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Šimėnas M, Klose D, Ptak M, Aidas K, Mączka M, Banys J, Pöppl A, Jeschke G. Magnetic excitation and readout of methyl group tunnel coherence. SCIENCE ADVANCES 2020; 6:eaba1517. [PMID: 32494689 PMCID: PMC7195165 DOI: 10.1126/sciadv.aba1517] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Accepted: 02/04/2020] [Indexed: 05/07/2023]
Abstract
Methyl groups are ubiquitous in synthetic materials and biomolecules. At sufficiently low temperature, they behave as quantum rotors and populate only the rotational ground state. In a symmetric potential, the three localized substates are degenerate and become mixed by the tunnel overlap to delocalized states separated by the tunnel splitting ν t . Although ν t can be inferred by several techniques, coherent superposition of the tunnel-split states and direct measurement of ν t have proven elusive. Here, we show that a nearby electron spin provides a handle on the tunnel transition, allowing for its excitation and readout. Unlike existing dynamical nuclear polarization techniques, our experiment transfers polarization from the electron spin to methyl proton spins with an efficiency that is independent of the magnetic field and does not rely on an unusually large tunnel splitting. Our results also demonstrate control of quantum states despite the lack of an associated transition dipole moment.
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Affiliation(s)
- M. Šimėnas
- Faculty of Physics, Vilnius University, Sauletekio av. 9, 10222 Vilnius, Lithuania
| | - D. Klose
- ETH-Zürich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland
| | - M. Ptak
- Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box-1410, PL-50-950 Wrocław 2, Poland
| | - K. Aidas
- Faculty of Physics, Vilnius University, Sauletekio av. 9, 10222 Vilnius, Lithuania
| | - M. Mączka
- Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box-1410, PL-50-950 Wrocław 2, Poland
| | - J. Banys
- Faculty of Physics, Vilnius University, Sauletekio av. 9, 10222 Vilnius, Lithuania
| | - A. Pöppl
- Felix Bloch Institute for Solid State Physics, Leipzig University, Linnéstr. 5, 04103 Leipzig, Germany
| | - G. Jeschke
- ETH-Zürich, Department of Chemistry and Applied Biosciences, Vladimir-Prelog-Weg 2, 8093 Zürich, Switzerland
- Corresponding author.
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Martínez JI, Alonso PJ, García-Rubio I, Medina M. Methyl rotors in flavoproteins. Phys Chem Chem Phys 2014; 16:26203-12. [DOI: 10.1039/c4cp03115f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
ENDOR evidence shows that methyl groups in flavin behave as quantum locked rotors.
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Affiliation(s)
- Jesús I. Martínez
- Instituto de Ciencia de Materiales de Aragón
- Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas
- Facultad de Ciencias
- 50009 Zaragoza, Spain
| | - Pablo J. Alonso
- Instituto de Ciencia de Materiales de Aragón
- Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas
- Facultad de Ciencias
- 50009 Zaragoza, Spain
| | - Inés García-Rubio
- Laboratory of Physical Chemistry
- ETH Zurich
- 8093 Zürich, Switzerland
- Centro Universitario de la Defensa
- 50090 Zaragoza, Spain
| | - Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular and Instituto de Biocomputación y Física de Sistemas Complejos (BIFI)
- Universidad de Zaragoza
- 50009 Zaragoza, Spain
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Krivokapić A, Øhman KT, Nelson WH, Hole EO, Sagstuen E. Primary oxidation products of 5-methylcytosine: methyl dynamics and environmental influences. J Phys Chem A 2009; 113:9633-40. [PMID: 19663491 DOI: 10.1021/jp904747j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The primary oxidation product in X-irradiated single crystals of 5-methylcytosine hemihydrate and 5-methylcytosine hydrochloride has been studied at 10 K, using electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and ENDOR-induced EPR (EIE) spectroscopies. The radical is characterized by large couplings to the methyl protons and appears to be deprotonated at N1 in both crystal systems. In the hydrochloride crystal the methyl group is completely frozen at 10 K, whereas in the hemihydrate crystal it undergoes tunneling rotation. For the hemihydrate crystal, four ENDOR lines associated with transitions within the A and E rotational states were followed in three planes of rotation. Large ENDOR shifts as measured by saturation of the high- and low-field parts of the EPR spectrum indicate that the rotation is rather slow. Sidebands due to mixing of A and E rotational states are expected for slow rotation and were observed in both the EPR and the EIE spectra. The ENDOR shifts and the sideband frequencies indicate a tunneling splitting between 40 and 60 MHz. Estimates of the barrier to rotation in both crystalline systems were calculated using cluster and single-molecule density functional theory methods, and the results are consistent with those obtained by analysis of the experimental results.
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