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- Guo, J. -H, et al.
(författare)
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Electronic structure study of the bases in DNA duplexes by in situ photon-in/photon-out soft X-ray spectroscopy
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 197-201
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Tidskriftsartikel (refereegranskat)abstract
- Understanding protein functionality is of fundamental importance in biochemistry. Soft X-ray transitions, where the core-level vacancies are filled by the valence-orbital electrons, give direct information about the chemical bonding. Soft X-ray absorption and emission study of poly(dG) -poly(dC) in aqueous solutions can elucidate the relation between the structure and functionality of proteins. We report the N K-edge soft X-ray absorption (XAS) and resonant soft X-ray emission spectroscopy (XES) to characterize the electronic structure near the Fermi level of DNA duplexes to specify the charge migration mechanism. Since N atoms are included in only bases in DNA duplexes, the XES spectra excited from N Is to unoccupied states purely extract the electronic orbital features of the bases in DNA. The fact that N atoms in different bonding environments form well-defined structure has been determined. The experimental findings provide the evidence for the charge-hopping and/or charge-transfer effects in understanding of electric conduction in DNA duplexes when electrons pass through the pi* states of DNA bases.
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| 4. |
- Guo, J.-H., et al.
(författare)
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Molecular structure of alcohol-water mixtures
- 2003
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 91:15
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Tidskriftsartikel (refereegranskat)abstract
- We use x-ray emission spectroscopy to elucidate the molecular structure of liquid methanol, water, and methanol-water solutions. We find that molecules in the pure liquid methanol predominantly persist as hydrogen-bonded chains and rings with six and/or eight molecules of equal abundance. For water-methanol solutions we find evidence of incomplete mixing at the microscopic level. Our results provide a new explanation for a smaller entropy increase in the solution due to water molecules bridging methanol chains to form rings.
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| 5. |
- Guo, J. H., et al.
(författare)
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The molecular structure of alcohol-water mixtures determined by soft-X-ray absorption and emission spectroscopy
- 2004
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 137-40:SI, s. 425-428
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Tidskriftsartikel (refereegranskat)abstract
- We have examined the influence of the intermolecular interaction on the local electronic structure by using X-ray absorption and emission spectra of liquid methanol, water, and their mixtures (in molar ratios of 9:1 and 7:3). We find a strong involvement of hydrogen bonding in the mixing of water and methanol molecules. The local electronic structure of water and methanol clusters, where water cluster is bridging within a 6-member open-ring structured methanol cluster, is separately determined. The experimental findings suggest an incomplete mixing of water-alcohol systems and a strong self- association between methanol chain and water cluster through hydrogen bonding. The enhancement of joint water-methanol open-ring structure owes the explanation to the loss of entropy of the aqueous solutions.
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| 7. |
- Guo, Jinghua, et al.
(författare)
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The interaction of cations and liquid water studied by resonant soft-X-ray absorption and emission spectroscopy
- 2005
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 144-147, s. 287-290
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Tidskriftsartikel (refereegranskat)abstract
- We report the soft-X-ray absorption and emission studies of NaCl, MgCl2, and AlCl3 in water solutions. The influences of cations on the water molecular structure can be seen as the absorption threshold edge shifted to high energy in the X-ray absorption spectra; the mixing of molecular orbital in 3a1 symmetry is reinforced as the intensity of 3a1 is further reduced; and the 1b1-emission peak shows the broadening and shift differently for Na+, Mg2+, and Al3+ water solutions, which indicates that the charge difference of the cations may not be the only playing role being responsible to the interactions between the cations and water molecules.
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| 8. |
- Hellgren, Niklas, et al.
(författare)
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Electronic structure of carbon nitride thin films studied by X-ray spectroscopy techniques
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 471:02-jan, s. 19-34
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Tidskriftsartikel (refereegranskat)abstract
- Magnetron-sputtered carbon nitride thin films with different structures and compositions were analyzed by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), as well as X-ray emission spectroscopy (XES). In all techniques, the carbon spectra are broad and featureless with little variation depending on growth conditions. The nitrogen spectra, on the other hand, show more distinct features, providing a powerful tool for structural characterization. By comparing the experimental spectra with calculations on different model systems, we are able to identify three major bonding structures of the nitrogen-N1: nitrile (C equivalent to N) bonds; N2: Pyridine-like N, i.e., N bonded to two C atoms; and N3: graphite-like N, i.e., N bonded to three C atoms as if substituted in a graphitic network, however, possibly positioned in a pentagon and/or with sp(3) carbon neighbors. The presence of N2 and N3 are best detected by XPS, while N1 is better detected by NEXAFS. The calculated XES spectra also give good indications how valence band spectra should be interpreted. Films grown at the higher temperatures ( greater than or equal to 350 degreesC) show a pronounced angular dependence of the incoming photon beam in NEXATS measurements, which suggests a textured microstructure with standing graphitic basal planes, while amorphous films grown at low temperatures show isotropic properties.
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- Kashtanov, Stepan, et al.
(författare)
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Characterization of aza-fullerene C58N2 isomers by X-ray spectroscopy
- 2003
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 371:02-jan, s. 98-104
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron and near-edge X-ray absorption fine-structure spectra (NEXAFS) of four isomers of C58N2 are predicted by means of density-functional theory calculations. A strong isomer dependence for both types of spectra are found. The spectroscopic findings are discussed in conjunction with results from electronic and geometric structure optimizations.
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| 10. |
- Kashtanov, Stepan, et al.
(författare)
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Chemical and electronic structures of liquid methanol from x-ray emission spectroscopy and density functional theory.
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:10
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Tidskriftsartikel (refereegranskat)abstract
- We have applied x-ray emission spectroscopy and density functional theory (DFT) to study the chemical and electronic structures of liquid methanol. The x-ray emission spectra at carbon and oxygen K edges of methanol in different hydrogen-bonded clusters are simulated. It is shown that hydrogen bonding strongly influences the spectral profile of O K emission, but not the C K emission. The methanol chain and ring conformations show a distinct difference in their electronic structures. The molecular orbitals of chains are strongly localized, whereas for the ring structures they show strong delocalization characteristics and behaviorlike covalent pi orbitals in a conjugated system. A comparison of experimental spectra and DFT calculations suggests that liquid methanol comprises combinations of rings and chains of methanol molecules linked with hydrogen bonds and is dominated by structures with the size of six and eight molecules.
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