Oxidation Dynamics of Methionine with Singlet Oxygen: Effects of Methionine Ionization and Microsolvation
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- 作者：Fangwei Liu ; Jianbo Liu
- 刊名：Journal of Physical Chemistry B
- 出版年：2015
- 出版时间：June 25, 2015
- 年：2015
- 卷：119
- 期：25
- 页码：8001-8012
- 全文大小：706K
- ISSN：1520-5207
文摘
We report an in-depth study on the gas-phase reactions of singlet O2[a1螖g] with methionine (Met) at different ionization and hydration states (including deprotonated [Met 鈥?H]鈭?/sup>, hydrated deprotonated [Met 鈥?H]鈭?/sup>(H2O)1,2, and hydrated protonated MetH+(H2O)1,2), using guided-ion-beam scattering mass spectrometry. The measurements include the effects of collision energy (Ecol) on reaction cross sections over a center-of-mass Ecol range from 0.05 to 1.0 eV. The aim of this study is to probe the influences of Met ionization and hydration on its oxidation mechanism and dynamics. Density functional theory calculations, Rice-Ramsperger-Kassel-Marcus modeling, and quasi-classical, direct dynamics trajectory simulations were performed to examine the properties of various complexes and transition states that might be important along reaction coordinates, probe reaction potential energy surfaces, and to establish the atomic-level mechanism for the Met oxidation process. No oxidation products were observed for the reaction of [Met 鈥?H]鈭?/sup> with 1O2 due to the high-energy barriers located in the product channels for this system. However, this nonreactive property was altered by the microsolvation of [Met 鈥?H]鈭?/sup>; as a result, hydroperoxides were captured as the oxidation products for [Met 鈥?H]鈭?/sup>(H2O)1,2 + 1O2. For the reaction of MetH+(H2O)1,2 + 1O2, besides formation of hydroperoxides, an H2O2 elimination channel was observed. The latter channel is similar to what was found in the reaction of dehydrated MetH+ with 1O2 (J. Phys. Chem. B 2011, 115, 2671). The reactions of hydrated protonated and deprotonated Met are all inhibited by Ecol, becoming negligible at Ecol 鈮?0.5 eV. The kinetic and dynamical consequences of microsolvation on Met oxidation and their biological implications are discussed.