Structure Determination of Zinc and Cadmium Dication Complexes with Intact and Deprotonated Histidyl Glycine and Glycyl Histidine Dipeptides.

Metalated intact and deprotonated histidyl glycine and glycyl histidine dipeptides were investigated in the gas phase by using infrared multiple photon dissociation (IRMPD) spectroscopy with light from a free-electron laser (FEL). The dipeptides M(GlyHis), M(HisGly), [M(GlyHis-H)], and [M(HisGly-H)], where M = Zn and Cd, were probed to elucidate how the His position along the peptide chain and ligand charge state might influence the structures observed in the gas phase. Simulated annealing calculations were performed to determine energetically low-lying conformers and isomers of these structures.

Hydrogen Tag Shifts as Vibrational Reporters for Positional Isomers of Formylphenides: Surprising Mobility of the Carbanion Center upon Collisional Decarboxylation of the Parent Benzoates.

Infrared photodissociation of weakly bound "mass tags" is widely used to determine the structures of ions by analyzing their vibrational spectra. Molecular hydrogen is a common choice for tagging in cryogenic radio-frequency ion traps. Although the H molecules can introduce distortions in the target species, we demonstrate an advantage of H tagging in the analysis of positional isomers adopted by the molecular anions derived from decarboxylation of formylbenzoates.

Characterization of the Oxazolone and Macrocyclic Motifs in the b ( = 2-5) Product Ions from Collision-Induced Dissociation of Protonated Oligoglycine Peptides with Isomer-Selective, Cryogenic Vibrational Spectroscopy.

Collision-induced dissociation (CID) of small, protonated peptides leads to the formation of b-type fragment ions that can occur with several structural motifs driven by different covalent intramolecular bonding arrangements. Here, we characterize the so-called "oxazolone" and "macrocycle" ion structures that occur upon CID of oligoglycine peptides (G) ions ( = 2-6). This is determined by acquiring the vibrational band patterns of the cryogenically cooled, D-tagged ions obtained using isomer-selective, two-color IR-IR photobleaching and analyzing them with predicted (DFT) harmonic spectra for the candidate structures.

Structures and Chemical Rearrangements of Benzoate Derivatives Following Gas Phase Decarboxylation.

Decarboxylation of carboxylate ions in the gas phase provides a useful window into the chemistry displayed by these reactive carbanion intermediates. Here, we explore the species generated by decarboxylation of two benzoate derivatives: 2-formylbenzoate (2FBA) and 2-benzoylbenzoate (2BBA). The nascent product anions are transferred to a cryogenic ion trap where they are cooled to ∼15 K and analyzed by their pattern of vibrational bands obtained with IR photodissociation spectroscopy of weakly bound H molecules.

Determination of the SmO bond energy by threshold photodissociation of the cryogenically cooled ion.

The SmO bond energy has been measured by monitoring the threshold for photodissociation of the cryogenically cooled ion. The action spectrum features a very sharp onset, indicating a bond energy of 5.596 ± 0.

On the Hydrogen Oxalate Binding Motifs onto Dinuclear Cu and Ag Metal Phosphine Complexes.

We report the binding geometries of the isomers that are formed when the hydrogen oxalate ((CO ) H=HOx) anion attaches to dinuclear coinage metal phosphine complexes of the form [M M dcpm (HOx)] with M=Cu, Ag and dcpm=bis(dicyclohexylphosphino)methane, abbreviated [MM] . These structures are established by comparison of isomer-selective experimental vibrational band patterns displayed by the cryogenically cooled and N -tagged cations with DFT calculations of the predicted spectra for various local minima. Two isomeric classes are identified that feature either attachment of the carboxylate oxygen atoms to the two metal centers (end-on docking) or attachment of oxygen atoms on different carbon atoms asymmetrically to the metal ions (side-on docking).

Chemical Reduction of Ni Cyclam and Characterization of Isolated Ni Cyclam with Cryogenic Vibrational Spectroscopy and Inert-Gas-Mediated High-Resolution Mass Spectrometry.

Ni cyclam (cyclam = 1,4,8,11-tetraazacyclotetradecane) is an efficient catalyst for the selective reduction of CO to CO. A crucial elementary step in the proposed catalytic cycle is the coordination of CO to a Ni cyclam intermediate. Isolation and spectroscopic characterization of this labile Ni species without solvent has proven to be challenging, however, and only partial IR spectra have previously been reported using multiple photon fragmentation of ions generated by gas-phase electron transfer to the Ni cyclam dication at 300 K.

Destruction and reconstruction of UO using gas-phase reactions.

While the strong axial U[double bond, length as m-dash]O bonds confer high stability and inertness to UO22+, it has been shown that the axial oxo ligands can be eliminated or replaced in the gas-phase using collision-induced dissociation (CID) reactions. We report here tandem mass spectrometry experiments initiated with a gas-phase complex that includes UO22+ coordinated by a 2,6-difluorobenzoate ligand. After decarboxylation to form a difluorophenide coordinated uranyl ion, [UO2(C6F2H3)]+, CID causes elimination of CO, and then CO and C2H2 in sequential dissociation steps, to leave a reactive uranium fluoride ion, [UF2(C2H)]+.

Collision-induced dissociation of [UO (NO )(O )] and reactions of product ions with H O and O.

We recently reported a detailed investigation of the collision-induced dissociation (CID) of [UO (NO ) ] and [UO (NO ) (O )] in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10.

Collision-induced dissociation of [UO (NO ) ] and [UO (NO ) (O )] and reactions of product ions with H O and O.

Electrospray ionization (ESI) can produce a wide range of gas-phase uranyl (UO ) complexes for tandem mass spectrometry studies of intrinsic structure and reactivity. We describe here the formation and collision-induced dissociation (CID) of [UO (NO ) ] and [UO (NO ) (O )] . Multiple-stage CID experiments reveal that the complexes dissociate in reactions that involve elimination of O , NO , or NO , and subsequent reactions of interesting uranyl-oxo product ions with (neutral) H O and/or O were investigated.

Characterization of the non-covalent docking motif in the isolated reactant complex of a double proton-coupled electron transfer reaction with cryogenic ion spectroscopy.

The solution kinetics of a proton-coupled electron transfer reaction involving two-electron oxidation of a Ru compound with concomitant transfer of two protons to a quinone derivative have been interpreted to indicate the formation of a long-lived intermediate between the reactants. We characterize the ionic reactants, products, and an entrance channel reaction complex in the gas phase using high-resolution mass spectrometry augmented by cryogenic ion IR photodissociation spectroscopy. Collisional activation of this trapped entrance channel complex does not drive the reaction to products but rather yields dissociation back to reactants.

Characterization of the alkali metal oxalates (MCO) and their formation by CO reduction via the alkali metal carbonites (MCO).

The reduction of carbon dioxide to oxalate has been studied by experimental Collisionally Induced Dissociation (CID) and vibrational characterization of the alkali metal oxalates, supplemented by theoretical electronic structure calculations. The critical step in the reductive process is the coordination of CO2 to an alkali metal anion, forming a metal carbonite MCO2- able to subsequently receive a second CO2 molecule. While the energetic demand for these reactions is generally low, we find that the degree of activation of CO2 in terms of charge transfer and transition state energies is the highest for lithium and systematically decreases down the group (M = Li-Cs).

Integration of High-Resolution Mass Spectrometry with Cryogenic Ion Vibrational Spectroscopy.

We describe an instrumental configuration for the structural characterization of fragment ions generated by collisional dissociation of peptide ions in the typical MS scheme widely used for peptide sequencing. Structures are determined by comparing the vibrational band patterns displayed by cryogenically cooled ions with calculated spectra for candidate structural isomers. These spectra were obtained in a linear action mode by photodissociation of weakly bound D molecules.

Isotope labeling and infrared multiple-photon photodissociation investigation of product ions generated by dissociation of [ZnNO(CHOH)]: Conversion of methanol to formaldehyde.

Electrospray ionization was used to generate species such as [ZnNO(CHOH)] from Zn(NO)•XHO dissolved in a mixture of CHOH and HO. Collision-induced dissociation of [ZnNO(CHOH)] causes elimination of CHOH to form [ZnNO(CHOH)]. Subsequent collision-induced dissociation of [ZnNO(CHOH)] causes elimination of 47 mass units (u), consistent with ejection of HNO.

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes.

The speciation and reactivity of uranium are topics of sustained interest because of their importance to the development of nuclear fuel processing methods, and a more complete understanding of the factors that govern the mobility and fate of the element in the environment. Tandem mass spectrometry can be used to examine the intrinsic reactivity (i.e.

Collision-induced dissociation of uranyl-methoxide and uranyl-ethoxide cations: Formation of UO2 H(+) and uranyl-alkyl product ions.

Rationale: The lower levels of adventitious H2 O in a linear ion trap allow the fragmentation reactions of [UO2 OCH3 ](+) and [UO2 OCH2 CH3 ](+) to be examined in detail.

Methods: Methanol- and ethanol-coordinated UO2 (2+) -alkoxide precursors were generated by electrospray ionization (ESI). Multiple-stage tandem mass spectrometry (MS(n) ) and collision-induced dissociation (CID) were performed using a linear ion trap mass spectrometer.

Common Questions About Streptococcal Pharyngitis.

Group A beta-hemolytic streptococcal (GABHS) infection causes 15% to 30% of sore throats in children and 5% to 15% in adults, and is more common in the late winter and early spring. The strongest independent predictors of GABHS pharyngitis are patient age of five to 15 years, absence of cough, tender anterior cervical adenopathy, tonsillar exudates, and fever. To diagnose GABHS pharyngitis, a rapid antigen detection test should be ordered in patients with a modified Centor or FeverPAIN score of 2 or 3.