Conformation of macromolecules in the gas phase: use of matrix-assisted laser desorption methods in ion chromatography.

Conformational data for macromolecules in the gas phase have been obtained by the coupling of a matrix-assisted laser desorption ion source to an ion chromatograph. A series of polyethylene glycol (PEG) polymers "cationized" (converted to a cation) by sodium ions (Na(+)PEG9 to Na(+)PEG19) and a protonated neurotransmitter protein, bradykinin, were studied. Mobilities of Na(+)PEG9 to Na(+)PEG19 are reported. Detailed modeling of Na(+)PEG9 with molecular mechanics methods indicates that the lowest energy structure has the Na(+) ion "solvated" by the polymer chain with seven oxygen atoms as nearest neighbors. The agreement between the model and experiment is within 1 percent for Na(+)PEG9, Na(+)PEG13, and Na(+)PEG17, giving strong support to both the method and the deduced structures. Similar agreement was obtained in initial studies that modeled experimental data for arginine-protonated bradykinin.