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The gas-phase ion-molecule identity exchange reactions of phenyl chalcogen iranium ions with alkenes have been examined experimentally in a linear ion trap mass spectrometer by isotope labeling experiments. The nature of both the alkene and the chalcogen play crucial roles, with the bimolecular rates for π-ligand exchange following the order: [PhTe( c -C 6 H 10 )] + + c -C 6 D 10 > [PhTe(C 2 D 4 )] + + C 2 H 4 > [PhSe( c -C 6 H 10 )] + + c -C 6 D 10 , with no reaction being observed for [PhSe(C 2 D 4 )] + + C 2 H 4 , [PhS(C 2 D 4 )] + + C 2 H 4 , and [PhS( c -C 6 H 10 )] + + c -C 6 D 10 . The experimental results correlate with RRKM modeling and density functional theory (DFT) calculations, which also demonstrates that these reactions proceed via associative mechanisms. Natural bond orbital (NBO) analysis reveals a shift in the association complexes from a σ-hole interaction to ones mirroring the π-p + and n-π* at the transition state in accordance with the rates of reaction.

Ion-molecule reactions between thiiranium ion 11 ( m/z 213) and cyclohexene and cis -cyclooctene resulted in the formation of addition products 17a and 17b ( m/z 295 and m/z 323, respectively) via an electrophilic addition pathway. Associative π-ligand exchange involving direct transfer of the PhS + moiety, which has been observed for analogous seleniranium ions in the gas phase, did not occur despite previous solution experiments suggesting it as a valid pathway. DFT calculations at the M06-2X/def2-TZVP level of theory showed high barriers for the exchange reaction, while the addition pathway was more plausible. Further support for this pathway was provided with Hammett plots showing the rate of reaction to increase as the benzylic position of thiiranium ion derivatives became more electrophilic (ρ = +1.69; R 2 = 0.974). The more reactive isomeric sulfonium ion 22 was discounted as being responsible for the observed reactivity with infrared spectroscopy and DFT calculations suggesting little possibility for isomerization. To further explore the differences in reactivity, thiiranium ion 25 and sulfonium ion 27 were formed independently, with the latter ion reacting over 260 times faster toward cis -cyclooctene than the thiiranium ion rationalized by calculations suggesting a barrierless pathway for sulfonium ion 27 to react with the cycloalkene.

Two gas-phase catalytic cycles involving C-F bond activation of trifluoroethanol and trifluoroacetic acid were detected by multistage mass spectrometry experiments. A binuclear dimolybdate centre [Mo 2 O 6 (F)] - acts as the catalyst in each cycle. The first cycle, entered via the reaction of [Mo 2 O 6 (OH)] - with trifluoroethanol and elimination of water to form [Mo 2 O 6 (OCH 2 CF 3 )] - , proceeds via four steps: (1) oxidation of the alkoxo ligand and its elimination as aldehyde; (2) reaction of [Mo 2 O 5 (OH)] - with trifluoroethanol and elimination of water to form [Mo 2 O 5 (OCH 2 CF 3 )]; (3) decomposition of the alkoxo ligand via loss of 1,1 difluoroethene; and (4) reaction of [Mo 2 O 6 (F)] - with a second equivalent of trifluoroethanol to regenerate Mo 2 O 6 (OCH 2 CF 3 )] - . Steps (2) and (3) do not occur at room temperature and require collisional activation to proceed. The second cycle is entered via the reaction of [Mo 2 O 6 (OH)] - with trifluoroacetic acid and elimination of water to form [Mo 2 O 6 (O 2 CCF 3 )] - and involves two steps only: (1) fluoride transfer to a molybdenum centre to form [Mo 2 O 6 (F)] - ; (2) reaction of [Mo 2 O 6 (F)] - with trifluoroacetic acid and loss of water to regenerate [Mo 2 O 6 (O 2 CCF 3 )] - . Comparisons are made with the chemistry of [Mo 2 O 6 (OH)] - reacting with acetic acid.

The deleterious cellular effects of ionizing radiation are well-known, but the mechanisms causing DNA damage are poorly understood. The accepted molecular events involve initial oxidation and deprotonation at guanine sites, triggering hydrogen atom abstraction reactions from the sugar moieties, causing DNA strand breaks. Probing the chemistry of the initially formed radical cation has been challenging. Here, we generate, spectroscopically characterize, and examine the reactivity of the Watson-Crick nucleobase pair radical cation in the gas phase. We observe rich chemistry, including proton transfer between the bases and propagation of the radical site in deoxyguanosine from the base to the sugar, thus rupturing the sugar. This first example of a gas-phase model system providing molecular-level details on the chemistry of an ionized DNA base pair paves the way toward a more complete understanding of molecular processes induced by radiation. It also highlights the role of radical propagation in chemistry, biology, and nanotechnology.

Collision-induced dissociation mass spectrometry of the ammonium ions 4a and 4b results in the formation of the seleniranium ion 5, the structure and purity of which were verified using gas-phase infrared spectroscopy coupled to mass spectrometry and gas-phase ion-mobility measurements. Ion-molecule reactions between the ion 5 (m/z = 261) and cyclopentene, cyclohexene, cycloheptene, and cyclooctene resulted in the formation of the seleniranium ions 7 (m/z = 225), 6 (m/z = 239), 8 (m/z = 253), and 9 (m/z = 267), respectively. Further reaction of seleniranium 6 with cyclopentene resulted in further π-ligand exchange giving seleniranium ion 7, confirming that direct π-ligand exchange between seleniranium ion 5 and cycloalkenes occurs in the gas phase. Pseudo-first-order kinetics established relative reaction efficiencies for π-ligand exchange for cyclopentene, cyclohexene, cycloheptene. and cyclooctene as 0.20, 0.07, 0.43, and 4.32. respectively. DFT calculations at the M06/6-31+G(d) level of theory provide the following insights into the mechanism of the π-ligand exchange reactions; the cycloalkene forms a complex with the seleniranium ion 5 with binding energies of 57 and 62 kJ/mol for cyclopentene and cyclohexene, respectively, with transition states for π-ligand exchange having barriers of 17.8 and 19.3 kJ/mol for cyclopentene and cyclohexene, respectively.

A new palladium mediated "one pot" synthesis of thioamides from aromatic carboxylic acids (ArCO 2 H + RNCS → ArC(S)NHR + CO 2 ) was discovered by gas-phase experiments and theoretical studies. Palladium-mediated decarboxylation of aromatic carboxylic acids followed by addition of substituted isothiocyanates leads to the corresponding thioamide derivatives.

Metalloenzymes preorganize the reaction environment to steer substrate(s) along the required reaction coordinate. Here, we show that phosphine ligands selectively facilitate protonation of binuclear silver hydride cations, [LAg2(H)](+) by optimizing the geometry of the active site. This is a key step in the selective, catalysed extrusion of carbon dioxide from formic acid, HO2CH, with important applications (for example, hydrogen storage). Gas-phase ion-molecule reactions, collision-induced dissociation (CID), infrared and ultraviolet action spectroscopy and computational chemistry link structure to reactivity and mechanism. [Ag2(H)](+) and [Ph3PAg2(H)](+) react with formic acid yielding Lewis adducts, while [(Ph3P)2Ag2(H)](+) is unreactive. Using bis(diphenylphosphino)methane (dppm) reshapes the geometry of the binuclear Ag2(H)(+) scaffold, triggering reactivity towards formic acid, to produce [dppmAg2(O2CH)](+) and H2. Decarboxylation of [dppmAg2(O2CH)](+) via CID regenerates [dppmAg2(H)](+). These gas-phase insights inspired variable temperature NMR studies that show CO2 and H2 production at 70 °C from solutions containing dppm, AgBF4, NaO2CH and HO2CH.

The rhenium dioxide anion [ReO2](-) reacts with carbon dioxide in a linear ion trap mass spectrometer to produce [ReO3](-) corresponding to activation and cleavage of a C-O bond. Isotope labeling experiments using [Re(18)O2](-) reveal that (18)O/(16)O scrambling does not occur prior to cleavage of the C-O bond. Density functional theory calculations were performed to examine the mechanism for this oxygen atom abstraction reaction. Because the spins of the ground states are different for the reactant and product ions ((3)[ReO2](-) versus (1)[ReO3](-)), both reaction surfaces were examined in detail and multiple [O2Re-CO2](-) intermediates and transition structures were located and minimum energy crossing points were calculated. The computational results show that the intermediate [O2Re(η(2)-C,O-CO2)](-) species most likely initiates C-O bond activation and cleavage. The stronger binding affinity of CO2 within this species and the greater instabilities of other [O2Re-CO2)](-) intermediates are significant enough that oxygen atom exchange is avoided.

Borohydrides react with silver salts to give products that span multiple scales ranging from discrete mononuclear compounds through to silver nanoparticles and colloids. The cluster cations [Ag3(H)(BH4)L3](+) are observed upon electrospray ionization mass spectrometry of solutions containing sodium borohydride, silver(I) tetrafluoroborate and bis(dimethylphosphino)methane (L(Me)) or bis(diphenylphosphino)methane (L(Ph)). By adding NaBH4 to an acetonitrile solution of AgBF4 and L(Ph), cooled to ca. -10 °C, we have been able to isolate the first mixed silver hydride borohydride nanocluster, [Ag3(μ3-H)(μ3-BH4)L(Ph)3]BF4, and structurally characterise it via X-ray crystallography. Combined gas-phase experiments (L(Me) and L(Ph)) and DFT calculations (L(Me)) reveal how loss of a ligand from the cationic complexes [Ag3(H)(BH4)L3](+) provides a change in geometry that facilitates subsequent loss of BH3 to produce the dihydride clusters, [Ag3(H)2Ln](+) (n = 1 and 2). Together with the results of previous studies (Girod et al., Chem. - Eur. J., 2014, 20, 16626), this provides a direct link between mixed silver hydride/borohydride nanoclusters, silver hydride nanoclusters, and silver nanoclusters.

Gas-phase studies utilizing ion-molecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes [(CH2CO2-C,O)M(CH3)](-) (M = Ni (5a), Pd (5b)) with allyl acetate proceed via oxidative addition to give M(IV) species [(CH2CO2-C,O)M(CH3)(η(1)-CH2-CH═CH2)(O2CCH3-O,O')](-) (6) that reductively eliminate 1-butene, to form [(CH2CO2-C,O)M(O2CCH3-O,O')](-) (4). The mechanism contrasts with the M(II)-mediated pathway for the analogous reaction of [(phen)M(CH3)](+) (1a,b) (phen = 1,10-phenanthroline). The different pathways demonstrate the marked effect of electron-rich metal centers in enabling higher oxidation state pathways. Due to the presence of two alkyl groups, the metal-occupied d orbitals (particularly dz(2)) in 5 are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from dz(2) to the C═C π* orbital is the key interaction leading to oxidative addition of allyl acetate to M(II). Upon collision-induced dissociation, 4 undergoes decarboxylation to form 5. These results provide support for the current exploration of roles for Ni(IV) and Pd(IV) in organic synthesis.

Although the deleterious effects of ozone on the human respiratory system are well-known, many of the precise chemical mechanisms that both cause damage and afford protection in the pulmonary epithelial lining fluid are poorly understood. As a key first step to elucidating the intrinsic reactivity of ozone with proteins, its reactions with deprotonated cysteine [Cys-H](-) are examined in the gas phase. Reaction proceeds at near the collision limit to give a rich set of products including 1) sequential oxygen atom abstraction reactions to yield cysteine sulfenate, sulfinate and sulfonate anions, and significantly 2) sulfenate radical anions formed by ejection of a hydroperoxy radical. The free-radical pathway occurs only when both thiol and carboxylate moieties are available, implicating electron-transfer as a key step in this reaction. This novel and facile reaction is also observed in small cys-containing peptides indicating a possible role for this chemistry in protein ozonolysis., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The bis(diphenylphosphino)methane (L = Ph2PCH2PPh2) ligated silver deuteride nanocluster dication, [Ag10D8L6](2+), has been synthesised in the condensed phase via the reaction of bis(diphenylphosphino)methane, silver nitrate and sodium borodeuteride in the methanol : chloroform (1 : 1) mixed solvent system. The photoionisation and photofragmentation of this mass-selected cluster were studied using a linear ion trap coupled to the DESIRS VUV beamline of the SOLEIL Synchrotron. At 15.5 eV the main ionic products observed are [Ag10D8L5](2+), [Ag10D8L4](2+), [Ag10D8L6](3+)˙, [Ag9D8L4](2+)˙, and [AgL2](+). The later two products arise from fragmentation of [Ag10D8L6](3+)˙. An analysis of the yields of these product ions as a function of the photon energy reveals the onset for the formation of [AgL2](+) and [Ag9D8L4](2+)˙ is around 2 eV higher than that for ionisation to produce [Ag10D8L5](3+)˙. The onset of ionisation energy of [Ag10D8L6](2+) was determined to be 9.3 ± 0.3 eV from a fit of the yield of the product ion, [Ag10D8L6](3+)˙, as a function of the VUV photon energy. DFT calculations at the RI-PBE/RECP-def2-SVP level of theory were carried out to search for a possible structure of the cluster and to estimate its vertical and adiabatic ionisation energies. The calculated lowest energy structure of the [Ag10D8L6](2+) nanocluster contains a symmetrical bicapped square antiprism as a silver core in which hydrides are located as a mix of triangular faces and edges. Four of the bisphosphines bind to the edges of the cluster core as bidentate ligands, the remaining two bisphosphines bind via a single phosphorus donor atom to each of the apical silver atoms. The DFT calculated adiabatic ionisation energy for this structure is 8.54 eV, in satisfactory agreement with experiment.

Guanine radical cations are formed upon oxidation of DNA. Deoxyguanosine (dG) is used as a model, and the gas-phase infrared (IR) spectroscopic signature and gas-phase unimolecular and bimolecular chemistry of its radical cation, dG˙(+), A, which is formed via direct electrospray ionisation (ESI/MS) of a methanolic solution of Cu(NO3)2 and dG, are examined. Quantum chemistry calculations have been carried out on 28 isomers and comparisons between their calculated IR spectra and the experimentally-measured spectra suggest that A exists as the ground-state keto tautomer. Collision-induced dissociation (CID) of A proceeds via cleavage of the glycosidic bond, while its ion–molecule reactions with amine bases occur via a number of pathways including hydrogen-atom abstraction, proton transfer and adduct formation. A hidden channel, involving isomerisation of the radical cation via adduct formation, is revealed through the use of two stages of CID, with the final stage of CID showing the loss of CH2O as a major fragmentation pathway from the reformed radical cation, dG˙(+). Quantum chemistry calculations on the unimolecular and bimolecular reactivity are also consistent with A being present as a ground-state keto tautomer.

Rationale: Non-covalent amino acid clusters are the subject of intense research in diverse areas including peptide bond formation studies or the determination of proton affinities or methylating abilities of amino acids. However, most of the research has focused on positive ions and little is known about anionic clusters., Methods: Fragmentation reactions of deprotonated tryptophan (Trp), [Trp-H](-) and Trp singly deprotonated non-covalently bound clusters [Trp(n) -H](-), n = 2, 3, 4, were investigated using low-energy collision-induced dissociation (CID) with He atoms, high-energy CID with Na atoms, and electron-induced dissociation (EID) with 20-35 eV electrons. Fragmentation of the monomeric Trp anion, where all labile hydrogens were exchanged for deuterium [d(4) -Trp-D](-), was investigated using low-energy CID and EID, in order to shed light on the dissociation mechanisms., Results: The main fragmentation channel for Trp cluster anions, [Trp(n) -H](-), n >1, is the loss of the neutral monomer. The fragmentation of the deprotonated Trp monomer induced by electrons resembles the fragmentation induced by high-energy collisions through electronic excitation of the parent. However, the excitation must precede in a different way, shown through only monomer loss from larger clusters, n >1, in case of EID, but intracluster chemistry in the case of high-energy CID., Conclusions: The anion of the indole ring C(8)H(6) N(-) has been identified in the product ion spectra of [Trp(n) -H](-) using all activation methods, thus providing a diagnostic marker ion. No evidence was found for formation of peptide bonds as a route to prebiotic peptides in the fragmentation reactions of these singly deprotonated Trp cluster ions., (Copyright © 2015 John Wiley & Sons, Ltd.)

A combination of gas-phase ion trap multistage mass spectrometry (MS(n)) experiments and density functional theory (DFT) calculations have been used to examine the mechanisms of the sequential decomposition reactions of copper cyanoacetate anions, [(NCCH2CO2)2Cu](-), introduced into the gas-phase via electrospray ionization. Gas phase IR spectroscopy, used to probe the coordination mode of the cyanoacetate ligands, revealed that the initial precursor ions are bound to the Cu via the carboxylate, [NCCH2CO2CuO2CCH2CN], 1. Multistage collision-induced dissociation (CID) of 1 gave sequential losses of CO2 and ethene. DFT calculations suggest that the lowest energy pathways for sequential decarboxylation involve Lewis acid mechanisms in which the binding of the cyanoacetate ligand sequentially rearranges from O to N: [NCCH2CO2CuO2CCH2CN](-) → [NCCH2CO2CuNCCH2CO2](-) → [NCCH2CO2CuNCCH2](-) + CO2 and [NCCH2CO2CuNCCH2](-) → [O2CCH2CNCuNCCH2](-) → [CH2CNCuNCCH2](-) + CO2. Loss of ethene involves sequential rearrangement of the binding of the cyanomethyl carbanion ligands from N to C: [CH2CNCuNCCH2](-) → [NCCH2CuNCCH2](-) → [NCCH2CuCH2CN](-). CH2=CH2 loss then proceeds via a 1,2-dyotropic rearrangement to form [NCCuCH2CH2CN](-) followed by β-cyanide transfer. This study highlights the rich mechanistic possibilities for metal mediated decarboxylation reactions involving ambidentate carboxylate ligands.

The ion-molecule reactions of the rhenium oxide anions, [ReOx](-) (x = 2 - 4) with the organic substrates methane, ethene, methanol and acetic acid have been examined in a linear ion trap mass spectrometer. The only reactivity observed was between [ReO(2)](-) and acetic acid. Isotope labelled experiments and high-resolution mass spectrometry measurements were used to assign the formulas of the ionic products. Collision-induced dissociation and ion-molecule reactions with acetic acid were used to probe the structures of the mass-selected primary product ions. Density functional theory calculations [PBE0/LanL2DZ6-311+G(d)] were used to suggest possible structures. The three primary product channels observed are likely to arise from the formation of: the metallalactone [ReO(2)(CH(2)CO(2))](-) (m/z 277) and H(2); [CH(3)ReO(2)(OH)](-) (m/z 251) and CO; and [ReO(3)](-) (m/z 235), H(2) and CH(2)CO.

Gas-phase carbon-carbon bond forming reactions, catalyzed by group 10 metal acetate cations [(phen)M(O2CCH3)](+) (where M = Ni, Pd or Pt) formed via electrospray ionization of metal acetate complexes [(phen)M(O2CCH3)2], were examined using an ion trap mass spectrometer and density functional theory (DFT) calculations. In step 1 of the catalytic cycle, collision induced dissociation (CID) of [(phen)M(O2CCH3)](+) yields the organometallic complex, [(phen)M(CH3)](+), via decarboxylation. [(phen)M(CH3)](+) reacts with allyl acetate via three competing reactions, with reactivity orders (% reaction efficiencies) established via kinetic modeling. In step 2a, allylic alkylation occurs to give 1-butene and reform metal acetate, [(phen)M(O2CCH3)](+), with Ni (36%) > Pd (28%) > Pt (2%). Adduct formation, [(phen)M(C6H11O2)](+), occurs with Pt (24%) > Pd (21%) > Ni(11%). The major losses upon CID on the adduct, [(phen)M(C6H11O2)](+), are 1-butene for M = Ni and Pd and methane for Pt. Loss of methane only occurs for Pt (10%) to give [(phen)Pt(C5H7O2)](+). The sequences of steps 1 and 2a close a catalytic cycle for decarboxylative carbon-carbon bond coupling. DFT calculations suggest that carbon-carbon bond formation occurs via alkene insertion as the initial step for all three metals, without involving higher oxidation states for the metal centers.

Multistage mass spectrometry and density functional theory (DFT) were used to characterise the small silver hydride nanocluster, [Ag3 H2 L](+) (where L=(Ph2 P)2 CH2 ) and its gas-phase unimolecular chemistry. Collision-induced dissociation (CID) yields [Ag2 HL](+) as the major product while laser-induced dissociation (LID) proceeds via H2 formation and subsequent release from [Ag3 H2 L](+) , giving rise to [Ag3 L](+) as the major product. Deuterium labelling studies on [Ag3 D2 L](+) prove that the source of H2 is from the hydrides and not from the ligand. Comparison of TD-DFT absorption patterns obtained for the optimised structures with action spectroscopy results, allows assignment of the measured features to structures of precursors and products. Molecular dynamics "on the fly" reveal that AgH loss is favoured in the ground state, but H2 formation and loss is preferred in the first excited state S1 , in agreement with CID and LID experimental findings. This indicates favourable photo-induced formation of H2 and subsequent release from [Ag3 H2 L](+) , an important finding in context of metal hydrides as a hydrogen storage medium, which can subsequently be released by heating or irradiation with light., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A combination of gas-phase ion-molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC≡CLiCl](-) reacts with water more rapidly than [HC≡CMgCl2](-), consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC≡CLiCl](-) or [HC≡CMgCl2](-) enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC≡CMgCl2](-) enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A bis(diphenylphosphino)methane-ligated trinuclear silver hydride nanocluster, [Ag3((Ph2P)2CH2)3(μ3-H)](BF4)2, featuring three silver(I) ions coordinated to a μ3-hydride, and its deuteride analogue, [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2, have been isolated and structurally characterized using electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography, NMR and IR spectroscopy. The position of the deuteride in [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2 was determined by neutron diffraction. ESI-MS of [Ag3L3(μ3-H/D)](BF4)2 [L = ((Ph2P)2CH2)2] produces [Ag3L3(μ3-H/D)](2+) and [Ag3L3(μ3-H/D)(BF4)](+). A rich gas-phase ion chemistry of [Ag3L3(μ3-H/D)](2+) is observed under conditions of collision-induced dissociation (CID) and electron-capture dissociation (ECD). CID gives rise to the following complementary ion pairs: [Ag3L2](+) and [L+(H/D)](+); [Ag2(H/D)L2](+) and [AgL](+); [Ag2(H/D)L](+) and [AgL2](+). ECD gives rise to a number of dissociation channels including loss of the bis(phosphine) ligand, fragmentation of a coordinated bis(phosphine) ligand via C-P bond activation, and loss of a hydrogen (deuterium) atom with concomitant formation of [Ag3L3](+). Under CID conditions, [Ag3L3(μ3-H/D)(BF4)](+) fragments via ligand loss, the combined loss of a ligand and [H,B,F4], and cluster fragmentation to give [Ag2(BF4)L2](+) and [Ag2(L-H)L](+) [where (L-H) = (Ph2P)2CH(-)].

Product and mechanistic studies were performed for the reaction of aromatic distonic peroxyl radical cations 4-PyrOO(•+) and 3-PyrOO(•+) with phenylacetylene (7) in the gas phase using mass spectrometric and computational techniques. PyrOO(•+) was generated through reaction of the respective distonic aryl radical cation Pyr(•+) with O2 in the ion source of the mass spectrometer. For the reaction involving the more electrophilic 4-PyrOO(•+), a rate coefficient of k1 = (2.2 ± 0.6) × 10(-10) cm(3) molecule(-1) s(-1) was determined at 298 K, while a value of k2 = (8.2 ± 2.1) × 10(-11) cm(3) molecule(-1) s(-1) was obtained for the reaction involving the less electrophilic 3-PyrOO(•+). This highlights the role of polar effects in these reactions, which are likely of high relevance for processes in combustions and atmospheric transformations. The mechanism was studied by computational methods, which showed that radical addition occurs exclusively at the less substituted alkyne site to give the distonic vinyl radical cation 8. The latter undergoes a series of subsequent rearrangements/fragmentations that are similar for both isomeric PyrOO(•+). γ-Fragmentation in 8 leads to the distonic aryloxyl radical cation PyrO(•+) and a singlet carbene 10. The product association complex [PyrO(•+) - 10] is the starting point for two important subsequent reactions, e.g., (i) rapid hydrogen transfer to form ketenyl radical 11 and the closed-shell species PyrOH(+), and (ii) oxygen transfer from PyrO(•+) to 10 that leads to α-keto aldehyde 13 and Pyr(•+), followed by hydrogen abstraction to give acyl radical 14 and PyrH(+). Additional major products are the closed-shell aromatic carbonyl compounds 20 and 30 that result from multistep rearrangements in vinyl radical 8, which are terminated by homolytic bond scission and release of neutral acyl radicals.

Oxidative damage to DNA yields guanine radical cations. Their gas-phase IR spectroscopic signature and acidity have been modelled by the radical cation of 9-methylguanine. Comparisons with quantum chemistry calculations suggest that radical cation formation produces the ground-state keto tautomer, which has an N-H acidity enhanced by ~470 kJ mol(-1).

The human metallo-chaperone protein Atox1 features a high affinity Cu(I) binding site Cys(12)GlyGlyCys(15) (KD = 10(-17.4) M at pH 7.0) and delivers copper to the trans-Golgi network (TGN). Atox1 may participate in the metabolism of the drug cis-Pt(NH3)2Cl2 (cisplatin), either as a component of its delivery to the nucleus or of its loss via transport to the TGN and beyond. The species of stoichiometry [Pt(NH3)2(Atox1)] was the sole adduct of stoichiometry Pt : Atox1 = 1 : 1 detected by mass spectrometry under non-denaturing conditions from solutions containing cisplatin and apo-Atox1. The ions [Atox1 + Pt(NH3)2(2+) + (z - 2)H(+)](z+) (z = 3 to 7) were observed and correspond to different protonation states of the 1 : 1 adduct. Adducts of stoichiometry Pt : Atox1 = 2 : 1 were also detected but 1 : 2 adducts were not detected. The related complex Pt(en)Cl2 (en = 1,2-diaminoethane) behaved similarly. Tandem mass spectrometry experiments using top-down and bottom-up sequencing techniques were carried out, respectively, on the intact platinated protein and on platinated peptides formed from proteolysis by trypsin. A new software programme (PolyCut) designed to analyse the complex high-resolution tandem mass spectra of fragment ions derived from proteins containing transition metal ions was applied to establish the binding site(s) of the platinum atom(s). The analysis, based on the entire isotope patterns, is consistent with the cysteine residues in the Cu(I)-binding sequence Cys(12)GlyGlyCys(15) being the primary coordination site.

Alkynylsilver cations, RC≡CAg2(+) (where R = Me and Ph) have been prepared in the gas phase using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. Two methods were used: (i) electrospray ionisation (ESI) of a mixture of AgNO3 (in MeOH/H2O/acetic acid) and the alkyne carboxylic acid to yield the appropriate silver acetylide cations RC≡CAg2(+), via a facile decarboxylation of the RC≡CCO2Ag2(+) precursor; (ii) ESI of silver acetylides, RC≡CAg, which yields a cluster of the type, [(RC≡CAg)12Ag2Cl](+). Regardless of the method of preparation, these alkynylsilver cations, RC≡CAg2(+), undergo ion-molecule reactions with allyliodide to yield the ionic products Ag2I(+) and [(RC≡CCH2CH=CH2)Ag](+). The CID spectrum of [(PhC≡CCH2CH=CH2)Ag](+) was compared to that of an authentic sample of the silver adduct of 5-phenyl-1-penten-4-yne. Both ions fragment to yield Ag(+) and the radical cation, PhC≡CCH2CH=CH2(+)˙, confirming that C-C bond coupling has taken place in the gas phase. DFT calculations were carried out on these C-C bond coupling reactions for the system R = Me. The reaction is highly exothermic and involves the initial coordination of the allyliodide to both silver atoms, with the iodine coordinating to one atom and the alkene moiety coordinating to the other. The overall mechanism of C-C bond coupling involves oxidative addition of the allyliodide followed by reductive elimination of RC≡CCH2CH=CH2, to ultimately yield two sets of reaction products: (i) Ag2I(+) and RC≡CCH2CH=CH2; and (ii) [(RC≡CCH2CH=CH2)Ag](+) and AgI.

The extent of internal energy deposition into ions upon storage, radial ejection, and detection using a linear quadrupole ion trap mass spectrometer is investigated as a function of ion size (m/z 59 to 810) using seven ion-molecule thermometer reactions that have well characterized reaction entropies and enthalpies. The average effective temperatures of the reactants and products of the ion-molecule reactions, which were obtained from ion-molecule equilibrium measurements, range from 295 to 350 K and do not depend significantly on the number of trapped ions, m/z value, ion trap q z value, reaction enthalpy/entropy, or the number of vibrational degrees of freedom for the seven reactions investigated. The average of the effective temperature values obtained for all seven thermometer reactions is 318 ± 23 K, which indicates that linear quadrupole ion trap mass spectrometers can be used to study the structure(s) and reactivity of ions at near ambient temperature.

A combination of multistage mass spectrometry experiments and density functional theory (DFT) calculations were used to examine the decarboxylation reactions of a series of metal carboxylate complexes bearing a fixed-charge phosphine ligand, [(O3SC6H4)(C6H5)2PM(I)O2CR](-) (M = Cu, Ag, Au; R = Me, Et, benzyl, Ph). Collision-induced dissociation (CID) of these complexes using an LTQ linear ion mass spectrometer results in three main classes of reactions being observed: (1) decarboxylation; (2) loss of the phosphine ligand; (3) loss of carboxylic acid. The gas-phase unimolecular chemistry of the resultant decarboxylated organometallic ions, [(O3SC6H4)(C6H5)2PM(I)R](-), were also explored using CID experiments, and fragment primarily via loss of the phosphine ligand. Energy-resolved CID experiments on [(O3SC6H4)(C6H5)2PM(I)O2CR](-) (M = Cu, Ag, Au; R = Me, Et, benzyl, Ph) using a Q-TOF mass spectrometer were performed to gain a more detailed understanding of the factors influencing coinage metal-catalyzed decarboxylation and DFT calculations on the major fragmentation pathways aided in interpretation of the experimental results. Key findings are that: (1) the energy required for loss of the phosphine ligand follows the order Ag < Cu < Au; (2) the ease of decarboxylation of the coordinated RCO2 groups follows the order of R: Ph < PhCH2 < Me < Et; (3) in general, copper is best at facilitating decarboxylation, followed by gold then silver. The one exception to this trend is when R = Ph and M = Au which has the highest overall propensity for decarboxylation. The influence of the phosphine ligand on decarboxylation is also considered in comparison with previous studies on metal carboxylates that do not contain a phosphine ligand.

Halide-templated tert-butylethynide Ag14 complexes undergo reversible exchange with copper(I) to afford a series of mixed Ag14-nCun (n = 1-6) species. Up to six silver atoms in the cluster can be replaced with copper(I) to give a core structure featuring a Ag8Cu6 rhombic dodecahedron. These clusters are useful models for investigating the chemical reactivity and photoluminescence of heterometallic d(10)-d(10) systems.

The benzoxyl radical is a key intermediate in the combustion of toluene and other aromatic hydrocarbons, yet relatively little experimental work has been performed on this species. Here, a combination of electrospray ionization (ESI), multistage mass spectrometry experiments, and density functional theory (DFT) calculations are used to examine the formation and fragmentation of a benzoxyl (benzyloxyl) distonic radical anion. Excited 4-carboxylatobenzoxyl radical anions were produced via two methods: (1) collision induced dissociation (CID) of the nitrate ester 4-(nitrooxymethyl)benzoate, (-)O2CC6H4CH2ONO2, and (2) reaction of ozone with the 4-carboxylatobenzyl radical anion, (-)O2CC6H4CH2(•). In neither case was the stabilized (-)O2CC6H4CH2O(•) radical anion intermediate detected. Instead, dissociation products at m/z 121 and 149 were observed. These products are attributed to benzaldehyde (O2(-)CC6H4CHO) and benzene ((-)O2CC6H5) products from respective loss of H and HCO radicals in the vibrationally excited benzoxyl intermediate. In no experiments was a product at m/z 120 (i.e., (-)O2CC6H4(•)) detected, corresponding to absence of the commonly assumed phenyl radical + CH2=O channel. The results reported suggest that distonic ions are useful surrogates for reactive intermediates formed in combustion chemistry.

Glucuronosyl diacylglycerides (GlcAGroAc2) are functionally important glycolipids and membrane anchors for cell wall lipoglycans in the Corynebacteria. Here we describe the complete synthesis of distinct acyl-isoforms of GlcAGroAc2 bearing both acylation patterns of (R)-tuberculostearic acid (C19:0) and palmitic acid (C16:0) and their mass spectral characterization. Collision-induced fragmentation mass spectrometry identified characteristic fragment ions that were used to develop "rules" allowing the assignment of the acylation pattern as C19:0 (sn-1), C16:0 (sn-2) in the natural product from Mycobacterium smegmatis, and the structural assignment of related C18:1 (sn-1), C16:0 (sn-2) GlcAGroAc2 glycolipids from M. smegmatis and Corynebacterium glutamicum. A synthetic hydrophobic octyl glucuronoside was used to characterize the GDP-mannose-dependent mannosyltransferase MgtA from C. glutamicum that extends GlcAGroAc2. This enzyme is an Mg(2+)/Mn(2+)-dependent metalloenzyme that undergoes dramatic activation upon reduction with dithiothreitol.

The gas-phase reactivity of the vanadium hydroxides [VO(2)(OH)(2)](-) and [V(2)O(5)(OH)](-) toward methanol was examined using a combination of ion-molecule reactions (IMRs) and collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer. Isotope-labeling experiments with CD(3)OH, (13)CH(3)OH, and CH(3)(18)OH were used to confirm the stoichiometry of ions and the observed sequence of reactions. The experimental data were interpreted with the aid of density functional theory calculations, carried out at the B3LYP/SDD6-311++G** level of theory. While [VO(2)(OH)(2)](-) is unreactive, [V(2)O(5)(OH)](-) undergoes a metathesis reaction to yield [V(2)O(5)(OCH(3))](-). The DFT calculations reveal that the metathesis reaction of methanol with [VO(2)(OH)(2)](-) suffers from a barrier of +0.52 eV (relative to separated reactants) but that the reaction of [V(2)O(5)(OH)](-) with methanol readily proceeds via addition/elimination reactions with both transition states being below the energy of the separated reactants. CID of [V(2)O(5)(OCH(3))](-) (m/z 213) yields three ions arising from activation of the methoxo ligand: [V(2), O(6), C, H](-) (m/z 211); [V(2), O(5), H](-) (m/z 183); and [V(2), O(4), H](-) (m/z 167). Additional experiments and DFT calculations suggest that these ions arise from losses of H(2), formaldehyde and the sequential losses of H(2) and CO(2), respectively. The use of an (18)O-labeled methoxo ligand in [V(2)O(5)((18)OCH(3))](-) (m/z 215) showed the competing losses of H(2)C(16)O and H(2)C(18)O and [H(2) and C(16)O(18)O] and [H(2) and C(16)O(2)], highlighting that (16)O/(18)O exchange between the methoxo ligand and the vanadium oxide occurs prior to the subsequent fragmentation of the ligand. DFT calculations reveal that a key step involves hydrogen atom transfer from the methoxo ligand to the oxo ligand of the same vanadium center, producing the intermediate [V(2)O(4)(OH)(OCH(2))](-) containing a ketyl radical ligand and a hydroxo ligand. This intermediate can either undergo CH(2)O loss, or the ketyl radical can couple with an oxo ligand of the adjacent vanadium center, producing [V(2)O(3)(μ(2)-O(2)CH(2))](-), which is a key intermediate in the (16)O/(18)O scrambling and in the H(2) loss channel.

The reaction of the aromatic distonic peroxyl radical cations N-methyl pyridinium-4-peroxyl (PyrOO(.+)) and 4-(N,N,N-trimethyl ammonium)-phenyl peroxyl (AnOO(.+)), with symmetrical dialkyl alkynes 10a-c was studied in the gas phase by mass spectrometry. PyrOO(.+) and AnOO(.+) were produced through reaction of the respective distonic aryl radical cations Pyr(.+) and An(.+) with oxygen, O(2). For the reaction of Pyr(.+) with O(2) an absolute rate coefficient of k(1)=7.1×10(-12) cm(3) molecule(-1) s(-1) and a collision efficiency of 1.2% was determined at 298 K. The strongly electrophilic PyrOO(.+) reacts with 3-hexyne and 4-octyne with absolute rate coefficients of k(hexyne)=1.5×10(-10) cm(3) molecule(-1) s(-1) and k(octyne)=2.8×10(-10) cm(3) molecule(-1) s(-1), respectively, at 298 K. The reaction of both PyrOO(.+) and AnOO(.+) proceeds by radical addition to the alkyne, whereas propargylic hydrogen abstraction was observed as a very minor pathway only in the reactions involving PyrOO(.+). A major reaction pathway of the vinyl radicals 11 formed upon PyrOO(.+) addition to the alkynes involves γ-fragmentation of the peroxy O-O bond and formation of PyrO(.+). The PyrO(.+) is rapidly trapped by intermolecular hydrogen abstraction, presumably from a propargylic methylene group in the alkyne. The reaction of the less electrophilic AnOO(.+) with alkynes is considerably slower and resulted in formation of AnO(.+) as the only charged product. These findings suggest that electrophilic aromatic peroxyl radicals act as oxygen atom donors, which can be used to generate α-oxo carbenes 13 (or isomeric species) from alkynes in a single step. Besides γ-fragmentation, a number of competing unimolecular dissociative reactions also occur in vinyl radicals 11. The potential energy diagrams of these reactions were explored with density functional theory and ab initio methods, which enabled identification of the chemical structures of the most important products., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Antigen-presenting molecules, encoded by the major histocompatibility complex (MHC) and CD1 family, bind peptide- and lipid-based antigens, respectively, for recognition by T cells. Mucosal-associated invariant T (MAIT) cells are an abundant population of innate-like T cells in humans that are activated by an antigen(s) bound to the MHC class I-like molecule MR1. Although the identity of MR1-restricted antigen(s) is unknown, it is present in numerous bacteria and yeast. Here we show that the structure and chemistry within the antigen-binding cleft of MR1 is distinct from the MHC and CD1 families. MR1 is ideally suited to bind ligands originating from vitamin metabolites. The structure of MR1 in complex with 6-formyl pterin, a folic acid (vitamin B9) metabolite, shows the pterin ring sequestered within MR1. Furthermore, we characterize related MR1-restricted vitamin derivatives, originating from the bacterial riboflavin (vitamin B2) biosynthetic pathway, which specifically and potently activate MAIT cells. Accordingly, we show that metabolites of vitamin B represent a class of antigen that are presented by MR1 for MAIT-cell immunosurveillance. As many vitamin biosynthetic pathways are unique to bacteria and yeast, our data suggest that MAIT cells use these metabolites to detect microbial infection.

Controversy resolved! A combination of gas-phase ion-molecule reactions and theoretical studies confirm bisligated mononuclear Au(I) complexes are unable to undergo oxidative addition of iodobenzene for Sonogashira coupling, but that the ligated gold clusters [Au(3)L(n)](+) (L=Ph(2)P(CH(2))(n)PPh(2); n=3-6) activate the C-I bond. DFT calculations on the transition states show that the linker size n tunes the cluster reactivity., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Silver acetylides and organic azides react under copper(I) catalysis to afford 1,4-disubstituted 1,2,3-triazoles. Mechanistic studies implicate a process involving transmetallation to copper acetylides prior to cycloaddition. This work demonstrates that silver acetylides serve as suitable precursors for entry into copper-mediated coupling reactions. This methodology allows the incorporation of volatile and difficult-to-handle acetylenes into the triazole core.

Previous studies have shown that highly reactive product ions formed by collision-induced dissociation (CID) of precursor ions generated via electrospray can readily react with residual solvent or drying gases, especially in ion trap mass spectrometers. Here we report on the rapid addition of nitrogen to the coordinatively unsaturated organoplatinum cation, [(phen)Pt(CH(3))](+) (phen=1,10-phenanthroline) formed via decarboxylation of the acetate complex [(phen)Pt(O(2) CCH(3))](+). This contrasts with the related coordinatively unsaturated group 10 cations: addition of nitrogen to [(phen)Pd(CH(3))](+) occurs at longer reaction times, whereas addition of nitrogen to [(phen)Ni(CH(3))](+) is virtually non-existent. To better understand these reactions, density functional theory (DFT) calculations were carried out at the B3LYP/SDD6-31+G(d) level of theory to determine the N(2)-binding energies of [(phen)M(CH(3))](+). [(phen)Pt(CH(3))](+) has a higher binding energy to N(2) (1.06 eV) than either [(phen)Ni(CH(3))](+) (0.61 eV) or [(phen)Pd(CH(3))](+) (0.66 eV), consistent with the experimental ease of addition of nitrogen to the coordinatively unsaturated organometallic complexes, [(phen)M(CH(3))](+). Finally, [(phen)M(CH(3))](+) are reactive to other background gases, forming [(phen)M(O(2))](.+) (for M=Ni) in reactions with oxygen and undergoing water addition (for M=Ni, Pd and Pt) and water addition/CH(4) elimination reactions to yield [(phen)M(OH)](+) (for M=Ni and Pt)., (Copyright © 2011 John Wiley & Sons, Ltd.)

Electrospray ionization and tandem mass spectrometry experiments have been used to study the fragmentation and electron-ion interactions of doubly charged zwitterionic clusters, [M(15) + 2H](2+) (where M = Glycine Betaine (GB), (CH(3))(3)N(+)CH(2)CO(2)(-), and Dimethylsulfonioacetate (DMSA), (CH(3))(2)S(+)CH(2)CO(2)(-)) which are close to the stability limit, i.e., the Coulomb repulsion of the charge within the cluster competes with attractive forces. The intercluster chemistry was studied using collision-induced dissociation (CID) and electron-induced dissociation (EID) in which the energy of the electrons has been varied from >0 to 30 eV. Experimental results suggest that the zwitterionic binding energy in the clusters follow the order GB > DMSA, which is consistent with theoretical calculations that highlight that the lower dipole moment of DMSA leads to a binding energy of DMSA that is 0.86 times smaller than that for GB. Multiply protonated clusters of both GB and DMSA dissociate through Coulomb explosion, which is in competition with neutral evaporation for DMSA. Electronic excitation of the cluster under EID conditions at higher electron energies >12 eV can lead to new intercluster reactions associated with bond cleavages where differences between the sulfur and nitrogen betaines are minor.

The fixed charge zwitterionic sulfur betaines dimethylsulfonioacetate (DMSA) (CH(3))(2)S(+)CH(2)CO(2)(-) and dimethylsulfoniopropionate (DMSP) (CH(3))(2)S(+)(CH(2))(2)CO(2)(-) have been synthesized and the structures of their protonated salts (CH(3))(2)S(+)CH(2)CO(2)H···Cl(-) [DMSA.HCl] and (CH(3))(2)S(+)(CH(2))(2)CO(2)H···Pcr(-) [DMSP.HPcr] (where Pcr = picrate) have been characterized using X-ray crystallography. The unimolecular chemistry of the [M+H](+) of these betaines was studied using two techniques; collision-induced dissociation (CID) and electron-induced dissociation (EID) in a hybrid linear ion trap Fourier transform ion cyclotron resonance mass spectrometer. Results from the CID study show a richer series of fragmentation reactions for the shorter chain betaine and contrasting main fragmentation pathways. Thus while (CH(3))(2)S(+)(CH(2))(2)CO(2)H fragments via a neighbouring group reaction to generate (CH(3))(2)S(+)H and the neutral lactone as the most abundant fragmentation channel, (CH(3))(2)S(+)CH(2)CO(2)H fragments via a 1,2 elimination reaction to generate CH(3)S(+)=CH(2) as the most abundant fragment ion. To gain insights into these fragmentation reactions, DFT calculations were carried out at the B3LYP/6-311++G(2d,p) level of theory. For (CH(3))(2)S(+)CH(2)CO(2)H, the lowest energy pathway yields CH(3)S(+)=CH(2)via a six-membered transition state. The two fragment ions observed in CID of (CH(3))(2)S(+)(CH(2))(2)CO(2)H are shown to share the same transition state and ion-molecule complex forming either (CH(3))(2)S(+)H or (CH(2))(2)CO(2)H(+). Finally, EID shows a rich and relatively similar fragmentation channels for both protonated betaines, with radical cleavages being observed, including loss of ˙CH(3).

The intrinsic methylating abilities of the known biological methylating zwitterionic agents, dimethylsulfonioacetate (DMSA), (CH(3))(2)S⁺CH(2)CO(2)(-) (1) and glycine betaine (GB), (CH(3))(3)N⁺CH(2)CO(2)(-) (2), have been examined via a range of gas phase experiments involving collision-induced dissociation (CID) of their proton-bound homo- and heterodimers, including those containing the amino acid arginine. The relative yields of the products of methyl cation transfer are consistent in all cases and show that protonated DMSA is a more potent methylating agent than protonated GB. Since methylation can occur at more than one site in arginine, the [M+CH(3)](+) ion of arginine, formed from the heterocluster [DMSA+Arg+H](+), was subject to an additional stage of CID. The resultant CID spectrum is virtually identical to that of an authentic sample of protonated arginine-O-methyl ester but is significantly different to that of an authentic sample of protonated N(G)-methyl arginine. This suggests that methylation has occurred within a salt bridge complex of [DMSA+Arg+H](+), in which the arginine exists in the zwitterionic form. Finally, density functional theory calculations on the model salts, (CH(3)CO(2)(-))[(CH(3))(3)S(+)] and (CH(3)CO(2)(-))[(CH(3))(4)N(+)], show that methylation of CH(3)CO(2)(-) by (CH(3))(3)S(+) is both kinetically and thermodynamically preferred over methylation by (CH(3))(4)N(+).

Electrospray ionization (ESI) of tryptophan gives rise to multiply charged, non-covalent tryptophan cluster anions, [Trp(n)-xH](x-), in a linear ion trap mass spectrometer, as confirmed by high-resolution experiments performed on a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The smallest multiply charged clusters that can be formed in the linear ion trap as a function of charge state are: x = 2, n = 7; x = 3, n = 16; x = 4, n = 31. The fragmentation of the dianionic cluster [Trp(9)-2H](2-) was examined via low-energy collision-induced dissociation (CID), ultraviolet photodissociation (UVPD) at 266  nm and electron-induced dissociation (EID) at electron energies ranging from >0 to 30  eV. CID proceeds mostly via charge separation and evaporation of neutral tryptophan. The smallest doubly charged cluster that can be formed via evaporation of neutral tryptophans is [Trp(7)-2H](2-), consistent with the observation of this cluster in the ESI mass spectrum. UVPD gives singly charged tryptophan clusters ranging from n = 2 to n = 9. The latter ion arises from ejection of an electron to give the radical anion cluster, [Trp(9)-2H](-·). The types of gas-phase EID reactions observed are dependent on the energy of the electrons. Loss of neutral tryptophan is an important channel at lower energies, with the smallest doubly charged ion, [Trp(7)-2H](2-), being observed at 19.8  eV. Coulomb explosion starts to occur at 19.8  eV to form the singly charged cluster ions [Trp(x)-H](-) (x = 1-8) via highly asymmetric fission. At 21.8  eV a small amount of [Trp(2)-H-NH(3)](-) is observed. Thus CID, UVPD and EID are complementary techniques for the study of the fragmentation reactions of cluster ions., (2010 John Wiley & Sons, Ltd.)

A combination of multistage mass spectrometry experiments and DFT calculations were used to examine the synthesis and reactivity of dimethylaurate. Collision induced dissociation (CID) of [(CH(3)CO(2))(4)Au](-) proceeded via reductive elimination of acetylperoxide to yield the diacetate [CH(3)CO(2)AuO(2)CCH(3)](-), which in turn underwent sequential CID decarboxylation reactions to yield the organoaurates [CH(3)CO(2)AuCH(3)](-) and [CH(3)AuCH(3)](-). The unimolecular chemistry of the dimethylaurate proceeds via a combination of bond homolysis to yield the methyl aurate radical anion [CH(3)Au] (-) as well as formation of the gold dihydride [HAuH](-). DFT calculations reveal that the latter anion is formed via a 1,2-dyotropic rearrangement to yield the isomer [CH(3)CH(2)AuH](-), followed by a beta-hydride elimination reaction. Ion-molecule reactions of [CH(3)AuCH(3)](-) with methyl iodide did not yield any products even at relatively high concentrations of the neutral substrate and longer reaction times, indicating a reaction efficiency of less than 1 in 20 000 collisions. DFT calculations were carried out on two different potential energy surfaces (PES) for the reaction of [CH(3)AuCH(3)](-) with CH(3)I: (i) an S(N)2 mechanism proceeding via a side-on transition state; and (ii) a stepwise mechanism proceeding via oxidative addition followed by reductive elimination. Both pathways have significant endothermic barriers, consistent with the lack of C-C bond coupling products being formed in the experiments. Finally, the reactivity of [CH(3)AuCH(3)](-) is compared to the previously studied [CH(3)AgCH(3)](-) and [CH(3)CuCH(3)](-), as well as condensed phase studies on dimethylaurate salts.

The gas phase fragmentation reactions of eta2 coordinated aldehydes in [VO2(eta2-OCHR)]-, which have previously been shown to play a role in the catalytic oxidation of alcohols to aldehydes, were examined using a combination of isotope labelling experiments and collision induced dissociation in a quadrupole ion trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations (DFT). The types of fragmentation reactions observed depend on the nature of the R group. When R = H, the dominant fragmentation channel involves formation of [VO2H2]-via loss of CO. Minor losses of H2 and CH2O are also observed. When R = Me, loss of H2 is observed to give rise to an ion at m/z 125 corresponding to the formula [V, O3, C2, H2]-. DFT calculations on the [VO2(eta2-OCHR)]- and their CID reaction products have identified minimum energy structures for all reactants and products involved. DFT calculations also provided insights into key intermediates on the potential energy surface associated with these fragmentation reactions, including: [(H2)VO2(CO)]- in the case of R = H; and [HVO2(eta1-OCHCH2)]- in the case of R = Me. The results presented provide insights into potential side reactions occurring during catalysis of alcohols over vanadium oxides, for instance, the over-oxidation of methanol to carbon monoxide.

Silver hexynyl cluster cations, [(C(4)H(9)CCAg)(n)Ag](+), exhibit a rich unimolecular chemistry that is dependant on the cluster size, n (1-5), cluster fragmentation (for all n > 1); C-C bond coupling (n = 3 & 4); C-H bond activation with comcomitant silver hydride formation (n = 1 & 4); C-C bond activation (n = 1 & 4).

Electrospray ionisation on a mixture of AgNO(3) (in MeOH/H(2)O/acetic acid), (CH(3)CO(2))(2)Cu (in MeOH) and acetic acid (in MeOH) yields the metal carboxylate cations CH(3)CO(2)Ag(2)(+), CH(3)CO(2)AgCu(+) and CH(3)CO(2)Cu(2)(+). Collision induced dissociation of these carboxylate cations yields the organometallic cations CH(3)Ag(2)(+), CH(3)AgCu(+) and CH(3)Cu(2)(+). The ion-molecule reactions of these organometallic cations with allyliodide were studied in a quadrupole ion trap mass spectrometer. C-C bond coupling occurred to yield the ionic products Ag(2)I(+), AgCuI(+) and Cu(2)I(+). DFT calculations were carried out on these C-C bond coupling reactions. In all cases, the reactions are highly exothermic and involve initial coordination of the allyliodide to both metal atoms, with the iodine coordinating to one atom and the alkene moiety coordinating to the other. The overall mechanism of C-C bond coupling involves oxidative addition of the allyliodide followed by reductive elimination of 1-butene.

Electrospray ionization (ESI) of solutions containing deoxyguanosine (dG) and tridentate platinum chloride complexes yields clusters of general formula [Pt(II)(L)(dG)(n)](2+), where L = 2,2':6',2'' terpyridine (terpy), or diethyltriamine (dien). When these clusters were mass selected and subjected to collision induced dissociation (CID), the primary fragmentation channels arise from loss of dG and protonated dG to yield the fragment ions [Pt(II)(L)(dG)(n-x)](2+) and [Pt(II)(L)(dG)(n-x)-H](+) respectively. The relative abundances of the [Pt(II)(L)(dG)(n-x)](2+) fragments depend on the nature of the ligand, L. The most abundant peaks observed were: n-x = 5 for terpy and n-x = 4 for dien. In order to further understand these gas phase reactions, molecular dynamics calculations were carried out. These simulated collision calculations not only predict with fidelity the experimental profiles for the relative abundances for the [Pt(II)(L)(dG)(n-x)](2+) fragments, for both terpy and dien ligand systems, but they also provide structural insights into the complex interplay of hydrogen bonding and stacking interactions within these clusters.

The chaperone protein CopC from Pseudomonas syringae features high-affinity binding sites (K (D) ~ 10(-13) M) for both Cu(I) (Met-rich) and Cu(II) (His-rich). When presented with these sites in the apoprotein, electrospray ionisation mass spectrometry confirmed that cis-Pt(NH(3))(2)Cl(2) (cisplatin) and the fragments [Pt(II)L](2+) (L is 1,2-diaminoethane, 2,2'-bipyridine) occupied the Cu(I) site specifically in the 1:1 Pt-CopC adducts (purified by cation-exchange chromatography). The cis-Pt(NH(3))(2) fragment was not present in these adducts (the dominant product for cisplatin was Pt-CopC in which all original ligands were displaced), while bidentate ligands L were retained in LPt-CopC adducts. In the context of the Met-rich Cu(I) pump Ctr1 as a significant entry point for cisplatin into mammalian cells, the present work confirms the ability of Met-rich sites in proteins to remove all ligands from cisplatin. It focuses attention on the potential of proteins that are part of the natural copper transport pathways to sequester the drug. These pathways are worthy of further study at the molecular level.

Aerial pingpong: The lithium acetate enolate anion, the prototypical lithium salt of an alpha-deprotonated carboxylate, was prepared in the gas phase by electrospray ionization (ESI) and collision-induced ionization (CID). Its structure, reactivity, and energetics are presented along with the results of high-level computations.

Multistage mass spectrometry (MS(n)) experiments reveal that gas phase silver iodide cluster cations, Ag(n)I(m)(+), are readily built up in a stepwise fashion via ion-molecule reactions between mass selected silver (Ag(3)(+) and Ag(5)(+)) or silver hydride (Ag(2)H(+) and Ag(4)H(+)) cluster cations and allyl iodide, in contrast to their reactions with methyl iodide, which solely result in ligation of the clusters. The stoichiometries of these clusters range from 1 < or = n < or = 5 and 1 < or = m < or = 4, indicating the formation of several new subvalent silver iodide clusters. Collision induced dissociation (CID) experiments were carried out on each of these clusters to shed some light on their possible structures. The products arising from CID of the Ag(n)I(m)(+) clusters are highly dependent on the stoichiometry of the cluster. Thus the odd-electron clusters Ag(4)I(2)(+) and Ag(5)I(+) fragment via loss of a silver atom. In contrast, the even-electron cluster ions all fragment via loss of AgI. In addition, Ag(2)I(2) loss is observed for the Ag(4)I(3)(+) and Ag(5)I(2)(+) clusters, while loss of Ag(3)I(3) occurs for the stoichiometric Ag(5)I(4)(+) cluster. DFT calculations were carried out on these Ag(n)I(m)(+) clusters as well as the neutrals associated with the ion-molecule and CID reactions. A range of different isomeric structures were calculated and their structures are described. A noteworthy aspect is that ligation of these silver clusters by I can have a profound effect on the geometry of the silver cluster. For example, D(3h) Ag(3)(+) becomes C(2v) Ag(3)I(+), which in turn becomes C(2h) Ag(3)I(2)(+). Finally, the DFT predicted thermochemistry supports the different types of reaction channels observed in the ion-molecule reactions and CID experiments.

The homocuprates [MeCuMe]- and [EtCuEt]- were generated in the gas phase by double decarboxylation of the copper carboxylate centers [MeCO2CuO2CMe]- and [EtCO2CuO2CEt]-, respectively. The same strategy was explored for generating the heterocuprates [MeCuR]- from [MeCO2CuO2CR]- (R = Et, Pr, iPr, tBu, allyl, benzyl, Ph). The formation of these organocuprates was examined by multistage mass spectrometry experiments, including collision-induced dissociation and ion-molecule reactions, and theoretically by density functional theory. A number of side reactions were observed to be in competition with the second stage of decarboxylation, including loss of the anionic carboxylate ligand and loss of neutral alkene via beta-hydride transfer elimination. Interpretation of decarboxylation of the heterocarboxylates [MeCO2CuO2CR]- was more complex because of the possibility of decarboxylation occurring at either of the two different carboxylate ligands and giving rise to the possible isomers [MeCuO2CR]- or [MeCO2CuR]-. Ion-molecule reactions of the products of initial decarboxylation with allyl iodide resulted in C-C coupling to produce the ionic products [ICuO2CR]- or [MeCO2CuI]-, which provided insights into the relative population of the isomers, and indicated that the site of decarboxylation was dependent on R. For example, [MeCO2CuO2CtBu]- underwent decarboxylation at MeCO2- to give [MeCuO2CtBu]-, while [MeCO2CuO2CCH2Ph]- underwent decarboxylation at PhCH2CO2- to give [MeCO2CuCH2Ph]-. Each of the heterocuprates [MeCuR]- (R = Et, Pr, iPr, allyl, benzyl, Ph) could be generated by the double decarboxylation strategy. However, when R = tBu, intermediate [MeCuO2CtBu]- only underwent loss of tBuCO2-, a consequence of the steric bulk of tBu disfavoring decarboxylation and stabilizing the competing channel of carboxylate anion loss. Detailed DFT calculations were carried out on the potential energy surfaces for the first and second decarboxylation reactions of all homo- and heterocuprates, as well as possible competing reactions. These reveal that in all cases the first decarboxylation reaction is favored over loss of the carboxylate ligand. In contrast, other reactions such as carboxylate ligand loss and beta-hydride transfer become more competitive with the second decarboxylation reaction.