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Transition-metal Complexes (transition-metal + complex)
Selected AbstractsEvidence for Spontaneous Release of Acrylates from a Transition-Metal Complex Upon Coupling Ethene or Propene with a Carboxylic Moiety or CO2CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007Michele Aresta Prof. Abstract The development of a new synthetic approach to acrylates based on the formation of alkyl esters of acrylic acids has been studied. A preformed Pd,COOMe moiety is used as a model system to investigate the insertion of an olefin into the PdC bond. The fast elimination of acrylate is observed. Density functional calculations support the experimental findings and allow the characterization of transition states along the reaction pathway. The first example of olefin/CO2 coupling with facile release of ethyl acrylate is also presented. [source] Triple-Decker Transition-Metal Complexes (CnHn)M(B6C)M(CnHn) (M = Fe, Ru, Mn, Re; n = 5, 6) Containing Planar Hexacoordinate Carbon AtomsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006Si-Dian Li Abstract A density functional theory investigation is presented in this work on a new class of triple-decker complexes (CnHn)M(B6X)M(CnHn) (M = Fe, Ru, Mn, Re; X = B, C, N; n = 5, 6) containing almost perfect planar hexacoordinate carbon atoms and other planar hexacoordinate nonmetals at the centers of the B6X middle-deckers. Effective d,, coordination interactions between the partially filled 3d orbitals of the transition-metal center and the delocalized , orbitals of the three parallel ligands maintain the stabilities of these triple-decker complexes. The strong IR absorption peaks of (CnHn)M(B6X)M(CnHn) complexes mainly originate from the in-plane and off-plane vibrations of their planar hexacoordinate nonmetal centers. The results obtained in this work provide a possible new approach to characterize planar hexacoordinate carbon-containing systems in future experiments and expand the structural domain of transition-metal complexes by introducing inorganic B6X middle-deckers into traditional sandwich-type structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Syntheses and Crystal Structures of Three New Borates Templated by Transition-Metal Complexes in situ.CHEMINFORM, Issue 32 2006Guo-Ming Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Transition-Metal Complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] with Naked Group,14 Atoms (E=C,Sn) as Ligands; Part 2: Complexation with W(CO)5CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2009Pattiyil Parameswaran Dr. Abstract Density functional calculations at the BP86/TZ2P level were carried out to understand the ligand properties of the 16-valence-electron(VE) Group,14 complexes [(PMe3)2Cl2M(E)] (1ME) and the 18-VE Group,14 complexes [(PMe3)2(CO)2M(E)] (2ME; M=Fe, Ru, Os; E=C, Si, Ge, Sn) in complexation with W(CO)5. Calculations were also carried out for the complexes (CO)5W,EO. The complexes [(PMe3)2Cl2M(E)] and [(PMe3)2(CO)2M(E)] bind strongly to W(CO)5 yielding the adducts 1ME,W(CO)5 and 2ME,W(CO)5, which have C2v equilibrium geometries. The bond strengths of the heavier Group,14 ligands 1ME (E=Si,Sn) are uniformly larger, by about 6,7,kcal,mol,1, than those of the respective EO ligand in (CO)5W-EO, while the carbon complexes 1MC,W(CO)5 have comparable bond dissociation energies (BDE) to CO. The heavier 18-VE ligands 2ME (E=Si,Sn) are about 23,25,kcal,mol,1 more strongly bonded than the associated EO ligand, while the BDE of 2MC is about 17,21,kcal,mol,1 larger than that of CO. Analysis of the bonding with an energy-decomposition scheme reveals that 1ME is isolobal with EO and that the nature of the bonding in 1ME,W(CO)5 is very similar to that in (CO)5W,EO. The ligands 1ME are slightly weaker , acceptors than EO while the ,-acceptor strength of 2ME is even lower. [source] Description of the Ground-State Covalencies of the Bis(dithiolato) Transition-Metal Complexes from X-ray Absorption Spectroscopy and Time-Dependent Density-Functional CalculationsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2007Kallol Ray Dr. Abstract The electronic structures of [M(LBu)2], (LBu=3,5-di- tert -butyl-1,2-benzenedithiol; M=Ni, Pd, Pt, Cu, Co, Au) complexes and their electrochemically generated oxidized and reduced forms have been investigated by using sulfur K-edge as well as metal K- and L-edge X-ray absorption spectroscopy. The electronic structure content of the sulfur K-edge spectra was determined through detailed comparison of experimental and theoretically calculated spectra. The calculations were based on a new simplified scheme based on quasi-relativistic time-dependent density functional theory (TD-DFT) and proved to be successful in the interpretation of the experimental data. It is shown that dithiolene ligands act as noninnocent ligands that are readily oxidized to the dithiosemiquinonate(,) forms. The extent of electron transfer strongly depends on the effective nuclear charge of the central metal, which in turn is influenced by its formal oxidation state, its position in the periodic table, and scalar relativistic effects for the heavier metals. Thus, the complexes [M(LBu)2], (M=Ni, Pd, Pt) and [Au(LBu)2] are best described as delocalized class,III mixed-valence ligand radicals bound to low-spin d8 central metal ions while [M(LBu)2], (M=Cu, Au) and [M(LBu)2]2, (M=Ni, Pd, Pt) contain completely reduced dithiolato(2,) ligands. The case of [Co(LBu)2], remains ambiguous. On the methodological side, the calculation led to the new result that the transition dipole moment integral is noticeably different for S1s,valence-, versus S1s,valence-, transitions, which is explained on the basis of the differences in radial distortion that accompany chemical bond formation. This is of importance in determining experimental covalencies for complexes with highly covalent metal,sulfur bonds from ligand K-edge absorption spectroscopy. [source] Iron,Palladium Association in the Preparation of Indoles and One-Pot Synthesis of Bis(indolyl)methanesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 32 2007Vincent Terrasson Abstract Indoles were prepared by annulation of the parent alkynylanilines with the use of a new FeCl3,PdCl2 catalytic combination. High yields were obtained by using low loadings of the transition-metal complex (FeCl3,PdCl2: 2 and 1 mol-%, respectively). One-pot accesses to bis(indolyl)methanes and trisubstituted indoles through annulation/Friedel,Crafts alkylation and annulation/1,4-Michael addition sequences, in which FeCl3 acts both as a cooxidant and a Lewis acid are described.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] All-Optical Integrated Logic Operations Based on Chemical Communication between Molecular SwitchesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2009Serena Silvi Dr. Abstract Molecular logic gates process physical or chemical "inputs" to generate "outputs" based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine-type photoacid and a ruthenium polypyridine complex that functions as a pH-controlled three-state luminescent switch. The light-triggered release of protons from the photoacid is used to control the state of the transition-metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical,chemical,optical) signal-transduction mechanism, inputs of violet light modulate a luminescence output in the red/far-red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation. [source] Three Novel Functional CdII Dicarboxylates with Nanometer Channels: Hydrothermal Synthesis, Crystal Structures, and Luminescence PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2007Yu-Peng Tian Abstract Three novel functional transition-metal complexes with H2A (H2A = 9-ethylcarbazole-3,6-dicarboxylic acid), Cd(HA)2(H2O)2 (1), [Cd(A)(phen)]·1.5H2O (2) (phen = 1,10-phenanthroline), and Cd(HA)2(bipy) (3) (bipy = 4,4,-bipyridine), have been successfully synthesized by a hydrothermal synthetic method and characterized by single-crystal X-ray diffraction, infrared spectroscopy, elemental analysis, thermogravimetric analysis, and photoluminescence. The results show that all of the complexes contain nanometer channels, while the coordination modes were changed by the addition of the mixed ligands. The 2D supramolecular open-framework 1 is constructed through hydrogen-bond and aromatic ,,, interactions. 2D coordination polymer 2 is constructed by ,,, interactions between adjacent metal-organic polymeric coordination chains. Interestingly, the 3D supramolecular architecture of 3 first formed 2D grid layers from 1D chains by intermolecular hydrogen bonds and then extended into a 3D structure through aromatic ,,, interactions. Furthermore, strong emissions from these complexes were also changed by the coordination modes in the solid state. However, complexes 1,3 show high thermal stability.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Structure and Magnetic Properties of a Tetranuclear Copper(II) Complex on the Basis of a 2-Substituted Glucopyranoside Schiff Base Ligand,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2006Anja Burkhardt Abstract Condensation of a derivatized 2-aminoglucose fragment with salicylaldehyde affords the new sugar-based Schiff base ligand benzyl 4,6- O -benzylidene-2-deoxy-2-salicylideneamino-,- D -glucopyranoside (H2L). The reaction of the dibasic ligand H2L with [Cu(CH3COO)2]·H2O leads to the formation of the tetranuclear copper(II) complex [{Cu(L)}4] (3) by a self-assembly process. The X-ray structural analysis of complex 3 which crystallizes together with two molecules of chloroform and one molecule of ethanol in the space group P212121 revealed for all copper atoms a NO3 coordination environment with a square-planar geometry. The tetranuclear molecule 3 consists of four chiral building blocks {Cu(L)} with the rare 2,3-coordination of the trans -configured donor atoms of the sugar backbone. The observed coordination mode of the building blocks exemplifies how chitosan-derived polysaccharide ligands can act as a chiral support for transition-metal complexes. The C-3 alcoholate oxygen atoms of the carbohydrate unit is bridging adjacent {Cu(L)} moieties resulting in an eight-membered Cu4O4 ring with a boat-like conformation. Temperature-dependent magnetic measurements of 3 indicate moderate antiferromagnetic interactions between the four copper(II) ions with a coupling constant of J = ,130 cm,1.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Triple-Decker Transition-Metal Complexes (CnHn)M(B6C)M(CnHn) (M = Fe, Ru, Mn, Re; n = 5, 6) Containing Planar Hexacoordinate Carbon AtomsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006Si-Dian Li Abstract A density functional theory investigation is presented in this work on a new class of triple-decker complexes (CnHn)M(B6X)M(CnHn) (M = Fe, Ru, Mn, Re; X = B, C, N; n = 5, 6) containing almost perfect planar hexacoordinate carbon atoms and other planar hexacoordinate nonmetals at the centers of the B6X middle-deckers. Effective d,, coordination interactions between the partially filled 3d orbitals of the transition-metal center and the delocalized , orbitals of the three parallel ligands maintain the stabilities of these triple-decker complexes. The strong IR absorption peaks of (CnHn)M(B6X)M(CnHn) complexes mainly originate from the in-plane and off-plane vibrations of their planar hexacoordinate nonmetal centers. The results obtained in this work provide a possible new approach to characterize planar hexacoordinate carbon-containing systems in future experiments and expand the structural domain of transition-metal complexes by introducing inorganic B6X middle-deckers into traditional sandwich-type structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis of Dicarboxylate "C-Clamp" 1,2-Diethynylarene Compounds as Potential Transition-Metal Ion HostsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2008Erwin Reisner Abstract We report an efficient convergent synthesis of a new type of C-clamp ligand with a 1,2-diethynylarene scaffold involving a chelate host capable of binding a guest molecule in its endo -dicarboxylate pocket. The chemistry involves a combination of palladium-catalyzed Sonogashira, Heck, and Suzuki cross-coupling reactions. The compounds 2,3-bis[2-(2,-carboxybiphenyl-4-yl)ethynyl]triptycene and 4,5-bis[2-(2,-carboxybiphenyl-4-yl)ethynyl]veratrole and their 2,-carboxy- m -terphenyl-4-yl analogues were designed as dinucleating ligands to assemble carboxylate-bridged transition-metal complexes with a windmill geometry. The X-ray crystal structure of one such C-clamp compound containing co-crystallized water molecules reveals strong hydrogen bonds of the aqua guest to the endo -oriented carboxylic acid entities of the C-clamp host. In addition, two syn -N-donor ligands were prepared as a synthetic scaffold to mimic the geometric arrangement of N-donor atoms in carboxylate-bridged dinuclear proteins. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Computational NMR Spectroscopy of Transition-Metal/Nitroimidazole Complexes: Theoretical Investigation of Potential RadiosensitizersHELVETICA CHIMICA ACTA, Issue 10 2005Teodorico The computed chemical shifts of transition-metal complexes with dimetridazole (=,1,2-dimethyl-5-nitro-1H -imidazole; 1), a prototypical nitro-imidazole-based radiosensitizer, are reported at the GIAO-BP86 and -B3LYP levels for BP86/ECP1-optimized geometries. These complexes comprise [MCl2(1)2] (M,=,Zn, Pd, Pt), [RuCl2(DMSO)2(1)2], and [Rh2(O2CMe)4(1)2]. Available ,(1H) and ,(15N) values, and ,,(1H) and ,,(15N) coordination shifts are well-reproduced theoretically, provided solvation and relativistic effects are taken into account by means of a polarizable continuum model and suitable methods including spin,orbit (SO) coupling, respectively. These effects are particularly important for the metal-coordinated N-atom, where the contributions from solvation and relativity can affect ,(15N) and ,,(15N) values up to 10,20,ppm. The 195Pt chemical shifts of cis - and trans -[PtCl2(1)2] are well-reproduced using the zero-order regular approximation including SO coupling (ZORA-SO). Predictions are reported for 99Ru and 103Rh chemical shifts, which suggest that these metal centers could be used as additional, sensitive NMR probes in their complexes with nitro-imidazoles. [source] The Orbitrap: a new mass spectrometerJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2005Qizhi Hu Abstract Research areas such as proteomics and metabolomics are driving the demand for mass spectrometers that have high performance but modest power requirements, size, and cost. This paper describes such an instrument, the Orbitrap, based on a new type of mass analyzer invented by Makarov. The Orbitrap operates by radially trapping ions about a central spindle electrode. An outer barrel-like electrode is coaxial with the inner spindlelike electrode and mass/charge values are measured from the frequency of harmonic ion oscillations, along the axis of the electric field, undergone by the orbitally trapped ions. This axial frequency is independent of the energy and spatial spread of the ions. Ion frequencies are measured non-destructively by acquisition of time-domain image current transients, with subsequent fast Fourier transforms (FFTs) being used to obtain the mass spectra. In addition to describing the Orbitrap mass analyzer, this paper also describes a complete Orbitrap-based mass spectrometer, equipped with an electrospray ionization source (ESI). Ions are transferred from the ESI source through three stages of differential pumping using RF guide quadrupoles. The third quadrupole, pressurized to less than 10,3 Torr with collision gas, acts as an ion accumulator; ion/neutral collisions slow the ions and cause them to pool in an axial potential well at the end of the quadrupole. Ion bunches are injected from this pool into the Orbitrap analyzer for mass analysis. The ion injection process is described in a simplified way, including a description of electrodynamic squeezing, field compensation for the effects of the ion injection slit, and criteria for orbital stability. Features of the Orbitrap at its present stage of development include high mass resolution (up to 150 000), large space charge capacity, high mass accuracy (2,5 ppm), a mass/charge range of at least 6000, and dynamic range greater than 10.3 Applications based on electrospray ionization are described, including characterization of transition-metal complexes, oligosaccharides, peptides, and proteins. Use is also made of the high-resolution capabilities of the Orbitrap to confirm the presence of metaclusters of serine octamers in ESI mass spectra and to perform H/D exchange experiments on these ions in the storage quadrupole. Copyright © 2005 John Wiley & Sons, Ltd. [source] How to Build Molecules with Large Magnetic AnisotropyCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2009Jordi Cirera Dr. Abstract Predicting single-molecule magnets? Magnetic anisotropy, a property that plays a key role in single-molecule magnets (SMMs), has been analyzed by using theoretical methods. Mononuclear complexes and the dependence of the magnetic anisotropy on their geometrical and electronic structure, as well as how such mononuclear complexes must be combined as building blocks to obtain polynuclear complexes with large anisotropy (see figure) are considered. The magnetic anisotropy of mononuclear transition-metal complexes has been studied by means of electronic structure calculations based on density functional theory. The variation of the zero-field splitting (ZFS) parameters has been analyzed for the following characteristic distortions: a tetragonal Jahn,Teller distortion, the Bailar twist, the Berry pseudorotation, and the planarization of tetrahedral complexes. Finally, the coupling of mononuclear building blocks in polynuclear complexes to obtain a large negative magnetic anisotropy necessary to improve their single-molecule-magnet (SMM) behavior has been studied. [source] Mixed-Transition-Metal Acetylides: Synthesis and Characterization of Complexes with up to Six Different Transition Metals Connected by Carbon-Rich Bridging UnitsCHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2008Rico Packheiser Dipl.-Chem. Abstract The synthesis and reaction chemistry of heteromultimetallic transition-metal complexes by linking diverse metal-complex building blocks with multifunctional carbon-rich alkynyl-, benzene-, and bipyridyl-based bridging units is discussed. In context with this background, the preparation of [1-{(,2 -dppf)(,5 -C5H5)RuCC}-3-{(tBu2bpy)(CO)3ReCC}-5-(PPh2)C6H3] (10) (dppf=1,1,-bis(diphenylphosphino)ferrocene; tBu2bpy=4,4,-di- tert -butyl-2,2,-bipyridyl; Ph=phenyl) is described; this complex can react further, leading to the successful synthesis of heterometallic complexes of higher nuclearity. Heterotetrametallic transition-metal compounds were formed when 10 was reacted with [{(,5 -C5Me5)RhCl2}2] (18), [(Et2S)2PtCl2] (20) or [(tht)AuCC-bpy] (24) (Me=methyl; Et=ethyl; tht=tetrahydrothiophene; bpy=2,2,-bipyridyl-5-yl). Complexes [1-{(,2 -dppf)(,5 -C5H5)RuCC}-3-{(tBu2bpy)(CO)3ReCC}-5-{PPh2RhCl2(,5 -C5Me5)}C6H3] (19), [{1-[(,2 -dppf)(,5 -C5H5)RuCC]-3-[(tBu2bpy)(CO)3ReCC]-5-(PPh2)C6H3}2PtCl2] (21), and [1-{(,2 -dppf)(,5 -C5H5)RuCC}-3-{(tBu2bpy)(CO)3ReCC}-5-{PPh2AuCC-bpy}C6H3] (25) were thereby obtained in good yield. After a prolonged time in solution, complex 25 undergoes a transmetallation reaction to produce [(tBu2bpy)(CO)3ReCC-bpy] (26). Moreover, the bipyridyl building block in 25 allowed the synthesis of Fe-Ru-Re-Au-Mo- (28) and Fe-Ru-Re-Au-Cu-Ti-based (30) assemblies on addition of [(nbd)Mo(CO)4] (27), (nbd=1,5-norbornadiene), or [{[Ti](,-,,,-CCSiMe3)2}Cu(NCMe)][PF6] (29) ([Ti]=(,5 -C5H4SiMe3)2Ti) to 25. The identities of 5, 6, 8, 10,12, 14,16, 19, 21, 25, 26, 28, and 30 have been confirmed by elemental analysis and IR, 1H, 13C{1H}, and 31P{1H} NMR spectroscopy. From selected samples ESI-TOF mass spectra were measured. The solid-state structures of 8, 12, 19 and 26 were additionally solved by single-crystal X-ray structure analysis, confirming the structural assignment made from spectroscopy. [source] Transition Metal Complexes Coordinated by an NAD(P)H Model Compound and their Enhanced Hydride-Donating Abilities in the Presence of a BaseCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Atsuo Kobayashi Dr. Abstract The ruthenium(II) and rhenium(I) complexes containing an NAD(P)H model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), as ligand, [Ru(tpy)(bpy)(BNAH)]2+ (1,a) and [Re(bpy)(CO)3(BNAH)]+ (1,b), were quantitatively produced by the reaction of the corresponding metal hydrido complexes with BNA+ (1-benzylnicotinamidium cation). In the presence of base with pKa=8.9, 1,a and 1,b have much greater reducing power than "free" BNAH. The oxidation potentials of 1,a in the absence and the presence of triethylamine were 0.55 V and ,0.04 V, respectively, versus Ag/AgNO3, whereas that of "free" BNAH was 0.30 V. Spectroscopic results clearly showed that the base extracts a proton from the carbamoyl group on 1,a and 1,b to give the deprotonated BNAH coordinating to the transition-metal complexes [Ru(tpy)(bpy)(BNAH,H+)]+ (3,a) and [Re(bpy)(CO)3(BNAH,H+)] (3,b); this deprotonation underlies the enhancement in reducing ability. The deprotonated forms 3,a and 3,b can efficiently reduce other NAD(P) models to give the corresponding 1,4-dihydro form, resulting in the deprotonated BNA+ being coordinated to the metal complexes [Ru(tpy)(bpy)(BNA+,H+)]2+ (2,a) and [Re(bpy)(CO)3(BNA+,H+)]+ (2,b); "free" BNAH and the protonated adducts 1,a and 1,b cannot act in this way. X-ray crystallography was performed on the PF6, salt of 2,a, and showed that the deprotonated nitrogen atom on the carbamoyl group coordinates to the ruthenium(II) metal center with a bond length of 2.086(3) Å. Infrared spectral data suggested that the deprotonated carbamoyl group on the reduced forms 3,a and 3,b is converted to the imido group, and that the oxygen atom coordinates to the metal center. [source] Monitoring the Formation of Coordination Complexes Using Electrospray Mass SpectrometryCHEMISTRY - AN ASIAN JOURNAL, Issue 5 2009Jennifer Abstract Linked-in: The rigid Schiff-base ligand cis,trans -1,3,5-tris(pyridine-2-carboxaldimino) cyclohexane (ttop) is synthesized, and its complexation to copper(II) salts at a range of stoichiometries is investigated crystallographically by using electrospray mass spectrometry. Further, in-situ mass spectrometry measurements allow the stepwise construction of the complexes to be observed. cis,trans -1,3,5-Triaminocyclohexane (trans -tach) has been shown to be an excellent ligand in the synthesis of discrete complexes, molecular clusters, and infinite architectures. Herein, we report the Schiff-base derivitization of trans -tach to form cis,trans -1,3,5- tris (pyridine-2-carboxaldimino) cyclohexane (ttop), and the complexation of this ligand with copper(II) salts. The complexation reaction leads to the crystallization of transition-metal complexes with nuclearities of 1, 2, and 4, and the formation of the complexes can be followed stepwise, in real time, using electrospray mass spectrometry. [source] | ||||||||||||||||||||||