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The effects of the identity and position of basic residues on peptide dissociation were explored in the positive and negative modes. Low-energy collision-induced dissociation (CID) was performed on singly protonated and deprotonated heptapeptides of the type: XAAAAAA, AAAXAAA, AAAAAXA and AAAAAAX, where X is arginine (R), lysine (K) or histidine (H) residues and A is alanine. For [M + H](+), the CID spectra are dominated by cleavages adjacent to the basic residues and the majority of the product ions contain the basic residues. The order of a basic residue's influence on fragmentation of [M + H](+) is arginine > histidine approximately lysine, which is also the order of decreasing gas-phase basicity for these amino acids. These results are consistent with the side chains of basic residues being positive ion charge sites and with the more basic arginine residues having a higher retention (i.e. sequestering) of the positive charge. In contrast, for [M-H](-) the identity and position of basic residues has almost no effect on backbone fragmentation. This is consistent with basic residues not being negative mode charge sites. For these peptides, more complete series of backbone fragments, which are important in the sequencing of unknowns, can be found in the negative mode. Spectra at both polarities contain C-terminal y-ions, but y(n)''(+) has two more hydrogens than the corresponding y(n)(-). Another major difference is the production of the N-terminal backbone series b(n)(+) in the positive mode and c(n)(-) in the negative mode. Thus, comparison of positive and negative ion spectra with an emphasis on searching for pairs of ions that differ by 2 Da (y(n)''(+) vs y(n)(-)) and by 15 Da (b(n)(+) vs c(n)(-)) may be a useful method for determining whether a product ion is generated from the C-terminal or the N-terminal end of a peptide. In addition, a characteristic elimination of NH=C=NH from arginine residues is observed for deprotonated peptides.

The formation of the nitrogen heterofullerene, C59N, following the ablation of a variety of fullerene derivatives, all of which possess organic ligands bound to the carbon cage through a nitrogen atom, has been investigated utilizing laser desorption/ionization mass spectrometry. Investigating the formation of cationic and anionic C59N+/-, this approach is found to be a new and very efficient way to implement the initially exohedral nitrogen atom into the carbon cage. The laser-induced heterofullerene formation is discussed in terms of the structure and the charge state dependency of the target material. In further experiments, the coalescence reactivity, leading toward the formation of larger clusters has been examined following laser ablation of thin films of the (C59N)2 dimer. Coalescence leads to two major reaction products, consisting of larger C n - 1N+ clusters which retain the nitrogen atom networked into a larger carbon cage and pure C n + (n = even) carbon clusters. The C n - 1N+ cluster formation is accompanied by abundant metastable transitions caused by the loss of CN and the resulting implications for the coalescence mechanism are discussed. Finally, evidence is presented for the delayed electron emission of C59N·. The observation of delayed ionization of heterofullerenes is unprecedented, revealing a similar resistance toward fragmentation as in the case of their all-carbon fullerene analogues.