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Waluk J. Nuclear Quantum Effects in Proton or Hydrogen Transfer. J Phys Chem Lett 2024; 15:598-607. [PMID: 38198616 PMCID: PMC10801683 DOI: 10.1021/acs.jpclett.3c03368] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 01/05/2024] [Accepted: 01/05/2024] [Indexed: 01/12/2024]
Abstract
Proton or hydrogen transfers, basic chemical reactions, proceed either by thermally activated barrier crossing or via tunneling. Studies of molecules undergoing single or double proton or hydrogen transfer in the ground or excited electronic state reveal that tunneling can dominate under conditions usually considered to favor the thermal process. Moreover, the tunneling probability strongly varies for excitation of certain vibrational modes, which changes the effective barrier and/or proton transfer distance. When the reaction is fast compared to vibrational relaxation, the mode selectivity can still be maintained for molecules in solutions at 293 K. These observations point to dangers of relating the calculated minimum energy paths and the associated barriers to the experimentally obtained activation energies. The multidimensional character of the reaction coordinate is obvious; it can dramatically change for slowly and rapidly relaxing environments. We postulate that the hydrogen bond definition should be extended by specifically including the role of molecular vibrations.
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Affiliation(s)
- Jacek Waluk
- Institute
of Physical Chemistry, Polish Academy of
Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
- Faculty
of Mathematics and Science, Cardinal Stefan
Wyszyński University, Dewajtis 5, 01-815 Warsaw, Poland
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Gorski A, Golec B, Wałecki W, Peukert S, Gil M, Gawinkowski S, Waluk J. Matrix isolation studies of vibrational structure of hemiporphycene. J Mol Struct 2020. [DOI: 10.1016/j.molstruc.2020.128497] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Kasprzycki P, Kopycki P, Listkowski A, Gorski A, Radzewicz C, Birch DJS, Waluk J, Fita P. Influence of local microenvironment on the double hydrogen transfer in porphycene. Phys Chem Chem Phys 2020; 22:17117-17128. [PMID: 32687131 DOI: 10.1039/d0cp02687e] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We performed time-resolved transient absorption and fluorescence anisotropy measurements in order to study tautomerization of porphycene in rigid polymer matrices at cryogenic temperatures. Studies were carried out in poly(methyl methacrylate) (PMMA), poly(vinyl butyral) (PVB), and poly(vinyl alcohol) (PVA). The results prove that in all studied media hydrogen tunnelling plays a significant role in the double hydrogen transfer which becomes very sensitive to properties of the environment below approx. 150 K. We also demonstrate that there exist two populations of porphycene molecules in rigid media: "hydrogen-transferring" molecules, in which tautomerization occurs on time scales below 1 ns and "frozen" molecules in which double hydrogen transfer is too slow to be monitored with nanosecond techniques. The number of "frozen" molecules increases when the sample is cooled. We explain this effect by interactions of guest molecules with a rigid host matrix which disturbs symmetry of porphycene and hinders tunnelling. Temperature dependence of the number of hydrogen-transferring molecules suggests that the factor which restores the symmetry of the double-minimum potential well in porphycene are intermolecular vibrations localized in separated regions of the amorphous polymer.
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Affiliation(s)
- Piotr Kasprzycki
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland. and Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, Warsaw 01-224, Poland.
| | - Przemysław Kopycki
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland.
| | - Arkadiusz Listkowski
- Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, Warsaw 01-224, Poland. and Faculty of Mathematics and Science, Cardinal Stefan Wyszyński University, Dewajtis 5, 01-815 Warsaw, Poland
| | - Aleksander Gorski
- Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, Warsaw 01-224, Poland.
| | - Czesław Radzewicz
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland.
| | - David J S Birch
- Photophysics Group, Centre for Molecular Nanometrology, Department of Physics, Scottish Universities Physics Alliance, University of Strathclyde, 107 Rottenrow East, Glasgow G4 0NG, UK
| | - Jacek Waluk
- Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 Kasprzaka, Warsaw 01-224, Poland. and Faculty of Mathematics and Science, Cardinal Stefan Wyszyński University, Dewajtis 5, 01-815 Warsaw, Poland
| | - Piotr Fita
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland.
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Abstract
Solutions of organic molecules containing one or more heterocycles with conjugated bonds may exist as a mixture of tautomers, but typically only a few of them are significantly populated even though the potential number grows combinatorially with the number of protonation and deprotonation sites. Generating the most stable tautomers from a given input structure is an important and challenging task, and numerous algorithms to tackle it have been proposed in the literature. This work describes a novel approach for tautomer prediction that involves the combined use of molecular mechanics, semiempirical quantum chemistry, and density functional theory. The key idea in our method is to identify the protonation and deprotonation sites using estimated micro-p Ka's for every atom in the molecule as well as in its nearest protonated and deprotonated forms. To generate tautomers in a systematic way with minimal bias, we then consider the full set of tautomers that arise from the combinatorial distribution of all such mobile protons among all protonatable sites, with efficient postprocessing to screen away high-energy species. To estimate the micro-p Ka's, we present a new method designed for the current task, but we emphasize that any alternative method can be used in conjunction with our basic algorithm. Our approach is therefore grounded in the computational prediction of physical properties in aqueous solution, in contrast to other approaches that may rely on the use of hard-coded rules of proton distribution, previously observed tautomerization patterns from a known chemical space, or human input. We present examples of the application of our algorithm to organic and drug-like molecules, with a focus on novel structures where traditional methods are expected to perform worse.
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Affiliation(s)
- Mark A Watson
- Schrödinger, Inc. , 120 West 45th Street , New York , New York 10036 , United States
| | - Haoyu S Yu
- Schrödinger, Inc. , 120 West 45th Street , New York , New York 10036 , United States
| | - Art D Bochevarov
- Schrödinger, Inc. , 120 West 45th Street , New York , New York 10036 , United States
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