Dynamic paths between neutral alanine-water and zwitterionic alanine-water clusters: single, double and triple proton transfer

Computations are presented for the alanine-(H2O)(n) (n = 1-3) and its zwitterion-(H2O)(n) clusters. We find that at least two water molecules need to bind to alanine to give stable alanine zwitterion-water cluster. Structures of the conformers are predicted, and their relative energies are compared. Detailed analysis is presented on the dynamic (proton transfer) pathways between the neutral alanine-(H2O)(n) and the zwitterionic alanine-(H2O)(n) (n = 2, 3) clusters, including the structures of the transition states. A variety of proton transfer pathways are predicted between alanine-(H2O)(n) and the zwitterion-(H2O)(n) clusters, depending on their structures: direct proton transfer, concerted double and triple proton transfer mechanism. (C) 2003 Elsevier Science B.V. All rights reserved.