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Journal Article 
Thermodynamics and Mechanisms of Protonated Diglycine Decomposition: A Computational Study 
Armentrout, PB; Heaton, AL 
In Press 
American Society for Mass Spectrometry. Journal
ISSN: 1044-0305 
We present a full computational description of the fragmentation reactions of protonated diglycine (H(+)GG). Relaxed potential energy surface scans performed at B3LYP/6-31 G(d) or B3LYP/6-311 + G(d,p) levels are used to map the reaction coordinate surfaces and identify the transition states (TSs) and intermediate reaction species for seven reactions observed experimentally in the succeeding companion paper. All structures are optimized at the B3LYP/6-311 + G(d,p) level, with single point energies of the key optimized structures calculated at B3LYP and MP2(full) levels using a 6-311 + G(2 d,2p) basis set. These theoretical structures and energies are compared with extensive calculations in the literature. Although the pathways elucidated here are generally in agreement with those previously outlined, new details and, for some reactions, lower energy transition states are located. Further, the mechanism for the combined loss of carbon monoxide and ammonia is explored for the first time. 
Diglycine; Protonated peptides; Mechanism; Mobile proton; Theoretical calculations