Partitioning of kinetic energy to internal energy in the low energy collision-induced dissociations of proton-bound dimers of polypeptides

Collision-induced dissociation (CID) of the proton-bound dimers of a set of pentapeptides (leucine enkephalin analogs) generated by electrospray ioniz ation is studied as a function of collision energy under conditions of sing le collisions with argon, As the collision energy is increased, the abundan ces of the two protonated peptides become more similar, indicating an incre ase in internal energy deposition, The effective temperature (T-eff) of the cluster ions is calculated by the kinetic method and found to increase app roximately linearly with collision energy. Knowing the fragmentation thermo chemistry, the ion internal energy is characterized using the kinetic metho d. The partitioning quotient for the conversion of laboratory kinetic energ y into internal energy for these cluster ions is 2% to 5% in the 50 eV to 2 00 eV collision energy range. Average relative standard deviations of multi ple measurements of partitioning quotients are around 15% and are mainly du e to uncertainties in ion abundance ratios. Unimolecular dissociation Rice- Ramsperger-Kassel-Marcus (RRKM) theory is used to calculate the relationshi p between the fragment ion abundance ratio and the total internal energy of the cluster ions. Comparison of these data with experiment allows the ener gy partitioning behavior to be characterized independently and more accurat ely. The partitioning quotient obtained in this way ranges from 2 +/- 1.0% (uncertainty is the standard derivation of multiple measurements) to 5 +/- 1.0%. These data are consistent with either an impulsive collisional activa tion mechanism or with collision complex formation. (Int J Mass Spectrom 18 5/186/187 (1999) 75-90) (C) 1999 Elsevier Science B.V.