Coordination Sphere Flexibility of Active-Site Models for Fe-Only Hydrogenase:  Studies in Intra- and Intermolecular Diatomic Ligand Exchange

2001 ◽  
Vol 123 (14) ◽  
pp. 3268-3278 ◽  
Author(s):  
Erica J. Lyon ◽  
Irene P. Georgakaki ◽  
Joseph H. Reibenspies ◽  
Marcetta Y. Darensbourg
Keyword(s):  
Coordination Sphere ◽  
Active Site ◽  
Ligand Exchange ◽  
Diatomic Ligand

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.

scholarly journals Asymmetry in the Ligand Coordination Sphere of the [FeFe] Hydrogenase Active Site Is Reflected in the Magnetic Spin Interactions of the Aza-propanedithiolate Ligand

2019 ◽  
Vol 10 (21) ◽  
pp. 6794-6799 ◽  
Author(s):  
Edward J. Reijerse ◽  
Vladimir Pelmenschikov ◽  
James A. Birrell ◽  
Casseday P. Richers ◽  
Martin Kaupp ◽  
...  
Keyword(s):  
Coordination Sphere ◽  
Active Site ◽  
Spin Interactions ◽  
Ligand Coordination ◽  
Magnetic Spin

Beyond the Active Site: The Impact of the Outer Coordination Sphere on Electrocatalysts for Hydrogen Production and Oxidation

2014 ◽  
Vol 47 (8) ◽  
pp. 2621-2630 ◽  
Author(s):  
Bojana Ginovska-Pangovska ◽  
Arnab Dutta ◽  
Matthew L. Reback ◽  
John C. Linehan ◽  
Wendy J. Shaw
Keyword(s):  
Hydrogen Production ◽  
Coordination Sphere ◽  
Active Site ◽  
Outer Coordination Sphere ◽  
The Impact

Noncovalent interactions between the second coordination sphere and the active site of [NiFeSe] hydrogenase

RSC Advances ◽  
2016 ◽  
Vol 6 (85) ◽  
pp. 81636-81646 ◽  
Author(s):  
Swaminathan Angeline Vedha ◽  
Gunasekaran Velmurugan ◽  
Ponnambalam Venuvanalingam
Keyword(s):  
Coordination Sphere ◽  
Active Site ◽  
Noncovalent Interactions ◽  
Second Coordination Sphere

QM/MM studies on seven truncated models of the oxidized as-isolated state of the [NiFeSe] Hases reveal the influence of the residues in the second coordination sphere on the active site.

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