Mechanism and rate coefficients of the gas phase OH hydrogen abstraction reaction from asparagine:: a quantum mechanical approach

Unrestricted density functional theory (B3LYP) calculations have been performed using the 6-311G(d,p) basis sets, to study the gas phase OH hydrogen abstraction reaction from asparagine. The structures of the different stationary points are discussed. Ring-like structures are found for the transition states. Reaction profiles are modeled including the formation of pre-reactive complexes, and negative net energy barriers are obtained. A complex mechanism involving the formation of a pre-reactive complex is proposed, and the rate coefficients are calculated using Conventional transition state theory over the temperature range 250-350 K. ZPE and thermal corrections to the energy for all the species, and BSSE corrections for the pre-reactive complex stabilization and for the energy barriers are included. The rate coefficients are proposed for the first time and it was found that the hydrogen abstraction occurs almost exclusively from the beta site. The following expressions, in L mol(-1) s(-1), are obtained for the alpha channel, beta channel and the overall temperature dependent rate constants: k(alpha) = (1.46 +/- 0.04) X 10(8) exp[(-1217 +/- 7)/T], k(beta) = (5.48 +/- 0.25) X 10(7) exp[(1483 +/- 13)/T], and k = (5.50 +/- 0.25) X 10(7) exp[(1482 +/- 13)/T], respectively. (C) 2002 Elsevier Science B.V. All rights reserved.