Hydrogen tunneling in condensed media

Suárez, Alberto; Silbey, R.

doi:10.1063/1.460565

Cited by 113 publications

(69 citation statements)

References 19 publications

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“…Related expressions have been derived for vibrationally nonadiabatic proton transfer reactions. [40][41][42][43][44][45] Invoking the additional approximation that the R-coordinate time correlation function is approximately constant on the timescale of the probability flux correlation function decay leads to the simpler expression [35] This rate expression is similar to the Marcus theory expression for electron transfer except for the factor of . It differs from Eq.…”

Section: Rate Calculationsmentioning

confidence: 92%

Theoretical studies of proton-coupled electron transfer: Models and concepts relevant to bioenergetics

Hammes‐Schiffer¹,

Hatcher²,

Ishikita³

et al. 2008

Coordination Chemistry Reviews

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Theoretical studies of proton-coupled electron transfer (PCET) reactions for model systems provide insight into fundamental concepts relevant to bioenergetics. A dynamical theoretical formulation for vibronically nonadiabatic PCET reactions has been developed. This theory enables the calculation of rates and kinetic isotope effects, as well as the pH and temperature dependences, of PCET reactions. Methods for calculating the vibronic couplings for PCET systems have also been developed and implemented. These theoretical approaches have been applied to a wide range of PCET reactions, including tyrosyl radical generation in a tyrosine-bound rhenium polypyridyl complex, phenoxyl/ phenol and benzyl/toluene self-exchange reactions, and hydrogen abstraction catalyzed by the enzyme lipoxygenase. These applications have elucidated some of the key underlying physical principles of PCET reactions. The tools and concepts derived from these theoretical studies provide the foundation for future theoretical studies of PCET in more complex bioenergetic systems such as Photosystem II.

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Section: Rate Calculationsmentioning

confidence: 92%

Theoretical studies of proton-coupled electron transfer: Models and concepts relevant to bioenergetics

Hammes‐Schiffer¹,

Hatcher²,

Ishikita³

et al. 2008

Coordination Chemistry Reviews

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“…The effects of the proton donoracceptor motion were explicitly included in theoretical treaments of PT [1][2][3][4][5] and PCET [6][7][8] reactions. The dependence of the nonadiabatic vibronic coupling V on the proton donoracceptor distance R is often represented in exponential form by expanding the natural logarithm of the coupling around the equilibrium proton donor-acceptor distance R 0 .…”

Section: Introductionmentioning

confidence: 99%

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

Soudackov

Hammes‐Schiffer

2015

The Journal of Chemical Physics

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Rate constant expressions for vibronically nonadiabatic proton transfer and proton-coupled electron transfer reactions are presented and analyzed. The regimes covered include electronically adiabatic and nonadiabatic reactions, as well as high-frequency and low-frequency proton donor-acceptor vibrational modes. These rate constants differ from previous rate constants derived with the cumulant expansion approach in that the logarithmic expansion of the vibronic coupling in terms of the proton donor-acceptor distance includes a quadratic as well as a linear term. The analysis illustrates that inclusion of this quadratic term in the framework of the cumulant expansion framework may significantly impact the rate constants at high temperatures for proton transfer interfaces with soft proton donor-acceptor modes that are associated with small force constants and weak hydrogen bonds. The effects of the quadratic term may also become significant in these regimes when using the vibronic coupling expansion in conjunction with a thermal averaging procedure for calculating the rate constant. In this case, however, the expansion of the coupling can be avoided entirely by calculating the couplings explicitly for the range of proton donor-acceptor distances sampled. The effects of the quadratic term for weak hydrogen-bonding systems are less significant for more physically realistic models that prevent the sampling of unphysical short proton donor-acceptor distances. Additionally, the rigorous relation between the cumulant expansion and thermal averaging approaches is clarified. In particular, the cumulant expansion rate constant includes effects from dynamical interference between the proton donor-acceptor and solvent motions and becomes equivalent to the thermally averaged rate constant when these dynamical effects are neglected. This analysis identifies the regimes in which each rate constant expression is valid and thus will be important for future applications to proton transfer and proton-coupled electron transfer in chemical and biological processes. C 2015 AIP Publishing LLC. [http://dx

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“…15 Theoretically, it was shown that T 2 or T 3 dependencies may arise from twophonon emission/absorption and Raman processes. 16,17 Recently, a much stronger temperature dependence was reported for the DϩHD→D 2 ϩH reaction in solid HD ͑Ref. 18͒ and the origin of the effect was considered theoretically.…”

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confidence: 99%

Cis→trans conversion of formic acid by dissipative tunneling in solid rare gases: Influence of environment on the tunneling rate

Pettersson

Maçôas

Khriachtchev

et al. 2002

The Journal of Chemical Physics

172

195

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The relaxation of the higher-energy cis conformer of formic acid to the lower-energy trans form by a tunneling mechanism has been investigated in low-temperature rare gas matrices. In the temperature range 8 -60 K, the tunneling takes place dominantly from the vibrational ground state of the cis form and the temperature dependence of the tunneling rate constant is influenced by the interactions with the environment. The temperature-dependent tunneling rates for HCOOH and DCOOH in solid Ar, Kr, and Xe are measured including data for molecules in different local environments within each host. It was found that the medium and the local environment has a significant influence on the tunneling rate. In reaction kinetics, tunneling of atoms is often negligible compared with over-barrier transitions. At very low temperatures, however, the population of energy states above the barrier becomes exceedingly small and tunneling becomes comparatively more important.1 In a condensed environment, phonons participate in a tunneling reaction and the environment should have some effect on tunneling reactions.2,3 However, in several previous experiments it was found that the tunneling rate constant was unaffected by the change of solvent. 1,4 -6 In this work, we have studied the conversion of cis formic acid ͑HCOOH͒ to trans formic acid in solid rare gases ͑Ar, Kr, Xe͒. This reaction is dominated by tunneling from the vibrational ground state at temperatures below 60 K. The results show that the tunneling rate depends strongly on the environment.The samples were made by mixing vapors of formic acid ͑FA͒ ͑KEBO lab, Ͼ99%͒ or its isotopomers ͑IT Isotope 95%-98% deuteration͒ with rare gases ͑Rg͒ Ar ͑AGA, 99.9999%͒, Kr ͑Air Liquid, 99.95%͒, Xe ͑AGA, 99.997%͒ in the gas phase in a proportion FA/RgϷ1/1000. The gas mixture was deposited on a CsI substrate at 15 K ͑Ar͒, 25 K ͑Kr͒ or 35 K ͑Xe͒ yielding highly monomeric matrices with respect to FA. Thickness of the sample was typically about 100 m. After deposition, the samples were cooled to ϳ8 K which was the lower limit for the cryostat ͑APD DE 202 A͒. The spectra were measured with a FTIR spectrometer ͑Nico-let 60 SX͒ with a resolution of 1 or 0.25 cm Ϫ1 . FA has energy minima in two planar forms differing by orientation of the hydroxyl group as shown in Fig. 1. The interconversion of the conformers involves mainly the torsional motion of the hydroxyl group. In the gas phase, cis-FA is 1365Ϯ30 cm Ϫ1 higher in energy than trans-FA. 7 The barrier from trans to cis has been calculated to be ϳ4200 cm Ϫ1. 8 In this work, cis-FA was prepared by exciting the vibrational transitions of trans-FA in rare-gas matrices with narrowband infrared radiation of an optical parametric oscillator ͑Sunlite, Continuum, FWHM ϳ0.1 cm Ϫ1 ͒. The excitation energy flows into the torsional coordinate inducing the conformer conversion. 9 The IR spectra of cis and trans FA differ significantly from each other making it possible to distinguish them easily in rare-gas matrices.9 FA is trapped in several sites correspo...

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Hydrogen tunneling in condensed media

Cited by 113 publications

References 19 publications

Theoretical studies of proton-coupled electron transfer: Models and concepts relevant to bioenergetics

Theoretical studies of proton-coupled electron transfer: Models and concepts relevant to bioenergetics

Nonadiabatic rate constants for proton transfer and proton-coupled electron transfer reactions in solution: Effects of quadratic term in the vibronic coupling expansion

Cis→trans conversion of formic acid by dissipative tunneling in solid rare gases: Influence of environment on the tunneling rate

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