Gas-phase clustering of protonated amino acids with acetonitrile

The gas-phase clustering reactions of protonated amino acids, AAH+ (AA = Ala, Val, Ser, Phe, Pro, Gln, Lys and Arg) with acetonitrile were studied with a pulsed ion-beam high-pressure mass spectrometer. The bond energies of the AAH+·(CH3CN) complexes range from 20 to 11 kcal/mol. While for AlaH+, ValH+, SerH+, PheH+, ProH+ and GlnH+, the solvation free energies decrease linearly with increasing gas-phase basicity of AA, deviations from the correlation are observed for LysH+ and ArgH+. The bonding free energies for AAH+·(CH3CN) are compared with those for AAH+·(H2O) and AAH+·(NH3).