title: Ions from Solution to the Gas Phase: A Molecular Dynamics Simulation of the Structural Evolution of Substance P during Desolvation of Charged Nanodroplets Generated by Electrospray Ionization.
abstract: Molecular dynamics (MD) simulations are used to model changes in the conformational preferences of a model peptide during the transition from a hydrated environment (charged nanodroplet generated by electrospray ionization) to the solvent-free peptide ion. The charged droplet consists of ∼2400 water molecules, 22 hydronium ions, and 10 chloride and contains a single Substance P (SP) [SP + 3H]3+ion (SP3+; amino acid sequence RPKPQQFFGLM-NH2). Initially, droplet shrinkage involves a combination of solvent evaporation and ejection of excess charge, primarily hydronium ions. Further droplet shrinkage leads to a series of fission events, which includes the loss of some Cl-ions. SP3+ions adapt to the smaller size droplet through small conformational changes that result in coiling of the hydrophobic C-terminus of the peptide on or near the droplet surface, intramolecular interactions involving the hydrophilic N-terminus of the peptide, and water-mediated interactions between the SP3+ion and H3O+and Cl-ions. Calculated collision cross sections (CCS) for SP3+ions at various stages of desolvation are consistent with the results obtained from cryogenic ion mobility-mass spectrometry (cryo-IM-MS) measurements. Specifically, early in the decay of the charged droplet SP3+ions favor an extended conformation, whereas a compact conformer is favored during the final stages of dehydration.
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Doyong
authors.initials: D
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Nicole
authors.initials: N
authors.lastname: Wagner
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Kerry
authors.initials: K
authors.lastname: Wooding
authors.affiliation: Department of Chemistry, Indiana University , Bloomington, Indiana 47405, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Clemmer
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: David H
authors.identifier: 0000-0003-0830-3914
authors.initials: DH
authors.lastname: Russell