Alex G. Harrison

University of Toronto, Toronto, Ontario, Canada

Are you Alex G. Harrison?

Claim your profile

Publications (155)389.37 Total impact

  • Alex G. Harrison
    International Journal of Mass Spectrometry 04/2014; · 2.14 Impact Factor
  • Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The effect of N-methylation on sequence scrambling in the fragmentation of b5 ions has been investigated by studying a variety of peptides containing sarcosine (N-methylglycine). The product ion mass spectra for the b5 ions derived from Sar-A-A-A-Y-A and Sar-A-A-Y-A-A show only minor signals for non-direct sequence ions the major fragmentation reactions occurring from the unrearranged structures. This is in contrast to the b5 ions where the Sar residue is replaced by Ala and sequence scrambling occurs. The b5 ion derived from Y-Sar-A-A-A-A shows a product ion mass spectrum essentially identical to the spectrum of the b5 ion derived from Sar-A-A-A-Y-A, indicating that in the former case macrocyclization has occurred but the macrocyclic form shows a strong preference to reopen to put the Sar residue in the N-terminal position. Similar results were obtained in the comparison of b5 ions derived from A-Sar-A-A-Y-A and Sar-A-A-Y-A-A. The product ion mass spectra of the MH(+) ions of Y-Sar-A-A-A-A and A-Sar-A-A-Y-A show substantial signals for non-direct sequence ions indicating that fragmentation of the MH(+) ions channels extensively through the respective b5 ions and further fragmentation of these species. Copyright © 2014 John Wiley & Sons, Ltd.
    Biological Mass Spectrometry 02/2014; 49(2):161-7. · 3.41 Impact Factor
  • Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The fragmentation reactions of the MH(+) ions as well as the b7, a7, and a7* ions derived therefrom have been studied in detail for the octapeptides MAAAAAAA, AAMAAAAA, AAAAMAAA, and AAAAAAMA. Ionization was by electrospray using a QqToF mass spectrometer, which allowed a study of the evolution of the fragmentation channels as a function of the collision energy. Not surprisingly, the product ion mass spectra for the b7 ions are independent of the original precursor sequence, indicating macrocyclization and reopening to the same mixture of protonated oxazolones prior to fragmentation. The results show that this sequence scrambling results in a distinct preference to place the Met residue in the C-terminal position of the protonated oxazolones. The a7 and a7* ions also produce product ion mass spectra independent of the original peptide sequence. The results for the a7 ions indicate that fragmentation occurs primarily from an amide structure analogous to that observed for a4 ions (Bythell et al. in J Am Chem Soc 132:14766-14779, 2010). Clearly, the rearrangement reaction they have proposed applies equally well to an ions as large as a7. The major fragmentation modes of the MH(+) ions at low collision energies produce b7, b6, and b5 ions. As the collision energy is increased further fragmentation of these primary products produces, in part, non-direct sequence ions, which become prominent at lower m/z values, particularly for the peptides with the Met residue near the N-terminus.
    Journal of the American Society for Mass Spectrometry 08/2013; · 3.59 Impact Factor
  • Source
    Alex G Harrison, Cagdas Tasoglu, Talat Yalcin
    [Show abstract] [Hide abstract]
    ABSTRACT: The fragmentation reactions of the MH(+) ions of Leu-enkephalin amide and a variety of heptapeptide amides have been studied in detail as a function of collision energy using a QqToF beam type mass spectrometer. The initial fragmentation of the protonated amides involves primarily formation of bn ions, including significant loss of NH3 from the MH(+) ions. Further fragmentation of these bn ions occurs following macrocyclization/ring opening leading in many cases to bn ions with permuted sequences and, thus, to formation of non-direct sequence ions. The importance of these non-direct sequence ions increases markedly with increasing collision energy, making peptide sequence determination difficult, if not impossible, at higher collision energies.
    Journal of the American Society for Mass Spectrometry 08/2013; · 3.59 Impact Factor
  • Source
    Arpád Somogyi, Alex G Harrison, Béla Paizs
    [Show abstract] [Hide abstract]
    ABSTRACT: Middle-sized b ( n ) (n ≥ 5) fragments of protonated peptides undergo selective complex formation with ammonia under experimental conditions typically used to probe hydrogen-deuterium exchange in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Other usual peptide fragments like y, a, a*, etc., and small b ( n ) (n ≤ 4) fragments do not form stable ammonia adducts. We propose that complex formation of b ( n ) ions with ammonia is characteristic to macrocyclic isomers of these fragments. Experiments on a protonated cyclic peptide and N-terminal acetylated peptides fully support this hypothesis; the protonated cyclic peptide does form ammonia adducts while linear b ( n ) ions of acetylated peptides do not undergo complexation. Density functional theory (DFT) calculations on the proton-bound dimers of all-Ala b ( 4 ), b ( 5 ), and b ( 7 ) ions and ammonia indicate that the ionizing proton initially located on the peptide fragment transfers to ammonia upon adduct formation. The ammonium ion is then solvated by N(+)-H…O H-bonds; this stabilization is much stronger for macrocyclic b ( n ) isomers due to the stable cage-like structure formed and entropy effects. The present study demonstrates that gas-phase guest-host chemistry can be used to selectively probe structural features (i.e., macrocyclic or linear) of fragments of protonated peptides. Stable ammonia adducts of b ( 9 ), b ( 9 ) -A, and b ( 9 ) -2A of A(8)YA, and b ( 13 ) of A(20)YVFL are observed indicating that even these large b-type ions form macrocyclic structures.
    Journal of the American Society for Mass Spectrometry 09/2012; · 3.59 Impact Factor
  • Source
    Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The doubly-protonated peptides Ala-Ala-Xaa-Ala-Ala-Ala-Arg show extensive loss of H(2)O when Xaa = Ser or Thr. Using quasi-MS(3) techniques the fragmentation reactions of the [M + 2H - H(2)O](+2) ions have been studied in detail. For both Ser and Thr, the [M + 2H - H(2)O](+2) ions show three primary fragmentation reactions, elimination of CH(3)CH=NH, elimination of one Ala residue, and elimination of two Ala residues, in all cases forming doubly-charged products. From a study of the further fragmentation of these products, it is concluded that elimination of two Ala residues results in formation of a three-membered aziridine ring by interaction with the adjacent amide function as H(2)O is lost. The elimination of one Ala residue results in formation of a five-membered oxazoline ring through interaction with the N-terminal adjacent carbonyl function as H(2)O is lost. The elimination of CH(3)CH=NH appears to involve formation of an eight-membered ring by interaction with the remote N-terminal carbonyl function as H(2)O is lost. However, this initial structure undergoes rearrangement through interaction with the adjacent C-terminal carbonyl function prior to further fragmentation. The [MH - H(2)O](+) ion of Ala-Ala-Ser-Ala-Ala-Ala also shows elimination of CH(3)CH=NH, one Ala residue and two Ala residues.
    Journal of the American Society for Mass Spectrometry 11/2011; 23(1):116-23. · 3.59 Impact Factor
  • Source
    Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: A detailed study has been made of the b(5) and a(5) ions derived from the amides H-Ala-Ala-Ala-Ala-Pro-NH(2), H-Ala-Ala-Ala-Pro-Ala-NH(2), and H-Ala-Ala-Pro-Ala-Ala-NH(2). From quasi-MS(3) experiments it is shown that the product ion mass spectra of the three b(5) ions are essentially identical, indicating macrocyclization/reopening to produce a common mixture of intermediates prior to fragmentation. This is in agreement with numerous recent studies of sequence scrambling in b ions. By contrast, the product ion mass spectra for the a(5) ions show substantial differences, indicating significant differences in the mixture of structures undergoing fragmentation for these three species. The results are interpreted in terms of a mixture of classical substituted iminium ions as well as protonated C-terminal amides formed by cyclization/rearrangement as reported recently for a(4) ions (Bythell, Maître , Paizs, J . Am. Chem. Soc. 2010, 132, 14761-14779). Novel fragment ions observed upon fragmentation of the a(5) ions are protonated H-Pro-NH(2) and H-Pro-Ala-NH(2) which arise by fragmentation of the amides. The observation of these products provides strong experimental evidence for the cyclization/rearrangement reaction to form amides and shows that it also applies to a(5) ions.
    Journal of the American Society for Mass Spectrometry 09/2011; 23(4):594-601. · 3.59 Impact Factor
  • Alex G. Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The fragmentation reactions of the doubly-protonated tryptic-type peptides APAAAAR, AAPAAAR, AAAPAAR and AAAAPAR have been studied using an electrospray/quadrupole/time-of-flight (QqTo F) mass spectrometer. The tendency to cleave amide bonds N-terminal to proline (P) is in competition with the tendency to cleave the second amide bond, counting from the N-terminus; the result of such competition depends on the position of the Pro residue. When the Pro residue is remote from the Arg (R) residue a strong proline effect is observed resulting in formation, to a large extent, of a doubly-charged y species and a neutral fragment, so-called asymmetric amide bond cleavage. By contrast, when the Pro residue approaches the C-terminal Arg residue the proline effect is reduced with respect to cleavage of the second amide bond; in both cases formation of singly-charged y and b ions, so-called symmetric bond cleavage, increases significantly in importance. The results are discussed in terms of relative energetics for symmetric and asymmetric bond cleavage as revealed by approximate proton affinities of the b species and the singly-charged y species.Graphical abstractView high quality image (65K)Research highlights▶ Tryptic-type peptides undergo symmetric or asymmetric amide bond cleavage.. ▶ Competition between cleavage N-terminal to Pro versus cleavage of second amide bond. ▶ Position of Pro residue has major effect on fragmentation modes.
    International Journal of Mass Spectrometry 09/2011; 306:182-186. · 2.14 Impact Factor
  • Alex. G. Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The use of variable low energy collision-induced dissociation to probe the energy dependence of the fragmentation of gaseous anions and, thus, to probe the potential energy surfaces involved, is illustrated using R(CH3)2CO- ions as an example. The fragmentation of proton-bound cluster ions [RO--H--OR’]- is discussed and it is shown that the relative intensities of RO- and R’O- can be related to the relative gas phase acidities of the alcohols ROH and R’OH. The use of both high energy and low energy collisional methods in confirming the structures of gaseous anions and in differentiating isomeric neutral structures is illustrated. It is shown that, for small anions at least, low energy collisional activation provides more certain structural information than high energy collisional activation.
    07/2011: pages 289-313;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The product ion spectra of proline-containing peptides are commonly dominated by y(n) ions generated by cleavage at the N-terminal side of proline residues. This proline effect is investigated in the current work by collision-induced dissociation (CID) of protonated Ala-Ala-Xxx-Pro-Ala (Xxx includes Ala, Ser, Leu, Val, Phe, and Trp) in an electrospray/quadrupole/time-of-flight (QqTOF) mass spectrometer and by quantum chemical calculations on protonated Ala-Ala-Ala-Pro-Ala. The CID spectra of all investigated peptides show a dominant y(2) ion (Pro-Ala sequence). Our computational results show that the proline effect mainly arises from the particularly low threshold energy for the amide bond cleavage N-terminal to the proline residue, and from the high proton affinity of the proline-containing C-terminal fragment produced by this cleavage. These theoretical results are qualitatively supported by the experimentally observed y(2)/b(3) abundance ratios for protonated Ala-Ala-Xxx-Pro-Ala (Xxx = Ala, Ser, Leu, Val, Phe, and Trp). In the post-cleavage phase of fragmentation the N-terminal oxazolone fragment with the Ala-Ala-Xxx sequence and Pro-Ala compete for the ionizing proton for these peptides. As the proton affinity of the oxazolone fragment increases, the y(2)/b(3) abundance ratio decreases.
    Journal of the American Society for Mass Spectrometry 06/2011; 22(6):1032-9. · 3.59 Impact Factor
  • Source
    Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The product ion mass spectra resulting from collisional activation of doubly-protonated tryptic-type peptides Ala-Ala-Xaa-Ala-Ala-Ala-Arg have been determined for Xaa = Ala(A), Ser(S), Val(V), Thr(T), Ile(I), Phe(F), Tyr(Y), Sar, Met(M), Trp(W), Pro(P), and Gln(Q). The major fragmentation reaction involves cleavage of the second amide bond (counting from the N-terminus) except for Xaa = Ser and Thr where elimination of H(2)O from the [M + 2H](+2) ion forms the base peak. In general, the extent of cleavage of the second amide bond shows little dependence on the identity of Xaa and little dependence on whether the bond cleavage involves symmetrical bond cleavage to form a y(5)/b(2) ion pair or asymmetrically to form y (5) (+2) and a neutral b(2) species. Notable exceptions to this generalization occur for Xaa equal to Pro or Sar. For Xaa = Pro only cleavage of the second amide bond is observed, consistent with a pronounced proline effect, i.e., cleavage N-terminal to Pro. When Xaa = Sar considerably enhanced cleavage of the second amide bond also is observed, suggesting that at least part of the proline effect relates to the tertiary nature of the amide nitrogen. In the competition between symmetric and asymmetric bond cleavage an attempt to establish a linear free energy correlation in relating ln(y(5)(+2)/y(5)) to PA(H-Xaa-OH) did not lead to a reasonable correlation although the trend of increasing y(5)(+2)/y(5) ratio with increasing proton affinity of H-Xaa-OH was clear. Proline showed a unique behavior in giving a much higher y(5)(+2)/y(5) ratio than any of the other residues studied.
    Journal of the American Society for Mass Spectrometry 05/2011; 22(5):906-11. · 3.59 Impact Factor
  • Roger S. Mercer, Alex G. Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The collisionally activated dissociation reactions of the C2 to C5 alkoxide ions have been studied for collisons occurring at 8 keV kinetic energy and also over the range 5 to 100 eV kinetic energy. The alkoxide ions fragment by 1,2-elimination of H2 and/or an alkane. Thus, primary alkoxide ions fragment by elimination of H2 only, secondary alkoxide ions show elimination of H2 and alkane molecules, while tertiary alkoxide ions show elimination of alkanes only. In alkane elimination, loss of CH4 is much more facilie than loss of larger alkanes. For secondary alkoxide ions, where more than one elimination reaction occurs, the energy dependence of fragmentation has been explored over the collision energy range 5 to 100 eV. The results are interpreted in terms of a step-wise mechanism involving formation of an anion-carbonyl compound ion-dipole complex, followed by proton abstraction by the H− or alkyl anion leading to the final products. The relative importance of the reaction channels is determined by the relative stabilities of these ion-dipole complexes.
    Canadian Journal of Chemistry 02/2011; 66(11):2947-2953. · 0.96 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The proton-transfer chemical ionization mass spectra of the C3 to C5 monoalkyl amines as well as a number of di- and tri-alkyl amines have been determined using H3+ and (in some cases) HCO+ as protonating agent. The RNH3+ ions fragment to form alkyl ions R+ and eliminate alkenes to form NH4+. In addition, abundant immonium ions are observed in the CI mass spectra corresponding to elimination of alkane from RNH3+ or to direct alkide ion abstraction from RNH2; these ions serve to characterize the alkyl groups attached to the α-carbon atom of the amine. Although alkane elimination from RNH3+ is the thermochemically favoured reaction, only R+ and NH4+ are formed in decomposition of metastable RNH3+ ions. The potential energy profile for fragmentation of i-C3H7NH3+ has been calculated by abinitio molecular orbital methods. These calculations show that CH4 elimination has a large energy barrier additional to the reaction endothermicity while formation of NH4+ has only a small additional barrier and formation of C3H7+ has no barrier additional to the endothermicity. It is concluded that the immonium ions probably arise primarily by direct alkide ion abstraction reactions.
    Canadian Journal of Chemistry 02/2011; 64(8):1652-1660. · 0.96 Impact Factor
  • Eric J. Reiner, Alex. G. Harrison, Richard D. Bowen
    [Show abstract] [Hide abstract]
    ABSTRACT: The collision-induced dissociation (CID) mass spectra of the [MH]+ ions of a variety of C4 to C6 mono-, di-, and tri-alkyl amines have been determined at 8 keV collision energy and also as a function of collision energy over the range 5–100 eV (laboratory scale). The two major primary fragmentation pathways observed following either mode of activation are (i) production of an alkyl cation by expulsion of ammonia or an alkyl amine, and (ii) formation of a smaller protonated amine by loss of an olefin. In addition, alkane elimination from [MH]+, by a variety of pathways, is a common reaction for protonated dialkyl and trialkyl amines, especially in the 8 keV spectra. However, these alkane elimination reactions are of considerably less importance in the low energy CID spectra because they have high onset energies. The differences observed in the spectra produced by the two methods of activation are discussed in terms of the distributions of internal energies deposited in [MH]+ by the collision process. Keywords: protonated amines, collision-induced fragmentation, energy-resolved mass spectrometry.
    Canadian Journal of Chemistry 02/2011; 67(12):2081-2088. · 0.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The MS n spectra of the [M ϩ H] ϩ and b 5 peaks derived from the peptides HAAAAA, AHAAAA, AAHAAA, AAAHAA, and AAAAHA have been measured, as have the spectra of the b 4 ions derived from the first four peptides. The MS 2 spectra of the [M ϩ H] ϩ ions show a substantial series of b n ions with enhanced cleavage at the amide bond C-terminal to His and substantial cleavage at the amide bond N-terminal to His (when there are at least two residues N-terminal to the His residue). There is compelling experimental and theoretical evidence for formation of nondirect sequence ions via cyclization/reopening chemistry in the CID spectra of the b ions when the His residue is near the C-terminus. The experimental evidence is less clear for ions when the His residue is near the N-terminus, although this may be due to the use of multiple alanine residues in the peptide making identifying scrambled peaks more difficult. The product ion mass spectra of the b 4 and b 5 ions from these isomeric peptides with cyclically permuted amino acid sequences are similar, but also show clear differences. This indicates less active cyclization/reopening followed by fragmentation of common structures for b n ions containing His than for sequences of solely aliphatic residues. Despite more energetically favorable cyclization barriers for the b 5 structures, the b 4 ions experimental data show more clear evidence of cyclization and sequence scrambling before fragmentation. For both b 4 and b 5 the energetically most favored structure is a macrocyclic isomer protonated at the His side chain. (J Am Soc Mass Spectrom 2010, 21, 1352–1363) © 2010 American Society for Mass Spectrometry P rotonated or multiply-protonated peptides are routinely sequenced by tandem mass spectrom-etry (MS/MS) [1–3] techniques. Under the predominantly-used, low-energy collisional activation conditions, protonated peptides usually fragment at amide bonds. In the ideal case, such fragmentation [4] only leads to series of direct b and/or y ions [5, 6] which contain the N-and C-terminus, respectively. It is these series of direct b and y ions, which are primarily utilized in bioinformatics algorithms to deduce the sequence information. The generation of nondirect sequence ions [7, 8] may lead to uncertainty in the interpretation of the observed product ion mass spectra. The presence of such ions violates one of the basic assumptions on which most current sequencing algorithms are based; that the primary sequence of the protonated peptide does not change during the MS/MS process. While it is known [9, 10] that y ions are protonated amino acids (y 1) or protonated, truncated peptides (y n , n Ͼ 1), the structures of the b ions present a much more complicated picture [11]. The acylium ion structure was originally proposed [6] for b ions, but extensive studies [11–17] have presented strong evidence that cyclization at the C-terminus to form a protonated oxazolone structure has, in fact, occurred. Quite recently, infrared multiple photon dissociation (IRMPD) [18 –22] and gas-phase H/D exchange (HDX) studies [23] provided experimental evidence for the protonated oxazolone structure for small b n ions (n ϭ 2– 4). Conversely, when a strong nucleophile is present in the peptide, alterna-tive side-chain cyclization reactions involving this nu-cleophile may also occur [4, 24 –31]. Oxazolone ring terminated b n ions dissociate by degradation of their C-termini [13, 32] to form the corresponding a n ion and shorter b i (i Ͻ n) fragments because the oxazolone ring is more labile than backbone amide bonds (the 'oxazolone' rule [33]). While these pathways dominate for small b n ions, this is not the case for larger b fragments where elimination of formally internal residues is often observed [7, 8, 33]. Early studies by Boyd and coworkers [34, 35] reported the formation of such nondirect sequence ions in the frag-mentation of doubly-charged b ions containing lysyl or ornithyl residues. Elimination of the formally internal residues was interpreted in terms of cyclization/re-opening reactions before fragmentation.
    Journal of the American Society for Mass Spectrometry 08/2010; 21:1352–1363. · 3.59 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The MS(n) spectra of the [M + H](+) and b(5) peaks derived from the peptides HAAAAA, AHAAAA, AAHAAA, AAAHAA, and AAAAHA have been measured, as have the spectra of the b(4) ions derived from the first four peptides. The MS(2) spectra of the [M + H](+) ions show a substantial series of b(n) ions with enhanced cleavage at the amide bond C-terminal to His and substantial cleavage at the amide bond N-terminal to His (when there are at least two residues N-terminal to the His residue). There is compelling experimental and theoretical evidence for formation of nondirect sequence ions via cyclization/reopening chemistry in the CID spectra of the b ions when the His residue is near the C-terminus. The experimental evidence is less clear for ions when the His residue is near the N-terminus, although this may be due to the use of multiple alanine residues in the peptide making identifying scrambled peaks more difficult. The product ion mass spectra of the b(4) and b(5) ions from these isomeric peptides with cyclically permuted amino acid sequences are similar, but also show clear differences. This indicates less active cyclization/reopening followed by fragmentation of common structures for b(n) ions containing His than for sequences of solely aliphatic residues. Despite more energetically favorable cyclization barriers for the b(5) structures, the b(4) ions experimental data show more clear evidence of cyclization and sequence scrambling before fragmentation. For both b(4) and b(5) the energetically most favored structure is a macrocyclic isomer protonated at the His side chain.
    Journal of the American Society for Mass Spectrometry 08/2010; 21(8):1352-63. · 3.59 Impact Factor
  • Alex. G. Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 30(20).
  • Source
    Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The collision induced dissociation of doubly-protonated (Ala)(x)His (x = 5, 6, 7, 8, 10) peptides have been studied. The major fragmentation reactions observed are symmetrical amide bond cleavages to give the complementary b(m) and y(N-m) ions, where N is the total number of residues in the peptide. Minor asymmetric cleavage to give doubly-protonated y ions also is observed, involving cleavage near the N-terminus. The shorter peptides (x = 5, 6, 7) show major cleavage of the second amide bond to yield b2 and y(N-2) ions, while (Ala)10His shows major symmetrical cleavage at the fourth and fifth amide bonds. (Ala)8His appears to be a transitional peptide in showing substantial symmetrical cleavage at the second, fourth, and fifth amide bonds. The results are in general agreement with the bifurcating nature of charge separation noted by Zubarev (J. Am. Soc. Mass Spectrom.2008, 19, 1755-1763) from a statistical analysis of a large body of doubly-protonated tryptic peptide CID mass spectra. It is shown that the b2 ion derived from doubly-protonated (Ala)5His has a protonated oxazolone structure.
    Journal of the American Society for Mass Spectrometry 08/2009; 20(10):1890-5. · 3.59 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: When ionized by electrospray from acidic solutions, the tripeptides Pro-His-Xaa (Xaa = Gly, Ala, Leu) form abundant doubly-protonated ions, [M + 2H]2+. Collision-induced dissociation (CID) of these doubly-protonated species results, in part, in formation of b(2)(2+) ions, which fragment further by loss of CO to form a(2)(2+) ions; the latter fragment by loss of CO to form the Pro and His iminium [immonium is commonly used in peptide MS work] ions. Although larger doubly-charged b ions are known, this represents the first detailed study of b(2)(2+) ions in CID of small doubly protonated peptides. The most abundant CID products of the studied doubly-protonated peptides arise mainly in charge separation involving two primary fragmentation channels, formation of the b2/y1 pair and formation of the a1/y2 pair. Combined molecular dynamics and density functional theory calculations are used to gain insight into the structures and fragmentation pathways of doubly-protonated Pro-His-Gly including the energetics of potential protonation sites, backbone cleavages, post-cleavage charge-separation reactions and the isomeric structures of b(2)(2+) ions. Three possible structures are considered for the b(2)(2+) ions: the oxazolone, diketopiperazine, and fused ring isomers. The last is formed by cleavage of the His-Gly amide bond on a pathway that is initiated by nucleophilic attack of one of the His side-chain imidazole nitrogens. Our calculations indicate the b(2)(2+) ion population is dominated by the oxazolone and/or fused ring isomers.
    Journal of the American Society for Mass Spectrometry 08/2009; 20(11):2135-43. · 3.59 Impact Factor
  • Source
    Alex G Harrison
    [Show abstract] [Hide abstract]
    ABSTRACT: The product ion mass spectra obtained by CID of the b(9) ions derived by loss of neutral alanine from the MH+ ion of the peptides Tyr(Ala)9, (Ala)4Tyr(Ala)5, and (Ala)8TyrAla are essentially identical, indicative of full cyclization reaction to a common intermediate before fragmentation. This leads to abundant nondirect sequence ions in the product ion mass spectra of the b9 ions. The product ion mass spectra of the b8 ions from the first two peptides also are essentially identical. The fragmentation of the MH+ ions also leads to low intensity nondirect sequence ions in the product ion mass spectra. N-terminal acetylation blocks the cyclization and eliminates nondirect sequence fragment ions in the product ion mass spectra.
    Journal of the American Society for Mass Spectrometry 08/2009; 20(12):2248-53. · 3.59 Impact Factor

Publication Stats

2k Citations
389.37 Total Impact Points

Institutions

  • 1978–2014
    • University of Toronto
      • Department of Chemistry
      Toronto, Ontario, Canada
  • 2012
    • The University of Arizona
      • Department of Chemistry and Biochemistry (College of Science)
      Tucson, AZ, United States
  • 2004–2011
    • German Cancer Research Center
      • Division of Biophysics of Macromolecules
      Heidelberg, Baden-Wuerttemberg, Germany
  • 2005
    • École Polytechnique Fédérale de Lausanne
      Lausanne, Vaud, Switzerland
  • 2002
    • University of Colorado at Boulder
      • Department of Chemistry and Biochemistry
      Boulder, Colorado, United States
  • 1997
    • University of Akron
      • Department of Chemistry
      Akron, OH, United States
  • 1990
    • Trent University
      • Department of Chemistry
      Peterborough, Ontario, Canada