Field ionization mass spectrometry as a facile method for the study of the thermal formation of radicals

Electron impact spectra of thermolysis products of organic salts heated in the ion source of a mass spectrometer may give rise to organic ions corresponding to the cation of the salt. Field ionization mass spectrometry has been used as a facile method for detemining whether such an ion is due to ionization of the corresponding radical present in the gas phase, or to an electron impact induced fragmentation of a reaction product of higher mass. By comparison of the electron impact and field ionization spectra of a series of N-methyl pyridinium, tropylium and 1,2-dithiolylium salts it has been found possible to identify the radicals formed thermolytically, when present.     

Generation of arylnitrenium ions by nitro-reduction and gas-phase synthesis of <Emphasis Type="Italic">N</Emphasis>-Heterocycles

Nitro-reduction by the vinyl halide radical cation CH2 = CH-X+* (X = Cl or Br) converts nitroaromatics into arylnitrenium ions, significant intermediates in carcinogenesis, and the present study reports on the scope and regioselectivity of this versatile reaction. The reaction is general for different kinds of substituted nitroaromatics; para/meta substitutents have little effect on the reaction while ortho substitutents result in low yields of arylnitrenium ions. The phenylnitrenium ion PhNH+ can be generated by chemical ionization (CI) of nitrobenzene using 1,2-dichloroethane as the reagent gas or by atmospheric pressure chemical ionization (APCI) of 1,2-dichloroethane solution doped with nitrobenzene. The chemical reactivities of the arylnitrenium ions include one-step ion/molecule reactions with nucleophiles ethyl vinyl ether and 1,3-dioxolanes, respectively, involving the direct formation of new CN bonds and synthesis of indole and benzomorpholine derivatives. The indole formation reaction parallels known condensed phase chemistry, while the concise morpholine-forming reaction remains to be sought in solution. The combination of collision-induced dissociation (CID) with novel ion/molecule reactions should provide a selective method for the detection of explosives such as TNT, RDX and HMX in mixtures using mass spectrometry. In addition to the reduction of the nitro group, reduction of methyl phenyl sulfone PhS(O)2Me to the thioanisole radical cation PhSMe+* occurs using the same chemical ionization reagent 1,2-dichloroethane. This probably involves an analogous reduction reaction by the reagent ion CH2 = CH-Cl+*.     

Mass spectra of new heterocycles: XI. Fragmentation of 5-(methylsulfanyl)-1-[2-(vinyloxy)ethyl]-1H-pyrrol-2-amines under electron impact and chemical ionization

Fragmentation patterns of the molecular ions of 5-(methylsulfanyl)-1-[2-(vinyloxy)ethyl]-1H-pyrrol- 2-amines generated by electron impact (70 eV) and chemical ionization (methane as reagent gas) were studied for the first time. The electron impact mass spectra of all the examined compounds showed abundant molecular ions whose subsequent fragmentation followed three main pathways: elimination of EtS radical, elimination of methyl radical from the MeS group, and cleavage of the C-N and/or C-C bonds which is accompanied by rearrangement processes. Further decomposition of the [M - EtS]⁺ ion is determined by the structure of the amino group. The chemical ionization mass spectra displayed strong molecular and [M + H]⁺ ion peaks together with representative series of fragment ion peaks. Unlike electron impact, the main decomposition pathway under chemical ionization is elimination of methylsulfanyl radical from the [M + H]⁺ ion to give abundant [M + H — MeS]⁺ ion.     

Effects of benzyl ether type dendrons as hole-harvesting antennas, and shielding for the neutralization of stilbene core radical cations with chloride ion during two-photon ionization of stilbene dendrimers having stilbene core and benzyl ether type dendrons

The two-photon ionization (TPI) process (308 and 266 nm) of stilbene dendrimers having a stilbene core and benzyl ether type dendrons has been investigated in an acetonitrile and 1,2-dichloroethane mixture (3:1) in order to elucidate the dendrimer effects. The quantum yield of the formation of stilbene core radical cation during the 308-nm TPI was independent of the dendron generation of the dendrimers, whereas a generation dependence of the quantum yield of the radical cation was observed during the 266-nm TPI, where both the stilbene core and benzyl ether type dendron were ionized, suggesting that the subsequent hole transfer occurs from the dendron to the stilbene core, and that the dendron acts as a hole-harvesting antenna. The neutralization rate of the stilbene core radical cation with the chloride ion, generated from the dissociative electron capture by 1,2-dichloroethane, decreased with the increase in the dendrimer generation, suggesting that the dendron is an effective shield of the stilbene core radical cation against the chloride ion.     

Functionalised oligoenes with unusual topologies: synthesis, electrochemistry and structural studies on redox-active

New [3]- and [4]-dendralenes bearing electron-donor 1,3-dithiole and ferrocene substituents have been synthesised. Compounds 8, 15 and 17 have been characterised by single-crystal X-ray diffraction. Two of the dithiole rings of 8 are conjugated (dihedral angle 9 degrees), while the third dithiole ring is almost orthogonal to this plane, and hence its pi-electron system is isolated. For the dendralene precursor molecule 15, the substituted cyclopentadienyl ring, two C=C bonds and fused dithiole and dithiine rings comprise an extended pi-conjugated system. In molecule 17 the potential conjugation path C(6)C(3) C(4)C(5)-C5Hs is distorted by an 8 degrees twist around the C(3)-C(4) bond and a 7 degrees twist around the C(5)-C(21) bond, and the delocalisation along the chain is insignificant. Solution electrochemical data demonstrate that the dendralenes are strong pi-electron donors, which give rise to dication, radical trication or tetracation species. Spectroelectrochemical studies on compounds 7 and 10 suggest that the radical species are situated within the linear 1,2-ethylenediylidene moieties and that a conformational change may occur at the dication redox stage. UV/Vis spectroscopic data are consistent with poor cross-conjugation in these systems.     

Behaviour of salts of very strong proton-sponge bases in the gas phase: Extended proximity effects and maintenance of the hydrogen bridge under soft ionization. An electron impact and liquid secondary ion mass spectrometric/collision-induced dissociation tandem mass spectrometric study

The liquid secondary ion mass spectrometry and electron impact ionization fragmentation pathways of 1,9-bis(dimethylamino)-2,8-dimethoxy-dibenzofuran (1), a new proton-sponge base with increased steric compression (buttressing) and much higher basicity (pK_a = 14.3), and of its monoprotonated (2) and monodeuterated (3) salts were invetigated in a collision-induced dissociation (CID) tandem mass spectrometric study supported by unimolecular linked scans at constant B/E, CID mass-analysed ion kinetic energy spectra and accurate mass measurements. They show an ‘extended’ proximity effect, involving the stepwise participation of all the four functional groups, in addition to the ‘normal’ proximity effect involving loss of Me₂NH and H˙. The behaviour of 1 appears to differ in some ways from that of its protonated (2) or deuterated (3) salts. The unprecedented observation of the maintenance of the hydrogen (or deuterium) bridge under soft ionization in the salts of very strong proton-sponge bases, which show buttressing effects in solution, is strong experimental support for the conservation of these buttressing effects in the gas phase, where the protonated (or deuterated) cations of salts such as 2 (or 3) are very stable, H⁺ (or D⁺) being completely ‘sequestered.’     

In search of a new class of stable nitroxide: synthesis and reactivity of a peri-substituted N,N-bissulfonylhydroxylamine

Acyclic bissulfonylnitroxides have never been isolated, and degrade through fragmentation. In an approach to stabilising a bissulfonylnitroxide radical, the cyclic, peri-substituted N,N-bissulfonylhydroxylamine, 2-hydroxynaphtho[1,8-de][1,3,2]dithiazine 1,1,3,3-tetraoxide (1), has been prepared by formal nitrogen insertion into the sulfur-sulfur bond of a sulfinylsulfone, naphtho[1,8-cd][1,2]dithiole 1,1,2-trioxide. The heterocyclic ring of 1 is shown to adopt a sofa conformation by X-ray crystallography, with a pseudo-axial hydroxyl group. N,N-Bissulfonylhydroxylamine 1 displays high thermal, photochemical and hydrolytic stability compared to acyclic systems. EPR analysis reveals formation of the corresponding bissulfonylnitroxide 2 upon oxidation of 1 with the Ce(IV) salts CAN and CTAN. Although 2 does not undergo fragmentation, it cannot be isolated, since hydrogen atom abstraction to reform 1 occurs in situ. The stability and reactivity of 1 and 2 are compared with the known cyclic benzo-fused N,N-bissulfonylhydroxylamine, N-hydroxy-O-benzenedisulfonimide (6), for which the X-ray data, and EPR of the corresponding nitroxide 10, are also reported for the first time.     

Electron impact mass spectral fragmentation patterns of 2a,4-disubstituted 5-benzoyl-2-chloro-2a,3,4,5-tetrahydroazeto[1,2-a][1,5]benzodiazepin-1( 2H)-ones

The mass spectrometric behaviour of six 2a,4-disubstituted 5-benzoyl-2-chloro-2a,3,4,5-tetrahydroazeto[1,2-a][1,5]benzodia zepin-1(2H)-ones has been studied with the aid of mass-analysed ion kinetic energy spectrometry and accurate mass measurements under electron impact ionization. All compounds show a tendency to eliminate a chlorine atom, a chlorine atom plus benzaldehyde, benzoyl radical, chloroketene or chlorine atom plus CO and H2O molecules to yield, respectively, [M-Cl]+ ions, 2a,4-disubstituted 2a,3-dihydroazeto[1,2-a][1,5]benzodiazepin-1(2H)-one ions, [M-PhCO]+ ions, 2,4-disubstituted 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions, or 1,2,4-trisubstituted 1H-1,7-benzodiazonine ions, which could also be formed from [M-Cl]+ ions by loss of CO and H2O molecules simultaneously. The [M-Cl]+ ions could further lose benzoyl radical to form [M-Cl-PhCO]+ ions, or lose benzoyl amide and undergo a rearrangement to form 4,6-disubstituted 1-benzoazocine-2(1H)-one ions. The [M-PhCO]+ ions could eliminate NH to produce 2a,4-disubstituted 2,2a,3,4-tetrahydroazeto[1,2,-a]quinolin-1-one ions, which could further eliminate chloroketene, CO and/or HCl to produce some important ions, respectively. 2,4-Disubstituted 1-benzoyl-2,3-dihydro-1H-1,5-benzodiazepine ions could lose benzoyl radical to yield 2,4-disubstituted 2,3-dihydro-1H-1,5-benzodiazepine ions, which could further yield other small fragment ions by loss of propene/styrene or small fragments.     

Mass spectral fragmentation of metal dithiocarbamate complex salts

A summary of the mass spectra of metal dithiocarbamate complex salts (ML₂ and ML₃) is presented. Only divalent metal dithiocarbamate ions without an electronic configuration containing an inert s-orbital electron pair exhibited both expulsion of a ligand radical (L) and the neutral even electron species (L–H) generated from the ligand via hydrogen transfer to the metal-containing fragment ion. Divalent metal dithiocarbamate ions can be generated either by direct electron impact ionization of gas phase ML₂ molecules or ionization of ML₃ molecules followed by loss of a ligand radical. A highly stable sp² hybridized, gas phase ion of a monobidentate lead dithiocarbamate complex is proposed.     

An Examination of the Coordination Chemistry of L2Pt(1,2-DITHIOLENES) Using Atmospheric Pressure Chemical Ionization Mass Spectrometry

Abstract

Atmospheric pressure chemical ionization mass spectrometry (APCI–MS) has been utilized in the characterization of two series of platinum dithiolene complexes, (COD)Pt(dt) 1, (COD)–Pt(edt) 2, (COD)Pt(dmid) 3, (COD)Pt(mnt) 4, (COD)Pt(eddo) 5, (COD)Pt(dddt) 6 and (Ph₃P)₂Pt(dt) 7, (Ph₃P)₂Pt(edt) 8, (Ph₃P)₂Pt(dmid) 9, (Ph₃P)₂Pt(dmit) 10, (Ph₃P)₂Pt(mnt) 11 (where COD = 1,5–cyclooctadiene, dt = ethane–1,2–dithiolate, edt = ethylene–1,2–dithiolate, dmid = 1,3–dithiole–2–oxo–4,5–dithiolate, dmit = 1,3–dithiole–2–thione–4,5–dithiolate, mnt = maleonitrile–1,2–dithiolate, eddo = 4–(ethylene–1′,2′–dithiolate)–1,3-dithiole–2–one, and dddt = 5,6–dihydro–1,4–dithiin–2,3–dithiolate). The series that contains triphenylphosphine is labile toward the loss of HPPh₃ ⁺. In addition, an orthometallated species involving the platinum and triphenylphosphine is identified. A dimer is identified for 2, which is shown to be a product of the experiment and not present in the parent material. In addition, a 1:1 adduct with NH₄ ⁺ is identified for 4 and 11 where the NH₄ ⁺ originates from the acid hydrolysis of acetonitrile. Finally, a highly unique ion, Pt⁺, a bare platinum ion, is observed in all COD complexes indicating that a radical mechanism must accompany the decomposition of the COD complexes during the fragmentation process.     

Investigation of 1,1′-disubstituted 4,4′-bipyridinium salts by various mass spectrometry techniques

The mass spectrometric behavior of symmetrically disubstituted 4,4′-bipyridinium salts under electron ionization (EI), electrospray ionization (ESI), direct analysis in real time (DART) ionization, and matrix-assisted laser desorption-ionization (MALDI) has been investigated. Electron ionization spectra were recorded using the direct injection of the probe at elevated temperature, when the salts were decomposed with the loss of counter-ions. In the case of ESI, primary ions are radical cations [Cat]^+· and cations [Cat-H]⁺, decomposed further by the loss of N-substituents. More complicated DART spectra revealed the peaks characterizing both bipyridyl group and organic substituents. MALDI spectra were rather simple and contained the peaks for [Cat]^{+ ·} ions that are structurally identical to radical cations formed during the reduction of the salts in solution. Among all the methods, DART and MALDI are suitable for the qualitative analysis of such bis-quaternary salts, while ESI is convenient for the quantitative analysis of these analytes.     

Atmospheric pressure ionization–tandem mass spectrometry of the phenicol drug family

In this work, the mass spectrometry behaviour of the veterinary drug family of phenicols, including chloramphenicol (CAP) and its related compounds thiamphenicol (TAP), florfenicol (FF) and FF amine (FFA), was studied. Several atmospheric pressure ionization sources, electrospray (ESI), atmospheric pressure chemical ionization and atmospheric pressure photoionization were compared. In all atmospheric pressure ionization sources, CAP, TAP and FF were ionized in both positive and negative modes; while for the metabolite FFA, only positive ionization was possible. In general, in positive mode, [M + H]⁺ dominated the mass spectrum for FFA, while the other compounds, CAP, TAP and FF, with lower proton affinity showed intense adducts with species present in the mobile phase. In negative mode, ESI and atmospheric pressure photoionization showed the deprotonated molecule [M–H]^?, while atmospheric pressure chemical ionization provided the radical molecular ion by electron capture. All these ions were characterized by tandem mass spectrometry using the combined information obtained by multistage mass spectrometry and high‐resolution mass spectrometry in a quadrupole‐Orbitrap instrument. In general, the fragmentation occurred via cyclization and losses or fragmentation of the N‐(alkyl)acetamide group, and common fragmentation pathways were established for this family of compounds. A new chemical structure for the product ion at m/z 257 for CAP, on the basis of the MS³ and MS⁴ spectra is proposed. Thermally assisted ESI and selected reaction monitoring are proposed for the determination of these compounds by ultra high‐performance liquid chromatography coupled to tandem mass spectrometry, achieving instrumental detection limits down to 0.1 pg. Copyright © 2013 John Wiley & Sons, Ltd.     

Even-electron ions: a systematic study of the neutral species lost in the dissociation of quasi-molecular ions

The collision-induced dissociations of the even-electron [M + H](+) and/or [M - H](-) ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH(3), SO(3)H in the negative ion mode, or NO(2) in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH(2) in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H](+) and [M - H](-) ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even-electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS-QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even-electron [M + H](+) and/or [M - H](-) ions (generated by ESI or APCI) with that of the corresponding odd-electron [M](+) ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion.     

Anion partitioning and ion-pairing behavior of anions in the extraction of cesium salts by 4,5' '-Bis(tert-octylbenzo)dibenzo-24-crown-8 in 1,2-dichloroethane

A systematic study of anion partitioning and ion pairing was performed for an extraction of individual cesium salts into 1,2-dichloroethane (1,2-DCE) using 4,5' '-bis(tert-octylbenzo)dibenzo-24-crown-8 as the cesium receptor. Equilibrium constants corresponding to the extraction of ion pairs and dissociated ions, formation of the 1:1 cesium/crown complex (confirmed by electrospray mass spectrometry), and dissociation of the ion pairs in water-saturated 1,2-DCE at 25 degrees C were obtained from equilibrium modeling using the SXLSQI program. The standard Gibbs energy of partitioning between water and water-saturated 1,2-DCE was determined for picrate, permanganate, trifluoromethanesulfonate, methanesulfonate, trifluoroacetate, and acetate anions. The dissociation of the organic-phase complex ion pair [Cs(4,4' '-bis(tert-octylbenzo)dibenzo-24-crown-8]+NO3- observed in the extraction experiments was shown to be consistent with the dissociation constant determined independently by conductance measurements. As attributed to the large effective radius of the complex cation, the evident anion discrimination due to ion pairing in the 1,2-DCE phase was relatively small, by comparison only a tenth of the discrimination exhibited by the anion partitioning. Only chloride and picrate exhibit evidence for significantly greater-than-expected ion-pairing tendency. These results provide insight into the inclusion properties of the clefts formed by opposing arene rings of the crown ether upon encapsulation of the Cs+ ion, whose weak anion recognition likely reflects the preferential inclusion of 1,2-DCE molecules in the clefts. Observed anion extraction selectivity in this system, which may be ascribed predominantly to solvent-induced Hofmeister bias selectivity toward large charge-diffuse anions, was nearly the same whether cesium salts were extracted as dissociated ions or ion pairs.     

Structures of gas phase C5H8 radical cations: A collisional ionization study

Collisional ionization (charge stripping) and charge exchange ionization spectrometry were utilized to determine structures of fourteen cyclic and acyclic C₅H₈ radical cations, including ionized 1,2- 1,3-, 1,4- and 2,3-pentadienes (-PD), isoprene, 1- and 3-methylcyclobutenes (1- and 3-MCB), 3-methyl-1,2-butadiene (3-M-1,2-BD), methenecyclobutane (MECB), cyclopentene, 3-methyl-1-butyne (3-MB), 1- and 2-pentynes and vinylcyclopropane (VCP). The pressure of the charge exchange reagent gas in the ion source was adjusted to generate ions of different energy contents. The structures of the C₅H₈ ions are energy dependent, and their isomerization reactions can be monitored as a function of the amount of internal energy deposited by charge exchange. 1,3-PD, isoprene and cyclopentene radical cations are identified as stable ion structures. 1-MCB, 3-M-1,2-BD and 3-MB radical cations isomerize to isoprene ions, whereas ionized VCP, 3-MCB, 1,2-PD, 2,3-PD, 1,4-PD, 1-pentyne and 2-pentyne ultimately isomerize to the [1,3-PD]⁺˙. Thermodynamic arguments are invoked to corroborate these isomerization reactions. The critical energies of the isomerizations are also estimated.     

Generation of ion-bound solvent clusters as reactant ions in dopant-assisted APPI and APLI

We provide experimental and theoretical evidence that the primary ionization process in the dopant-assisted varieties of the atmospheric pressure ionization methods atmospheric pressure photoionization and atmospheric pressure laser ionization in typical liquid chromatography–mass spectrometry settings is—as suggested in the literature—dopant radical cation formation. However, instead of direct dopant radical cation–analyte interaction—the broadly accepted subsequent step in the reaction cascade leading to protonated analyte molecules—rapid thermal equilibration with ion source background water or liquid chromatography solvents through dopant ion–molecule cluster formation occurs. Fast intracluster chemistry then leads to almost instantaneous proton-bound water/solvent cluster generation. These clusters interact either directly with analytes by ligand switching or association reactions, respectively, or further downstream in the intermediate-pressure regions in the ion transfer stages of the mass spectrometer via electrical-field-driven collisional decomposition reactions finally leading to the predominantly observed bare protonated analyte molecules [M?+?H]⁺.     

Laser-based ion mobility spectrometer for the direct analysis of aromatic compounds in liquids

A laser-based ionization source for the direct analysis of liquid samples in ion mobility (IM) spectrometry is presented and characterized. Ionization of aromatic substances in liquids is achieved, analogous to atmospheric pressure laser ionization (APLI) in mass spectrometry, by vaporizing the liquid and subsequently ionizing the aromatic substances by resonance-enhanced multiphoton ionization (REMPI). The effects of parameters, such as composition and flow rate of the solvent as well as laser wavelength and pulse energy, are systematically investigated. The characterization of the IM spectrometer is carried out by means of selected substances from diverse fields of applications, e.g., polycyclic aromatic hydrocarbons (PAH), pesticides, wood preservatives and drug compounds. Limits of detection (LOD) down to 10 fmol and linear ranges up to three orders of magnitude are established. In addition to direct laser ionization, indirect laser ionization via dopants (toluene) for substances with low ionization efficiencies is investigated. Ionization occurs as a result of proton transfer from toluene radical cations to substances of sufficiently high proton affinities. As a result of indirect laser ionization, LOD could be decreased by up to two orders of magnitude. Ionization products are investigated by means of a combination of IM and mass spectrometer. Depending on the substance investigated primary ions (radical cations) and secondary ions (protonated molecules) resulting from ion molecule reactions are formed.     

Enhanced detection of sulfo-peptides as onium salts in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A new two-component system, consisting of a matrix and an onium salt as comatrix, is described for detection of sulfo-peptides in the positive mode by matrix-assisted desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). Binary iodonium salts were superior to quaternary phosphonium salts in terms of suppression of desulfation and salt formation with the carboxyl group. Of the iodonium salts examined, bis(4-tert-butylphenyl)iodonium (BTI) hexafluorophosphate and bromide were most effective in giving intensive molecular ion signals in the form of [M(BTI)+BTI](+). The conditions optimized for O-sulfated tyrosine-containing peptides could be applicable for O-sulfated serine- and threonine-containing peptides. In the case of a phospho-peptide, a molecular ion appeared more intensively as a proton adduct than as a BTI adduct.     

The preparation and characterisation of bimetallic iridium(II) complexes containing derivatised bridging naphthalene-1,8-disulfur or 4,5-dithiolato acephenanthrylene ligands

Oxidative addition of the disulfide compounds naphtho[1,8-cd][1,2]dithiole, 2-tert-butylnaptho[1,8-cd][1,2]dithiole, 2,7-di-tert-butylnaphtho[1,8-cd][1,2]dithiole, 4,5-dithiaacephenanthrylene and the thio/sulfinyl and thio/sulfonyl compounds naphtho[1,8-cd][1,2]dithiole 1-oxide, and naphtho[1,8-cd][1,2]dithiole 1,1-dioxide respectively to [[Ir(mu-Cl)(cod)](2)] give dinuclear Ir-Ir bonded Ir(II) compounds [[IrCl(cod)](2)(mu(2)-1,8-S(2)-nap)] 1, [[IrCl(cod)](2)(mu(2)-1,8-S(2)-2-(t)Bu-nap)] 2, [[IrCl(cod)](2)(mu(2)-1,8-S(2)-2,7-di-(t)Bu-nap)]] 3, [[IrCl(cod)](2)(mu(2)-4,5-S(2)-phenan)] 4, [[IrCl(cod)](2)(mu(2)-1-S,8-[S(O)]-nap)] 5 and [[IrCl(cod)](2)(mu(2)-1-S,8-[S(O)(2)]-nap)] 6 where the di-sulfur ligands act as bridges between the two Ir(II) metal centres. The compounds were obtained in moderate to good yields as orange or deep red powders or crystalline solids. Five of the new complexes have been structurally characterised and were found to have Ir-Ir bond lengths in the range 2.7630(8) to 2.8113(11) A.     

Structural determination of the novel fragmentation routes of zwitteronic morphine opiate antagonists naloxonazine and naloxone hydrochlorides using electrospray ionization tandem mass spectrometry

Electrospray ionization quadrupole time-of-flight (ESI-QqToF) mass spectra of the zwitteronic salts naloxonazine dihydrochloride 1 and naloxone hydrochloride 2, a common series of morphine opiate receptor antagonists, were recorded using different declustering potentials. The singly charged ion [M+H-2HCl](+) at m/z 651.3170 and the doubly charged ion [M+2H-2HCl](2+) at m/z 326.1700 were noted for naloxonazine dihydrochloride 1; and the singly charged ion [M+H-HCl](+) at m/z 328.1541 was observed for naloxone hydrochloride 2. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) experiments established the fragmentation routes of these compounds. In addition to the characteristic diagnostic product ions obtained, we noticed the formation of a series of radical product ions for the zwitteronic compounds 1 and 2, and also the formation of a distonic ion product formed from the singly charged ion [M+H-HCl](+) of naloxone hydrochloride 2. Confirmation of the various established fragmentation routes was effected by conducting a series of ESI-CID-QqTof-MS/MS product ion scans, which were initiated by CID in the atmospheric pressure/vacuum interface using a higher declustering potential. Deuterium labeling was also performed on the zwitteronic salts 1 and 2, in which the hydrogen atoms of the OH and NH groups were exchanged with deuterium atoms. Low-energy CID-QqTof-MS/MS product ion scans of the singly charged and doubly charged deuteriated molecules confirmed the initial fragmentation patterns proposed for the protonated molecules. Precursor ion scan analyses were also performed with a conventional quadrupole-hexapole-quadrupole tandem mass spectrometer and allowed the confirmation of the genesis of some diagnostic ions.