Gas-phase deprotonation and hydrogen/deuterium (H/D) exchange reactions for ions from three model dodecapeptides were studied by Fourier transform ion cyclotron resonance mass spectrometry. Molecular dynamics calculations were employed to provide information on conformations and Coulomb energies. The peptides, (KGG)4, (K2G4)2, and K4G8, each contain four high basicity lysine residues and eight low basicity glycine residues; however, in the present work only three lysine residues were protonated. Proton transfer reactions with a series of reference amines revealed apparent gas-phase acidities in a narrow range of 207. 3–209. 6 kcal/mol, with deprotonation efficiencies following the order [K4G8+3H]3+ > [(KGG)4+3H]3+ > [(K2G4)2+3H]3+. The three ions also react similarly with d4-methanol: each exchanged a maximum of 23–25 of their 25 labile hydrogens, with the first 15–17 exchanges occurring at rate constants of (1. 6–2. 6) × 10?11 cm3 molecule?1 s?1. The experimental results agree with molecular modeling findings of similar conformations and Coulomb energies for the three peptide ions. The [M+3H]3+ data are compared to data obtained previously in our laboratory for the “fully” protonated [M+4H]4+ (Zhang, X.; Ewing, N. P.; Cassady, C. J. Int. J. Mass Spectrom. Ion Phys., in press). For (KGG)4 and (K2G4)2, there is a marked difference in H/D exchange reactivity between 3+ ions and 4+ ions. The 4+ ions, which have diffuse conformations, slowly exchange only 14 hydrogens, whereas their more compact 3+ counterparts exchange 23–25 hydrogens at a 5-times greater rate. In contrast, the 3+ and 4+ ions of K4G8 have similar compact conformations and exchange reactivity. The results indicate that a multiply hydrogen-bonded intermediate between the deuterating reagent and the peptide ion is necessary for facile H/D exchange. The slower, incomplete H/D exchange of [(KGG)4+4H]4+ and [(K2G4)2+4H]4+ is attributed to the inability of their protonated lysine n-butylamino groups (which extend away from the peptide backbone) to form this intermediate. 相似文献
In this study, we systematically investigated gas-phase fragmentation behavior of [M + nH + OH]n•+ ions formed from peptides containing intra-molecular disulfide bond. Backbone fragmentation and radical initiated neutral
losses were observed as the two competing processes upon low energy collision-induced dissociation (CID). Their relative contribution
was found to be affected by the charge state (n) of [M + nH + OH]n•+ ions and the means for activation, i.e., beam-type CID or ion trap CID. Radical initiated neutral losses were promoted in
ion-trap CID and for lower charge states where mobile protons were limited. Beam-type CID and dissociation of higher charge
states of [M + nH + OH]n•+ ions generally gave abundant backbone fragmentation, which was highly desirable for characterizing peptides containing disulfide
bonds. The amount of sequence information obtained from CID of [M + nH + OH]n•+ ions was compared with that from CID of disulfide bond reduced peptides. For the 11 peptides studied herein, similar extent
of sequence information was obtained from these two methods. 相似文献
The gas-phase H/D exchange of bradykinin [M + H]+, [M + Na]+, [M + 2H]2+, and [M + H + Na]2+ ions; des-Arg1-bradykinin, des-Arg9-bradykinin, and bradykinin fragment 2-7 [M + H]+ ions; and O-methylbradykinin [M + H]+ and [M + 2H]2+ ions with D2O have been examined by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry at 9.4 T. The different peptides vary widely in exchange rate and extent of deuterium incorporation. H/D exchange was slowest and deuterium incorporation was least for bradykinin [M + H]+, [M + H + Na]2+ and bradykinin methyl ester [M + 2H]2+ ions. In contrast, H/D exchange and extent of deuteration are higher for des-Arg1-bradykinin, des-Arg9-bradykinin, and bradykinin fragment 2-7 [M + H]+ ions; and highest for bradykinin [M + Na]+ and [M + 2H]2+, and O-methylbradykinin [M + H]+. Because the most likely site of protonation is the guanidino group of arginine, the above reactivity pattern strongly supports a zwitterion form for protonated gas-phase bradykinin. 相似文献
The gas-phase H/D exchange reactions of arginine (R) and arginine-containing di- and tri-peptide (gly-arg (GR), arg-gly (RG), gly-gly-arg (GGR), gly-arg-gly (GRG) and arg-gly-gly (RGG)) [M+H]+ ions with deuterated ammonia (ND3) were investigated by using Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR), ion mobility-mass spectrometry
(IM-MS), ab initio and density functional theory-based molecular orbital calculations and molecular modeling. Three exchanges are observed for
arginine and arginine-containing tri-peptide [M+H]+ ions, whereas the di-peptide [M+H]+ ions undergo a single H/D exchange. In addition, C-terminal methylation blocks H/D exchange of arginine and the arginine-containing
peptide [M+H]+ ions, and a single H/D exchange is observed for N-terminal acetylated arginine [M+H]+ ions. A general mechanism for H/D exchange involving a collision complex that is best described as a “solvated salt-bridge”
structure is proposed. 相似文献
Gas-phase hydrogen/deuterium exchange of D2O with [M+H]+ ions of angiotensin II, angiotensin I, [Sar1]-angiotensin II, bradykinin, des-Arg1-bradykinin, des-Arg9-bradykinin, luteinizing hormone releasing hormone (LH-RH), and substance P has been examined by Fourier transform ion cyclotron resonance mass spectrometry at 9.4 tesla. Because the FTICR dynamic range increases quadratically with magnetic field, parent ions from a mixture of several peptides may be confined simultaneously for long periods at high pressure (e. g., 1 h at 1×10?5 torr) without quadrupolar axialization (and its attendant ion heating), for faster data acquisition and better controlled comparisons between different peptides. A high magnetic field also facilitates stored waveform inverse Fourier transform (SWIFT) isolation of monoisotopic [M+H]+ parent ions, so that deuterium incorporation patterns may be determined directly without the need for isotopic distribution deconvolution. Finally, a higher magnetic field provides for a greatly extending trapping period, for measurement of much slower rates. Angiotensin I, angiotensin II, and [Sar1]-angiotensin II are found to undergo a rapid exchange. Angiotensin II and [Sar1]-angiotensin II exhibit multiple deuterium uptake distributions, corresponding to multiple gas-phase conformations. In contrast, substance P exchanges slowly and LH-RH displays no observable exchange. Comparison of the relative H/D exchange rates for bradykinin and its des-Arg-derivatives supports the hypothesis that bradykinin adopts a folded gas-phase conformation that unfolds upon removal of either terminal arginine residue. 相似文献
A novel mass spectrometer with the capability of ion manipulation and enrichment was developed to perform gas‐phase ion/ion reactions followed by product ions accumulation. The development of this apparatus opens opportunities for more complex sequences of ion manipulations, thus offers the potential on extensive application involving ion/ion reaction. Here, cleavage of disulfide bond in peptide was demonstrated based upon this ion manipulation and enrichment mass spectrometer. Two typical peptides including S‐glutathionylated ARACAKA with an intermolecular disulfide bond, and oxytocin with an intramolecular disulfide bond were chosen as typical samples to demonstrate the ability of the apparatus. After ion/ion reaction between selected peptide cations and periodate ions (IO4?), two kinds of product ions (eg, [M + O + H]+ and [M + H + Na + IO4]+) were enriched with a number of accumulation events. Afterwards, the enriched ions were subjected to activation, and the disulfide bond cleavage was clearly observed from the tandem mass spectra. These results illustrate the potential of this apparatus for ion manipulation performing ion/ion reaction, and low abundance product ion enrichment. 相似文献
The use of 5-aminosalicylic acid (5-ASA) as a new matrix for in-source decay (ISD) of peptides including mono- and di-phosphorylated
peptides in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is described. The use of 5-ASA in MALDI-ISD
has been evaluated from several standpoints: hydrogen-donating ability, the outstanding sharpness of molecular and fragment
ion peaks, and the presence of interference peaks such as metastable peaks and multiply charged ions. The hydrogen-donating
ability of several matrices such as α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (2,5-DHB), 1,5-diaminonaphthalene
(1,5-DAN), sinapinic acid (SA), and 5-ASA was evaluated by using the peak abundance of a reduction product [M + 2H + H]+ to that of non-reduced protonated molecule [M + H]+ of the cyclic peptide vasopressin which contains a disulfide bond (S-S). The order of hydrogendonating ability was 1,5-DAN
> 5-ASA > 2,5-DHB > SA = CHCA. The chemicals 1,5-DAN and 5-ASA in particular can be classified as reductive matrices. 5-ASA
gave peaks with higher sharpness for protonated molecules and fragment ions than other matrices and did not give any interference
peaks such as multiply-protonated ions and metastable ions in the ISD mass spectra of the peptides used. Particularly, 1,5-DAN
and 5-ASA gave very little metastable peaks. This indicates that 1,5-DAN and 5-ASA are more “cool” than other matrices. The
1,5-DAN and 5-ASA can therefore be termed “reductive cool” matrix. Further, it was confirmed that ISD phenomena such as N-Cα
bond cleavage and reduction of S-S bond is a single event in the ion source. The characteristic fragmentations, which form
a− and (a + 2)-series ions, [M + H − 15]+, [M + H − 28]+, and [M + H − 44]+ ions in the MALDI-ISD are described. 相似文献
The collision-induced decompositions of the [M – H]? and [M + Li]+ ions of a few dinucleoside phenylphosphonates were studied using fast atom bombardment and linked scanning at constant B/E. Deprotonation takes place on the base or sugar moieties. The [M – H]? ion decomposes mainly by cleavage on either side of the phosphonate linkage, leading to the formation of mononucleotide fragment ions and also by cleavage of the basesugar bond. Rupture of the 3′-phosphonate bond is preferred. Unlike the normal charged nucleotides, these neutral nucleotides do not eliminate a neutral base from the [M – H]? ion. However, the mononucleotide fragment ions which can have the charge on the phosphorus oxygen eliminate neutral bases by charge-remote fragmentation. The 4,4′-dimethoxytrityl (DMT)-protected nucleotides show the additional fragmentation of loss of DMT. Li+ attachment can occur at several sites in the molecule. As observed for the [M – H]? ion, the major cleavage occurs on either side of the phosphonate bond in the fully deprotected nucleotides, cleavage of the ester bond on C(3′) being preferred. Cleavage of the 5′-phosphonate bond is not observed in the DMT-protected nucleotides. Many of the fragmentations observed can be explained as arising from charge-remote reactions. 相似文献
Protonated nitroarginine, [RNO2 + H]+, which contains the nitroguanidine ‘explosophore,’ undergoes homolytic N – N nitro-imine bond cleavage to expel NO2? and form a radical cation of arginine in high yield (100 % relative abundance) upon low-energy collision-induced dissociation (CID). Other ionization states of nitroarginine, including [RNO2 - H]–, and a fixed-charge derivative of nitroarginine do not expel NO2? (<1 %), but instead dissociate via heterolytic bond cleavage with abundant losses of small molecules (N2O and H2N2O2) from the nitroguanidine group. The effects of proton mobility on the CID reactions of nitroarginine containing peptides was investigated for peptide derivatives of leucine enkephalin, including XYGGFLRNO2, X = D, G, K, and R, by examining the different protonation states: [M – H]–; [M + H]+; and [M + 2H]2+. For [M + H]+ containing the less basic N-terminal residues (X = D, G) and all [M + 2H]2+, mobile proton fragmentation reactions that result in peptide sequence ions dominate. In contrast, for peptides containing the basic N-terminal residues (R and K), the CID spectra of both the [M – H]– and [M + H]+ are dominated by the losses of small even-electron neutrals from the nitroarginine side-chain. The fraction of nitroguanidine directed fragmentation of the nitroarginine side chain that results in bond homolysis to form [XYGGFLR]+? by expulsion of NO2? increases by more than 10 times as the protonation state changes from [M – H]– (<10 %) to [M + 2H]2+ (ca. 90 %) and by about four times as the acidity of the [M + H]+N-terminal residue increases from R (19.0 %) to D (76.5 %). These results indicate that protonated peptides containing nitroarginine can undergo non-canonical mobile proton triggered radical fragmentation.
The role that a metal ion can have in promoting disulfide bond cleavage has been assessed by surveying the tandem mass spectra of the following metal complexes of model peptides containing an intermolecular disulfide bond: [M--H+Cu(II)](+); [M--H+Cu(II)(bipy)](+); [M+Ag(I)](+); and [M+Au(I)(PMe(3))](+). In comparison to previously studied protonated peptides, these binary and ternary metal complexes generally yield more abundant S--S and/or C--S bond cleavage. In general, [M--H+Cu(II)](+) ions cleave the adjacent C--S bond more readily, while the [M+Au(I)(PMe(3))](+) ion cleaves the S--S bond more readily. The ternary metal complex [M--H+Cu(II)(bipy)](+), on the other hand, fragments by exclusive loss of the bipyridyl ligand for the larger model peptides studied. Of all coinage metal systems studied, Me(3)PAu(+) is superior in promoting disulfide bond cleavage. 相似文献
Multiply-charged peptide cations comprised of two polypeptide chains (designated A and B) bound via a disulfide linkage have been reacted with SO2-* in an electrodynamic ion trap mass spectrometer. These reactions proceed through both proton transfer (without dissociation) and electron transfer (with and without dissociation). Electron transfer reactions are shown to give rise to cleavage along the peptide backbone, loss of neutral molecules, and cleavage of the cystine bond. Disulfide bond cleavage is the preferred dissociation channel and both Chain A (or B)-S* and Chain A (or B)-SH fragment ions are observed, similar to those observed with electron capture dissociation (ECD) of disulfide-bound peptides. Electron transfer without dissociation produces [M + 2H]+* ions, which appear to be less kinetically stable than the proton transfer [M + H]+ product. When subjected to collision-induced dissociation (CID), the [M + 2H]+* ions fragment to give products that were also observed as dissociation products during the electron transfer reaction. However, not all dissociation channels noted in the electron transfer reaction were observed in the CID of the [M + 2H]+* ions. The charge state of the peptide has a significant effect on both the extent of electron transfer dissociation observed and the variety of dissociation products, with higher charge states giving more of each. 相似文献
Functional group interactions have been observed to affect gas-phase ion-molecule chemistry in a quadrupole ion trap mass spectrometer. Gas-phase methylation and collisionactivated dissociation reactions of a series of related acids and esters allows an evaluation of the structural factors that influence reactivity and functional group interactions of these compounds. Examination of the [M+H]+ or [M+15]+ product ions by collision-activated dissociation has provided insight into the conformations from which diacids and diesters undergo electrophilic addition. Collision-activated dissociation has provided not only more detailed information on the structures of the ions, but also the data necessary for confident mechanistic interpretation. Labeling studies were done to probe fragmentation pathways. Upon activation of the [M+CD3]+ products of dimethyl maleate and dimethyl succinate, formed from reaction of the neutrals with CD3OCD2+ ions, a rapid interfunctional group methyl transfer causes scrambling of the methyls prior to elimination of dimethyl ether or methanol. The [M+15]+ ions of dimethyl maleate are believed to lose dimethyl ether through a rate-determining 1,6-methyl transfer, whereas the [M+15]+ ions of dimethyl succinate eliminate methanol through a rate-determining 1,5-proton transfer. 相似文献
The gas-phase chemistry of anionic [M + Cat2+ – 3H]? complexes between Ca2+-specific peptides and the alkaline earth metal ions Mg2+, Ca2+ and Ba2+ is reported. The metal ion complexes were studied using fast atom bombardment, collision-induced decomposition (CID) and molecular mechanical calculations. The CID reactions and molecular mechanical calculations revealed that the Ca2+–peptide complexes are bound differently to the Mg2+– and Ba2+–peptide complexes and that the intrinsic (gas-phase) chemistry is reflected by known aqueousphase chemistry. 相似文献
Electrospray ionization (ESI) on mixtures of acidic fibrinopeptide B and two peptide analogs with trivalent lanthanide salts generates [M + Met + H]4+, [M + Met]3+, and [M + Met –H]2+, where M = peptide and Met = metal (except radioactive promethium). These ions undergo extensive and highly efficient electron transfer dissociation (ETD) to form metallated and non-metallated c- and z-ions. All metal adducted product ions contain at least two acidic sites, which suggest attachment of the lanthanide cation at the side chains of one or more acidic residues. The three peptides undergo similar fragmentation. ETD on [M + Met + H]4+ leads to cleavage at every residue; the presence of both a metal ion and an extra proton is very effective in promoting sequence-informative fragmentation. Backbone dissociation of [M + Met]3+ is also extensive, although cleavage does not always occur between adjacent glutamic acid residues. For [M + Met – H ]2+, a more limited range of product ions form. All lanthanide metal peptide complexes display similar fragmentation except for europium (Eu). ETD on [M + Eu – H]2+ and [M + Eu]3+ yields a limited amount of peptide backbone cleavage; however, [M + Eu + H]4+ dissociates extensively with cleavage at every residue. With the exception of the results for Eu(III), metallated peptide ion formation by ESI, ETD fragmentation efficiencies, and product ion formation are unaffected by the identity of the lanthanide cation. Adduction with trivalent lanthanide metal ions is a promising tool for sequence analysis of acidic peptides by ETD.
The gas phase H/D exchange reactions of bradykinin (M + 3H)3+ ions with D2O and DI were monitored in a quadrupole ion trap mass spectrometer. The H/D exchange kinetics of both chemical probes (D2O and DI) indicate the presence of two noninterconverting reactive gas phase ion populations of bradykinin (M + 3H)3+ at room temperature. The H/D exchange involving DI, however, generally proceeds faster than that involving D2O. The rate observations described here can be rationalized on the basis of the "relay mechanism" (see Campbell et al. J. Am. Chem. Soc. 1995, 117, 12840-12854) recently proposed to account for H/D exchange between D2O and gaseous protonated polypeptides. The higher exchange rate with DI is believed to arise primarily as a result of its lower gas-phase acidity relative to that of D2O and, secondarily, as a result of the longer bond length of DI relative to that of OD in D2O. 相似文献
Matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) and theoretical calculations
[density functional theory (DFT)] were utilized to investigate the influence of cysteine side chain on Cu+ binding to peptides and how Cu+ ions competitively interact with cysteine (−SH/SO3H) versus arginine. Results from theoretical and experimental (fragmentation reactions) studies on [M+Cu]+ and [M+2Cu−H]+ ions suggest that cysteine side chains (−SH) and cysteic acid (−SO3H) are important Cu+ ligands. For example, we show that Cu+ ions are competitively coordinated to the −SH or SO3H groups; however, we also present evidence that the proton of the SH/SO3H group is mobile and can be transferred to the arginine guanidine group. For [M+2Cu−H]+ ions, deprotonation of the −SH/SO3H group is energetically more favorable than that of the carboxyl group, and the resulting thiolate/sulfonate group plays
an important role in the coordination structure of [M+2Cu−H]+ ions, as well as the fragmentation patterns. 相似文献