Electrospray ionization of large multiply charged species proceeds via Dole's charged residue mechanism

The maximum charge z(max) on a variety of electrospray ions of globular pro teins retaining their native structure, as well as naturally compact starbu rst dendrimers is compared to the Rayleigh charge z(R) (based on a water sp here with the ion mass). For most published data examined, z(max) is betwee n 65% and 110% of Z(R), providing strong support in favor of Dole's charged residue mechanism, at least for masses from 3.3 kD up to 1.4 MD. Other lar ge but less compact ions from proteins and linear chains of polyethylene gl ycols (PEGs) have z(max) values considerably larger than z(R), apparently i mplying that they also form as charged residues, though from non-spherical drops held together by the polymer backbone. (C)2000 Elsevier Science B.V. All rights reserved.