Environmental Effects on Proton Transfer. Ab Initio Calculations on Systems in a Semi-Classical, Polarizable Environment

Duijnen, Piet Th. van; Thole, B. T.

doi:10.1007/978-94-015-6918-7_6

“…[ 5 , 9 ] From the theoretical view, the subtle interplay of the partner molecules has significant influence on proton tunneling. [ 10 , 11 , 12 , 13 ] Previous experimental studies have shown that the surrounding environment can modify the proton transfer rate,[ 14 , 15 , 16 , 17 , 18 , 19 ] however, little experimental data is available on how the proton tunneling process is affected by the environment at the few‐molecules level. Herein, we report the direct observation and precise measurement of proton transfer of the formic acid dimer lying on the surface of an aromatic π system.…”

mentioning

confidence: 99%

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Li

¹

,

Tikhonov

²

,

Schnell

³

2021

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Proton transfer via tunneling is a fundamental quantum-mechanical phenomenon. We report rotational spectroscopy measurements of this process in the complex of the formic acid dimer with fluorobenzene. The assignment of the spectrum indicates that this complex exists in the form of a p-p stacked structure. Each rotational transition of the parent isotopologue exhibits splitting. Isotopic substitution experiments show that the spectral splitting results from doubleproton transfer tunneling in the formic acid dimer. Presence of fluorobenzene as a neighboring molecule does not quench the double proton transfer in the formic acid dimer but decreases its tunneling splitting from 341(3) MHz to 267.608(1) MHz. Calculations suggest that the presence of the weakly bounded fluorobenzene does not influence the activation energy of the proton transfer. The fluorobenzene is reoriented with respect to the formic acid dimer during the course of the reaction, slowing down the proton transfer motion.

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“…Thus, an accurate description of proton tunneling influenced by nearby molecules is important for understanding many chemical processes, including biochemical ones [5, 9] . From the theoretical view, the subtle interplay of the partner molecules has significant influence on proton tunneling [10–13] . Previous experimental studies have shown that the surrounding environment can modify the proton transfer rate, [14–19] however, little experimental data is available on how the proton tunneling process is affected by the environment at the few‐molecules level.…”

Section: Figurementioning

confidence: 99%

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Li

¹

,

Tikhonov

²

,

Schnell

³

2021

View full text Add to dashboard Cite

Proton transfer via tunneling is a fundamental quantum-mechanical phenomenon. We report rotational spectroscopy measurements of this process in the complex of the formic acid dimer with fluorobenzene. The assignment of the spectrum indicates that this complex exists in the form of a p-p stacked structure. Each rotational transition of the parent isotopologue exhibits splitting. Isotopic substitution experiments show that the spectral splitting results from doubleproton transfer tunneling in the formic acid dimer. Presence of fluorobenzene as a neighboring molecule does not quench the double proton transfer in the formic acid dimer but decreases its tunneling splitting from 341(3) MHz to 267.608(1) MHz. Calculations suggest that the presence of the weakly bounded fluorobenzene does not influence the activation energy of the proton transfer. The fluorobenzene is reoriented with respect to the formic acid dimer during the course of the reaction, slowing down the proton transfer motion.

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“…The sheer size of the environment, i.e., the solvent and the en zyme protein that surround the active site, make it very impractical, if not impossible, to attempt to describe it with an ab-initio quantum chemical approach. Approximate methods taking into account the salient properties of the environment are needed, and approaches to this problem are currently being developed [28,30,32,34,38,39]. The protein can be considered as the immediate environment of the active site and, being a fairly rigid structure, can be approximated by an ensemble of microscopic charges and polarizable dipoles positioned on the atoms of the protein.…”

Section: The Effect Of the Protein Environmentmentioning

confidence: 99%

Effect of Local Environment and Protein on the Mechanism of Action of Superoxide Dismutase

Osman¹

1986

Enzyme

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Quantum mechanical simulations of the mechanism of action of superoxide dismutase (SOD) indicate that the presence ot Arg-141 in the active site of the enzyme is responsible for the formation of an intermediate complex between superoxide and the enzyme in which the copper is not reduced. The analysis of the local environmental effects of Arg-141 shows that this residue prevents the reduction of copper by forming a hydrogen bond to superoxide and by generating an electric field in the active site that opposes the transfer of an electron from superoxide to copper. The protein enhances the effect of the opposing field generated by Arg-141. Local changes in the environment of the copper ion, simulated by stretching the Cu-NE2 (His-61) bond also do not induce an electron transfer from superoxide to copper. The protein increases the energies required for this stretch through the electric field it generates near the active site. These results are further support for the new proposed mechanism of action of SOD which is based on the inability of superoxide to reduce the cupric ion in the enzyme.

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Environmental Effects on Proton Transfer. Ab Initio Calculations on Systems in a Semi-Classical, Polarizable Environment

Cited by 7 publications

References 25 publications

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Double Proton Transfer Across a Table: The Formic Acid Dimer–Fluorobenzene Complex

Effect of Local Environment and Protein on the Mechanism of Action of Superoxide Dismutase

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