Relative dissociation energies of protonated peptides by electrospray ionization surface induced dissociation

Relative dissociation energies (RDEs) are obtained for the major fragment i ons produced by electrospray ionization/surface-induced dissociation of sin gly protonated triglycine, tetraglycine, leucine enkephalin, and leucine en kephalin arginine. A previously described data analysis method (Lim, H,; et al. J, Phys. Chem, B 1998, 102, 4753) is employed to analyze the energy-re solved mass spectra by subtracting out the distribution of energy transferr ed to the surface, integrating over the distribution of the incident ion en ergy, and taking into account the precursor ion initial internal energy and kinetic energy distributions. These variables are optimized by anchoring t he RDE for the lowest energy fragment of a given precursor ion to its liter ature values and then using these optimized parameters to obtain the other RDEs. The RDEs of the four major fragments of triglycine vary from 2.4 eV f or the ba fragment ion to 6.0 eV for the at ion. The RDEs of the four major fragments of tetraglycine vary from 3.2 eV for the y(2) ion to 5.7 eV for the at ion. The leucine enkephalin RDEs range from 1.1 eV for the be ion to 2.1 eV for the bz ion. The leucine enkephalin arginine RDEs all lay betwee n 2.5 and 3.5 eV,The overall trend of fragmentation order for all peptides is (y(n), b(n)) < a(n) and is consistent with the results from other experi ments. The peptide RDEs presented here are only as accurate as the literatu re values to which they are anchored. Determination of absolute dissociatio n energies from SID data wilt require further refinement of the data analys is method.