Dynamics of Glycine Dications in the Gas Phase: Ultrafast Intramolecular Hydrogen Migration versus Coulomb Repulsion

2013 ◽  
Vol 4 (22) ◽  
pp. 3903-3909 ◽  
Author(s):  
Sylvain Maclot ◽  
Dariusz Grzegorz Piekarski ◽  
Alicja Domaracka ◽  
Alain Méry ◽  
Violaine Vizcaino ◽  
...  
Keyword(s):  
Gas Phase ◽  
Coulomb Repulsion ◽  
Hydrogen Migration ◽  
Intramolecular Hydrogen

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

Serine–Ca2+ versus serine–Cu2+ complexes — A theoretical perspective

2010 ◽  
Vol 88 (8) ◽  
pp. 759-768 ◽  
Author(s):  
Al Mokhtar Lamsabhi ◽  
Otilia Mó ◽  
Manuel Yáñez
Keyword(s):  
Gas Phase ◽  
Electron Density ◽  
Potential Energy Surfaces ◽  
Metal Ion ◽  
Theoretical Perspective ◽  
Binding Energies ◽  
Interacting Systems ◽  
Intramolecular Hydrogen ◽  
Energy Surfaces ◽  
Doubly Charged

The association of Ca2+ and Cu2+ to serine was investigated by means of B3LYP DFT calculations. The [serine–M]2+ (M = Ca, Cu) potential energy surfaces include, as does the neutral serine, a large number of conformers, in which a drastic reorganization of the electron density of the serine moiety is observed. This leads to significant changes in the number and strength of the intramolecular hydrogen bonds existing in the neutral serine tautomers. In some cases, a proton is transferred from the carboxylic OH group to the amino group and accordingly, some of the more stable [serine–M]2+ complexes can be viewed as the result of the interaction of the zwiterionic form of serine with the doubly charged metal ion. Whereas the interaction between Ca2+ and serine is essentially electrostatic, that between Cu2+ and serine has a non-negligible covalent character, reflected in larger electron densities at the bond critical points between the metal and the base, in the negative values of the electron density between the two interacting systems, and in much larger Cu2+ than Ca2+ binding energies. More importantly, the interaction with Cu2+ is followed by a partial oxidation of the base, which is not observed when the metal ion is Ca2+. The main consequence is that in Cu2+ complexes a significant acidity enhancement of the serine moiety takes place, which strongly favors the deprotonation of the [serine–Cu]2+ complexes. This is not the case for Ca2+ complexes. Thus, [serine–Ca]2+ complexes, like those formed by urea, thiourea, selenourea, or glycine, should be detected in the gas phase. Conversely, the complexes with Cu2+ should deprotonate spontaneously and therefore only [(serine–H)–Cu]+ monocations should be experimentally accessible.

Imaging intramolecular hydrogen migration with time- and momentum-resolved photoelectron diffraction

2021 ◽  
Author(s):  
Fukiko Ota ◽  
Shigeru Abe ◽  
Keisuke Hatada ◽  
Kiyoshi Ueda ◽  
Sergio Díaz-Tendero ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Cross Section ◽  
Time Resolution ◽  
Ultrafast Spectroscopy ◽  
Scattering Cross Section ◽  
Photoelectron Diffraction ◽  
Hydrogen Migration ◽  
Scattering Cross ◽  
Intramolecular Hydrogen

Imaging ultrafast hydrogen migration with few- or sub-femtosecond time resolution is a challenge for ultrafast spectroscopy due to the lightness and small scattering cross section of the moving hydrogen atom....

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