OH Hydrogen Abstraction Reactions from Alanine and Glycine: A Quantum Mechanical Approach ANNIA GALANO, 1,3 J. RAÚL ALVAREZ-IDABOY, 2,3 LUIS A. MONTERO, 3 ANNIK VIVIER–BUNGE 1 1 Universidad Autónoma Metropolitana, Iztapalapa, 09340, México D. F., México 2 Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, 07730, México D. F., México 3 Laboratorio de Química Computational y Teórica, Facultad de Química, Universidad de La Habana, La Habana 10400, Cuba Received 19 April 2000; accepted 26 February 2001 ABSTRACT: Density functional theory (B3LYP and BHandHLYP) and unrestricted second-order Møller–Plesset (MP2) calculations have been performed using 3-21G, 6-31G(d,p), and 6-311 G(2d,2p) basis sets, to study the OH hydrogen abstraction reaction from alanine and glycine. The structures of the different stationary points are discussed. Ring-like structures are found for all the transition states. Reaction profiles are modeled including the formation of prereactive complexes, and very low or negative net energy barriers are obtained depending on the method and on the reacting site. ZPE and thermal corrections to the energy for all the species, and BSSE corrections for B3LYP activation energies are included. A complex mechanism involving the formation of a prereactive complex is proposed, and the rate coefficients for the overall reactions are calculated using classical transition state theory. The predicted values of the rate coefficients are 3.54 × 10 8 L · mol -1 · s -1 for glycine and 1.38 × 10 9 L · mol -1 · s -1 for alanine. c  2001 John Wiley & Sons, Inc. J Comput Chem 22: 1138–1153, 2001 Keywords: hydroxyl radical; glycine; alanine; amino acids; abstraction reaction; rate coefficients Correspondence to: J. R. Alvarez-Idaboy; e-mail: jidaboy@ imp.mx Contract/grant sponsors: Cuban Ministerio de Educación Su- perior, the German Academic Exchange Service, and the Third World Academy of Sciences; contract/grant number: 97-144. RG/CHE/LA (TWAS research grant) Contract/grant sponsor: Instituto Mexicano del Petróleo; con- tract/grant number: FIES-95-97-VI Journal of Computational Chemistry, Vol. 22, No. 11, 1138–1153 (2001) c  2001 John Wiley & Sons, Inc.