The precision of mass measurements in a Penning trap is directly proportional to an ion's charge state and can be increased by using highly charged ions (HCI) from an Electron Beam Ion Trap (EBIT). By bombarding the injected and trapped singly charged ions with an intense electron beam, the charge state of the ions is rapidly increased. To use this method for short-lived isotopes, very high electron beam current densities are required of the TITAN EBIT, built and commissioned at the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany and transported to TRIUMF for the TITAN on-line facility. This EBIT has produced charge states as high as Kr34+ and Ba54+ with electron beams of up to 500 mA and 27 keV. Once the EBIT is operational at full capacity (5 A, 60 keV), most species can be bred into a He-like configuration within tens of ms.

Cytochrome P450 (CYP) family 4 constitutes monoxygenases responsible for hydroxylation of fatty acids and other lipids. For example, CYP4F3 metabolizes leukotrienes and CYP4F8 prostaglandin H. Importantly, six of the twelve CYP4 enzymes are orphans, i.e., with an unknown biological function. The catalytic activity of the enzyme CYP4F8 is known in seminal vesicles, but not in skin or psoriatic lesions, where CYP4F8 is highly expressed. The orphan CYP4F22 is also expressed in skin, and mutations in its gene has been linked to the rare skin disease lamellar ichthyosis, together with, inter alia, mutations in the genes of 12R-LOX and eLOX3. These enzymes appear to constitute a pathway producing hydroperoxides and epoxyalcohols from arachidonic acid. CYP4F22 is hypothesized to act in a consecutive step within this pathway. The aim of this thesis was to develop analytical methods to prepare and analyze hydroperoxides and epoxyalcohols derived from fatty acids by LC-MS/MS, and to investigate the catalytic performance of CYP4F8 and CYP4F22 for these substrates. The 12R-hydroperoxide of arachidonic acid (12R-HPETE) was prepared by autoxidation and separated from other hydroperoxides by chiral HPLC. MS/MS analysis showed that the hydroperoxides were unstable within the ion trap, but were stabilized by an increase in the isolation width. From the hydroperoxides, epoxyalcohols were generated by hematin treatment, and separated by normal phase HPLC. MS/MS spectra of several epoxyalcohols, derived both from arachidonic acid and linoleic acid, were characterized with aid of [2H]isotopomers and MS3 analysis. Apart from metabolic studies the thesis also include detailed information on MS/MS analysis of several oxygenated fatty acids, with proposed fragmentation mechanisms. The open reading frame of CYP4F22 was expressed in a recombinant yeast system, and LC-MS/MS analysis revealed that CYP4F22 catalyzed ω3 hydroxylation of arachidonic acid, but not any of the tested epoxyalcohols. In contrast, CYP4F8 metabolizes an epoxyalcohol derived from 12R-HPETE, 11R,12R-epoxy-10-hydroxyeicosatrienoic acid, to the ω3 hydroxy metabolite. Conclusively, it was demonstrated that LC-MS/MS could be used for the analysis and separation of hydroperoxides and epoxyalcohols for metabolic studies.

Positive-ion electrospray ionisation Fourier transform ion cyclotron resonance and ion trap mass spectrometry have been used to investigate the reactions of the flavonoids 3-hydroxyflavone, 5-hydroxyflavone, 5-methoxyflavoe, quercetin, quercitrin and rutin with monovalent Li+, Na+, K+ and Cs+, divalent Cu2+, Zn2+ and Pb2+ and trivalent La3+ and Eu3+ metal cations. The effect of capillary-skimmer potential difference and the ion residence time in the hexapole ion trap of the Fourier transform ion cyclotron resonance mass spectrometer are systematically investigated for the flavonoid-alkali and divalent metal ion experiment. It is observed that these variables impact significantly on the type of ions observed in the ESI experiments and hence the mass spectra. The binding selectivity of alkali metal ions towards 3-hydroxyflavone, 5-hydroxyflavone and 5-methoxyflavone are determined using the results from FTICR mass spectrometry experiments. The selectivity order follows the order Li+>Na+>K+ for individual flavonoids. Collision-induced dissociation experiments are carried out by Fourier transform ion cyclotron resonance and ion trap mass spectrometry to compare the fragmentation behaviour of metal-flavonoid complexes. Low energy collision-induced dissociation experiments of the [2L+M]+ for 3-hydroxyflavone, 5-hydroxyflavone and 5-methoxyflavone alkali metal complexes show the loss of ligand only. When the energy is increased only the lithiated dimer [2L+Li]+ for 5-methoxyflavone shows the loss of methyl radical along with the ligand. For quercitrin the predominant dissociation pathways are the loss of rhamnose for Li+, Na+ and K+ complexes although aglycone loss is also observed for the K+ complex. The favourable dissociation pathways for rutin are the loss of disaccharide, aglycone and rhamnose for the Na+ complex and the loss of disaccharide for the K+ complex. Collision-induced dissociation data are also used to determine the threshold dissociation energies for displacement of one flavonoid ligand from alkali metal flavonoid complexes. The threshold dissociation energies for loss of one ligand from [2L+M]+ of 5-methoxyflavone and quercitrin follow the order Li+ > Na+ > K+, rutin follows the order Na+ > K+ > Li+ , and 3-hydroxyflavone and 5-hydroxyflavone follow the order Li+ > Na+. For the same metal cation experiment, 5-methoxyflavone system has the highest dissociation energy compared to the 3-hydroxyflavone and 5-hydroxyflavone experiment. Preliminary DFT calculations show that the calculated dissociation energies follow the same trend as the experimental dissociation energies for the simple flavonoid alkali metal cation experiments. For 5-methoxyflavone-divalent metal cation (Zn2+, Cu2+ and Pb2+) complexes loss of methyl radical is the common process. CO loss is also observed for the Zn2+ complex whereas CHO and H2O losses are observed for Cu2+. For 3-hydroxyflavone and 5-hydroxyflavone divalent metal cation experiments loss of ligand is the dominant process. Zn2+ and Cu2+ complexes also show CO loss. La3+ and Er3+ with the same flavonoids show the ligand as the dominant product. For quercetin-divalent metal cation experiment, ligand loss is the dominant process. For quercitrin and rutin various dissociation products are observed where the dissociation occurs via the loss of the rhamnose and/or the disaccharide moieties. Similar dissociation patterns are also observed for La3+ and Er3+ complexes for quercitrin and rutin.

A large aspect ratio leads to higher ion capacity in miniaturized ion trap mass spectrometers. The aspect ratio (AR) of an ion trap represents the ratio between an extended trapping dimension and the characteristic trapping dimension. In contrast to linear and rectilinear traps, changing the AR of a toroidal ion trap (TorIT) results in changes to the degree of curvature and shape of the trapping potential, and hence, on performance as a mass analyzer. SIMION simulations show that higher-order terms in the trapping potential vary strongly for small and moderate AR values (below ~10), with the effects asymptotically flattening for larger AR values. Because of the asymmetry in electrode geometry, the trapping center does not coincide with the geometric center of the trap, and this displacement also varies with AR. For instance, in the asymmetric TorIT, the saddle point in the trapping potential and the geometric trap center differ from +0.6 to -0.4 mm depending on AR. Ion secular frequencies also change with the AR. Whereas ions in the simplified TorIT have stable trajectories for any value of AR, ions in the asymmetric TorIT become unstable at large AR values. Variations in high-order terms, the trapping center, and secular frequencies with AR are a unique feature of toroidal traps, and require significant changes in trap design and operation as the aspect ratio is changed.

Selective gas-phase dissociation strategies have been developed for the characterization of cross-linked peptides and proteins in quadrupole ion trap mass spectrometers. An infrared chromogenic cross-linker (IRCX) containing a phosphotriester afforded rapid differentiation of cross-linked peptides from unmodified ones in proteolytic digests of cross-linked proteins by selective infrared multiphoton dissociation (IRMPD). Only the cross-linked peptides containing the chromogenic phosphate underwent IRMPD and unmodified peptides were not affected by IR irradiation. IRMPD of IRCX-cross-linked peptides yielded uncross-linked y-ion sequence tags of the constituent peptides due to secondary dissociation of all primary product ions which contained the chromophore, thus allowing successful de novo sequencing of the cross-linked peptides. Peptides cross-linked via a two-step conjugation strategy through the formation of a bis-arylhydrazone (BAH) bond were selectively dissociated by ultraviolet radiation at 355 nm. The BAH-cross-linked peptides could be distinguished from not only unmodified peptides but also dead-end modified peptides based on the selectivity of ultraviolet photodissociation. In a complementary approach, electron transfer dissociation of BAH-cross-linked peptides resulted in preferential cleavage of the hydrazone bond which produced two modified peptides. These modified peptides were subsequently interrogated by CID which allowed for the original site of cross-linking to be pinpointed. IRMPD was implemented in a dual pressure linear ion trap to demonstrate successful photodissociation of peptides having modest absorptivities. Peptides were observed to efficiently dissociation by IR irradiation exclusively in the low pressure cell whereas no dissociation was observed in the high pressure cell due to extensive collisional cooling. IRMPD provided greater sequence coverage of the peptides than CID and yielded product ion mass spectra which were predominantly composed of singly charged product ions which simplified spectral interpretation. IRMPD was further applied for the sequencing of small-interfering RNA. Complete sequence coverage was obtained and the results were compared to CID. / text

This thesis describes theoretical and experimental work whose main aim is the development of techniques for using trapped ⁴³Ca⁺ ions for quantum information processing. I present a rate equations model of ⁴³Ca⁺, and compare it with experimental data. The model is then used to investigate and optimise an electron-shelving readout method from a ground-level hyperfine qubit. The process is robust against common experimental imperfections. A shelving fidelity of up to 99.97% is theoretically possible, taking 100 μs. The laser pulse sequence can be greatly simplified for only a small reduction in the fidelity. The simplified method is tested experimentally with fidelities up to 99.8%. The shelving procedure could be applied to other commonly-used species of ion qubit. An entangling two-qubit quantum controlled-phase gate was attempted between a ⁴⁰Ca⁺ and a ⁴³Ca⁺ ion. The experiment did not succeed due to frequent decrystallisation of the ion pair, and strong motional decoherence. The source of the problems was never identified despite significant experimental effort, and the decision was made to suspend the experiments and continue them in an improved ion trap which is under construction. A sequence of pi-pulses, inspired by the Hahn spin-echo, was derived that is capable of greatly reducing dephasing of any qubit. If the qubit precession frequency varies with time as an nth-order polynomial, an (n+1) pulse sequence is theoretically capable of perfectly cancelling the resulting phase error. The sequence is used on a 43Ca+ magnetic-field-sensitive hyperfine qubit, with 20 pulses increasing the coherence time by a factor of 75 compared to an experiment without any spin-echo. In our ambient noise environment the well-known Carr-Purcell-Meiboom-Gill dynamic-decoupling method was found to be comparably effective.

This thesis describes experimental demonstrations of high-fidelity readout of trapped ion quantum bits ("qubits") for quantum information processing. We present direct single-shot measurement of an "optical" qubit stored in a single calcium-40 ion by the process of resonance fluorescence with a fidelity of 99.991(1)% (surpassing the level necessary for fault-tolerant quantum computation). A time-resolved maximum likelihood method is used to discriminate efficiently between the two qubit states based on photon-counting information, even in the presence of qubit decay from one state to the other. It also screens out errors due to cosmic ray events in the detector, a phenomenon investigated in this work. An adaptive method allows the 99.99% level to be reached in 145us average detection time. The readout fidelity is asymmetric: 99.9998% is possible for the "bright" qubit state, while retaining 99.98% for the "dark" state. This asymmetry could be exploited in quantum error correction (by encoding the "no-error" syndrome of the ancilla qubits in the "bright" state), as could the likelihood values computed (which quantify confidence in the measurement outcome). We then extend the work to parallel readout of a four-ion string using a CCD camera and achieve the same 99.99% net fidelity, limited by qubit decay in the 400us exposure time. The behaviour of the camera is characterised by fitting experimental data with a model. The additional readout error due to cross-talk between ion images on the CCD is measured in an experiment designed to remove the effect of qubit decay; a spatial maximum likelihood technique is used to reduce this error to only 0.2(1)x10^{-4} per qubit, despite the presence of ~4% optical cross-talk between neighbouring qubits. Studies of the cross-talk indicate that the readout method would scale with negligible loss of fidelity to parallel readout of ~10,000 qubits with a readout time of ~3us per qubit. Monte-Carlo simulations of the readout process are presented for comparison with experimental data; these are also used to explore the parameter space associated with fluorescence detection and to optimise experimental and analysis parameters. Applications of the analysis methods to readout of other atomic and solid-state qubits are discussed.

Using a cryogenic linear 22-pole rf ion trap, rate coefficients for H/D exchange reactions of OH− with D2 (1) and OD− with H2 (2) have been measured at temperatures between 11 K and 300 K with normal hydrogen. Below 60 K, we obtained k1 = 5.5 × 10−10 cm3 s−1 for the exoergic reaction (1). Upon increasing the temperature above 60 K, the data decrease with a power law, k1(T) [similar] T−2.7, reaching ≈1 × 10−10 cm3 s−1 at 200 K. This observation is tentatively explained with a decrease of the lifetime of the intermediate complex as well as with the assumption that scrambling of the three hydrogen atoms is restricted by the topology of the potential energy surface. The rate coefficient for the endoergic reaction (2) increases with temperature from 12 K up to 300 K, following the Arrhenius equation, k2 = 7.5 × 10−11 exp(−92 K/T) cm3 s−1 over two orders of magnitude. The fitted activation energy, EA-Exp = 7.9 meV, is in perfect accordance with the endothermicity of 24.0 meV, if one accounts for the thermal population of the rotational states of both reactants. The low mean activation energy in comparison with the enthalpy change in the reaction is mainly due to the rotational energy of 14.7 meV contributed by ortho-H2 (J = 1). Nonetheless, one should not ignore the reactivity of pure para-H2 because, according to our model, it already reaches 43% of that of ortho-H2 at 100 K. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Infrared multiple photon dissociation (IRMPD) spectroscopy has been coupled with electronic structure calculations in order to elucidate the structures of several small biological molecules including: uracil, 5-fluorouracil, 5-fluorocytosine, ferulic acid, and a number of their related analogs. IRMPD is a powerful technique, that when combined with electronic structure calculations can provide convincing evidence for the structural characterization of ions in the gas phase. Isomers of uracil and 5-fluorouracil (5-FU) have been characterized by calculations performed at the MP2(full)/aug-cc-pVTZ level of theory; however, infrared multiple photon dissociation spectroscopy experiments proved to be unsuccessful for these species. Geometry optimization and frequency calculations have isolated the dominant isomer(s) for neutral and deprotonated uracil and 5-fluorouracil, along with several cluster interactions involving water, methanol, ammonia, and methylamine. For both uracil and 5-FU, a single relevant neutral isomer was determined, with each isomer existing in the diketo, as opposed to the enol form. Following the deprotonation of this neutral isomer, both uracil and 5-FU were permitted to form anionic cluster ions with water, methanol, ammonia, or methylamine, and based on the relative Gibbs free energies (298 K) of the calculated isomers, relevant cluster interactions were determined. For each cluster, several sites of intramolecular interaction were found to exist; however, interaction at the site of deprotonation was the most favourable in every instance. Ionic hydrogen bond interactions have been found in several clusters formed by 5-fluorocytosine (5-FC). The chloride and trimethylammonium cluster ions, in addition to the cationic and anionic dimers have been characterized by infrared multiple photon dissociation (IRMPD) spectroscopy and electronic structure calculations performed at the B2PLYP/aug-cc-pVTZ//B3LYP/6-311+G(d,p) level of theory. IRMPD spectra in combination with calculated spectra and relative energetics have indicated, quite conclusively, that a single isomer for each 5-FC cluster that is likely being observed experimentally except in the case of the anionic dimer, in which a combination of isomers is probable. For the 5-FC-trimethylammonium cluster specifically, the calculated spectrum of the lowest energy isomer matches the experimental spectrum remarkably well. Interestingly, the cationic dimer of 5-FC was found to have a single energetically relevant isomer (Cationic-IV) in which a unique tridentate ionic hydrogen bond interaction is formed. The three sites of intramolecular ionic hydrogen bonds in this isomer interact very efficiently, leading to a significantly large calculated enthalpy of binding of 180 kJ/mol. The magnitude of the calculated binding energy for this species, in combination with the strong correlation between the simulated and IRMPD spectra, indicates that the tridentate-bound dimer is observed predominantly in experiment. Comparison of the calculated relative Gibbs free energies (298 K) for this species with several of the other isomers considered also supports the likelihood of the dominant protonated dimer existing as Cationic-IV. Protonated ferulic acid has been characterized using infrared multiple photon dissociation spectroscopy and electronic structure calculations at the B3LYP/6-311+G(d,p) level of theory. Neutral ferulic acid has been determined to undergo protonation on the carbonyl oxygen of the acid group, forming an ion of m/z 195. Due to its extensively conjugated structure, protonated ferulic acid (m/z 195) is observed to yield three stable fragment ions in IRMPD experiments. It is proposed that two parallel fragmentation pathways of protonated ferulic acid are being observed. First, proton transfer occurs from the carbonyl oxygen to the hydroxyl oxygen within the acid group, resulting in the loss of water and subsequently carbon monoxide, forming ions of m/z 177 and 149, respectively. The second proposed fragmentation pathway undergoes proton transfer from the phenolic group to the methoxy group resulting in loss of methanol and rearrangement to a five-membered ring of m/z 163. IRMPD spectra have been obtained for the ions m/z 195 and m/z 177, and anharmonic calculations have been performed on these species at the B3LYP/6-311+G(d,p) level of theory. The calculated anharmonic spectra for these ions match the experimental spectrum exceptionally well and strongly support the proposed fragmentation mechanisms.

Hochgeladene Ionen stellen einen extremen Zustand der Materie dar, wie sie vornehmlich in kosmischen Plasmen zu finden ist. Die labormäßige Erzeugung und (spektroskopische) Untersuchung hochgeladener Ionen liefert wichtige Daten und Erkenntnisse für die Astrophysik und Fusionsforschung. Aufgrund ihrer zum Teil exotischen Eigenschaften besitzen hochgeladene Ionen ein großes Potential für eine Vielzahl neuer Anwendungen. Die bisher weltweit einzige Elektronenstrahl-Ionenfalle, die hochgeladene Ionen bis hin zu vollständig ionisierten Ionen unter Raumtemperaturbedingungen erzeugen und bereitstellen kann, die Dresden EBIT, ist Gegenstand der vorgelegten Arbeit. Die Dresden EBIT zeichnet sich neben ihrer Kompaktheit und einer einfachen Bedienung durch ihre Langzeitstabilität aus. Sowohl über Röntgenspektren als auch über die Extraktion der Ionen aus der EBIT konnte für eine Reihe von Elementen der Nachweis der Erzeugung von vollständig ionisierten Ionen bis Z=28 erbracht werden. Für schwere Elemente können Ionenladungszustände bis hin zu neonähnlichen Ionen erzeugt werden. Entscheidenden Einfluss auf den erzielten mittleren Ladungszustand hat die Ioneneinschlusszeit. Die zeitliche Entwicklung der Ladungszustandsverteilung, wie sie im Zusammenspiel der verschiedenen atomaren Prozesse simuliert werden kann, ist sowohl an einer Reihe von röntgenspektroskopischen Messungen als auch anhand von Extraktionsspektren untersucht worden. Neben der Beladung der EBIT mit gasförmigen Elementen ist insbesondere die Beladung mit Metallen, d. h. mit einem möglichst breiten Spektrum an Elementen gefordert. Die Beladung mit leichtflüchtigen metallorganischen Verbindungen, die über das Gaseinlassventil eingebracht werden können, hat sich als erfolgreiche und preiswerte Alternative zu einer MEVVA-Quelle erwiesen. Die Beladung mit Metallionen ist am Beispiel verschiedener Untersuchungen gezeigt. Der monoenergetische Elektronenstrahl gestattet neben der Untersuchung von Anregungs- und Ionisationsprozessen insbesondere die der wichtigen Rekombinationsprozesse des Strahlenden Einfangs und der Dielektronischen Rekombination. Der Einsatz eines Kristalldiffraktionsspektrometers erlaubt trotz einer aufwendigen Kalibrierung und sehr langen Messzeiten die Auflösung einzelner Übergänge in hochgeladenen Ionen. Hauptanwendungsfeld der Dresden EBIT wird der Einsatz als Ionenquelle sein. Aus den Untersuchungen des extrahierten Gesamtionenstroms können die Bedingungen für einen möglichst großen Ionenstrom und einen optimalen Ionenstrahltransport abgeleitet werden. Eine optimale Ausnutzung der Eigenschaften hochgeladener Ionen erfordert die Separation der einzelnen Ladungszustände. Der Nachweis der sehr kleinen Ionenströme erfolgt über die kapazitive Messung in einem Faradaycup. Die Messung der Ladungszustandsverteilung in Abhängigkeit von den Parametern der EBIT gibt zusätzliche Aufschlüsse über die Eigenschaften der Ionenfalle.