Collision-induced dissociation of polyprotonated oligonucleotides produced by electrospray ionization.
The efficient production of polyprotonated oligonucleotides, studied at n < or = 19, occurs from water/propan-2-ol solutions over an ammonium acetate concentration range between 2.5 and 40 mm and a pH range from 5 to 11. Average charge-state levels observed were approximately half of those found in mass spectra of polyanionic oligonucleotides, reflecting differences in sites of ionization: heterocyclic bases for protonation and phosphodiester backbone for deprotonation. Collision-induced dissociation mass spectra show three principal reaction paths: (1) release of protonated bases, with abundances dictated largely by base proton affinity; (2) phosphodiester chain cleavage at C3'-O3' indicative of sequence in the 3'-->5' direction; and (3) chain cleavage concomitant with base loss giving furan-type ions indicative of sequence in the 5'-->3' direction, analogous to reactions of polyanionic oligonucleotides. Thymine residues undergo very little protonation, resulting in characteristic absence of phosphodiester cleavage on the 3' side of T sites, producing mass-ladder gaps representing dinucleotides.
Ni
J
J
Department of Medicinal Chemistry, University of Utah, Salt Lake City 84112, USA.
Mathews
M A
MA
McCloskey
J A
JA
D000085:Acetates / Q000737:chemistry; D004563:Electrochemistry; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D009841:Oligonucleotides / Q000737:chemistry*; D011522:Protons; D012997:Solvents
D000085:Acetates; D009841:Oligonucleotides; D011522:Protons; D012997:Solvents; C018824:ammonium acetate