Changes in water reorientation dynamics at electrified graphene interfaces arise from the interfa... more Changes in water reorientation dynamics at electrified graphene interfaces arise from the interfaces’ impact on water hydrogen-bond exchanges; the asymmetric behavior with electrode potential sign is quantitatively described by an extended jump model.
We construct a theoretical framework for the description of nonequilibrium solvation and solvent ... more We construct a theoretical framework for the description of nonequilibrium solvation and solvent participation in the reaction coordinate for solution reactions. The framework is illustrated by a model of reactive dipole isomerization. We show that a multidimensional reaction coordinate picture is equivalent to a one dimensional description in which a generalized friction characterizes and quantifies nonequilibrium solvation effects on the reaction rate. The adiabatic regime where equilibrium solvation and mean potential ideas are correct is identified. Several distinct regimes of nonequilibrium solvation are identified and described in molecular terms. In the effective mass regime, equilibrium solvation ideas give the reaction barrier curvature correctly, but solvent inertia modifies the barrier passage rate. In the nonadiabatic regime, the solvent is ‘‘frozen’’ during the barrier passage and cannot provide equilibrium solvation. In the polarization caging regime, the reacting spec...
ABSTRACT The first, key step of water oxidation catalysis by the ruthenium blue dimer transition ... more ABSTRACT The first, key step of water oxidation catalysis by the ruthenium blue dimer transition metal complex has been studied via density functional methods and with extensive explicit solvation, starting from the oxidized catalytically active form of the dimer. This step is the rate-limiting O–O single bond formation. This reaction is found to involve several proton transfers through a proton relay chain, synergetically coupled to electron flow through the μ-oxo bridge of the dimer. The barrier for the O–O formation step is found to arise primarily from the surrounding aqueous solvent, suggesting that it might be substantially lowered in suitable environments. Some remarks are given concerning the following, penultimate step prior to the formation of dioxygen and the stable form of the dimer, in which it is suggested that another proton relay chain is at play.
Conflicting experimental results for the electrocatalytic reduction of CO2 to CH3OH on a glassy c... more Conflicting experimental results for the electrocatalytic reduction of CO2 to CH3OH on a glassy carbon electrode by the 6,7-dimethyl-4-hydroxy-2-mercaptopteridine have been recently reported [ J. Am. Chem. Soc. 2014 , 136 , 14007 - 14010 , J. Am. Chem. Soc. 2016 , 138 , 1017 - 1021 ]. In this connection, we have used computational chemistry to examine the issue of this molecule's ability to act as a hydride donor to reduce CO2. We first determined that the most thermodynamically stable tautomer of this aqueous compound is its oxothione form, termed here PTE. It is argued that this species electrochemically undergoes concerted 2H(+)/2e(-) transfers to first form the kinetic product 5,8-dihydropteridine, followed by acid-catalyzed tautomerization to the thermodynamically more stable 7,8-dihydropteridine PTEH2. While the overall conversion of CO2 to CH3OH by three successive hydride and proton transfers from this most stable tautomer is computed to be exergonic by 5.1 kcal/mol, we predict high activation free energies (ΔG(‡)HT) of 29.0 and 29.7 kcal/mol for the homogeneous reductions of CO2 and its intermediary formic acid product by PTE/PTEH2, respectively. These high barriers imply that PTE/PTEH2 is unable, by this mechanism, to homogeneously reduce CO2 on a time scale of hours at room temperature.
Proceedings of the National Academy of Sciences, 2007
Water molecule rotational dynamics within a chloride anion's first hydration shell are invest... more Water molecule rotational dynamics within a chloride anion's first hydration shell are investigated through simulations. In contrast to recent suggestions that the ion's hydration shell is rigid during a water's reorientation, we find a labile hydration sphere, consistent with previous assessments of chloride as a weak structure breaker. The nondiffusive reorientation mechanism found involves a hydrogen-bond partner switch with a large amplitude angular jump and the water's departure from the anion's shell. An analytic extended jump model accounts for the simulation results, as well as available NMR and ultrafast spectroscopic data, and resolves the discrepancy between them.
Changes in water reorientation dynamics at electrified graphene interfaces arise from the interfa... more Changes in water reorientation dynamics at electrified graphene interfaces arise from the interfaces’ impact on water hydrogen-bond exchanges; the asymmetric behavior with electrode potential sign is quantitatively described by an extended jump model.
We construct a theoretical framework for the description of nonequilibrium solvation and solvent ... more We construct a theoretical framework for the description of nonequilibrium solvation and solvent participation in the reaction coordinate for solution reactions. The framework is illustrated by a model of reactive dipole isomerization. We show that a multidimensional reaction coordinate picture is equivalent to a one dimensional description in which a generalized friction characterizes and quantifies nonequilibrium solvation effects on the reaction rate. The adiabatic regime where equilibrium solvation and mean potential ideas are correct is identified. Several distinct regimes of nonequilibrium solvation are identified and described in molecular terms. In the effective mass regime, equilibrium solvation ideas give the reaction barrier curvature correctly, but solvent inertia modifies the barrier passage rate. In the nonadiabatic regime, the solvent is ‘‘frozen’’ during the barrier passage and cannot provide equilibrium solvation. In the polarization caging regime, the reacting spec...
ABSTRACT The first, key step of water oxidation catalysis by the ruthenium blue dimer transition ... more ABSTRACT The first, key step of water oxidation catalysis by the ruthenium blue dimer transition metal complex has been studied via density functional methods and with extensive explicit solvation, starting from the oxidized catalytically active form of the dimer. This step is the rate-limiting O–O single bond formation. This reaction is found to involve several proton transfers through a proton relay chain, synergetically coupled to electron flow through the μ-oxo bridge of the dimer. The barrier for the O–O formation step is found to arise primarily from the surrounding aqueous solvent, suggesting that it might be substantially lowered in suitable environments. Some remarks are given concerning the following, penultimate step prior to the formation of dioxygen and the stable form of the dimer, in which it is suggested that another proton relay chain is at play.
Conflicting experimental results for the electrocatalytic reduction of CO2 to CH3OH on a glassy c... more Conflicting experimental results for the electrocatalytic reduction of CO2 to CH3OH on a glassy carbon electrode by the 6,7-dimethyl-4-hydroxy-2-mercaptopteridine have been recently reported [ J. Am. Chem. Soc. 2014 , 136 , 14007 - 14010 , J. Am. Chem. Soc. 2016 , 138 , 1017 - 1021 ]. In this connection, we have used computational chemistry to examine the issue of this molecule's ability to act as a hydride donor to reduce CO2. We first determined that the most thermodynamically stable tautomer of this aqueous compound is its oxothione form, termed here PTE. It is argued that this species electrochemically undergoes concerted 2H(+)/2e(-) transfers to first form the kinetic product 5,8-dihydropteridine, followed by acid-catalyzed tautomerization to the thermodynamically more stable 7,8-dihydropteridine PTEH2. While the overall conversion of CO2 to CH3OH by three successive hydride and proton transfers from this most stable tautomer is computed to be exergonic by 5.1 kcal/mol, we predict high activation free energies (ΔG(‡)HT) of 29.0 and 29.7 kcal/mol for the homogeneous reductions of CO2 and its intermediary formic acid product by PTE/PTEH2, respectively. These high barriers imply that PTE/PTEH2 is unable, by this mechanism, to homogeneously reduce CO2 on a time scale of hours at room temperature.
Proceedings of the National Academy of Sciences, 2007
Water molecule rotational dynamics within a chloride anion's first hydration shell are invest... more Water molecule rotational dynamics within a chloride anion's first hydration shell are investigated through simulations. In contrast to recent suggestions that the ion's hydration shell is rigid during a water's reorientation, we find a labile hydration sphere, consistent with previous assessments of chloride as a weak structure breaker. The nondiffusive reorientation mechanism found involves a hydrogen-bond partner switch with a large amplitude angular jump and the water's departure from the anion's shell. An analytic extended jump model accounts for the simulation results, as well as available NMR and ultrafast spectroscopic data, and resolves the discrepancy between them.
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Papers by James T. Hynes