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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.

Graphical abstract Highlights • Dihydroxy magnesium carboxylate anions, first discovered in meteorites, have been prepared in the gas-phase. • Sequential CID and IMR are used to synthesise [(RCO 2)Mg(OH) 2 ]– from [(RCO 2)Mg(O 2 CCH 3) 2 ]– precursor ions generated via ESI. • DFT calculations provide structures and energetics associated with these CID and IMR reactions. • The CID fragmentation reactions of [(RCO 2)Mg(OH) 2 ]– are described. Abstract Dihydroxy magnesium carboxylates, [(RCO 2)Mg(OH) 2 ]–, a previously unknown class of compounds, have recently been discovered in meteorites using electrospray ionisation (ESI) ultra high-resolution mass spectrometry (HRMS) and collision-induced dissociation (CID) experiments (A. Ruf et al., Proc. Natl. Acad. Sci. U.S.A. 114 (2017) 2819). Here we present two general strategies for the gas-phase synthesis of [(RCO 2)Mg(OH) 2 ]– (where R = CH 3 and CH 3 (CH 2) 14) in a linear quadrupole ion trap mass spectrometer using combinations of CID and ion-molecule reactions (IMR) with water. Both involve the same first step (Step 1), where [(RCO 2)Mg(O 2 CCH 3) 2 ]– precursor ions generated via ESI are mass selected and subjected to decarboxylation. In Route I the resultant organomagnesate [(RCO 2)Mg(CH 3)(O 2 CCH 3)]– is subjected to the following reactions: Step 2a involves decarboxylation via CID to give [(RCO 2)Mg(CH 3) 2 ]– which undergoes an IMR in Step 3a to give [(RCO 2)Mg(CH 3)(OH)]–. For Route II [(RCO 2)Mg(CH 3)(O 2 CCH 3)]– undergoes an IMR to give in Step 2b, [(RCO 2)Mg(OH)(O 2 CCH 3)]–, which in Step 3b fragments under CID to give [(RCO 2)Mg(CH 3)(OH)]–. Both routes converge in the final Step 4, where the organometallic ion [(RCO 2)Mg(CH 3)(OH)]– reacts with water to give the desired dihydroxy magnesium carboxylate, [(RCO 2)Mg(OH) 2 ]–. All ion molecule reactions proceed rapidly and cleanly to produce the hydroxides. In contrast, the decarboxylation reactions are in competition with other pathways including loss of the carboxylate anion and loss of a neutral ligand to give a magnesium coordinated enolate of acetate. DFT calculations were used to examine the structures and energies of species involved in the competing reactions associated with each of the steps. [ABSTRACT FROM AUTHOR]

The extent of internal energy deposition using three different plasma-based ionization mass spectrometry (MS) methods, atmospheric pressure chemical ionization (APCI), direct analysis in real time (DART), and active capillary dielectric barrier discharge ionization (DBDI), was investigated using benzylammonium 'thermometer' ions. Ions formed by DBDI were activated significantly less than those that were formed by DART and APCI under these conditions. Thermal ion activation by DART can be reduced slightly by positioning the DART source further from the capillary entrance to the MS and reducing the heat that is applied tometastable atoms exiting theDART source. For example, the average ion internal energy distribution decreased by less than 10%(166.9±0.3 to 152.2±1.0 kJ mol-1) when the distance between the DART source and the MS was increased by 250% (10 to 25mm). By lowering the DART temperature from 350 to 150°C, the internal energy distributions of the thermometer ions decreased by ~15% (169.93±0.83 to 150.21±0.52 kJ mol-1). Positioning the DART source nozzle more than 25mm from the entrance to the MS and decreasing the DART temperature further resulted in a significant decrease in ion signal. Thus, varying themajorDART ion source parameters had minimal impact on the 'softness' of the DART ion source under these conditions. Overall, these data indicate that DBDI can be a significantly 'softer' ion source than two of the most widely used plasma-based ion sources that are commercially available. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 noncovalently bound clusters [Trpn-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 [d4-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, [Trpn-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 C8H6N- has been identified in the product ion spectra of [Trpn-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. [ABSTRACT FROM AUTHOR]

Dithiocarboxylicacids, RCS2H, and their esters, RCS2R′,are useful reagents that can be synthesized bythe reaction of carbon disulfide with organometallic reagents. Herethe coinage-metal-mediated transformation of acetate to dithioacetateis explored in the gas phase using multistage mass spectrometry experimentsin a linear ion trap mass spectrometer in conjunction with densityfunctional theory (DFT) calculations. The ion–molecule reactionsbetween coinage-metal dimethylmetalate anions [CH3MCH3]−(M = Au, Ag, Cu), formed via double decarboxylationof the metal acetate anions, [CH3CO2MO2CCH3]−, and carbon disulfide, were examined.Only [CH3CuCH3]−reacts withCS2with a reaction efficiency of 0.8% of the collisionrate to yield the adduct [CH3CuS2CCH3]−(77.5%) as well as CH3CS2–(22.5%). Collision-induced dissociation (CID)of the adduct [CH3CuS2CCH3]−gives CH3CS2–as the majorproduct, with a small amount of [CuS2CCH2]−being formed via loss of methane. DFT calculationsreveal the following. (i) [CH3CuCH3]−reacts via oxidative addition to form a Cu(III) intermediate, followedby reductive elimination of CH3CS2–, which is captured by Cu to form [CH3CuS2CCH3]−. This energetic adduct can fragment vialoss of CH3CS2–or can becollisionally cooled by the helium bath gas used in the experiments.(ii) Loss of CH4from [CH3CuS2CCH3]−also involves a Cu(III) intermediateand results in formation of the metalladithiolactone [Cu(CH2CS2)]−. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Productand mechanistic studies were performed for the reactionof 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 respectivedistonic aryl radical cation Pyr•+with O2in the ion source of the mass spectrometer. For the reaction involvingthe more electrophilic 4-PyrOO•+, a rate coefficientof k1= (2.2 ± 0.6) × 10–10cm3molecule–1s–1was determined at 298 K, while a value of k2= (8.2 ± 2.1) × 10–11cm3molecule–1s–1was obtained for the reaction involving the less electrophilic 3-PyrOO•+. This highlights the role of polar effects in thesereactions, which are likely of high relevance for processes in combustionsand atmospheric transformations. The mechanism was studied by computationalmethods, which showed that radical addition occurs exclusively atthe less substituted alkyne site to give the distonic vinyl radicalcation 8. The latter undergoes a series of subsequentrearrangements/fragmentations that are similar for both isomeric PyrOO•+. γ-Fragmentation in 8leads tothe distonic aryloxyl radical cation PyrO•+anda singlet carbene 10. The product association complex[PyrO•+– 10] is the startingpoint for two important subsequent reactions, e.g., (i) rapid hydrogentransfer to form ketenyl radical 11and the closed-shellspecies PyrOH+, and (ii) oxygen transfer from PyrO•+to 10that leads to α-keto aldehyde 13and Pyr•+, followed by hydrogen abstractionto give acyl radical 14and PyrH+. Additionalmajor products are the closed-shell aromatic carbonyl compounds 20and 30that result from multistep rearrangementsin vinyl radical 8, which are terminated by homolyticbond scission and release of neutral acyl radicals. [ABSTRACT FROM AUTHOR]

Cobalt-mediated decarboxylative Glaser-like C-C bond coupling of carboxylates has been studied in the gas phase using collision-induced dissociation (CID) multistage mass spectrometry (MS[sup n]) experiments. Both the identity of the carboxylate RCO[sup -][sub 2] (R= Me, HC≡C, MeC≡C, and PhC≡C) and the nuclearity of the complex ([CoCl(O[sub 2]CR)[sub 2]][sup -] versus [Co[sub 2]Cl[sub 3](O[sub 2]CR)[sub 2]][sup -]) play a role in the types of reactions observed and their relative activation energies. In the first stage of CID, the mononuclear complex [CoCl(O[sub 2]CMe)[sub 2]][sup -] undergoes decarboxylation, while the dinuclear [Co[sub 2]Cl[sub 3](O[sub 2]CMe)[sub 2]][sup -] undergoes cluster fission to yield [CoCl[sub 3]][sup -]; all acetylenic carboxylate complexes [CoCl(O[sub 2]CR)[sub 2]][sup -] and [Co[sub 2]Cl[sub 3](O[sub 2]CR)[sub 2]][sup -] undergo decarboxylation. Isolation of the decarboxylated products followed by a second stage of CID results in a second decarboxylation event for all systems except for [CoCl(Me)(O[sub 2]CMe)][sup -], which undergoes bond homolysis. In the final stage of CID, all acetylenic complexes undergo Glaser coupling, forming reduced Co anions. Overall dinuclear cobalt clusters are superior to mononuclear complexes at promoting decarboxylation and reductive coupling. The order of reactivity among the acetylide ligands is PhC≡C > MeC≡C > HC≡C. [ABSTRACT FROM AUTHOR]

Thereactions of water with the coordinatively unsaturated group 10 organometalliccations [(L)M(R)]+(4; where L = 1,10-phenanthroline(phen), neocuproine (neo); M = nickel, palladium, platinum; R = CH3, C6H5, CH2C6H5), formed via decarboxylation of the carboxylate complexes[(L)M(O2CR)]+, were examined in the gas phaseusing a combination of multistage mass spectrometry experiments andDFT calculations at the M06/SDD6-31+G(d) level of theory. Two maintypes of primary product ions were observed: the aqua adduct [(L)M(R)(H2O)]+(5) and the hydroxide [(L)M(OH)]+(7), formed via a hydrolysis reaction. A secondaryproduct ion, arising from formation of the adduct [(L)M(OH)(H2O)]+, was also observed when L = phen, R = CH3, and M = Pt. The rates of reaction of 4andthe product branching ratios for 5and 7were dependent upon the nature of M, L, and R. When L = phenand R = CH3, the hydroxide 7dominates forNi, with the adduct 5as the major product for both Pdand Pt. For R = C6H5the rate of the reactionis slower, while for R = CH2C6H5noreaction occurs. Replacing the phen auxiliary ligand with neo dramaticallyslows down the rate of reaction with water. DFT calculations revealthat an acid–base hydrolysis mechanism is favored over an oxidativeaddition/reductive elimination mechanism proceeding via the M(IV)intermediate [(L)M(CH3)(H)(OH)]+. Furthermore,the relative energies calculated for the barriers of these hydrolysisreactions are consistent with the experimentally observed reactivitytrends. This mechanism is also supported by RRKM theory/master equationsimulations, which demonstrate that formation of the aqua adduct andhydroxide can be explained by competition between unimolecular dissociationand collisional deactivation of the chemically activated reactionadduct within the ion trap. The lack of reactivity of the benzyl systemsappears to arise from η3bindingof the benzyl group, which blocks access to the incoming water. Finally,links are made to group 10 three-coordinate organometallic complexesin the condensed phase. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bis(diphenylphosphino)methane (dppm) protected Au cluster cations, [Au x L1 y ] z+, were formed via condensed phase synthesis. [•] These and organometallic clusters [Au x L1 y (CH(PPh2)2)] n+ (x =5, y =3, n =2; x =14, y=6, n =3) were observed via ESI/MS. [•] Their unimolecular chemistry was examined via CID and ECD. [•] A range of pathways appear for CID including dppm loss, cluster fragmentation and C P bond activation of dppm. [•] The main ECD reaction was charge reduction which was sometimes followed by ligand loss or C P bond activation of dppm. [Copyright &y& Elsevier]

Eine massenspektrometrische Analyse zeigt, dass die Umsetzung von Silbersalzen mit Natriumborhydrid in Gegenwart eines Diphosphanliganden nicht zu reinen Silber ‐ Nanoclusterkationen führt, sondern zu neuartigen Silberhydrid ‐ Nanoclusterkationen. Diese Entdeckung beflügelte die Flüssigphasensynthese, Isolierung und Charakterisierung von [Ag3{(Ph2P)2CH2}3(μ3 ‐ H)(μ3 ‐ Cl)]BF4 ⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

Mass spectrometry shows the way! MS analysis of silver salts treated with sodium borohydride in the presence of a bis(phosphino) ligand revealed the formation of novel silver hydride nanocluster cations instead of all silver nanocluster cations. This serendipitous discovery prompted the condensed‐phase synthesis, isolation, and characterization of [Ag3{(Ph2P)2CH2}3(μ3‐H)(μ3‐Cl)]BF4⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

Mass spectrometry shows the way! MS analysis of silver salts treated with sodium borohydride in the presence of a bis(phosphino) ligand revealed the formation of novel silver hydride nanocluster cations instead of all silver nanocluster cations. This serendipitous discovery prompted the condensed‐phase synthesis, isolation, and characterization of [Ag3{(Ph2P)2CH2}3(μ3‐H)(μ3‐Cl)]BF4⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

Eine massenspektrometrische Analyse zeigt, dass die Umsetzung von Silbersalzen mit Natriumborhydrid in Gegenwart eines Diphosphanliganden nicht zu reinen Silber ‐ Nanoclusterkationen führt, sondern zu neuartigen Silberhydrid ‐ Nanoclusterkationen. Diese Entdeckung beflügelte die Flüssigphasensynthese, Isolierung und Charakterisierung von [Ag3{(Ph2P)2CH2}3(μ3 ‐ H)(μ3 ‐ Cl)]BF4 ⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

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+Ṗ, 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. [ABSTRACT FROM AUTHOR]

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 10 a- 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, O2. For the reaction of Pyr.+ with O2 an absolute rate coefficient of k1=7.1×10−12 cm3 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 khexyne=1.5×10−10 cm3 molecule−1 s−1 and koctyne=2.8×10−10 cm3 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. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution multistage mass spectrometric studies of isotope-labelled derivatives of a fixed-charge labelled sugar triazole assisted the identification of 5-hydroxy-1,2,3-triazoles as byproducts of the copper(I)-catalyzed cycloaddition of azides and terminal alkynes. Reaction optimization with inclusion of the auxiliary ligand, tris(benzyltriazolylmethyl)amine furnished an improved ligation protocol in which formation of the 5-hydroxytriazole is mitigated. [Copyright &y& Elsevier]

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 [(CH3CO2)4Au]−proceeded viareductive elimination of acetylperoxide to yield the diacetate [CH3CO2AuO2CCH3]−, which in turn underwent sequential CID decarboxylation reactions to yield the organoaurates [CH3CO2AuCH3]−and [CH3AuCH3]−. The unimolecular chemistry of the dimethylaurate proceeds viaa combination of bond homolysis to yield the methyl aurate radical anion [CH3Au]−as well as formation of the gold dihydride [HAuH]−. DFT calculations reveal that the latter anion is formed viaa 1,2-dyotropic rearrangement to yield the isomer [CH3CH2AuH]−, followed by a β-hydride elimination reaction. Ion-molecule reactions of [CH3AuCH3]−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 [CH3AuCH3]−with CH3I: (i) an SN2 mechanism proceeding viaa side-on transition state; and (ii) a stepwise mechanism proceeding viaoxidative 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 [CH3AuCH3]−is compared to the previously studied [CH3AgCH3]−and [CH3CuCH3]−, as well as condensed phase studies on dimethylaurate salts. [ABSTRACT FROM AUTHOR]

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 β-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 producethe 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]- underwentdecarboxylation 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 β-hydride transfer become more competitive with the second decarboxylation reaction. [ABSTRACT FROM AUTHOR]

The chaperone protein CopC from Pseudomonas syringae features high-affinity binding sites ( K D ~ 10−13 M) for both CuI (Met-rich) and CuII (His-rich). When presented with these sites in the apoprotein, electrospray ionisation mass spectrometry confirmed that cis-Pt(NH3)2Cl2 (cisplatin) and the fragments [PtIIL]2+ (L is 1,2-diaminoethane, 2,2′-bipyridine) occupied the CuI site specifically in the 1:1 Pt–CopC adducts (purified by cation-exchange chromatography). The cis-Pt(NH3)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 CuI 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. [ABSTRACT FROM AUTHOR]

The mystery of why water and salt contaminants destroy organometallic reagents has been solved by G. N. Khairallah, G. da Silva, and R. A. J. O'Hair in their Communication on page 10979 ff. The addition of an individual salt molecule to an organometallic reagent dramatically enhances its reactivity towards water. This second metal center plays an active role in altering the fundamental chemical transformations that take place when water attacks the organometallic compound. [ABSTRACT FROM AUTHOR]

Mass Spectrometry Man saves the day! Traveling from his home on planet Gas Phase, he used his ESI‐MS powers to provide G. N. Khairallah, P. S. Donnelly, R. A. J. O'Hair, and co‐workers with vital information for their Communication on page 8391 ff. MS Man's powers revealed the formation of novel silver hydride nanocluster cations in silver salts reduced by sodium borohydride in the presence of a bis(phosphino) ligand, and led the way to the condensed‐phase synthesis, isolation, and characterization of [Ag3{(Ph2P)2CH2}3(μ3‐H)(μ3‐Cl)]BF4⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

When the bis(diphenylphosphino)methane (dppm) ligated silver hydride nanocluster salt [Ag 3 (L) 3 ( μ 3 -H)](BF 4 ) 2 is allowed to react with NaBH 4 in a methanol/chloroform solution for 5 mins., and then diluted with acetonitrile and subjected to electrospray ionization mass spectrometry (ESI/MS), a range of silver hydride nanocluster dications are observed including: [Ag 8 H 6 L 5 ] 2+ and [Ag x H x−2 L 6 ] 2+ , where x = 9–15 and L = dppm. All of these clusters are no longer present in the ESI mass spectrum at 40 mins after mixing. Multistage mass spectrometry (MS n ) experiments were carried out to determine the fragmentation chemistry of [Ag 10 H 8 L 6 ] 2+ under conditions of collision-induced dissociation (CID). The initial CID reactions involve sequential loss of two ligands (L) to produce [Ag 10 H 8 L 4 ] 2+ . Further isolation and CID of [Ag 10 H 8 L 4 ] 2+ resulted in a rich series of product ions which arise from three classes of fragmentation reactions: (i) cluster fission to yield complementary ion pairs [Ag 10−x H 8-(x−1) L 4−y ] + and [Ag x H x−1 L y ] + (x = 1, 2 and 4); (ii) ligand loss associated with cluster fission to yield pairs of singly charged clusters [Ag 10−x H 8-(x−1) L 4−y ] + and [Ag x H x−1 L y−1 ] + (x = 1–4); (iii) ligand loss with concomitant loss of all the hydrides, presumably as four molecules of hydrogen to give the ligated silver cluster, [Ag 10 L 3 ] 2+ . The subsequent fragmentation reactions of the product ions were also examined. Most of the singly charged ligated silver hydride clusters fragment to form [Ag x H x−1 L y ] + . The exceptions are [Ag 9 H 8 L 2 ] + and [Ag 7 H 6 L 2 ] + which, upon ligand loss also release all of the hydrides to form the ligated silver clusters, [Ag 9 L] + and [Ag 7 L] + respectively. DFT calculations were carried out to examine how the cluster geometry changes for the following processes: [Ag 10 H 8 L 6 ] 2+ → [Ag 10 H 8 L 4 ] 2+ + 2L → [Ag 10 H 8 L 3 ] 2+ + L → [Ag 10 L 3 ] 2+ + 4H 2 . Losses of 2 L from [Ag 10 H 8 L 6 ] 2+ and L from [Ag 10 H 8 L 4 ] 2+ were calculated to be endothermic by 2.9 and 1.9 eV respectively, but the subsequent loss of 4H 2 from [Ag 10 H 8 L 3 ] 2+ is exothermic by 0.2 eV. [ABSTRACT FROM AUTHOR]