Gas‐phase basicities of some amino acid dimers

This paper gives the first demonstration that the kinetic method can be used to determine molecular pair thermochemical values. Fragmentation of proton‐bound trimers is used to determine the gas‐phase basicities (GB) of molecular dimers (the so‐called molecular‐pair gas‐phase basicities). The set of equations necessary for data evaluation, i.e. extension of the so‐called kinetic method, is discussed. Proton‐bound amino acid trimers have been studied as examples. The GB of glycine dimers (G 2 ) is 190.1 kcal/mol at 970 K, 4.0kcal/mol higher than that of glycine (G). The GB of alanine (A) and valine (V) dimers have also been determined; these are 192.4 (A 2 ) and 194.4 (V 2 ) kcal/mol. The GB of mixed dimers is very close to the average of the respective homo dimers, 191.4 (GA); 192.0 (GV) and 193.2 (AV) kcal/mol. Experimental errors in the relative GB values of various dimers are estimated to be less than 0.3 kcal/mol.