1
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Rostkowska H, Lapinski L, Nowak MJ. Hydrogen-atom tunneling in small thioamides: N-methylthiourea, thiobenzamide and 2-cyanothioacetamide. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2024; 313:124139. [PMID: 38503255 DOI: 10.1016/j.saa.2024.124139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 02/26/2024] [Accepted: 03/06/2024] [Indexed: 03/21/2024]
Abstract
The most stable thione tautomeric forms of N-methylthiourea, thiobenzamide and 2-cyanothioacetamide were isolated in low-temperature argon matrices. The higher-energy thiol tautomers of these compounds were generated upon irradiation of matrix-isolated monomers with UV (λ > 270 nm) light. For N-methylthiourea and thiobenzamide, kept in the dark at 3.5 K for a long period of time, a spontaneous thiol → thione hydrogen atom tunneling transformation occurred. Only the thiol isomers with the favorably oriented hydrogen atom of the imino group underwent these hydrogen-atom tunneling processes. The other thiol isomers, with the hydrogen atom of the imino group oriented towards the sulfur atom, did not undergo the thiol → thione conversion. For the photogenerated thiol forms of 2-cyanothioacetamide, no spontaneous thiol → thione tautomeric transformation was detected. Instead, only the spontaneous conformational change of one S-H rotamer of the thiol 2-cyanothioacetamide tautomer into the other S-H rotamer was observed.
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Affiliation(s)
- Hanna Rostkowska
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Leszek Lapinski
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
| | - Maciej J Nowak
- Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warsaw, Poland.
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2
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Góbi S, Keresztes B, Schneiker A, Tarczay G. UV photolysis of thiourea and its N-methylated derivative in cryogenic matrices. Phys Chem Chem Phys 2024; 26:9963-9974. [PMID: 38477114 DOI: 10.1039/d4cp00016a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/14/2024]
Abstract
Exploration of the photolytic dynamics of sulfurous compounds is essential, eventually contributing not only to our comprehension of their fundamental organic chemistry but also shedding light on astrophysical implications. This study aims to investigate two astrochemically relevant sulfur-containing molecules, namely, thiourea (TU) and its N-methylated counterpart, N-methyl thiourea (NMTU), in cryogenic matrices. These molecules were deposited both in solid Ar and in a quantum host, specifically in solid para-H2 matrices, with the latter exhibiting unique properties. The deposited matrices were exposed to a series of UV laser irradiation at various wavelengths to investigate the decomposition paths of TU and NMTU. As a result of the UV photolysis, a plethora of degradation products could be observed in every case. Based on the presence of these product molecules, some considerations can be made regarding the decomposition mechanism of the parent molecules. The use of different matrices allowed for assessing their influence on the decay mechanism, while applying tunable laser light provided insights into the wavelength dependency of the processes.
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Affiliation(s)
- Sándor Góbi
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary.
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary
| | - Barbara Keresztes
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary.
- Hevesy György PhD School of Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary
| | - Anita Schneiker
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary.
- Hevesy György PhD School of Chemistry, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary
| | - György Tarczay
- Laboratory of Molecular Spectroscopy, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary.
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group, Institute of Chemistry, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary
- Centre for Astrophysics and Space Science, ELTE Eötvös Loránd University, PO Box 32, Budapest H-1518, Hungary
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3
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Bernhardt B, Schauermann M, Solel E, Eckhardt AK, Schreiner PR. Equilibrating parent aminomercaptocarbene and CO 2 with 2-amino-2-thioxoacetic acid via heavy-atom quantum tunneling. Chem Sci 2022; 14:130-135. [PMID: 36605744 PMCID: PMC9769125 DOI: 10.1039/d2sc05388h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Accepted: 11/17/2022] [Indexed: 11/19/2022] Open
Abstract
The search for methods to bind CO2 and use it synthetically as a C1-building block under mild conditions is an ongoing endeavor of great urgency. The formation of heterocyclic carbene-carbon dioxide adducts occurs rapidly when the carbene is generated in solution in the presence of CO2. Here we demonstrate the reversible formation of a complex of the hitherto unreported aminomercaptocarbene (H2N-C̈-SH) with CO2 isolated in solid argon by photolysis of 2-amino-2-thioxoacetic acid. Remarkably, the complex disappears in the dark as deduced by time-dependent matrix infrared measurements, and equilibrates back to the covalently bound starting material. This kinetically excluded process below ca. 8 K is made possible through heavy-atom quantum mechanical tunneling, as also evident from density functional theory and ab initio computations at the CCSD(T)/cc-pVTZ level of theory. Our results provide insight into CO2 activation using a carbene and emphasize the role of quantum mechanical tunneling in organic processes, even involving heavy atoms.
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Affiliation(s)
- Bastian Bernhardt
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - Markus Schauermann
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - Ephrath Solel
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - André K. Eckhardt
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
| | - Peter R. Schreiner
- Institute of Organic Chemistry, Justus Liebig UniversityHeinrich-Buff-Ring 1735392 GiessenGermany
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4
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Nunes CM, Roque JP, Doddipatla S, Wood SA, McMahon RJ, Fausto R. Simultaneous Tunneling Control in Conformer-Specific Reactions. J Am Chem Soc 2022; 144:20866-20874. [PMID: 36321916 PMCID: PMC9776521 DOI: 10.1021/jacs.2c09026] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We present here a new example of chemical reactivity governed by quantum tunneling, which also highlights the limitations of the classical theories. The syn and anti conformers of a triplet 2-formylphenylnitrene, generated in a nitrogen matrix, were found to spontaneously rearrange to the corresponding 2,1-benzisoxazole and imino-ketene, respectively. The kinetics of both transformations were measured at 10 and 20 K and found to be temperature-independent, providing clear evidence of concomitant tunneling reactions (heavy-atom and H-atom). Computations confirm the existence of these tunneling reaction pathways. Although the energy barrier between the nitrene conformers is lower than any of the observed reactions, no conformational interconversion was observed. These results demonstrate an unprecedented case of simultaneous tunneling control in conformer-specific reactions of the same chemical species. The product outcome is impossible to be rationalized by the conventional kinetic or thermodynamic control.
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Affiliation(s)
- Cláudio M. Nunes
- University
of Coimbra, CQC-IMS, Department of Chemistry, 3004-535 Coimbra, Portugal,
| | - José P.
L. Roque
- University
of Coimbra, CQC-IMS, Department of Chemistry, 3004-535 Coimbra, Portugal
| | - Srinivas Doddipatla
- University
of Coimbra, CQC-IMS, Department of Chemistry, 3004-535 Coimbra, Portugal
| | - Samuel A. Wood
- Department
of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706-1322, United States
| | - Robert J. McMahon
- Department
of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706-1322, United States
| | - Rui Fausto
- University
of Coimbra, CQC-IMS, Department of Chemistry, 3004-535 Coimbra, Portugal
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5
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Bertram L, Roberts SJ, Powner MW, Szabla R. Photochemistry of 2-thiooxazole: a plausible prebiotic precursor to RNA nucleotides. Phys Chem Chem Phys 2022; 24:21406-21416. [PMID: 36047336 PMCID: PMC7613695 DOI: 10.1039/d2cp03167a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Potentially prebiotic chemical reactions leading to RNA nucleotides involve periods of UV irradiation, which are necessary to promote selectivity and destroy biologially irrelevant side products. Nevertheless, UV light has only been applied to promote specific stages of prebiotic reactions and its effect on complete prebiotic reaction sequences has not been extensively studied. Here, we report on an experimental and computational investigation of the photostability of 2-thiooxazole (2-TO), a potential precursor of pyrimidine and 8-oxopurine nucleotides on early Earth. Our UV-irradiation experiments resulted in rapid decomposition of 2-TO into unidentified small molecule photoproducts. We further clarify the underlying photochemistry by means of accurate ab initio calculations and surface hopping molecular dynamics simulations. Overall, the computational results show efficient rupture of the aromatic ring upon the photoexcitation of 2-TO via breaking of the C-O bond. Consequently, the initial stage of the divergent prebiotic synthesis of pyrimidine and 8-oxopurine nucleotides would require periodic shielding from UV light either with sun screening chromophores or through a planetary scenario that would protect 2-TO until it is transformed into a more stable intermediate compound, e.g. oxazolidinone thione.
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Affiliation(s)
- Lauren Bertram
- EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, UK
| | - Samuel J Roberts
- Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.,MRC Laboratory of Molecular Biology, Cambridge, UK
| | - Matthew W Powner
- Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK
| | - Rafał Szabla
- EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, UK.,Department of Physical and Quantum Chemistry, Faculty of Chemistry, Wrocław University of Science and Technology, 50-370 Wrocław, Poland.
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6
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Robson B. De novo protein folding on computers. Benefits and challenges. Comput Biol Med 2022; 143:105292. [PMID: 35158120 DOI: 10.1016/j.compbiomed.2022.105292] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2021] [Revised: 01/19/2022] [Accepted: 01/20/2022] [Indexed: 01/05/2023]
Abstract
There has been recent success in prediction of the three-dimensional folded native structures of proteins, most famously by the AlphaFold Algorithm running on Google's/Alphabet's DeepMind computer. However, this largely involves machine learning of protein structures and is not a de novo protein structure prediction method for predicting three-dimensional structures from amino acid residue sequences. A de novo approach would be based almost entirely on general principles of energy and entropy that govern protein folding energetics, and importantly do so without the use of the amino acid sequences and structural features of other proteins. Most consider that problem as still unsolved even though it has occupied leading scientists for decades. Many consider that it remains one of the major outstanding issues in modern science. There is crucial continuing help from experimental findings on protein unfolding and refolding in the laboratory, but only to a limited extent because many researchers consider that the speed by which real proteins folds themselves, often from milliseconds to minutes, is itself still not fully understood. This is unfortunate, because a practical solution to the problem would probably have a major effect on personalized medicine, the pharmaceutical industry, biotechnology, and nanotechnology, including for example "smaller" tasks such as better modeling of flexible "unfolded" regions of the SARS-COV-2 spike glycoprotein when interacting with its cell receptor, antibodies, and therapeutic agents. Some important ideas from earlier studies are given before moving on to lessons from periodic and aperiodic crystals, and a possible role for quantum phenomena. The conclusion is that better computation of entropy should be the priority, though that is presented guardedly.
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Affiliation(s)
- Barry Robson
- Ingine Inc.Cleveland Ohio and The Dirac Foundation, Oxfordshire, UK.
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7
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Lapinski L, Rostkowska H, Nowak MJ. Distinct class of photoinduced hydrogen-atom-transfer processes: phototautomerizations in molecules with no intramolecular hydrogen bond in the structure. INT REV PHYS CHEM 2022. [DOI: 10.1080/0144235x.2022.2030613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Affiliation(s)
- Leszek Lapinski
- Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
| | - Hanna Rostkowska
- Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
| | - Maciej J. Nowak
- Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
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8
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Rostkowska H, Luchowska A, Lapinski L, Nowak MJ. Effect of a Solid-Hydrogen Environment on UV-Induced Hydrogen-Atom Transfer in Matrix-Isolated Heterocyclic Thione Compounds. J Phys Chem A 2021; 125:7437-7448. [PMID: 34406775 PMCID: PMC8419844 DOI: 10.1021/acs.jpca.1c05538] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
To shed more light
on the mechanisms of UV-induced hydrogen-atom-transfer
processes in heterocyclic molecules, phototautomeric thione →
thiol reactions were investigated for thione compounds isolated in
low-temperature Ar as well as in n-H2 (normal hydrogen)
matrices. These studies concerned thione compounds with a five-membered
heterocyclic ring and thione compounds with a six-membered heterocyclic
ring. The experimental investigation of 2-thioimidazole and 3-thio-1,2,4-triazole
(thione compounds with a five-membered heterocyclic ring) revealed
that for the compounds isolated in solid n-H2 only trace
amounts of thiol photoproducts were photogenerated; even though for
the same compounds isolated in the solid Ar matrix, the thione → thiol photoconversion
was nearly
total. In contrast to that, for 3-thiopyridazine and 2-thioquinoline
(thione compounds with a six-membered heterocyclic
ring) isolated in solid n-H2, the UV-induced thione →
thiol conversion occurred with the yield reaching 25–50% of
the yield of the analogous process observed for the same species isolated
in solid Ar. The obtained experimental results allow us to conclude
that the dissociation–association mechanism nearly exclusively
governs the phototransformation in thione heterocycles with high barriers
for tautomerization (such as thione compounds with a five-membered
ring), whereas the strictly intramolecular hydrogen-atom shift contributes
to the mechanism of hydrogen-atom transfer in thione heterocycles
with lower barriers (such as thione compounds with a six-membered
ring).
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Affiliation(s)
- Hanna Rostkowska
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
| | - Anna Luchowska
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
| | - Leszek Lapinski
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
| | - Maciej J Nowak
- Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland
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9
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Pereira NAM, Nunes CM, Reva I, Fausto R. Evidence of IR-Induced Chemistry in a Neat Solid: Tautomerization of Thiotropolone by Thermal, Electronic, and Vibrational Excitations. J Phys Chem A 2021; 125:6394-6403. [PMID: 34275275 DOI: 10.1021/acs.jpca.1c04081] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Thiotropolone isolated in argon and xenon matrices (as monomers) or in a neat solid (as the crystalline or amorphous state) at low temperature was found to exist only in the thione-enol form. Visible light irradiation (λ ≥ 400 nm) leads to thione-enol → thiol-keto tautomerization in matrices and under neat solid conditions at 15 K. The assignment of the IR spectra of the two thiotropolone tautomers (thione-enol and thiol-keto) was carried out with the support of B3LYP/6-311+G(2d,p) computations. The thiol-keto form generated in situ in a neat solid was found to tautomerize back to the thione-enol upon annealing up to 100 K. Gaussian-4 (G4) computations estimate that such a tautomerization process has an energy barrier of ∼25 kJ mol-1, which is consistent with the observations. Moreover, it was found that narrowband IR irradiation of the thiol-keto form in a neat solid, at the frequency of its CH stretching overtones/combination modes, also induces tautomerization to the thione-enol form. Such a result constitutes an important demonstration of vibrationally induced chemistry under neat solid conditions.
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Affiliation(s)
- Nelson A M Pereira
- CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Cláudio M Nunes
- CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
| | - Igor Reva
- CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal.,CIEPQPF, Department of Chemical Engineering, University of Coimbra, 3030-790 Coimbra, Portugal
| | - Rui Fausto
- CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
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10
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On the nature of inter- and intramolecular interactions involving benzo[h]quinoline and 10-hydroxybenzo[h]quinoline: Electronic ground state vs excited state study. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2021.130126] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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11
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Bernhardt B, Dressler F, Eckhardt AK, Becker J, Schreiner PR. Characterization of the Simplest Thiolimine: The Higher Energy Tautomer of Thioformamide. Chemistry 2021; 27:6732-6739. [PMID: 33496350 PMCID: PMC8252572 DOI: 10.1002/chem.202005188] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2020] [Revised: 01/21/2021] [Indexed: 12/21/2022]
Abstract
As sulfur‐containing organic molecules thioamides and their isomers are conceivable intermediates in prebiotic chemistry, for example, in the formation of amino acids and thiazoles and resemble viable candidates for detection in interstellar media. Here, we report the characterization of parent thioformamide in the solid state via single‐crystal X‐ray diffraction and its photochemical interconversion to its hitherto unreported higher energy tautomer thiolimine in inert argon and dinitrogen matrices. Upon photogeneration, four conformers of thiolimine form, whose ratio depends on the employed wavelength. One of these conformers interconverts due to quantum mechanical tunneling with a half‐life of 30–45 min in both matrix materials at 3 and 20 K. A spontaneous reverse reaction from thiolimine to thioformamide is not observed. To support our experimental findings, we explored the potential energy surface of the system at the AE‐CCSD(T)/aug‐cc‐pCVTZ level of theory and computed tunneling half‐lives with the CVT/SCT approach applying DFT methods.
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Affiliation(s)
- Bastian Bernhardt
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - Friedemann Dressler
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - André K Eckhardt
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - Jonathan Becker
- Institute of Inorganic and Analytical Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
| | - Peter R Schreiner
- Institute of Organic Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35390, Giessen, Germany
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12
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Mosquera-Lois I, Ferro-Costas D, Fernández-Ramos A. Chemical reactivity from the vibrational ground-state level. The role of the tunneling path in the tautomerization of urea and derivatives. Phys Chem Chem Phys 2020; 22:24951-24963. [PMID: 33140774 DOI: 10.1039/d0cp04857g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recent developments of low-temperature techniques are providing valuable knowledge about chemical processes that manifest in the quantum regimen. The tunneling effect from the vibrational ground-state is the main mechanism of these reactions, which usually involves the motion or transfer of hydrogen atoms. Theoretical methods can enrich the information supplied by these experimental methods through an insightful analysis of the tunneling process. In this context, canonical variational transition state theory with multidimensional tunneling corrections (CVT/MT) can handle this type of reaction, and it has been applied to several systems within the small-curvature approximation for tunneling (SCT). This method is of proven reliability for polyatomic reactions occurring at room temperature and above, but no tests have been performed to check its performance when only the lowest energy level is populated. In this work, we compare SCT against the least-action tunneling (LAT) method to study the tautomerization and cis-trans interconversion reactions in the enol forms of urea, thiourea, and selenourea. To the best of our knowledge, this is the first time that the LAT method is applied to a polyatomic reaction occurring in the deep-tunneling region. The theoretical results indicate that the reaction mechanisms are controlled by tunneling. The SCT and LAT tautomerization reaction times are in good agreement with the experimental values; however, LAT seems superior to SCT for reactions (tautomerizations) that involve moderate reaction path curvature, whereas the opposite is true for reactions with small curvature (interconversions). These results led us to introduce and recommend the microcanonically optimized tunneling path that selects the tunneling probability as the maximum between the SCT and LAT tunneling probabilities.
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Affiliation(s)
- Irea Mosquera-Lois
- Center for Research in Biological Chemistry and Molecular Materials (CIQUS), University of Santiago de Compostela, 15782 Santiago de Compostela, Spain.
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13
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14
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Nunes CM, Pereira NAM, Reva I, Amado PSM, Cristiano MLS, Fausto R. Bond-Breaking/Bond-Forming Reactions by Vibrational Excitation: Infrared-Induced Bidirectional Tautomerization of Matrix-Isolated Thiotropolone. J Phys Chem Lett 2020; 11:8034-8039. [PMID: 32869645 DOI: 10.1021/acs.jpclett.0c02272] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Infrared vibrational excitation is a promising approach for gaining exceptional control of chemical reactions, in ways that cannot be attained via thermal or electronic excitation. Here, we report an unprecedented example of a bond-breaking/bond-forming reaction by vibrational excitation under matrix isolation conditions. Thiotropolone monomers were isolated in cryogenic argon matrices and characterized by infrared spectroscopy and vibrational computations (harmonic and anharmonic). Narrowband near-infrared irradiations tuned at frequencies of first CH stretching overtone (5940 cm-1) or combination modes (5980 cm-1) of the OH tautomer, the sole form of the compound that exists in the as-deposited matrices, led to its conversion into the SH tautomer. The tautomerization in the reverse direction was achieved by vibrational excitation of the SH tautomer with irradiation at 5947 or 5994 cm-1, corresponding to the frequencies of its CH stretching combination and overtone modes. This pioneer demonstration of bidirectional hydroxyl ↔ thiol tautomerization controlled by vibrational excitation creates prospects for new advances in vibrationally induced chemistry.
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Affiliation(s)
- Cláudio M Nunes
- University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal
| | - Nelson A M Pereira
- University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal
| | - Igor Reva
- University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal
| | - Patrícia S M Amado
- Centre of Marine Sciences, CCMAR, and Department of Chemistry and Pharmacy, University of Algarve, 8005-139 Faro, Portugal
| | - Maria L S Cristiano
- Centre of Marine Sciences, CCMAR, and Department of Chemistry and Pharmacy, University of Algarve, 8005-139 Faro, Portugal
| | - Rui Fausto
- University of Coimbra, CQC, Department of Chemistry, 3004-535 Coimbra, Portugal
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15
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Eckhardt AK, Erb FR, Schreiner PR. Conformer-specific [1,2] H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC-C[combining umlaut]-OH). Chem Sci 2019; 10:802-808. [PMID: 30774874 PMCID: PMC6345350 DOI: 10.1039/c8sc03720e] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 10/31/2018] [Indexed: 11/21/2022] Open
Abstract
We report the gas-phase preparation of cyanohydroxycarbene by high-vacuum flash pyrolysis of ethyl 2-cyano-2-oxoacetate and subsequent trapping of the pyrolysate in an inert argon matrix at 3 K. After irradiation of the matrix with green light for a few seconds singlet trans-cyanohydroxycarbene rearranges to its cis-conformer. Prolonged irradiation leads to the formation of cyanoformaldehyde and isomeric isocyanoformaldehyde. Cis- and trans-cyanohydroxycarbene were characterized by matching matrix IR and UV/Vis spectroscopic data with ab initio coupled cluster and TD-DFT computations. Trans-cyanohydroxycarbene undergoes a conformer-specific [1,2]H-tunnelling reaction through a 33.3 kcal mol-1 barrier (the highest penetrated barrier of all H-tunnelling reactions observed to date) to cyanoformaldehyde with a half-life of 23.5 ± 0.5 d; this is the longest half-life reported for an H-tunnelling process to date. During the tunnelling reaction the cis-conformer remains unchanged over the same period of time and the Curtin-Hammett principle does not apply. NIR irradiation of the O-H stretching overtone does not enhance the tunnelling rate via vibrational activation. Push-pull stabilisation of hydroxycarbenes through σ- and π-withdrawing groups therefore is even more stabilizing than push-push substitution.
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Affiliation(s)
- André K Eckhardt
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17, 35392 Giessen , Germany .
| | - Frederik R Erb
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17, 35392 Giessen , Germany .
| | - Peter R Schreiner
- Institute of Organic Chemistry , Justus Liebig University , Heinrich-Buff-Ring 17, 35392 Giessen , Germany .
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16
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Góbi S, Nunes CM, Reva I, Tarczay G, Fausto R. S–H rotamerizationviatunneling in a thiol form of thioacetamide. Phys Chem Chem Phys 2019; 21:17063-17071. [DOI: 10.1039/c9cp03417j] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Rotamerization of the S–H groupviahydrogen tunneling is reported for the first time.
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Affiliation(s)
- Sándor Góbi
- CQC
- Department of Chemistry
- University of Coimbra
- Coimbra
- Portugal
| | | | - Igor Reva
- CQC
- Department of Chemistry
- University of Coimbra
- Coimbra
- Portugal
| | - György Tarczay
- Laboratory of Molecular Spectroscopy
- Institute of Chemistry
- ELTE Eötvös Loránd University
- H-1518 Budapest
- Hungary
| | - Rui Fausto
- CQC
- Department of Chemistry
- University of Coimbra
- Coimbra
- Portugal
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Góbi S, Reva I, Csonka IP, M. Nunes C, Tarczay G, Fausto R. Selective conformational control by excitation of NH imino vibrational antennas. Phys Chem Chem Phys 2019; 21:24935-24949. [DOI: 10.1039/c9cp05370k] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We provide experimental evidence for the occurrence of selective and reversible conformational control over the SH group by vibrational excitation of remote NH groups. Using an imino group that acts as a molecular antenna has no precedents.
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Affiliation(s)
- Sándor Góbi
- CQC
- Department of Chemistry
- University of Coimbra
- Coimbra
- Portugal
| | - Igor Reva
- CQC
- Department of Chemistry
- University of Coimbra
- Coimbra
- Portugal
| | - István Pál Csonka
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group
- Institute of Chemistry
- ELTE Eötvös Loránd University
- H–1518 Budapest
- Hungary
| | | | - György Tarczay
- MTA-ELTE Lendület Laboratory Astrochemistry Research Group
- Institute of Chemistry
- ELTE Eötvös Loránd University
- H–1518 Budapest
- Hungary
| | - Rui Fausto
- CQC
- Department of Chemistry
- University of Coimbra
- Coimbra
- Portugal
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