Resumo

GALANO, Annia; ALVAREZ-IDABOY, J. Raúl; AGACINO, Esther  e  RUIZ-SANTOYO, Ma. Esther. Quantum Mechanical Approach to Leucine + OH Gas Phase Reaction: Mechanism and Kinetics. Rev. Soc. Quím. Méx [online]. 2004, vol.48, n.2, pp.139-145. ISSN 0583-7693.

The gas phase OH hydrogen abstraction reaction from leucine has been studied using Density Functional Theory (B3LYP) calculations and the 6-311G(d,p) basis set. The structures of the different stationary points are discussed. Reaction profiles are modeled including the formation of pre-reactive complexes, and negative net activation energy is obtained for the overall reaction. BSSE corrections are included. A complex mechanism is proposed, and the rate coefficients are calculated using Transition State Theory over the temperature range 250 - 350 K. The rate coefficients are proposed for the first time and it was found that in the gas phase the hydrogen abstraction occurs almost exclusively from the gamma site. The following expressions, in L⋅mol^-1⋅s^-1, are obtained for the alpha and gamma H-abstraction channels, and for the overall temperature dependent rate constants, respectively: k_α = (2.19 ± 0.05) x 10⁷ exp[(905 ± 12)/T], k_γ = (3.19 ± 0.05) x 10⁷ exp[(2450 ± 10)/T], and k_tot = (3.80 ± 0.08) x 10⁷ exp[(2378 ± 12)/T].

Palavras-chave : leucine; OH radical; H abstraction; rate; mechanism.

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