Browsing by Author "Lin, Yi-Shiue"

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Core Excitation, Specific Dissociation, and the Effect of the Size of Aromatic Molecules Connected to Oxygen: Phenyl Ether and 1,3-Diphenoxybenzene
(2014-09-11)
Lin, Yi-Shiue
;
Lin, Shu-Yu
;
Lee, Yuan T.
;
Tseng, Chien-Ming
;
Ni, Chi-Kung
Near-edge X-ray absorption fine structure (NEXAFS) spectra of phenyl ether at the carbon K-edge and 1,3-diphenoxybenzene at both the carbon and oxygen K-edges were measured in the total ion yield mode using X-rays from a synchrotron and a reflectron time-of-flight mass spectrometer. Time-dependent density functional theory was adopted to calculate the carbon and oxygen K-edge NEXAFS spectra of phenol, phenyl ether, and 1,3-diphenoxybenzene. The assignments and a comparison of the experimental and calculated spectra are presented. The mass spectra of ionic products formed after X-ray absorption at various excitation energies are also reported. Specific dissociations were observed for the 1s --> pi* transition of phenyl ether. In comparison with phenol and phenyl ether, the dependence of the fragmentation on the excitation site and destination state was weak in 1,3-diphenoxybenzene, likely as a result of delocalization of the valence electrons and rapid randomization of energy.
Highly Selective Dissociation of a Peptide Bond Following Excitation of Core Electrons
(2015-06-18)
Lin, Yi-Shiue
;
Tsai, Cheng-Cheng
;
Lin, Huei-Ru
;
Hsieh, Tsung-Lin
;
Chen, Jien-Lian
The controlled breaking of a specific chemical bond with photons in complex molecules remains a major challenge in chemistry. In principle, using the K-edge absorption of a particular atomic element, one might excite selectively a specific atomic entity in a molecule. We report here highly selective dissociation of the peptide bonds in N-methylformamide and N-methylacetamide on tuning the X-ray wavelength to the K-edge absorption of the atoms connected to (or near) the peptide bond. The high selectivity (56-71%) of this cleavage arises from the large energy shift of X-ray absorption, a large overlap of the Is orbital and the valence pi* orbital that is highly localized on a peptide bond with antibonding character, and the relatively low bond energy of the peptide bonds. These characteristics indicate that the high selectivity on bond dissociation following core excitation could be a general feature for molecules containing peptide bonds.
Measurement and prediction of the NEXAFS spectra of pyrimidine and purine and the dissociation following the core excitation
(2015-09-01)
Lin, Yi-Shiue
;
Lin, Huei-Ru
;
Liu, Wei-Lun
;
Lee, Yuan T.
;
Tseng, Chien-Ming
Near-edge X-ray absorption fine structure spectra of pyrimidine and purine at the carbon and nitrogen K-edges were measured using synchrotron radiation and a reflectron time-of-flight mass spectrometer. Spectrum assignments based on the time-dependent density functional theory calculation were presented. From the comparison of the experimental and theoretical results, the nature of various core-excitation transitions and the chemical shifts in the absorption energies were elucidated. The dissociation fragments following the core excitation were analyzed, and the enhancements on the fragment branching ratios were observed. The possible identities and dissociation mechanisms of the major fragments were discussed. (C) 2015 Elsevier By. All rights reserved .
Near-Edge X-ray Absorption Fine Structure Spectra and Site-Selective Dissociation of Phenol
(2014-03-06)
Lin, Yi-Shiue
;
Lu, Kun-Ta
;
Lee, Yuan T.
;
Tseng, Chien-Ming
;
Ni, Chi-Kung
A time-of-flight mass spectrometer with orthogonal acceleration and soft X-rays from synchrotron radiation were utilized to measure near-edge X-ray absorption fine structure (NEXAFS) spectra of carbon and oxygen in phenol and the corresponding ionic fragments following core excitation. The photon energies were in the range of 284-298 eV for the carbon K-edge and 529.5-554.5 eV for the oxygen K-edge. The total ion yield, ion intensity for each ionic fragment, and ion intensity ratio, defined as ion intensity divided by total ion yield, were measured as a function of photon energy. Possible mechanisms of dissociation are proposed and enhancements of specific products of dissociation are reported. In general, the enhancement of these specific products is small in the carbon K-edge region but is clear for some products at the oxygen K-edge. In particular, elimination of the H atom from the hydroxyl group was observed only at the oxygen K-edge. One remarkable result is that an excitation of a core-level electron of oxygen greatly enhanced the cleavage of specific C-C bonds.
Selectivity of peptide bond dissociation on excitation of a core electron: Effects of a phenyl group
(2016-09-01)
Tsai, Cheng-Cheng
;
Chen, Jien-Lian
;
Hu, Wei-Ping
;
Lin, Yi-Shiue
;
Lin, Huei-Ru
The selective dissociation of a peptide bond upon excitation of a core electron in acetanilide and N-benzylacetamide was investigated. The total-ion-yield near-edge X-ray absorption fine structure spectra were recorded and compared with the predictions from time-dependent density functional theory. The branching ratios for the dissociation of a peptide bond are observed as 16-34% which is quite significant. This study explores the core-excitation, the X-ray photodissociation pathways, and the theoretical explanation of the NEXAFS spectra of organic molecules containing both a peptide bond and a phenyl group. (C) 2016 Elsevier B.V. All rights reserved.
Specific dissociation of core-excited pyrimidine nucleobases
(2018-08-16)
Chiang, Yu-Ju
;
Lin, Yi-Shiue
;
Lin, Huei-Ru
;
Liu, Chen-Lin
;
應用化學系
Total-ion-yield near-edge X-ray absorption fine structure spectra of pyrimidine nucleobases were recorded. The phenomenon of specific dissociation, such as a larger branching ratio of some ionic fragments at resonant excitation energies, was observed. From the details of the specific dissociation channels, the larger branching yields at pi*-resonant excitations indicate that local bond cleavages around the atom excited is responsible for producing these ions; local excitation thus plays a major role in the site-specific dissociations. Using the NEXAFS spectra, representative ions and their branching ratios, we propose some improved ways to determine the quantities of pyrimidine nucleobases in DNA and RNA. (C) 2018 Elsevier B.V. All rights reserved.