britt ◽  
Michael A. Marletta
Keyword(s):  
Coordination Sphere ◽  
Secondary Coordination Sphere ◽  
Polysaccharide Monooxygenase

Deciphering the role of anions and secondary coordination sphere in tuning anisotropy in Dy(III) air‐stable D5h SIMs

2021 ◽  
Author(s):  
Ramaswamy Murugavel ◽  
Sandeep K. Gupta ◽  
Sourav Dey ◽  
Thayalan Rajeshkumar ◽  
Gopalan Rajaraman
Keyword(s):  
Coordination Sphere ◽  
Secondary Coordination Sphere

scholarly journals Deciphering the role of anions and secondary coordination sphere in tuning anisotropy in Dy(III) air-stable D5h SIMs

2021 ◽  
Author(s):  
Sandeep Gupta ◽  
Sourav Dey ◽  
Thayalan Rajeshkumar ◽  
Gopalan Rajaraman ◽  
Ramaswamy Murugavel
Keyword(s):  
High Temperature ◽  
Crystal Field ◽  
Coordination Sphere ◽  
Energy Barrier ◽  
Blocking Temperature ◽  
High Symmetry ◽  
Coordination Geometry ◽  
Secondary Coordination Sphere ◽  
Hydrogen Bonded

Precise control of the crystal field and symmetry around the paramagnetic spin centre has recently facilitated the engineering of high-temperature single-ion magnets (SIMs), the smallest possible units for future spin-based devices. In the present work, we report a series of air-stable seven coordinate Dy(III) SIMs {[L2Dy(H2O)5][X]3·L2·n(H2O), n = 0, X = Cl (1), n = 1, X = Br (2), I (3)} possessing pseudo-D5h symmetry or pentagonal bipyramidal coordination geometry with high anisotropy energy barrier (Ueff) and blocking temperature (TB). While the strong axial coordination from the sterically encumbered phosphonamide, tBuPO(NHiPr)2 (L), increases the overall anisotropy of the system, the presence of high symmetry significantly quenches quantum tunnelling of magnetization, which is the prominent deactivating factor encountered in SIMs. Although the local coordination geometry and the symmetry around the Dy(III) in all the three complexes are similar and display only slight deviations, the variation of halide anions in the secondary coordination sphere which is hydrogen-bonded to the coordinated equatorial water molecules, show subtle alteration in the magnetic properties. The energy barrier (Ueff) and the blocking temperature (TB) decrease in the order 3 > 2 > 1 with the change of anions from larger iodide to smaller strongly hydrogen-bonded chloride in the secondary coordination sphere. Ab initio CASSCF/RASSI-SO/SINGLE_ANISO calculations further provide deeper insights into the dynamics of magnetic relaxation in addition to the role of the secondary coordination sphere in modulating the anisotropy of the D5h systems, using diverse models. Thus, in addition to the importance of the crystal field and the symmetry to obtain high-temperature SIMs, this study also probes the significance of the secondary coordination sphere that can be tailored to accomplish novel SIMs.

scholarly journals Beyond the Active Site: Mechanistic Investigations of the Role of the Secondary Coordination Sphere and Beyond on Multi-Electron Electrocatalytic Reactions and Their Relations Between Kinetics and Thermodynamics

2020 ◽  
Author(s):  
Vincent Wang
Keyword(s):  
Thermodynamic Parameters ◽  
Coordination Sphere ◽  
Active Site ◽  
Rate Constants ◽  
Reduction Reaction ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Secondary Coordination Sphere ◽  
Catalytic Rate ◽  
Rate Limiting

<p>The development of an electrocatalyst with a rapid turnover frequency, low overpotential and long-term stability is highly desired for fuel-forming reactions, such as water splitting and CO<sub>2</sub> reduction. The findings of the scaling relationships between the catalytic rate and thermodynamic parameters over a wide range of electrocatalysts in homogeneous and heterogeneous systems provide useful guidelines and predictions for designing better catalysts for those redox reactions. However, such relationships also suggest that a catalyst with a high catalytic rate is typically associated with a high overpotential for a given reaction. Inspired by enzymes, the introduction of additional interactions through the secondary coordination sphere beyond the active site, such as hydrogen-bonding or electrostatic interactions, have been shown to offer a promising avenue to disrupt these unfavorable relationships. Herein, we further investigate the influence of these cooperative interactions on the faster chemical steps, in addition to the rate-limiting step widely examined before, for molecular electrocatalysts with the structural and electronic modifications designed to facilitate the dioxygen reduction reaction, CO<sub>2</sub> reduction reaction and hydrogen evolving reaction. Based on the electrocatalytic kinetic analysis, the rate constants for faster chemical steps and their correlation with the corresponding thermodynamic parameters are evaluated. The results suggest that the effects of the secondary coordination sphere and beyond on these fuel-forming reactions are not necessarily beneficial for promoting all chemical steps and no apparent relation between rate constants and thermodynamic parameters are found in some cases studied here, which may implicate the design of electrocatalysts in the future. Finally, these analyses demonstrate that the characteristic features for voltammograms and foot-of-the-wave-analysis plots are associated with the specific kinetic phenomenon among these multi-electron electrocatalytic reactions, which provides a useful framework to probe the insights of chemical and electronic modifications on the catalytic steps quantitatively (i.e. kinetic rate constants) and to optimize some of critical steps beyond the rate-limiting step.</p>

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