The osmoprotectant 3-dimethylsulfoniopropionate (DMSP) occurs in Gramineae and Compositae, but its synthesis has been studied only in the latter. The DMSP synthesis pathway was therefore investigated in the salt marsh grass Spartina alterniflora Loisel.
The resonance two-photon ionization (R2PI) spectra of the jet-cooled aniline dimers (An-d 0 ) 2 , (An-d 5 ) 2 , and (An-d 7 ) 2 have been recorded; the first 225 cm -1 region above the (An-d 0 ) 2 origin was also reproduced by fluorescence excitation spectroscopy. Relatively sharp structure near the origin of the local excited state is attributed to intermolecular modes, perhaps of multiple conformers. Broader features at higher energies are assigned to symmetric ring modes coupled to an underlying excimer state. The dispersed fluorescence spectrum excited at the dimer electronic origin suggests that excimer formation occurs soon after the local excited state is pumped. Molecular dynamics simulations support the inference from the spectroscopic observations that hydrogen bonding governs the structure of the aniline dimer.
The fragmentation of peptides, to which a positive charge is attached at the N-terminus, was studied by matrix-assisted laser desorption/ionization postsource decay mass spectrometry. In these experiments, the tris[(2,4,6-trimethoxyphenyl)phosphonium] acetyl group is covalently attached. The main advantage of this modification is that the resulting spectra are simplified and the fragment ions observed consist predominantly of a(n)-type ions. We report the results for charge-derivatized peptides formed following enzymatic digestion of phosphoenolpyruvate carboxykinase. Specific fragmentation of bonds within aspargine and threonine residues are observed and are discussed. The understanding of the mechanistic aspects of the fragmentation process is essential to formulate a simple and straightforward mass spectrometric strategy for peptide sequencing using these charged derivatives.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.