LAUSR

We report a novel charge inversion ion/ion reaction that converts multiply charged protein cations to multiply charged protein anions via a single ion/ion collision using highly charged anions derived from nano-electrospray ionization (nESI) of hyaluronic acids (HAs). This type of charge inversion reaction is demonstrated with cations derived from cytochrome c, apo-myoglobin, and carbonic anhydrase (CA) cations. For example, the reaction has been demonstrated to convert the [CA+22H]22+ carbonic anhydrase cation to a distribution of anions as high in absolute charge as [CA-19H]19-. Ion/ion reactions involving multiply-charged ions of opposite polarity have previously been observed to result predominantly in the attachment of the reactant ions. All mechanisms for ion/ion charge inversion involving low energy ions proceed via the formation of a long-lived complex. Factors that underlie the charge inversion of protein cations to high anionic charge states in reaction with HA anions are hypothesized to include: i) the relatively high charge densities of the HA anions that facilitate the extraction of multiple protons from the protein leading to multiply-charged protein anions, ii) the relatively high sum of absolute charges of the reactants that leads to high initial energies in the ion/ion complex, and iii) the relatively high charge of the ion/ion complex following the multiple proton transfers that tends to destabilize the complex.