Theoretical study of the interaction between cytosine and hydrogen peroxide

Theoretical calculation was performed to study the solvent effect for the 1,2-hydrogen shift from hydrogen peroxide (H2O2) (1) to water oxide (O-OH2) (2). Stationary points including transition structures (TSs) were optimized with no geometrical constraint at Becke3LYP/6-311++G** level. All stationary points were tested by frequency analysis and IRC calculation. The activation energies (ΔE[Formula: see text]) and heats of reaction (ΔH0) were evaluated at Becke3LYP/6-311++G**//Becke3LYP/6-311++G** level of theory. The following points were clarified: (i) inclusion of polarization function (*) and diffusion function (+) for calculation hardly affected the energetic of the reaction; (ii) judging from the change of ΔE[Formula: see text] and ΔH0 values, the reaction is predicted to be accelerated by the increase of involving H2O; (iii) proton-relaying mechanism considerably reduced ΔE[Formula: see text] values; (iv) the endothermicity became monotonically small as the number of solvating H2O molecules increased. The calculation suggests that the formation of water oxide (O-OH2) (2) from H2O2 (1) is promoted by a proton-relaying pathway in protic media (such as H2O).Key words: theoretical calculation, ab initio, transition structure, 1,2-hydrogen shift, water oxide.

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On the Importance of Water Molecules in the Theoretical Study of Polyphenols Reactivity toward Superoxide Anion

Journal of Theoretical Chemistry ◽

10.1155/2014/740205 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

Laure Lespade

Keyword(s):

Hydrogen Peroxide ◽

Superoxide Anion ◽

Fruits And Vegetables ◽

Theoretical Study ◽

Radical Scavenging ◽

Aerobic Condition ◽

Human Organism ◽

Radical Scavenger ◽

Water Molecules ◽

Pathological State

Numerous studies have shown the benefits of a diet rich in fruits and vegetables. These benefits are partly due to the radical scavenging properties of polyphenols contained in fruits and vegetables since polyphenols can fight against an excess of radicals which goes along inflammation in a certain number of diseases. This pathological state, called oxidative stress, results from the aerobic condition of human organism when OH radical, hydrogen peroxide, superoxide anion, or peroxynitrite is produced in excess. If hydrogen peroxide is easily handled by human defense against radicals, the other radicals can cause damage to biological constituents like lipids, cell membranes, and other biomolecules. This paper is devoted to the theoretical study of the interaction of superoxide anion (O2•-) with a very potent radical scavenger, 1,2,4,6,8-pentahydroxynaphthalene. The importance of hydration of superoxide radical for the reactivity is analyzed. Potential energy surfaces (PES) are calculated for different number of water molecules around the radical and it is shown that the transition barrier vanishes when complete hydration with six water molecules is explicitly handled. The nature of the reactivity is determined by using the natural bond orbital (NBO) analysis.

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