Double proton transfer (DPT) reactions in three guanine-guanine (GG) dimers, a guanine-thymine wobble (wGT) base pair, and a model compound 4(3H)-pyrimidinone (k-PP) dimer have been investigated using ab initio MO calculations and liquid-phase infrared (IR) spectroscopy. The calculations suggest that the DPT processes in these dimers are energetically accessible. Temperature-dependent IR measurements of the model compound reveal that slight thermal energy can induce the DPT reaction, and hence the enol tautomer can result. The present study demonstrates a potential pathway for the generation of the mutagenic amino-enol form of guanine. (C) 2008 Elsevier B.V. All rights reserved.