Alkali metal-mediated proline aggregation in solution observed by coldspray ionization mass spectrometry

L-Proline aggregates to form cyclic clusters in the presence of alkali metal ions in solution, whereas a large-scale-aggregated chain structure was observed for several other amino acids. The major cyclic clusters are suggested to be constructed from trimeric and tetrameric subunits on the basis of direct solution analysis by coldspray ionization mass spectrometry.