Variable Temperature Mass Spectrometry Research Articles

Thermal decomposition of triruthenium dodecacarbonyl investigated by variable-temperature mass spectrometry in the gas phase

The thermal decomposition processes of chemically prepared triruthenium dodecacarbonyl, Ru3(CO)12, were investigated by variable-temperature mass spectrometry (MS) in the gas phase. Ru3(CO)12 was sublimated and merged in a molecular beam of He and CO gases and was heated to a high temperature in an extension tube. Subsequently, it was probed by MS after photoionization at 7.89 eV. CO ligand molecules were sequentially released in the temperature range of 500–900 K, forming Ru3. Among the intermediate cluster compositions, Ru3(CO)7 was the most thermally durable cluster, while Ru3(CO)3, Ru3(CO)5, and Ru3(CO)10 were less durable and decomposed within a narrow temperature range.

Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications.

The radioactive isotopes scandium-44/47 and lutetium-177 are gaining relevance for radioimaging and radiotherapy, resulting in a surge of studies on their coordination chemistry and subsequent applications. Although the trivalent ions of these elements are considered close homologues, dissimilar chemical behavior is observed when they are complexed by large ligand architectures due to discrepancies between Lu(III) and Sc(III) ions with respect to size, chemical hardness, and Lewis acidity. Here, we demonstrate that Lu and Sc complexes of 1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane (H3mpatcn) and its corresponding bioconjugate picaga-DUPA can be employed to promote analogous structural features and, subsequently, biological properties for coordination complexes of these ions. The close homology was evidenced using potentiometric methods, computational modeling, variable temperature mass spectrometry, and pair distribution function analysis of X-ray scattering data. Radiochemical labeling, in vitro stability, and biodistribution studies with Sc-47 and Lu-177 indicate that the 7-coordinate ligand environment of the bifunctional picaga ligand is compatible with biological applications and the future investigation of β-emitting, picaga-chelated Sc and Lu isotopes for radiotherapy.

General Approach to Direct Measurement of the Hydration State of Coordination Complexes in the Gas Phase: Variable Temperature Mass Spectrometry.

The formation of ternary aqua complexes of metal-based diagnostics and therapeutics is closely correlated to their in vivo efficacy but approaches to quantify the presence of coordinated water ligands are limited. We introduce a general and high-throughput method for characterizing the hydration state of para- and diamagnetic coordination complexes in the gas phase based on variable-temperature ion trap tandem mass spectrometry. Ternary aqua complexes are directly observed in the mass spectrum and quantified as a function of ion trap temperature. We recover expected periodic trends for hydration across the lanthanides and distinguish complexes with several inner-sphere water ligands by inspection of temperature-dependent speciation curves. We derive gas-phase thermodynamic parameters for discernible inner- and second-sphere hydration events, and discuss their application to predict solution-phase behavior. The differences in temperature at which water binds in the inner and outer spheres arise primarily from entropic effects. The broad applicability of this method allows us to estimate the hydration states of Ga, Sc, and Zr complexes under active preclinical and clinical study with as-yet undetermined hydration number. Variable-temperature mass spectrometry emerges as a general tool to characterize and quantitate trends in inner-sphere hydration across the periodic table.

EPR detection of Fe(V)=O active species in nonheme iron-catalyzed oxidations

Abstract Very recently, in situ cryospray-assisted variable temperature mass spectrometry (VT-MS) has been used to obtain the first convincing evidence for a HO–Fe V =O intermediate in the catalyst system [( Me2 PyTACN)Fe II (OTf) 2 ] ( 4 )/H 2 O 2 ( Me2 PyTACN = 1-(2′-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane, OTf = OSO 2 CF 3 ). The herein presented EPR spectroscopic study of the same system witnesses the formation of S = 1/2 reactive iron species. Its EPR parameters, in combination with its reactivity pattern toward cyclohexene and with independently obtained VT-MS data, allow for its reasonable assignment to the reactive [( Me2 PyTACN)Fe V =O(OH)] 2 + ( 4c ) species.

Observation of Fe(V)=O using variable-temperature mass spectrometry and its enzyme-like C–H and C=C oxidation reactions

Oxo-transfer chemistry mediated by iron underpins many biological processes and today is emerging as synthetically very important for the catalytic oxidation of C-H and C=C moieties that are hard to activate conventionally. Despite the vast amount of research in this area, experimental characterization of the reactive species under catalytic conditions is very limited, although a Fe(V)=O moiety was postulated. Here we show, using variable-temperature mass spectrometry, the generation of a Fe(V)=O species within a synthetic non-haem complex at -40 °C and its reaction with an olefin. Also, with isotopic labelling we were able both to follow oxygen-atom transfer from H(2)O(2)/H(2)O through Fe(V)=O to the products and to probe the reactivity as a function of temperature. This study pioneers the implementation of variable-temperature mass spectrometry to investigate reactive intermediates.

Vapor Deposition of Lithium Tantalate with Volatile Double Alkoxide Precursors

AbstractStoichiometric vapor deposition of LiTaO3 is demonstrated by thermal evaporation of volatile LiTa(OButn)6, controlled vapor phase partial-hydrolysis, and subsequent polycondensation reactions on a heated substrate surface. Fully dense, amorphous LiTaO3 film of up to 34 μm thick can be obtained at high deposition rate of 23 μm per hour. Single phase LiTaO3 films are obtained by annealing as deposited films. The vapor phase species responsible for the stoichiometric vapor deposition appeared to be Li2Ta2(OButn)12 from variable temperature mass spectrometry results.