Hydrogen transfer from guest molecule to radical in adjacent hydrate-cages

Ohgaki, Kazunari; Nakatsuji, Kentaro; Takeya, Kei; Tani, Atsushi; Sugahara, Takeshi

doi:10.1039/b715284a

Cited by 31 publications

(51 citation statements)

References 4 publications

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“…This implies that there is some hostguest interaction, and indeed, hydrogen-bonding is known to occur for a variety of guest molecules in clathrate hydrates, including small ethers. [31][32][33] To explore the possibility of strong radical-host interactions, we performed a DFT calculation on tetrahydrofuran-3-yl (the H isotopomer of 1) at the center of a single cage of 28 water molecules arranged to mimic the 5 12 .) The focus of the present paper is on the identification of guest radicals.…”

Section: Resultsmentioning

confidence: 99%

“…The study of controlled reactions in clathrate hydrates has led to the suggestion that they be used as "nano-reactors". 7 Free radicals can be created in clathrate hydrates by photolysis of either the guest 8 or the host water molecules, 9 but most studies employ γ-irradiation, [10][11][12][13][14][15][16] and thence reaction of guest molecules with the transient products (H, OH, e -) of water radiolysis. At low temperature hydrogen atoms (H or D) can be detected by electron spin resonance (ESR).…”

Section: Introductionmentioning

confidence: 99%

“…16,17 Organic free radicals can also be characterized by ESR, and monitoring their signal intensities in temperature annealing studies has provided evidence for H-atom transfer reactions. [12][13][14] A different strategy, which we have followed, is to create radicals through reactions of muonium, and to study the muoniated radicals by muon spin spectroscopy. [18][19][20][21][22][23] Muonium (Mu) is the single-electron atom with a positive muon as nucleus.…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Free Radicals in Clathrate Hydrates of Furan, 2,3-Dihydrofuran, and 2,5-Dihydrofuran by Muon Spin Spectroscopy

et al. 2016

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In addition to their importance as abundant hydrocarbon deposits in nature, clathrate hydrates are being studied as potential media for hydrogen and carbon dioxide storage, and as "nano-reactors" for small molecules. However, little is known about the behaviour of reactive species in such materials. We have employed muon spin spectroscopy to characterize various organic free radicals which reside as isolated guests in structure II clathrates. The radicals are formed by reaction of atomic muonium (Mu) with the guest molecules: furan and two isomeric dihydrofurans. Muonium is essentially a light isotope of hydrogen, and adds to unsaturated molecules in the same manner as H. We have determined muon and proton hyperfine coupling constants for the muoniated radicals formed in the clathrates and also in neat liquids at the same temperature. DFT calculations were used to guide the spectral assignments and distinguish between competing radical products for Mu addition to furan and 2,3-dihydrofuran. Relative signal amplitudes provide yields and thus the relative reactivities of the C4 and C5 addition sites in these molecules. Spectral features, hyperfine constants and reactivities all indicate that the radicals do not tumble freely in the clathrate cages in the same way that they do in liquids.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Characterization of Free Radicals in Clathrate Hydrates of Furan, 2,3-Dihydrofuran, and 2,5-Dihydrofuran by Muon Spin Spectroscopy

et al. 2016

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“…We have reported the thermal stabilities of methyl, ethyl, and propyl radicals in the γ-ray-irradiated simple methane [1,2], ethane [3], and propane [4] hydrate systems. The radicals in other clathrate hydrates have been investigated [5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Intermolecular Hydrogen Transfer in Isobutane Hydrate

et al. 2012

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Electron spin resonance (ESR) spectra of butyl radicals induced with γ-ray irradiation in the simple isobutane (2-methylpropane) hydrate (prepared with deuterated water) were investigated. Isothermal annealing results of the γ-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a hydrogen atom from the isobutane molecule through shared hexagonal-faces of adjacent large cages. During this "hydrogen picking" process, the isobutyl radical is apparently transformed into a tert-butyl radical, while the sum of isobutyl and tert-butyl radicals remains constant. The apparent transformation from isobutyl to tert-butyl radicals is an irreversible first-order reaction and the activation energy was estimated to be 35 ± 3 kJ/mol, which was in agreement with the activation energy (39 ± 5 kJ/mol) of hydrogen picking in the γ-ray-irradiated propane hydrate with deuterated water.

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“…[21][22][23][24][25] There is clear evidence from some of these experiments of H-atom transfer from an alkyl radical in one cavity to a guest molecule in a neighbouring cage. [26][27][28] Our own experiments make use of muonium as an H-atom analogue. Muonium (Mu = µ + e -) is a single-electron atom with a positive muon (mass 0.11343 u) as nucleus, and is effectively a light isotope of hydrogen.…”

Section: Introductionmentioning

confidence: 99%

Characterization of free radicals in clathrate hydrates of pyrrole, thiophene, and isoxazole by muon spin spectroscopy

et al. 2018

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Gas hydrates have long been of interest to the petrochemical industry but there has been growing interest in potential applications for carbon dioxide sequestration and hydrogen storage. This has prompted many fundamental studies of structure and host-guest interactions, but there has been relatively little investigation of chemical reactions of the guest molecules. In previous work we have shown that it is possible to use muon spin spectroscopy to characterize H-atom-like muonium and muoniated free radicals formed in clathrate hydrates. Muonium forms in clathrate hydrates of cyclopentane and tetrahydrofuran, whereas furan and its dihydro-derivatives form radicals. The current work extends studies to clathrates hydrates of other 5-membered heterocycles: thiophene, pyrrole and isoxazole. All form structure II hydrates. In addition to the clathrates, pure liquid samples of the heterocycles were studied to aid in the assignment of radical signals and for comparison with the enclathrated radicals. Similar to furan, two distinct radicals are formed when muonium reacts with thiophene and pyrrole. However, only one muoniated radical was detected from isoxazole. Muon, proton and nitrogen hyperfine constants were determined and compared with values predicted by DFT calculations to aid the structure assignments. The results show that Mu adds preferentially to the carbon adjacent to the heteroatom in thiophene and pyrrole, and to the carbon adjacent to O in isoxazole. The same radicals are formed in clathrates, but the spectra have broader signals, suggesting slower tumbling. Furthermore, additional signals in the avoided levelcrossing spectra indicate anisotropy consistent with restricted motion of the radicals in the clathrate cages.

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Hydrogen transfer from guest molecule to radical in adjacent hydrate-cages

Abstract: Electron spin resonance measurement of gamma-ray-irradiated propane hydrates shows that the normal propyl radical withdraws hydrogen from the adjacent propane molecule through the hexagonal planes of the hydrate cage without water molecule bridging.

Cited by 31 publications

References 4 publications

Characterization of Free Radicals in Clathrate Hydrates of Furan, 2,3-Dihydrofuran, and 2,5-Dihydrofuran by Muon Spin Spectroscopy

Characterization of Free Radicals in Clathrate Hydrates of Furan, 2,3-Dihydrofuran, and 2,5-Dihydrofuran by Muon Spin Spectroscopy

Intermolecular Hydrogen Transfer in Isobutane Hydrate

Characterization of free radicals in clathrate hydrates of pyrrole, thiophene, and isoxazole by muon spin spectroscopy

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