Development of cation/anion "interaction" scales for ionic liquids through ESI-MS measurements

Electrospray ionization mass spectrometry applied to ionic liquids allowed the study of loosely bonded supramolecules, originating from these organic salts. Based on the observation that ionic liquids formed cationic [C(q+1)X(q)](+) and anionic [C(q)X(q+1)](-) supramolecular aggregates, we have investigated mixed networks, formed by different cations coordinated to a selected anion or by different anions bonded to a given cation, i.e., [C1...X...C2](+) and [X1...C...X2](-), with the aim to build a scale of the cation-anion interaction strength. The qualitative order of intrinsic bond strength to Br- was found to be the following: [emim](+) > [bmim](+) > [mor1,2](+) > [hmim]+ > [omim](+) > [mor1,4](+) > [bupy](+) > [bpyrr](+) > [picol](+) > [bm(2)im](+) > [TBA](+). Similarly, the interaction energies to 1-butyl-3-methylimidazolium (bmim) species envisaged two classes of anions: species tightly coordinated to the cationic moiety that include CF3COO(-), Br(-), N(CN)2(-), and BF4(-) and anions loosely interacting with the alkylimidazolium species such as OTf(-), PF6(-), and Tf2N(-).     

Influence of the interaction between hydrogen sulfide and ionic liquids on solubility: experimental and theoretical investigation

The solubility of H(2)S in a series of 1-butyl-3-methylimidazolium ([bmim](+)) based ionic liquids (ILs) with different anions, chloride, tetrafluoroborate ([BF(4)](-)), hexafluorophosphate ([PF(6)](-)), triflate ([TfO](-)), and bis(trifluoromethyl)sulfonylimide ([Tf(2)N]-), and in a series of [Tf(2)N] ILs with different cations, i.e., N-alkyl-N'-methylimidazolium, 2-methyl-N-methyl-N'-alkyimidazolium, N-alkylpyridinium, N-butyl-N-methylpyrrolidinium, and N-alkyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium has been determined using medium-pressure NMR spectroscopy. The observed solubilities are significantly higher than those reported for many other gases in ILs, suggesting the occurrence of specific interactions between H2S and the examined ILs. Quantum chemical calculations have been used to investigate at a molecular level the interaction between H2S and the [bmim](+)-based ILs.     

Structural characterization of glycoporphyrins by electrospray tandem mass spectrometry

Porphyrin derivatives having a galactose or a bis(isopropylidene)galactose structural unit, linked by ester or ether bonds, were characterized by electrospray tandem mass spectrometry (ES-MS/MS). The electrospray mass spectra of these glycoporphyrins show the corresponding [M + H](+) ions. For the glycoporphyrins with pyridyl substituents and those having a tetrafluorophenyl spacer, the doubly charged ions [M + 2H](2+) were also observed in ES-MS with high relative abundance. The fragmentation of both [M + H](+) and [M + 2H](2+) ions exhibited common fragmentation pathways for porphyrins with the same sugar residue, independently of the porphyrin structural unit and type of linkage. ES-MS/MS of the [M + H](+) ions of the galactose-substituted porphyrins gave the fragment ions [M + H - C(2)H(4)O(2)](+), [M + H - C(3)H(6)O(3)](+), [M + H - C(4)H(8)O(4)](+) and [M + H - galactose residue](+). The fragmentation of the [M + 2H](2+) ions of the porphyrins with galactose shows the common doubly charged fragment ions [porphyrin + H](2+), [M + 2H - C(2)H(4)O(2)](2+), [M + 2H - C(4)H(8)O(4)](2+), [M + 2H - galactose residue](2+) and the singly charged fragment ions [M + H - C(3)H(6)O(3)](+) and [M + H - galactose residue](+). The fragmentation of the [M + H](+) ions of glycoporphyrins with a protected galactosyl residue leads mainly to the ions [M + H - CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2)](+), [M + H - 2CO(CH(3))(2) - CO](+), [M + H - C(10)H(16)O(4)](+) and [M + H - protected galactose](+). The doubly charged ions [M + 2H](2+) fragment to give the doubly charged ions [porphyrin + H](2+) and the singly charged ions [M + H - protected galactose residue](+) and [M + H - CO(CH(3))(2)](+). For the porphyrins where the sugar structural unit is linked by an ester bond, [M + 2H](2+), ES-MS/MS showed a major and typical fragmentation corresponding to combined loss of a sugar structural unit and further loss of water, leading to the ion [M + 2H - sugar residue - H(2)O](2+), independently of the structure of the sugar structural unit. These results show that ES-MS/MS can be a powerful tool for the characterization of the sugar structural unit of glycoporphyrins, without the need for chemical hydrolysis.     

Electrospray ionization tandem mass spectrometric studies of competitive pyridine loss from platinum(II) ethylenediamine complexes by the kinetic method

The competition between pyridine ligand loss in square planar Pt(II) complexes has been examined using the doubly and singly charged ions of complexes consisting of platinum(ethylenediamine) coordinated to two different substituted pyridines. Collision induced dissociation (CID) of [Pt(en)Py(1)Py(2)](2+) (where Py(1) = one of ten different substituted pyridines and Py(2) = pyridine) results in loss of the protonated pyridines to yield the singly charged platinum ions [Pt(en)Py(1)-H](+) and [Pt(en)Py(2)-H](+). In contrast, fragmentation of [Pt(en)Py(1)Py(2)-H](+) results in neutral pyridine loss to yield the ions [Pt(en)Py(1)-H](+) and [Pt(en)Py(2)-H](+). In the latter case, the correlation between relative losses of each pyridine compared to their gas-phase proton affinities is poor. A novel chloride ion abstraction reaction occurs for the fragmentation of [Pt(en)Py(1)Py(2)](2+) when Py(1) = o-C(5)H(4)CIN and Py(2) = C(5)H(5)N, to yield the [Pt(en)(Cl)Py(2)](+) and [o-C(5)H(4)N](+) pair of ions. In order to model this process the competition between nitrogen and chlorine binding in [Pt(NH(3))(3)(o-NC(5)H(4)Cl)](2+) has been examined using density functional theory (DFT) calculations at the B3LYP/LANL2DZ level of theory. Both adducts are minima with the N adduct being more stable than the Cl adduct by 22.7 kcal mol(-1). Furthermore, the Cl adduct exhibits a significant stretching of the C-Cl bond (to 1.935 A), consistent with the observed chloride ion abstraction reaction, which is endothermic by 9.0 kcal mol(-1) (relative to the N adduct).     

Nucleophilicity in ionic liquids. 3. Anion effects on halide nucleophilicity in a series of 1-butyl-3-methylimidazolium ionic liquids

We have continued the study of halide nucleophilicity in ionic liquids, concentrating on the effect of changing the anion ([BF(4)](-), [PF(6)](-), [SbF(6)](-), [OTf](-), and [N(Tf)(2)](-)) when the cation is [bmim](+) (where bmim = 1-butyl-3-methylimidazolium). It was found that the nucleophilicities of all the halides were lower in all of the ionic liquids than in dichloromethane. Changing the anion affected the order of halide nucleophilicity, e.g., in [bmim][BF(4)] the order of nucleophilicity was Cl(-)>Br(-)>I(-) while in [bmim][N(Tf)(2)] the order was Cl(-)相似文献   

Probing the mechanisms of the self ion-molecule reactions of dopamine in an ion trap mass spectrometer

Our previous work was the first to report [M+CH](+) and [M+C(2)H(3)](+) ions in the self ion-molecule reactions (SIMR) of two aza-crown ethers in an ion trap mass spectrometer (ITMS). In this study, the CH and C(2)H(3) addition ions were also found in the SIMR of dopamine. The SIMR of dopamine lead to the formation of the protonated molecules ([M+H](+)), of adduct ions ([M+F](+), where F represents fragment ions), and of [M+CH](+), [M+C(2)H(3)](+) and [2M+H](+) ions. Based on the combination of the results of isolation experiments and semi-empirical calculations, the reactive site for the formation of the [M+H](+) and [M+CH](+) ions of dopamine is proposed to be the amino group.     

Validation of speciation techniques: a study of chlorozincate(II) ionic liquids

The speciation of chlorozincate(II) ionic liquids, prepared by mixing 1-octyl-3-methylimidazolium chloride, [C(8)mim]Cl, and zinc(II) chloride in various molar ratios, χ(ZnCl(2)), was investigated using Raman spectroscopy and differential scanning calorimetry; the Gutmann acceptor number, which is a quantitative measure of Lewis acidity, was also determined as a function of the composition. These results were combined with literature data to define the anionic speciation; in the neat liquid phase, the existence of Cl(-), [ZnCl(4)](2-), [Zn(2)Cl(6)](2-), [Zn(3)Cl(8)](2-), and [Zn(4)Cl(10)](2-) anions was confirmed. From two chlorozincate(II) ionic liquids with [C(2)mim](+) cations (χ(ZnCl(2)) = 0.33 and χ(ZnCl(2)) = 0.50), crystals have been obtained, revealing the structures of [C(2)mim](2)[ZnCl(4)] and [C(2)mim](2)[Zn(2)Cl(6)] forming three-dimensional hydrogen-bond networks. The compound [C(2)mim](2){Zn(4)Cl(10)} was crystallized from the χ(ZnCl(2)) = 0.75 composition, showing an open-framework structure, with the first example of zinc in a trigonal-bipyramidal chloride coordination. Reinvestigation of the electrospray ionization mass spectrometry of these systems demonstrated that it is an unreliable technique to study liquid-phase speciation.     

Reactions of ionic species from acetonitrile with long-chain saturated and unsaturated alcohols

Ten long-chain saturated and unsaturated alcohols were reacted with the ionic species [C(2) H(2) N](+) and [C(3) H(4) N](+) generated by ionization of acetonitrile into an ion trap. The mass spectra of the compounds under investigation show the formation of [M -H](+), [M + C(2) H(2) N](+) and [M + C(2) H(4) N](+) ions in the case of saturated alcohols, whereas for monounsaturated and polyunsaturated derivatives additional peaks corresponding to [M + H](+) and [M + H -H(2) O](+) are observed. The reaction mechanisms were investigated by means of D- and (13)C-labelled acetonitrile. Collisional experiments were performed on the [M + C(3) H(4) N](+) species from the polyunsaturated alcohols in order to identify any possibly diagnostic fragments for the identification of the double bond positions. Copyright 1999 John Wiley & Sons, Ltd.     

Electrospray ionization mass spectrometry of ginsenosides

Ginsenosides R(b1), R(b2), R(c), R(d), R(e), R(f), R(g1), R(g2) and F(11) were studied systematically by electrospray ionization mass spectrometry in positive- and negative-ion modes with a mobile-phase additive, ammonium acetate. In general, ion sensitivities for the ginsenosides were greater in the negative-ion mode, but more structural information on the ginsenosides was obtained in the positive-ion mode. [M + H](+), [M + NH(4)](+), [M + Na](+) and [M + K](+) ions were observed for all of the ginsenosides studied, with the exception of R(f) and F(11), for which [M + NH(4)](+) ions were not observed. The signal intensities of [M + H](+), [M + NH(4)](+), [M + Na](+) and [M + K](+) ions varied with the cone voltage. The highest signal intensities for [M + H](+) and [M + NH(4)](+) ions were obtained at low cone voltage (15-30 V), whereas those for [M + Na](+) and [M + K](+) ions were obtained at relatively high cone voltage (70-90 V). Collision-induced dissociation yielded characteristic positively charged fragment ions at m/z 407, 425 and 443 for (20S)-protopanaxadiol, m/z 405, 423 and 441 for (20S)-protopanaxatriol and m/z 421, 439, 457 and 475 for (24R)-pseudoginsenoside F(11). Ginsenoside types were identified by these characteristic ions and the charged saccharide groups. Glycosidic bond cleavage and elimination of H(2)O were the two major fragmentation pathways observed in the product ion mass spectra of [M + H](+) and [M + NH(4)](+). In the product ion mass spectra of [M - H](-), the major fragmentation route observed was glycosidic bond cleavage. Adduct ions [M + 2AcO + Na](-), [M + AcO](-), [M - CH(2)O + AcO](-), [M + 2AcO](2-), [M - H + AcO](2-) and [M - 2H](2-) were observed at low cone voltage (15-30 V) only.     

Electrospray and chemical ionization mass spectrometry of di-n-butyl sulfate. Unimolecular chemistry of its protonated form and quantification method by liquid chromatography/electrospray ionization tandem mass spectrometry

Di-n-butyl sulfate (DNBS) has been studied by electrospray (ESI) and chemical (CI) ionization mass spectrometry. The use of methanol as solvent in electrospray ionization allows observation of relatively abundant [DNBS + CH(3)OH + H](+) ions (m/z 243) which upon collision dissociate to [DNBS + H](+) ions (m/z 211). In both ESI and CI experiments, it is found that [DNBS + H](+) ions lead to m/z 113 daughter ions. The composition of this m/z 113 fragment ion and its mechanism of formation have been established by high resolution measurements and CID-MIKE experiments. An 'internal substitution' reaction involving an ion-neutral intermediate is proposed to explain the formation of a [C(8)H(17)](+) ion (m/z 113) by loss of a H(2)SO(4) molecule. Finally, a LC/ESI-MS/MS quantification method is proposed in which a detection limit of di-n-butyl sulfate in the ppm range is obtained. It is suggested that the quantification method might be extended to higher dialkyl sulfates. Copyright 2000 John Wiley & Sons, Ltd.     

Gas phase ion chemistry of charged silver(I) adenine ions via multistage mass spectrometry experiments and DFT calculations

Electrospray ionization (ESI) of solutions containing adenine and AgNO(3) yields polymeric [Ad(x)+ Ag(y)-zH]((y-z)+) species. Density functional theory (DFT) calculations have been used to examine potential structures for several of the smaller ions while multistage mass spectrometry experiments have been used to probe their unimolecular reactivity (via collision-induced dissociation (CID)) and bimolecular reactivity (via ion-molecule reactions with the neutral reagents acetonitrile, methanol, butylamine and pyridine). DFT calculations of neutral adenine tautomers and their silver ion adducts provide insights into the binding modes of adenine. We find that the most stable [Ad + Ag](+) ion does not correspond to the most stable neutral adenine tautomer, consistent with previous studies that have shown that transition metal ions can stabilize rare tautomeric forms of nucleobases. Both the charge and the stoichiometry of the [Ad(x)+ Ag(y)-zH]((y-z)+) complexes play pivotal roles in directing the types of fragmentation and ion-molecule reactions observed. Thus, [Ad(2)+ Ag(2)](2+) is observed to dissociate to [Ad + Ag](+) and to react with butylamine via proton transfer, while [Ad(2)+ Ag(2)- H](+) fragments via loss of neutral adenine to form the [Ad + Ag(2)- H](+) ion and does not undergo proton transfer to butylamine. DFT calculations on several isomeric [Ad(2)+ Ag(2)](2+) ions suggest that planar centrosymmetric cations, in which two adjacent silver atoms are bridged by two N7H adenine tautomers via N(3),N(9)-bidentate interactions, are the most stable. The [Ad + Ag(2)-H](+) ion adds two neutral reagents in ion-molecule reactions, consistent with the presence of two vacant coordination sites. It undergoes a silver atom loss to form the [Ad + Ag - H](+) radical cation, which in turn fragments quite differently to the even electron [Ad + Ag](+) ion. Several other pairs of radical cation/even electron adenine-silver complexes were also found to undergo different fragmentation reactions.     

A remarkable anion effect on palladium nanoparticle formation and stabilization in hydroxyl-functionalized ionic liquids

Pd nanoparticles (NPs) with a small size and narrow size distribution were prepared from the decomposition of Pd(OAc)(2) in a series of hydroxyl-functionalized ionic liquids (ILs) comprising the 1-(2'-hydroxylethyl)-3-methylimidazolium cation and various anions, viz. [C(2)OHmim][OTf] (2.4 ± 0.5 nm), [C(2)OHmim][TFA] (2.3 ± 0.4 nm), [C(2)OHmim][BF(4)] (3.3 ± 0.6 nm), [C(2)OHmim][PF(6)] (3.1 ± 0.7 nm) and [C(2)OHmim][Tf(2)N] (4.0 ± 0.6 nm). Compared with Pd NPs isolated from the non-functionalized IL, [C(4)mim][Tf(2)N] (6.2 ± 1.1 nm), it would appear that the hydroxyl group accelerates the formation of the NPs, and also helps to protect the NPs from oxidation once formed. Based on the amount of Pd(OAc)(2) that remains after NP synthesis (under the given conditions) the ease of formation of the Pd NPs in the [C(2)OHmim](+)-based ILs follows the trend [Tf(2)N](-), [PF(6)](-) > [BF(4)](-) > [OTf](-) > [TFA](-). Also, the ability of the [C(2)OHmim](+)-based ILs to prevent the Pd NPs from undergoing oxidation follows the trend [Tf(2)N](-) > [PF(6)](-) > [TFA](-) > [OTf](-) > [BF(4)](-). DFT calculations were employed to rationalize the interactions between Pd NPs and the [C(2)OHmim](+) cation and the various anions.     

Precipitation of a dioxouranium(VI) species from a room temperature ionic liquid medium

The novel complex 1-butyl-3-methylimidazolium mu(4)-(O,O,O',O'-ethane-1,2-dioato)-bis[bis(nitrato-O,O)dioxouranate(VI)] (1) has been precipitated from a room-temperature ionic liquid medium containing 1-butyl-3-methylimidazolium nitrate, nitric acid, and acetone. X-ray analysis of complex 1 shows the unit cell contains four [C(4)mim](+) cations and two independent [[UO(2))(NO(3))(2)](2)(mu(4)-C(2)O(4))](2-) moieties, both of which are located about inversion centers. The [C(4)mim](+) cations are arranged such that they produce large channels in which the anions are located. This arrangement of [[(UO(2))(NO(3))(2)](2)(mu(4)-C(2)O(4))](2-) groups is unique to this compound. Crystal data for compound 1: M = 1154.56, monoclinic, space group P2(1)/c, a = 15.452(2) A, b = 20.354(3) A, c = 10.822(4) A, beta = 106.84(2) degrees, U = 3258(1) A(-)(3), Z = 4, mu = 10.023 mm(-1), R(int) = 0.0788.     

Structural isomerism in tris-tolyl halo-phosphonium and halo-arsonium tri-halides, [(CH3C6H4)3EX][X3], (E = P, As; X = Br, I)

The group 15 ligands (o-CH(3)C(6)H(4))(3)P, (m-CH(3)C(6)H(4))(3)P, (p-CH(3)C(6)H(4))(3)P, Ph(3)As, (o-CH(3)C(6)H(4))(3)As and (p-CH(3)C(6)H(4))(3)As have been reacted with two equivalents of di-iodine or di-bromine to yield complexes of formula R(3)EX(4) (E = P, As; X = I, Br). These halogenated group 15 compounds are ionic, [R(3)EX][X(3)] consisting of halo-phosphonium or halo-arsonium cations and trihalide anions. These adducts exhibit structural isomerism and may exist either as simple 1:1 ion pairs, [R(3)EX][X(3)], isomer (A), which display a weak XX interaction between cation and anion, or as a 2:1 complex, which consists of a [{R(3)EX}(2)X(3)](+) cationic species made up of two [R(3)EX](+) cations interacting with one [X(3)](-) anion. The overall charge is balanced by a second [X(3)](-) anion. These 2:1 species also exhibit structural isomerism due to subtle differences in the connectivity of the [{R(3)EX}(2)X(3)](+) fragment, as the {R(3)EX}(+) units may either interact at the same end of the [X(3)](-) ion, to give a Y-shaped motif, isomer (B), or at opposite ends, giving a Z-shaped motif, isomer (C). The type of structural isomer formed is related to the way in which [Ar(3)EX](+) cations pack together via aryl embraces. Isomer (A) and (C) structures form chains of side-to-side, anti-parallel embracing cations. In (A) and (C) structures a square-like stacking motif of cations is observed. In contrast, isomer (B) structures feature side-to-side, parallel embracing cations, and do not exhibit the square motif.     

Regioselective synthesis and electron impact mass spectral fragmentation differentiation of 2- or 3-isopropylthio, phenylthiosuccinic acid 4-methyl/isopropyl ethers

2- and 3-isopropylthio/phenylthiosuccinic acid 4-methyl/isopropyl esters were synthesized regioselectively by Michael additions of isopropylthiol/thiophenol to maleic anhydride, followed by alcoholysis with methanol/isopropanol. Their mass spectrometric behavior has been studied with the aid of mass-analyzed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate an alkoxy group, an alcohol, or an alkoxycarbonyl group from the respective molecular ion. Some molecular ions also show a tendency to eliminate a molecule of water, propene or CO(2). The [M - MeCH = CH(2)](+) ions could further lose H(2)O to form substituted succinic anhydride ions, or lose CO(2) to form 3-substituted propionic acid ions. Both of these ions could further yield other small fragment ions by loss of CO(2)H, CO or other small fragments. It has been found that 2-isopropylthio- and 3-phenylthiosuccinic acid 4-esters show more abundant [M - H(2)O](+) peaks than their 3-isopropylthio and 2-phenylthio isomers in their mass spectra.     

Structural characterization of hexoses and pentoses using lead cationization. An electrospray ionization and tandem mass spectrometric study

The analytical potential of the complexation of isomeric underivatized hexoses (D-glucose, D-galactose, D-mannose, D-talose, D-fructose), methylglycosides (1-O-methyl-alpha-D-glucose and 1-O-methyl-beta-D-glucose) and pentoses (D-ribose, D-xylose, D-arabinose and D-lyxose) by Pb(2+) ions, was investigated by electrospray ionization and tandem mass spectrometry (MS/MS). Pb(2+) ions react mainly with monosaccharides by proton abstraction to generate [Pb(monosaccharide)(m) - H](+) ions (m = 1-3). At low cone voltage, a less abundant series of doubly charged ions of general formula [Pb(monosaccharide)(n)](2+) is also observed. The maximum number n of monosaccharides surrounding a single Pb(2+) ion depends on the metal : monosaccharide ratio. Our study shows that MS/MS experiments have to be performed to differentiate Pb(2+)-coordinated monosaccharides. Upon collision, [Pb(monosaccharide) - H](+) species mainly dissociate according to cross-ring cleavages, leading to the elimination of C(n)H(2n)O(n) neutrals. The various fragmentation processes observed allow the C(1), C(2) and C(4) stereocenters of aldohexoses to be characterized, and also a clear distinction aldoses and fructose. Furthermore, careful analysis of tandem mass spectra also leads to successful aldopentose distinction. Lead cationization combined with MS/MS therefore appears particularly useful to identify underivatized monosaccharides.     

Nucleophilicity in ionic liquids. 2.(1) Cation effects on halide nucleophilicity in a series of bis(trifluoromethylsulfonyl)imide ionic liquids

In this work, the nucleophilicities of chloride, bromide, and iodide have been determined in the ionic liquids [bmim][N(Tf)(2)], [bm(2)im][N(Tf)(2)], and [bmpy][N(Tf)(2)] (where bmim = 1-butyl-3-methylimidazolium, bm(2)im = 1-butyl-2,3-dimethylimidazolium, bmpy = 1-butyl-1-methylpyrrolidinium, and N(Tf)(2) = bis(trifluoromethylsulfonyl)imide). It was found that in the [bmim](+) ionic liquid, chloride was the least nucleophilic halide, but that changing the cation of the ionic liquid affected the relative nucleophilicities of the halides. The activation parameters DeltaH(), DeltaS(), and DeltaG() have been estimated for the reaction of chloride in each ionic liquid, and compared to a similar reaction in dichloromethane, where these parameters were found for reaction by both the free ion and the ion pair.     

Reactivity of [Fe4S4(SR)4]2-,3- clusters with sulfonium cations: analogue reaction systems for the initial step in biotin synthase catalysis

The first step in catalysis by a class of iron-sulfur enzymes that includes biotin synthase is the one-electron reductive cleavage of the obligatory cofactor S-adenosylmethionine by an [Fe(4)S(4)](+) cluster to afford methionine and the deoxyadenosyl radical (DOA*). To provide detailed information about the reactions of sulfonium ions with [Fe(4)S(4)](2+,+) clusters, the analogue reaction systems [Fe(4)S(4)(SR')(4)](2)(-)(,3)(-)/[PhMeSCH(2)R](+) (R' = Et (4, 6), Ph (5, 7); R = H (8), COPh (9), p-C(6)H(4)CN (10)) were examined by (1)H NMR spectroscopy. Sulfonium ions 8-10 react completely with oxidized clusters 4 and 5 to afford PhSMe and R'SCH(2)R in equimolar amounts as a result of electrophilic attack by the sulfonium ion on cluster thiolate ligands. Reactions are also complete with reduced clusters 6 and 7 but afford, depending on the substrate, the additional products RCH(3) (R = PhCO, p-C(6)H(4)CN) and the ylid PhMeS=CHR or (p-NCC(6)H(4)CH(2))(2). Redox potentials of 9 and 10 allow electron transfer from 6 or 7. The reaction systems 6/9,10 and 7/9,10 exhibit two reaction pathways, reductive cleavage and electrophilic attack, in an ca. 4:1 ratio inferred from product distribution. Cleavage is a two-electron process and, for example in the system 6/9, is described by the overall reaction 2[Fe(4)S(4)(SR')(4)](3)(-) + 2[PhMeSCH(2)R](+) --> 2[Fe(4)S(4)(SR')(4)](2)(-) + PhSMe + RCH(3) + PhMeS=CHR. This and other reactions may be summarized as [PhMeSCH(2)R](+) + 2e(-) + H(+) --> PhSMe + RCH(3); proposed reaction sequences parallel those for electrochemical reduction of sulfonium ions. This work demonstrates the intrinsic ability of [Fe(4)S(4)](+) clusters with appropriate redox potentials to reductively cleave sulfonium substrates in overall two-electron reactions. The analogue systems differ from the enzymes in that DOA* is generated in a one-electron reduction and is sufficiently stabilized within the protein matrix to abstract a hydrogen atom from substrate or an amino acid residue in a succeeding step. In the present systems, the radical produced in the initial step of the reaction sequence, [Fe(4)S(4)(SR')(4)](3)(-) + [PhMeSCH(2)R](+) --> [Fe(4)S(4)(SR')(4)](2)(-) + PhSMe + RCH(2)*, is not stabilized and is quenched by reduction and protonation.     

Analysis of triacetone triperoxide (TATP) and TATP synthetic intermediates by electrospray ionization mass spectrometry

The explosive triacetone triperoxide (TATP) has been analyzed by electrospray ionization mass spectrometry (ESI-MS) on a linear quadrupole instrument, giving a 62.5 ng limit of detection in full scan positive ion mode. In the ESI interface with no applied fragmentor voltage the m/z 245 [TATP + Na](+) ion was observed along with m/z 215 [TATP + Na - C(2)H(6)](+) and 81 [(CH(3))(2)CO + Na](+). When TATP was ionized by ESI with an applied fragmentor voltage of 75 V, ions at m/z 141 [C(4)H(6)O(4) + Na](+) and 172 [C(5)H(9)O(5) + Na](+) were also observed. When the precipitates formed in the synthesis of TATP were analyzed before the reaction was complete, a new series of ions was observed in which the ions were separated by 74 m/z units, with ions occurring at m/z 205, 279, 353, 427, 501, 575, 649 and 723. The series of evenly spaced ions is accounted for as oligomeric acetone carbonyl oxides terminated as hydroperoxides, [HOOC(CH(3))(2){OOC(CH(3))(2)}(n)OOH + Na](+) (n = 1, 2 ... 8). The ESI-MS spectra for this homologous series of oligoperoxides have previously been observed from the ozonolysis of tetramethylethylene at low temperatures. Precipitates from the incomplete reaction mixture, under an applied fragmentor voltage of 100 V in ESI, produced an additional ion observed at m/z 99 [C(2)H(4)O(3) + Na](+), and a set of ions separated by 74 m/z units occurring at m/z 173, 247, 321, 395, 469 and 543, proposed to correspond to [CH(3)CO{OOC(CH(3))(2)}(n)OOH + Na](+) (n = 1,2 ... 5). Support for the assigned structures was obtained through the analysis of both protiated and perdeuterated TATP samples.     

Interactions of nucleosides with CrO(4) (2-) and Cr(3+) as studied by electrospray ionization mass spectrometry

The interactions of CrO(4) (2-) and Cr(3+) with nucleosides studied by electrospray ionization mass spectrometry (ESI-MS) are reported. In water, the nucleosides which do not contain the NH(2) group form the unstable [M+HCrO(4)](-) anion. In the presence of a reducing agent, namely methanol, chromate anion forms stable complexes with nucleosides, [M+CH(3)CrO(4)](-) anions. The fragmentation of [M+CH(3)CrO(4)](-) anions involve elimination of the methanol molecule. Chromium cation-nucleoside complexes were not observed in water. In methanol solutions, adenosine and cytidine form [(M-H)+CrOCH(3)](+) and [(M-H)(2)+Cr](+) ions. Most probably, deprotonated imine tautomers form complexes in which a metal cation is simultaneously coordinated by two nitrogen atoms. Complexes containing chloride anions and a few methanol molecules were observed for other nucleosides. Guanosine and inosine form doubly charged ions of the type [M(2)+CrOCH(3)](2+) that probably contain a bond between the oxygen atom and the chromium cation, (HN(1)--C(6)==O)(2) (....)Cr(3+)).