scholarly journals The Role of Counterions in Intermolecular Radical Coupling of Ru-bda Catalysts

2021 ◽  
Author(s):  
Juan Angel de Gracia Triviño ◽  
Mårten S. G. Ahlquist
Keyword(s):  
Free Energy ◽  
Water Oxidation ◽  
Water Solution ◽  
Hydrophobic Effect ◽  
Solvent Polarity ◽  
Ion Pairing ◽  
Hydrophobic Effects ◽  
Radical Coupling ◽  
Double Charge ◽  
Doubly Charged

AbstractIntermolecular radical coupling (also interaction of two metal centers I2M) is one of the main mechanisms for O–O bond formation in water oxidation catalysts. For Ru(bda)L2 (H2bda = 2,2′-bipyridine-6,6′-dicarboxylate, L = pyridine or similar nitrogen containing heterocyclic ligands) catalysts a significant driving force in water solution is the hydrophobic effects driven by the solvent. The same catalyst has been successfully employed to generate N2 from ammonia, also via I2M, but here the solvent was acetonitrile where hydrophobic effects are absent. We used a classical force field for the key intermediate [RuVIN(bda)(py)2]+ to simulate the dimerization free energy by calculation of the potential mean force, in both water and acetonitrile to understand the differences and similarities. In both solvents the complex dimerizes with similar free energy profiles. In water the complexes are essentially free cations with limited ion paring, while in acetonitrile the ion-pairing is much more significant. This ion-pairing leads to significant screening of the charges, making dimerization possible despite lower solvent polarity that could lead to repulsion between the charged complexes. In water the lower ion pairing is compensated by the hydrophobic effect leading to favorable dimerization despite repulsion of the charges. A hypothetical doubly charged [RuVIIN(bda)py2]2+ was also studied for deeper understanding of the charge effect. Despite the double charge the complexes only dimerized favorably in the lower dielectric solvent acetonitrile, while in water the separated state is more stable. In the doubly charged catalyst the effect of ion-pairing is even more pronounced in acetonitrile where it is fully paired similar to the 1+ complex, while in water the separation of the ions leads to greater repulsion between the two catalysts, which prevents dimerization. Graphic Abstract

Kinetics of Ion-Pair Effect of Aquation of Bromopentaammine Cobalt(III) Complex in Different Dicarboxylate Media

2011 ◽  
Vol 324 ◽  
pp. 166-169 ◽  
Author(s):  
Farah Zeitouni ◽  
Gehan El-Subruiti ◽  
Ghassan Younes ◽  
Mohammad Amira
Keyword(s):  
Free Energy ◽  
Solvent Effect ◽  
Compensation Effect ◽  
Ion Pairing ◽  
Reaction Rates ◽  
Ion Pair ◽  
Free Energy Of Activation ◽  
Different Types ◽  
Different Temperatures ◽  
Kinetics Of

The rate of aquation of bromopentaammine cobalt(III) ion in the presence of different types of dicarboxylate solutions containing tert-butanol (40% V/V) have been measured spectrophotometrically at different temperatures (30-600°C) in the light of the effects of ion-pairing on reaction rates and mechanism. The thermodynamic and extrathermodynamic parameters of activation have been calculated and discussed in terms of solvent effect on the ion-pair aquation reaction. The free energy of activation ∆Gip* is more or less linearly varied among the studied dicarboxylate ion-pairing ligands indicating the presence of compensation effect between ∆Hip* and ∆Sip*. Comparing the kip values with respect of different buffers at 40% of ter-butanol is introduced.

scholarly journals Effects of Solvent Polarity on Solvation Free Energy, Dipole Moment, Polarizability, Hyperpolarizability and Molecular Properties of Metronidazole

2016 ◽  
Vol 19 (1) ◽  
pp. 9-14 ◽  
Author(s):  
Mohammad Firoz Khan ◽  
Ridwan Bin Rashid ◽  
Md Yeunus Mian ◽  
Mohammad S Rahman ◽  
Mohammad A Rashid
Keyword(s):  
Free Energy ◽  
Dipole Moment ◽  
Gas Phase ◽  
Chemical Potential ◽  
Solvent Polarity ◽  
Solvation Free Energy ◽  
Molecular Properties ◽  
Chemical Hardness ◽  
Electrophilicity Index ◽  
Polar Solvents

A computational study of medium effect on solvation free energy, dipole moment, polarizability, hyperpolarizability and different molecular properties like chemical hardness & softness, chemical potential, electronegativity and electrophilicity index of metronidazole have been reported in this paper. Becke, 3-parameter, Lee-Yang-Parr (B3LYP) level of theory with 6-31G (d,p) basis set was applied for gas phase and solution. The effect of solvent polarity on solvation free energy, dipole moment, polarizability, hyperpolarizability and molecular properties were calculated by employing Solvation Model on Density (SMD). The solvation free energies and dipole moment of metronidazole were found to be increased in nonpolar to polar solvents. The dipole moment of metronidazole was higher in different solvent than that of the gas phase. Moreover, from non-polar to polar solvents the chemical potential, electronegativity and electrophilicity index were increased. On the other hand, opposite relation was found in the case of chemical hardness and softness. The results obtained in this study may lead to understand the stability and reactivity of metronidazole and the results will be of assistance to use the title molecule as reaction intermediates and pharmaceuticals.Bangladesh Pharmaceutical Journal 19(1): 9-14, 2016

Hydrometallurgical thermodynamics. I. Effect of sulfate ion-pairing and ion-solvation on the copper-iron redox equilibrium in aqueous acetonitrile

1983 ◽  
Vol 36 (9) ◽  
pp. 1687 ◽  
Author(s):  
BW Clare ◽  
P Singh ◽  
P Mangano ◽  
AJ Parker ◽  
DM Muir
Keyword(s):  
Water Solution ◽  
Pure Water ◽  
Ion Pairing ◽  
Ion Solvation ◽  
Sulfate Ion ◽  
Redox Equilibrium ◽  
Small Shift ◽  
Enthalpy Changes ◽  
The Right ◽  
Iron Redox

The copper-iron redox equilibrium is shifted to the right CuII+FeII↔CuI+FeIII by strong ion-pairing of sulfate ion with FeIII and by specific solvation of CuI with acetonitrile. The equilibrium constant has been measured by direct e.m.f. and spectroscopic methods between pH 0-2 and found to be about 107 higher for practical solutions of sulfates in acetonitrile/water than that calculated for perchlorates in pure water. Enthalpies and free energies of transfer of these ions from water to acetonitrile/water show that the shift in equilibrium to Cul+FeIII in acetonitrile/water solution is strongly favoured by enthalpy changes associated with copper(I)-acetonitrile ion-solvation. Ion-pairing of sulfate ion with iron(III) results in an increase in entropy and a small shift of the equilibrium to the right.

scholarly journals Modeling the Catalyst Activation Step in a Metal–Ligand Radical Mechanism Based Water Oxidation System

Inorganics ◽  
2019 ◽  
Vol 7 (5) ◽  
pp. 62 ◽  
Author(s):  
Nitish Govindarajan ◽  
Evert Jan Meijer
Keyword(s):  
Water Oxidation ◽  
Density Functional ◽  
Radical Mechanism ◽  
Catalyst Activation ◽  
Activation Barriers ◽  
Radical Coupling ◽  
Rate Determining Step ◽  
Highly Active ◽  
Solvent Molecules ◽  
Metal Ligand

Designing catalysts for water oxidation (WOCs) that operate at low overpotentials plays an important role in developing sustainable energy conversion schemes. Recently, a mononuclear ruthenium WOC that operates via metal–ligand radical coupling pathway was reported, with a very low barrier for O–O bond formation, that is usually the rate-determining step in most WOCs. A detailed mechanistic understanding of this mechanism is crucial to design highly active oxygen evolution catalysts. Here, we use density functional theory based molecular dynamics (DFT-MD) with an explicit description of the solvent to investigate the catalyst activation step for the [Ru(bpy) 2 (bpy–NO)] 2 + complex, that is considered to be the rate-limiting step in the metal–ligand radical coupling pathway. We find that a realistic description of the solvent environment, including explicit solvent molecules and thermal motion, is crucial for an accurate description of the catalyst activation step, and for the estimation of the activation barriers.

Nuclear magnetic resonance studies. XV. Conformational free energy of the formyl group

1967 ◽  
Vol 45 (23) ◽  
pp. 2955-2961 ◽  
Author(s):  
G. W. Buchanan ◽  
J. B. Stothers ◽  
Siu-Tzyy Wu
Keyword(s):  
Free Energy ◽  
Solvent Polarity ◽  
Formyl Group ◽  
Proton Spectroscopy ◽  
Kcal Mole ◽  
Magnetic Resonance Studies ◽  
Average Value ◽  
Cis And Trans ◽  
Line Positions ◽  
Conformational Free Energy

Proton spectroscopy has been employed to determine the conformational free energy (− ΔG0) of a formyl group bonded to a cyclohexane ring. The cis- and trans-4-t-butyl derivatives were used as models for the axial and equatorial formyl groups in cyclohexanecarboxaldehyde and 1-methylcyclohexanecarboxaldehyde. The wiggle-beat technique was used to determine the spectral line positions and separations because of the relatively small differences involved. The − ΔG0 values were found to be relatively insensitive to solvent polarity and concentration over the range 10–50 mole %. For 10 mole % solutions the average value of − ΔG0CHO was found to be 1.38 kcal/mole.

scholarly journals Reconciling NMR Structures of the HIV-1 Nucleocapsid Protein (NCp7) using Extensive Polarizable Force Field Free-Energy Simulations

2019 ◽  
Author(s):  
Léa El Khoury ◽  
Frédéric Célerse ◽  
Louis Lagardere ◽  
Luc-Henri Jolly ◽  
Étienne Derat ◽  
...  
Keyword(s):  
Free Energy ◽  
Force Field ◽  
Water Solution ◽  
Energy Difference ◽  
Umbrella Sampling ◽  
Energy Stability ◽  
Functional Protein ◽  
Relative Free Energy ◽  
Energy Simulations ◽  
Experimental Findings

The Human Immunodeficiency Virus Type 1 nucleocapsid 7 (NCp7) is a multi-functional protein formed by N-terminal and C-terminal domains surrounding two Zn-fingers, linked by a stretch of basic residues, which play a key role in the viral replication. We report the first NCp7 polarizable molecular dynamics (MD) study using the AMOEBA force field complemented by non-polarizable CHARMM simulations. Specifically, we compared the relative free-energy stability of two extreme conformations: a compact one having two aromatic residues from each finger, partially stacked, denoted A; and an unfolded one, with the two residues apart, denoted B. Each of these conformations had been previously experimentally advocated to prevail in solution. We compared their theoretical relative free-energy stability using accelerated MD sampling techniques (Steered MD and Umbrella Sampling) and showed that there was a low free energy difference between them. As A and B do not differ in stability by more than 1-1.5 kcal/mol, they should thus coexist in water solution reconciling earlier NMR experimental findings.

scholarly journals Measuring Theoretical Descriptors of Water Oxidation: Free Energy Differences Between Intermediates Using Time-Resolved Optical Spectroscopy

2021 ◽  
Author(s):  
Ilya Vinogradov ◽  
Suryansh Singh ◽  
Hanna Lyle ◽  
Aritra Mandal ◽  
Jan Rossmeisl ◽  
...  
Keyword(s):  
Free Energy ◽  
Water Oxidation ◽  
Oxidation Reaction ◽  
Equilibrium Constants ◽  
Semiconductor Surface ◽  
Free Energies ◽  
Time Resolved ◽  
Time Resolved Spectroscopy ◽  
Material Surfaces ◽  
The Stability

<p>Theoretical descriptions differentiate catalytic activity of material surfaces for the water oxidation reaction by the stability of the reactive oxygen (O*) intermediate. The underlying conjecture is that there are several meta-stable steps of the reaction, each connected by free energy differences critically dependent on O*. Recently <i>in-situ, </i>time-resolved spectroscopy of the (<i>photo<br> </i>)-electrochemical water oxidation reaction identified the vibrational and optical signatures of O* time-evolution. However, there has been little connection between these inherently kinetic experiments and the underlying thermodynamic parameters of the theory. Here, we discover that picosecond optical spectra of the O* population modulated by a shift in reaction equilibria defines an effective equilibrium constant (K<sub>eff</sub>) containing the relevant free-energy differences. A Langmuir isotherm as a function of electrolyte pH extracts K<sub>eff</sub> using a model titania system (SrTiO<sub>3</sub>). The results show how to obtain equilibrium constants of individual reaction steps on material surfaces, which had not been experimentally accessible previously. Further, we find that for a photo-excited reaction on a semiconductor surface tuning past a pH defined by K<sub>eff</sub> doubles the initial O* population. That the free energies of the catalytic surface are definable through a time-resolved spectroscopy, alongside the finding that the surface recollects its explicit equilibrium with the electrolyte, provides a new and critical connection between theory and experiment by which to tailor the pathway of water oxidation and other surface reactions.</p>

Ion Pairing in Protic Ionic Liquids Probed by Far-Infrared Spectroscopy: Effects of Solvent Polarity and Temperature

ChemPhysChem ◽  
2014 ◽  
Vol 15 (12) ◽  
pp. 2604-2609 ◽  
Author(s):  
Koichi Fumino ◽  
Verlaine Fossog ◽  
Peter Stange ◽  
Kai Wittler ◽  
Wigbert Polet ◽  
...  
Keyword(s):  
Ionic Liquids ◽  
Infrared Spectroscopy ◽  
Solvent Polarity ◽  
Far Infrared ◽  
Ion Pairing ◽  
Far Infrared Spectroscopy ◽  
Protic Ionic Liquids

scholarly journals Fluorescence Quenching by Reversible Charge Separation Followed by Ions Recombination and Their Separation Suppressed by Coulomb Attraction

2012 ◽  
Vol 2012 ◽  
pp. 1-7
Author(s):  
A. I. Burshtein ◽  
A. B. Doktorov
Keyword(s):  
Experimental Data ◽  
Free Energy ◽  
Fluorescence Quenching ◽  
Charge Separation ◽  
Solvent Polarity ◽  
Present Theory ◽  
Diffusion Control ◽  
Strong Coulomb ◽  
Volmer Constant ◽  
Coulomb Attraction

The Stern-Volmer constant is specified for the luminescence quenched by reversible ionization of excited molecules. The exergonic branch of the Rehm-Weller free energy dependence of this constant is known to be a plateau determined by irreversible ionization being under diffusion control. In the endergonic region the ionization is reversible and competes with the irreversible in-cage recombination of ions and their escape from the cage. At strong Coulomb attraction the latter phenomenon is shown to be negligible compared to the former that determines the shape and location of the descending branch of the Rehm-Weller curve. At weaker Coulomb attraction (at higher solvent polarity), this curve turns down at larger endergonicity. The experimental data obtained in solvents of different polarities are put in order and in full accordance with present theory.

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