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 dimer (G(2)) is 190.1 kcal/mol at 970 K, 4.0 kcal/mol higher than that of glycine (G). The GB of alanine (A) and valine (V) dimers have also been determined; these are 192.4 (At) and 194.4 (V-2) kcal/mol. The GB of mixed dimers is very close to the average of the respective home 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.