Collision-induced Dissociation Results Research Articles

Interactions of CyMe4 -BTBP ligand with lanthanides and actinides: Insights from ESI-MS and DFT calculations.

Electrospray Ionization Mass Spectrometry (ESI-MS) technique and density functional theory (DFT) calculations were combined to study the formation of the complexes of lanthanides (Ln = La, Ce, Nd, Sm, Eu, Yb) and actinides (UO2 2+ , Th4+ ) with CyMe4 -BTBP (6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2']bipyridine) to understand the mechanisms during the extraction process. Mass spectrometry titrations showed the formation of the complexation in acetonitrile. For lanthanides, only 1:2 complexes ([Ln(L)2 ]3+ , [Ln(L)2 (CH3 CN)]3+ ), [Ln(L)2 (NO3 )]2+ ) were found at low [Ln]/[L] concentration ratios, whereas the 1:1 complexes ([Ln(L)(NO3 )2 ]+ ) were observed when the [Ln]/[L] concentration ratio reached 1.0. For uranyl complexes, 1:1 complex ([UO2 L(NO3 )]+ ) was the only species within the measuring range. Th4+ complexes had two compositions: 1:1 and 1:2, in which 1:2 species was the dominant complex. Collision-induced dissociation (CID) was employed to characterize the fragmentation process. The fragmentation process was unfolded sequentially on both sides of CyMe4 -BTBP ligand with the loss of alkyl groups and cleavage of triazinyl rings. The CID results of CyMe4 -BTBP complexes revealed a slight difference depending on the metal center. The DFT calculations showed that the stable complexes formed in acetonitrile solution were consistent with the ESI-MS results.

Investigation of protonated base pairs between hypoxanthine and DNA bases by MS and MP2 methods

Hypoxanthine (I) is the nucleobase of inosine. In this work, we employed second-order Møller-Plesset perturbation(MP2) method to investigate the protonation properties of hypoxanthine(I), adenine(A), cytosine (C), guanine (G), and thymine (T). The order of proton affinity is as follows: cytosine (N 3 and O 2 (N 3 ) side) ≈ guanine (N 7 ) > adenine (N 1 ) > hypoxanthine (N 7 ) > thymine(O 4 (N 3 side)). To compare the stability of protonated base pairs between I and DNA bases, we investigated the collision-induced dissociation (CID) behavior of the pairs using tandem mass spectrometry method. And the full geometry optimization has been performed for the studied complexes by the MP2 method. Based on the CID results and calculated structures, the stability of the protonated base pairs in DNA decreased in the following order: (I:A+H) + > (I:C+H) + > (I:G+H) + > (I+H:T) + . We investigated the protonated base pairs between hypoxanthine (I) and DNA bases using CID and MP2 methods. The results show that the order of the binding strength of protonated base pairs is (I:C+H) + ˃ (I:A+H) + ˃ (I:G+H) + ˃ (I+H:T) + . If we consider the double helix structure of DNA and the binding effect of the skeleton, the stability order of protonated base pairs in DNA is (I:A+H) + > (I:C+H) + > (I:G+H) + > (I+H:T) + .

Gas-Phase Complexes of Americium and Lanthanides with a Bis-triazinyl Pyridine: Reactivity and Bonding of Archetypes for F-Element Separations.

Bis-triazinyl pyridines (BTPs) exhibit solution selectivity for trivalent americium over lanthanides (Ln), the origins of which remain uncertain. Here, electrospray ionization was used to generate gas-phase complexes [ML3]3+, where M = La, Lu, or Am and L is EtBTP 2,6-bis(5,6-diethyl-1,2,4-triazin-3-yl)-pyridine. Collision-induced dissociation (CID) of [ML3]3+ in the presence of H2O yielded a protonated ligand [L(H)]+ and hydroxide [ML2(OH)]2+ or hydrate [ML(L-H)(H2O)]2+, where (L-H)- is a deprotonated ligand. Although solution affinities indicate stronger binding of BTPs toward Am3+ versus Ln3+, the observed CID process is contrastingly more facile for M = Am versus Ln. To understand the disparity, density functional theory was employed to compute potential energy surfaces for two possible CID processes, for M = La and Am. In accordance with the CID results, both the rate determining transition state barrier and the net energy are lower for [AmL3]3+ versus [LaL3]3+ and for both product isomers, [ML2(OH)]2+ and [ML(L-H)(H2O)]2+. More facile removal of a ligand from [AmL3]3+ by CID does not necessarily contradict stronger Am3+-L binding, as inferred from solution behavior. In particular, the formation of new bonds in the products can distort kinetics and thermodynamics expected for simple bond cleavage reactions. In addition to correctly predicting the seemingly anomalous CID behavior, the computational results indicate greater participation of Am 5f versus La 4f orbitals in metal-ligand bonding.

Coordination Structure and Fragmentation Chemistry of the Tripositive Lanthanide-Thio-Diglycolamide Complexes.

Tripositive Ln(TMTDA)33+ complexes (Ln = La-Lu except Pm, TMTDA = tetramethyl 3-thio-diglycolamide) were observed in the gas phase by electrospray ionization of LnCl3 and TMTDA mixtures. Collision-induced dissociation (CID) was employed to investigate their fragmentation chemistry, which revealed the influence of metal center as well as ligand on the ligated complexes. Ln(TMTDA)2(TMTDA-45)3+ resulting from Ccarbonyl-N bond cleavage of TMTDA and hydrogen transfer was the major CID product for all Ln(TMTDA)33+ except Eu(TMTDA)33+, which predominantly formed charge-reducing product EuII(TMTDA)22+ via electron transfer from TMTDA to Eu3+. Density functional theory calculations on the structure of La(TMTDA)33+ and Lu(TMTDA)33+ revealed that Ln3+ was coordinated by six Ocarbonyl atoms from three neutral TMTDA ligands, and both complexes possessed C3h symmetry. The Sether atom deviating from the ligand plane was not coordinated to the metal center. On the basis of the CID results of Ln(TMTDA)33+, Ln(TMGA)33+, and Ln(TMOGA)33+, the fragmentation chemistry associated with the ligand depends on the coordination mode, while the redox chemistry of these tripositive ions is related to the nature of both metal centers and diamide ligands.

Electrospray production and collisional dissociation of lanthanide/methylsulfonyl anion complexes: Sulfur dioxide anion as a ligand

Gas-phase lanthanide-SO2 complexes, Ln(CH3SO2)3(SO2)−, were produced by collision induced dissociation (CID) of Ln(CH3SO2)4− precursors prepared by electrospray ionization. For all lanthanides except Eu, CID of Ln(CH3SO2)4− resulted in CH3 loss to form Ln(CH3SO2)3(SO2)−, which spontaneously react with O2 to form Ln(CH3SO2)3(O2)−. CID of Eu(CH3SO2)4− produced only Eu(CH3SO2)3−, with reduction from Eu(III) to Eu(II). For Ln=Yb and Sm, the Ln(CH3SO2)4− underwent neutral ligand loss to form Ln(CH3SO2)3−, which reacted with O2 to yield Ln(CH3SO2)3(O2)−, recovering the Ln(III) oxidation state. The CID results show parallels to condensed-phase Ln3+/Ln2+ redox chemistry. Density functional theory (DFT) calculations on Ln(CH3SO2)3(SO2)− for Ln=La, Yb and Lu reveal that SO2 acts as a bidentate oxygen bound ligand for doublet ground-state La(CH3SO2)3(SO2)− and Lu(CH3SO2)3(SO2)−, while the ground state for Yb(CH3SO2)3(SO2)− is an open-shell singlet with a monodentate SO2 ligand. Loss of CH3 is computed to be much more favorable than neutral ligand loss for La(CH3SO2)4− and Lu(CH3SO2)4−, whereas both channels are comparable in energy for Yb(CH3SO2)4−, in accord with the experiments. DFT results for fragmentation of Cu(CH3SO2)2− reveal that formation of the organometallic complex, Cu(CH3SO2)(CH3)−, is energetically most favorable, in agreement with contrasting fragmentation pathways of copper and lanthanide complexes.

Tandem mass spectrometric analysis and density functional theory calculations on the fragmentation behavior of two tetradecanoylingenol regioisomers from Euphorbia wallichii

Two structurally similar bioactive regioisomers, 3-O-tetradecanoylingenol and 20-O-tetradecanoylingenol, from Euphorbia wallichii presented quite different fragmentation behaviors. Revealing the related fragmentation pathways may improve the efficiency of characterization and identification of such type of compounds. The two regioisomers were subjected to collision-induced dissociation (CID) on Finnigan LCQ(DECA) and LTQ Orbitrap XL instruments. Based on the CID results, the possible fragmentation pathways were proposed and investigated with density functional theory (DFT) calculations. Elimination of C(14)H(28)O(2) (tetradecanoic acid) for 3-O-tetradecanoylingenol and the sequential losses of C(4)H(8) (butylene) for 20-O-tetradecanoylingenol were observed in ESI-MS/MS, witnessed also by HR-ESI-MS/MS. The fragmentation pathways were proposed and verified by calculating the activation energy of their transition states by DFT calculations. Based on the observations, fragmentation pathways for the two regioisomers were proposed and verified by calculating the energy of the reactants, products and the corresponding transition states using DFT. This report should have value in rapid identification of the derivatives of ingenol and other regioisomers in natural products.

Proteome Analysis of Sorangium cellulosum Employing 2D-HPLC-MS/MS and Improved Database Searching Strategies for CID and ETD Fragment Spectra

Shotgun proteome analysis of the myxobacterial model strain for secondary metabolite biosynthesis Sorangium cellulosum was performed employing off-line two-dimensional high-pH reversed-phase HPLC x low-pH ion-pair reversed-phase HPLC and dual tandem mass spectrometry with collision-induced dissociation (CID) and electron transfer dissociation (ETD) as complementary fragmentation techniques. Peptide identification using database searching was optimized for ETD fragment spectra to obtain the maximum number of identifications at equivalent false discovery rates (1.0%) in the evaluation of both fragmentation techniques. In the database search of the CID MS/MS data, the mass tolerance was set to the well-established 0.3 Da window, whereas for ETD data, it was widened to 1.1 Da to account for hydrogen-rearrangement in the radical-intermediate of the peptide precursor ion. To achieve a false discovery rate comparable to the CID results, we increased the significance threshold for peptide identification to 0.001 for the ETD data. The ETD based analysis yielded about 74% of all peptides and about 78% of all proteins compared to the CID-method. In the combined data set, 952 proteins of S. cellulosum were confidently identified by at least two peptides per protein, facilitating the study of the function of regulatory proteins in the social myxobacteria and their role in secondary metabolism.

Metal-Mediated Formation of Gas-Phase Amino Acid Radical Cations,

The results from an investigation of the collision-induced dissociation (CID) of the ternary complexes [Cu(II)(terpy)(AA)](2+) are presented (terpy = 2,2':6',2' '-terpyridine; AA = one of the twenty common amino acids). These complexes show a rich gas-phase chemistry, which depends on the identity of the amino acid. For the histidine-, lysine- and tryptophan-containing complexes, oxidative dissociation of the amino acid is observed, yielding the amino acid radical cation. The results of further mass selection and CID of these amino acid radical cations are presented. The CID of the series [Fe(III)(salen)(AA)](+) (where salen = N,N'-ethylenebis(salicylideneaminato)) is also examined. These complexes undergo loss of the neutral amino acid in all cases, although the radical cation of arginine is also produced and its subsequent fragmentation examined. B3-LYP/6-31G(d) computations were carried out to test aspects of the proposed fragmentation mechanism of the histidine and arginine radical cations.

Substituent effect on ion–molecule reaction of disubstituted benzenes with acetone plasma

We investigated the ion–molecule reactions of disubstituted benzenes with acetone or acetone-d 6 as reagent gases under chemical ionization conditions, and the fragmentation reactions of the adduct ions (mostly acetyl ion and protonated acetone adducts) using collision-induced dissociation (CID) technique. The CID results of [M+A dD] + ions of phenylamine derivatives suggest that the phenylamine derivatives have higher proton affinities than acetone. Our experiments also suggest: (1) electron-releasing substituents favor the adduct reactions, while electron-withdrawing groups do not; (2) the position and properties of substituting groups have an effect on the relative abundances of the adduct ions; (3) the fragmentation reaction of the acetyl adduct ion formed by the reaction of ortho-phenylenediamine with acetyl ion is similar to the reductive alkylation reaction in the liquid phase.

Practical considerations when using radio frequency-only quadrupole ion guide for atmospheric pressure ionization sources with time-of-flight mass spectrometry.

Construction details and performance evaluation of a radio frequency (rf)-only quadrupole ion guide for use with an electrospray ionization time-of-flight mass spectrometer is presented in this paper. Angiotensin III and cytochrome c were used in these experiments to investigate the ion transmission properties of the rf-only quadrupole for different m/z species. In addition, influence of ion kinetic energies along with the characteristic fragmentation due to collision induced dissociation (CID) were studied. These experiments demonstrate that the transmissions of different m/z ions were not only dependent on the frequency and magnitude of the rf waveform, which is similar to a high vacuum rf-only quadrupole ion guide, but also on the pressure inside the quadrupole chamber. For the pressure range tested, low m/z ions are better focused with increasing pressure. As expected, transmission of ions are subject to space charge limitations when significant numbers of ions are focused on the axis of the quadrupole. It is also observed that CID results are related to transverse motion and longitude motion of ions inside the quadrupole region. Consequently, CID is useful for fragmentation of linear peptides and it is not effective (in present configuration) for large bulky proteins. The kinetic energy of ions that enter the repelling region of the TOFMS is ultimately determined by the ensemble effect resulting from the dc bias potential of the quadrupole (the dominant factor), skimmer-2, pressure inside the quadrupole chamber, and jet expansion. While this system is tested with an ESI source, the operational principle and design criteria are directly applicable for improving other atmospheric pressure ionization sources with time-of-flight mass analyzers such as an inductively coupled plasma ion source.

Gas phase conformations of synthetic polymers: poly (methyl methacrylate) oligomers cationized by sodium ions

Gas phase conformations of a series of poly(methyl methacrylate) (PMMA) oligomers cationized by sodium ions were investigated experimentally and theoretically. Ion chromatography and molecular mechanics methods were used to measure the cross sections of Na +(PMMA)3 to Na +(PMMA)11 (i.e. from the 3-mer to the 11-mer). Collision induced dissociation (CID) of Na +(PMMA)10 is also reported. The dominant fragment peaks in the CID spectrum are solely in the low mass-to-charge range and correspond to the loss of 1–2 monomer units from each end of the oligomer. The fragments also retain the Na + ion indicating that the ion interacts with both ends of PMMA. Molecular modeling of the Na +(PMMA) oligomers support this finding. The calculations show that the lowest energy structures are U-shaped with Na + bound to multiple carbonyl oxygen atoms near both ends of the oligomer. The cross sections of these structures agree with those obtained from the ion chromatography experiments. Ion chromatography and molecular dynamics simulations also show that the cross sections are independent of temperature between 300 and 600 K, further supporting the indication that the Na + ion strongly binds to both ends of the oligomer. A mechanism for the surprising CID results is suggested.

A study of the dissociation of CH3CH2SH+ by collisional activation: Evidence of nonstatistical behavior

The absolute total cross sections for CH3CH2+, C2H4+, C2H3+, CH3+, CH2SH+(CH3S+), CH2S+(HCSH+), CHS+(CSH+), and H2S+ produced by the collision-induced dissociation (CID) reaction of CH3CH2SH++Ar have been measured in the center-of-mass collision energy (Ec.m.) range of 1–42 eV. Using the charge transfer probing technique, we found that the mass 47 product ions have overwhelmingly the CH2SH+ structure. The onsets for CH3CH2+, C2H4+, C2H3+, CH2SH+, H2S+, and CH3+ are consistent with their corresponding thermochemical thresholds. The formation of the higher energy channels CH3CH2++SH and CH3+CH2SH+, which involve the C–S and C–C bond scissions, are found to dominate in the entire Ec.m. range. The lower energy channel corresponding to the formation of CH3CHSH++H is not found. The strong preference observed for the formation of the higher energy channels is in accord with the conclusion obtained in the recent CID study of CH3SH+, providing evidence that the CID of CH3CH2SH+ is also nonstatistical. The high yields of CH3CH2++SH and CH2SH++CH3 are attributed to the more efficient translational to vibrational energy transfer for the low frequencies C–S and C–C stretching modes than for the high frequencies C–H and S–H stretching modes, along with the weak couplings between these low and high frequencies vibrational modes of CH3CH2SH+. The relative abundances of product ions formed by the single-photon ionization of CH3CH2SH were also measured for comparison with the CID results. The CH3CHSH++H channel is observed in the photoionization of CH3CH2SH. Similar to the finding in the photoionization of CH3SH, the relative abundances of fragment ions formed in the photoionization of CH3CH2SH are in qualitative accord with statistical predictions. To rationalize the dissociation mechanisms of CH3CH2SH+, we have also performed ab initio calculations to locate the possible transition structures for the observed dissociation channels.

Collision-induced dissociation and post-source decay of model dodecapeptide ions containing lysine and glycine

Collision-induced dissociation (CID) and post-source decay (PSD) of a series of model dodecapeptide ions have been studied by ESI-FT-ICR and MALDI-TOF, respectively. Low-energy CID of quadruply protonated peptide ions, [M + 4H] 4+, where M = (KGG) 4, (K 2G 4) 2, and K 4G 8, was conducted under both on-resonance irradiation and sustained off-resonance irradiation (SORI) conditions. The fragmentation patterns observed were very sequence dependent. For (KGG) 4, the major product ions involved y-cleavages occurring on the C-terminal side of the lysine residues. These dissociation sites and the corresponding charge states of the product ions can be explained on the basis of the four protons being primarily localized on lysine residues. For (K 2G 4) 2, both y and b series ions were observed as dissociation products. The observation of b ions in the vicinity of the C-terminus is not consistent with the model of protons being localized on lysine residues. The data suggest that, during the CID process, protons may migrate to the less basic C-terminal glycine residue in order to minimize Coulomb repulsion. This is also supported by CID studies of K 4G 8 where the major dissociation products are b type ions formed from cleavages near the C-terminus. In contrast with the CID results, PSD of [M + H] + from all three peptides leads to formation of almost complete series of y and b type ions, with cleavages at the lysine residues often being most prominent. In summary, it was found that low-energy CID of [M + 4H] 4+ in an ESI-FT-ICR yielded pronounced cleavages at the basic lysine residues, which may provide information about the number and locations of basic residues; however, PSD of [M + H] + in a MALDI-TOF provided a wider range of fragment ions that should prove useful in peptide sequencing.

On the structures and fragmentation of [Me 2S∵SMe 2] + and [Et 2S∵SEt 2] +: Tandem mass spectrometry metastable and collision-induced dissociation results

An experimental study of the metastable and collision-induced dissociation (CID) spectra of [Me2S∵SMe2]+ and [Et2S∵SEt2]+ has been carried out. These ions are examples of species that contain two-center-three-electron (2c–3e) sulfur-sulfur bonds. The metastable and CID spectra provide experimental evidence of the atomic connectivity and of the 2c–3e bonds. The metastable cleavage of the S∵S 2c–3e bonds appears to occur with no reverse activation barriers and to result in small average kinetic energy releases. Fragmentation of the same bonds by CID results in the most intense product for both ions. Comparisons with the metastable and CID spectra of [MeSSMe]+, an ion with a two-center-two-electron (2c–2e) sulfur-sulfur bond, are made and strongly support the difference in the sulfur-sulfur bonding.

NO(X 2Π) product state distributions in molecule–surface collision-induced dissociation: Direct inelastic scattering of n,i-C3F7NO from MgO(100) at Eincident≤7.0 eV

Molecule–surface collision-induced dissociation (CID) has been studied for n-C3F7NO and i-C3F7NO molecular beams scattered from MgO(100) at incident kinetic energies (Eincident) up to 7 eV. The NO fragment was detected state selectively using two-photon, two-frequency ionization, and rotational and spin–orbit distributions are reported for several Eincident values. State and angle-resolved signals were integrated to give CID yields, which increased sharply with Eincident . In most cases, rotational excitation could be described by separate temperatures for each spin–orbit state. The upper 2∏3/2 state was underpopulated relative to statistical predictions (e.g., for n-C3F7NO at Eincident =5.0 eV, the spin–orbit temperature was ∼170 K, while Trot was ∼500 K). The CID results are compared to NO state distributions derived from the photodissociation of expansion-cooled molecules under collision-free conditions, at different energies (E°) above D0. These distributions were measured for both n-C3F7NO and i-C3F7NO up to E°∼4500 cm−1, and rotational excitation within each spin–orbit state was statistical, except at E°≥3000 cm−1. As with CID, a low [2∏3/2]/[2∏1/2] ratio was observed, and the reaction mechanism is probably unimolecular decomposition via the lowest triplet surface T1 with little or no exit channel barrier. The pronounced similarities between the CID and photodissociation results suggest that common reaction mechanisms may be operative. All of the CID results are compatible with direct inelastic scattering followed by unimolecular reaction on the S0 and/or T1 potential surfaces.

Some gas-phase ion–molecule reactions of acetone

Photoionization of acetone is used to produce the ground electronic state molecular ion with little internal or translational energy. Ion–molecule reactions occurring under thermal energy conditions lead to the formation of the proton bound dimer of acetone at mTorr pressures, the rate constant of which reaction has been measured. The structures of various reactant and product ions are investigated using collision-induced dissociation (CID) reactions at collision energies up to 15 eV. These low-energy CID results are compared with 8 keV CID structures obtained using a conventional high-pressure double-focussing mass spectrometer.

Energy transfer in collisional activation. Energy dependence of the fragmentation of n-alkylbenzene molecular ions

n-Alkylbenzene molecular ions, C 6H 5CH 2R +·, show two major fragmentation routes, reactions (1) and (2). C 6H 5CH 2R +· → C 7H 7 ++R · → C 7H 8 + +(R-H) Using charge exchange mass spectrometry, the C 7H 7 +/C 7H 8 +· ratio was found to increase from 0 at ∼ 2 eV internal energy to values ranging from ∼ 8 (R = C 3H 7) to ∼ 2 (R = C 7H 15) at ∼ 7 eV internal energy of the fragmenting C 6H 5CH 2R +· ions. The low energy (tandem quadrupole) collision-induced dissociation (CID) of C 6H 5CH 2R +· ions show increasing C 7H 7 +/C 7H 8 +· ratios with increasing ion kinetic energy but reach plateau values, dependent on the identity of R, at ∼ 60 eV collision energy using N 2 and Ar collision gases. From a comparison of the CID and charge exchange results, the average kinetic energy transformed into internal energy on collision is evaluated. The energy transfer efficiency is high (33–87%) and increases with increasing degrees of vibrational freedom in the ion. These results are consistent with the formation of a collision complex between the ion and the neutral species in which the relative translational energy is converted into vibrational energy of the complex. The high energy (8 keV) CID of the alkylbenzene molecular ions shows that the average energy transfer is in the range 4.5–6.7 eV, again increasing with increasing size of the alkylbenzene.