Rate coefficients and mechanism of the gas phase OH hydrogen abstraction reaction from serine: a quantum mechanical approach

Unrestricted density functional theory (B3LYP) calculations have been performed using the 6-311G(d,p) basis sets, to study the hydrogen abstraction from serine by OH in the gas phase. 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 activation energies are obtained, after including basis set superposition error corrections. 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. The rate coefficients are proposed for the first time. The following expressions, in L mol(-1) s(-1), are found for the alpha channel, beta channel and the overall temperature-dependent rate coefficients: k(alpha) = (2.76 +/- 0.08) X 10(8) exp[(1389 +/- 8)/T], k(beta) = (1.26 +/- 0.07) X 10(8) exp[(1524 +/- 17)/T] and k(tot) = (3.91 +/- 0.17) X 10(8) exp[(1446 +/- 12)/T], respectively. (C) 2003 Elsevier B.V. All rights reserved.