title: Structures, fragmentation, and protonation of trideoxynucleotide CCC mono- and dianions.
abstract: Both quantum chemical calculations and ESI mass spectrometry are used here to explore the gas-phase structures, energies, and stabilities against collision-induced dissociation of a relatively small model DNA molecule--a trideoxynucleotide with the sequence CCC, in its singly and doubly deprotonated forms, (CCC-H)(-) and (CCC-2H)(2-), respectively. Also, the gas-phase reactivity of these two anions was measured with HBr, a potential proton donor, using an ESI/SIFT/QqQ instrument. The computational results provide insight into the gas-phase structures of the electrosprayed (CCC-2H)(2-) and (CCC-H)(-) anions and the neutral CCC, as well as the proton affinities of the di- and monoanions. The dianion (CCC-2H)(2-) was found to dissociate upon CID by charge separation via two competing channels: separation into deprotonated cytosine (C-H)(-) and (CCC-(C-H)-2H)(-), and by w(1)(-)/a(2)(-) cleavage of the backbone. The monoanion (CCC-H)(-) loses a neutral cytosine upon CID, and an H/D-exchangeable proton, presumably residing on one of the phosphate groups, is transferred to the partially liberated (C-H)(-) before dissociation. This was confirmed by MS/MS experiments with the deuterated analog. The reaction of (CCC-2H)(2-) with HBr was observed to be rapid, k=(1.4+/-0.4) x 10(-9) cm(3) molecule(-1) s(-1), and to proceed both by addition (78%) and by proton transfer (22%) while (CCC-H)(-) reacts only by HBr addition, k=(7.1+/-2.1) x 10(-10) cm(3) molecule(-1) s(-1). This is in accord with the computed proton affinities of (CCC-2H)(2-) and (CCC-H)(-) anions that bracket the known proton affinity of Br(-).
authors.affiliation: Department of Chemistry and Centre for Research in Mass Spectrometry, York University, Toronto, Ontario, Canada.
authors.forename: Janna
authors.initials: J
authors.lastname: Anichina
authors.forename: Stefan
authors.initials: S
authors.lastname: Feil
authors.forename: Einar
authors.initials: E
authors.lastname: Uggerud
authors.forename: Diethard K
authors.initials: DK
authors.lastname: Bohme
mesh_terms: D003062:Codon / Q000737:chemistry*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry*; D011392:Proline / Q000737:chemistry; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D003062:Codon; D009838:Oligodeoxyribonucleotides; D011522:Protons; D011392:Proline