Electronic coupling in mixed-valence dinuclear ferrocenes and cobaltocenes with saturated bridging groups

We have synthesised a series of new dinuclear metallocenes [{M(Cp*)(C5H4)}2X] (Cp* = eta5-pentamethylcyclopentadienyl; M = Fe, Co, X = CMe2, SiMe2, GeMe2; M = Fe, X = Si2Me4). For the neutral dicobalt complexes, magnetic susceptibility measurements reveal intramolecular antiferromagnetic interactions of -21 and -14 cm(-1) for SiMe2- and GeMe2-bridged species, respectively, but negligible interaction for the CMe2-bridged compound. In contrast, intervalence charge-transfer (IVCT) data for the mixed-valence monocations of both Fe and Co complexes show electronic coupling to decrease in the order CMe2 > SiMe2 > GeMe2. This suggests that electronic coupling is principally through-space in contrast to results found from previous studies. The IVCT data also show much stronger coupling in the dicobalt species versus their diiron analogues.     

Simultaneous measurement of metabolic stability and metabolite identification of 7-methoxymethylthiazolo[3,2-a]pyrimidin-5-one derivatives in human liver microsomes using liquid chromatography/ion-trap mass spectrometry

A liquid chromatography/mass spectrometry (LC/MS) method using an atmospheric pressure chemical ionisation source was used to measure the metabolic stability and metabolite identification of 7-methoxymethylthiazolo[3,2-a]pyrimidin-5-one derivative (1) in human liver microsomes. After 15 min incubation with human liver microsomes, compound 1 exhibited metabolic turnover of 44%. Data-dependent tandem mass spectrometry (MS/MS) scanning was used to generate product ion spectra from the protonated ions of the compound and its metabolites. An unusual metabolite at m/z 407 corresponding to the [M-24+H]+ ion was identified for compound 1. Interestingly, the formation of the [M-24+H]+ ion was not observed in the analogues wherein the fused thieno double bond was substituted (2) and the thieno group replaced by a fused benzo derivative (3). Compounds 2 and 3 exhibited metabolic turnovers of 24 and 30%, yielding oxidative metabolites corresponding to [M+16] and [M+32]+, respectively. Based on these facts the mechanism for [M-24]+ formation in compound 1 through an initial epoxide formation on the double bond of the fused thieno ring followed by hydrolytic ring opening and deacylation is envisaged.     

Deprotonation reactions of zirconium and hafnium amide complexes H2N-M[N(SiMe3)2]3 and subsequent silyl migration from amide -N(SiMe3)2 to imide =NH ligands

Ammonolysis of previously reported Cl-M[N(SiMe3)2]3 (M = Zr, 1a; Hf, 1b) leads to the formation of peramides H2N-M[N(SiMe3)2]3 (M = Zr, 2a; Hf, 2b) which upon deprotonation by LiN(SiMe3)2 or Li(THF)3SiPh2But yields imides Li+(THF)n{HN(-)-M[N(SiMe3)2]3} (M = Zr, 3a; Hf, 3b). One -SiMe3 group in 3a-b undergoes silyl migration from a -N(SiMe3)2 ligand to the imide =NH ligand to give Li+(THF)2{Me3SiN(-)-M[NH(SiMe3)][N(SiMe3)2]2} (M = Zr, 4a; Hf, 4b) containing an imide =N(SiMe3) ligand. The kinetics of the 3a --> 4a conversion was investigated between 290 and 315 K and was first-order with respect to 3a. The activation parameters for this silyl migration are DeltaH++ = 13.3(1.3) kcal/mol and DeltaS++ = -34(3) eu in solutions of 3a (in toluene-d8 with 1.07 M THF) prepared in situ. THF in the mixed solvent promoted the 3a --> 4a reaction. The effect of THF on the rate constants of the conversion has been studied, and the kinetics of the reaction was 3.4(0.6)th order with respect to THF. Crystal and molecular structures of H2N-Zr[N(SiMe3)2]3 (2a) and 4a-b have been determined.     

Mass spectrometry for the characterization of unsulfated chondroitin oligosaccharides from 2-mers to 16-mers. Comparison with hyaluronic acid oligomers

This study reports for the first time the complete liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS) and tandem mass spectrometry (MS/MS) analyses performed in negative ion mode of saturated unsulfated chondroitin oligosaccharides up to 16-mers and comparison with hyaluronic acid (HA) oligomers differing only in the nature of the hexosamine residue. MS/MS of the chondroitin disaccharide on the singly charged precursor at m/z 396.1 afforded a glycosidic cleavage C1 product ion at m/z 192.9. In the tetrasaccharide, C2 (m/z 396.0) and C3 (m/z 572.0) product anions were generated by glycosidic cleavage. A C5 [M-2H]2- product ion at m/z 475.1 was generated by the glycosidic cleavage of the hexasaccharide, and a C7 ion (m/z 664.6, charge state of -2) was produced from the octasaccharide. The same fragmentation pattern of deprotonated oligomers was observed for the largest oligosaccharides, from 10- to 16-mers. There has been no previous report of MS/MS spectra for unsulfated chondroitin oligomers of these sizes. Unsulfated saturated chondroitin oligosaccharides with x-mer units and larger than a tetrasaccharide dissociate to almost exclusively form CX-1-type ions. Saturated HA oligomers also afforded the same fragmentation pattern as deprotonated oligomers by ESI-MS and MS/MS analyses. Thus, under the experimental conditions used in the current study, we were unable to distinguish between unsulfated chondroitin and HA.     

Self-assembly formation of the magic ion of (H2O)20O+: observation of nanoscale cages of oxygenated water clusters induced from iron nanoparticles

For the first time, we observed a stable and intense ion (m/z 376) of the oxygenated water cluster ion ((H(2)O)(20)O(+)) produced from simply spraying an aqueous solution of iron nanoparticles (Fe NPs) into an electrospray mass spectrometry (ESI-MS) system. Tandem mass spectrometric (MS/MS and MS/MS/MS) results were applied to identify the assignments of the fragment ions of m/z 376 in order to explore the possible structures of this cluster ion. The possible structures of the (H(2)O)(20)O(+) ions are proposed as pentagonal dodecahedron water clathrate cages from the results of tandem mass spectrometry since eliminations of five water molecules were frequently observed in the MS/MS results for many subsequent fragment ions of m/z 376. The formation of this oxygenated water cluster ion ((H(2)O)(20)O(+)) in ESI-MS is attributed to the high surface reactivity and surface energy of Fe NPs during ESI processes (under high temperature and high voltage (5 kV) of ESI spray environment). We believe that the observation of self-assembly formation of oxygenated water clusters is an important issue in nanoscience as well as in the fields of water clusters.     

An improved liquid chromatography/tandem mass spectrometry method for the determination of 8-oxo-7,8-dihydro-2'-deoxyguanosine in DNA samples using immunoaffinity column purification

The analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) represents an important biomarker of oxidative stress. A sensitive method for the detection of 8-oxodG in DNA samples has been developed that utilizes immunoaffinity column purification of 8-oxodG followed by liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS) multiple reaction monitoring (MRM) mode analysis. An internal standard of stable-isotopically labelled 8-oxodG containing [(15)N(5)] was added prior to the enzymatic digestion of DNA to deoxynucleosides, which was then subjected to immunoaffinity column purification followed by microbore positive ion LC/MS/MS MRM. The 8-oxo-7,8-dihydroguanine (8-oxoG) base product ion at m/z 168 was monitored following cleavage of the glycosidic bond of the 8-oxodG [M+H](+) ion at m/z 284. Similar determinations were made for [(15)N(5)]8-oxodG by monitoring the [(15)N(5)]8-oxoG base product ion at m/z 173 formed from the [M+H](+) ion at m/z 289. The introduction of the immunoaffinity column purification step into the method represents a significant improvement for the accurate determination of 8-oxodG since all artefactual peaks that are observed following the direct injection of digested DNA onto the LC/MS/MS system are removed. The identity of these artefactual peaks has been confirmed to be 2'-deoxyguanosine (dG), thymidine (dT) and 2'-deoxyadenosine (dA). The presence of these artefactual peaks in MRM mode analysis can be explained as a consequence of a concentration effect due to their considerably higher relative abundance in DNA compared to 8-oxodG. The highest signal intensity was observed for the artefactual peak for dA due to the fact that the adenine base formed an adduct with methanol, which is a constituent of the mobile phase. The resulting [M+H](+) ion at m/z 284 (dA m/z 252 + CH(3)OH m/z 32) gave rise to a product ion at m/z 168 following the loss of deoxyribose in MRM mode analysis. Control calf thymus DNA was digested to deoxynucleosides and unmodfied deoxynucleosides were removed by immunoaffinity column purification; the enriched 8-oxodG was determined by LC/MS/MS MRM. The level of 8-oxodG in control calf thymus DNA was determined to be 28.8 +/- 1.2 8-oxodG per 10(6) unmodified nucleotides (n = 5) using 5 microg of digested DNA. The limit of detection of the microbore LC/MS/MS MRM for 8-oxodG was determined to be 25 fmol on-column with a signal-to-noise ratio of 3.5.     

Determination of the metabolites of gestrinone in human urine by high performance liquid chromatography, liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry

Gestrinone was studied by high performance liquid chromatography (HPLC) for screening and by gas chromatography/mass spectrometry (GC/MS) for confirmation. When the chromatograms of blank, spiked urine and dosed urine were compared by HPLC, two unknown metabolites were found and these were excreted as the conjugated forms. Metabolites 1 and 2 were tested by LC/MS and LC/MS/MS and both had parent ions at m/z 325. The fragment ion of metabolite 1 was at m/z 263 and ions for metabolite 2 were m/z 307 [MH - H(2)O](+), 289, 279 and 241. LC/MS/MS of m/z 263 as the parent ion of metabolite 1 gave fragment ions at m/z 245 and 217, which were assumed to be [263 - H(2)O](+) and [235 - H(2)O](+), respectively. The trimethylsilyl (TMS)-enol-TMS ether derivative of gestrinone displayed three peaks in its GC/MS chromatogram, formed by tautomerism.     

Isotope edited product ion assignment by α-N labeling of peptides with [2H3(50%)]2,4-Dinitrofluorobenzene

An isotopic modification of Sanger's method for identifying peptide N-termini has been developed to assist peptide sequencing by tandem mass spectrometry. Tryptic peptides, such as Val-His-Leu-Thr-Pro-Val-Glu-Lys, are derivatized with an equimolar mixture of 2,4-dinitrofluorobenzene and [2H3]2,4-dinitrofluorobenzene. Under optimized derivatization conditions, the alpha-amino group could be derivatized while the epsilon-amine of the lysine side chain and the imidazole of histidine remained underivatized. The alpha-dinitrophenyl modified peptides were characterized by electrospray ionization-tandem mass spectrometry (ESI-MS/MS) and liquid chromatography (LC)-ESI-MS. The [M + H]+ ions showed a doublet pattern with a delta m/z of 3 and the [M + 2H]2+ ions were recognized as doublets with a delta m/z of 1.5. MS/MS was employed where both isotopic [M + 2H]2+ ions were alternately subjected to collision-induced dissociation in the second quadrupole. Fragmentation in the ionization source generated identical product ion patterns that were observed during fragmentation in the second quadrupole. In the product ion mass spectra, the N-terminal a and b ions (no c ion observed) are doublets with a delta m/z of 3 or 1.5, while the C-terminal y and z ions (no x ion observed) are singlets appearing at identical masses. Thus, the product ions containing the N-terminus derivatized with a dinitrophenyl group are unequivocally distinguished from the product ions containing the C-terminus. The dinitrophenyl modification generally enhanced the production of a and b ions without diminishing y and z ion yields.     

Rapid liquid chromatography-tandem mass spectrometry method for quantification of ziprasidone in human plasma

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the determination of ziprasidone (ZIP) in human plasma was developed. ZIP and N-methyl ziprasidone as internal standard (IS) were extracted from alkalinized plasma using tert- butyl methyl ether. Separation was performed isocratically on a C8 column with 90% acetonitrile containing 2 mmol/L ammonium acetate as a mobile phase with a total run time of 2.5 min. MS/MS transitions of m/z 413 --> 194 and m/z 427 --> 177 of the analyte and internal standard were used for quantification. Confirmatory ions of m/z 413 --> 177 and m/z 427 --> 180 were collected as well. The calibration curve based on peak-area ratio was linear up to at least 200 ng/mL with a detection limit of 0.1 ng/mL. The method showed satisfactory reproducibility with a coefficient of variation of less than 5%. The method was successfully applied to the analysis of ZIP in spiked human plasma.     

Applications of CE-ESI-MS/MS analysis to structural elucidation of methylenecyclohexane ozonolysis products in the particle phase

The composition of secondary organic aerosol (SOA) from the gas phase ozonolysis of methylenecyclohexane was analyzed in a series of indoor aerosol chamber experiments. Capillary electrophoresis-electrospray ionization-ion trap mass spectrometry (CE/ESI-ITMS) was used for qualitative and quantitative analysis of SOA constituents. A number of dicarboxylic acids in the range of C(5)-C(6), such as adipic acid and glutaric acid, were found as major components of the organic products. Besides these smaller compounds, the formation of higher-molecular-weight compounds were observed under both neutral and acidic conditions. MS/MS experiments were carried out in order to obtain information on the monomer units and the structure of the dimers. MS(2) experiments of the two most prominent dimers with a mass-to-charge ratio (m/z) of 257 and m/z 273 yielded common fragments of m/z 83, 129 or 145. Based on the fragmentation patterns, these dimers are tentatively identified as carboxylate ester acids containing a unit of adipic acid in the structure. The dimer with m/z 257 was nearly 60% of the total detected compounds for both the neutral and acidic seed particle experiments.     

The distinction of underivatized monosaccharides using electrospray ionization ion trap mass spectrometry

A convenient method for distinguishing underivatized isomeric monosaccharides has been established using electrospray ionization ion trap mass spectrometry (ESI-ITMS). Mass spectra of hexoses (glucose, galactose, and mannose), N-acetylhexosamines (N-acetylglucosamine, N-acetylgalactosamine, and N-acetylmannosamine) and hexosamines (glucosamine, galactosamine, and mannosamine) dissolved in solvent containing 1 mM ammonium acetate were obtained in the positive ion mode. Glucose was distinguished from galactose and mannose in the MS(2) spectrum of the [M+NH(4)](+) ion at m/z 198. The MS(3) spectra generated from [M+NH(4)-H(2)O-NH(3)](+) at m/z 163 showed that galactose and mannose could be distinguished by the ratio of peak intensities at m/z 145 and 127, while the three N-acetylhexosamine and hexosamine stereochemical isomers could be identified by the relative abundance ratios of product ions observed in MS(3) spectra. The investigation of MS and MS(2) spectra from complexes of these monosaccharides with Na(+) and Pb(2+) failed to distinguish these monosaccharide isomers. Therefore, multiple stage mass analysis by ESI-ITMS using either [M+NH(4)](+) or [M+H](+) was useful to distinguish between the isomers of monosaccharides.     

Synthesis, characterization, and catalytic activity of rare earth metal amides supported by a diamido ligand with a CH2SiMe2 link

A series of four coordinate rare earth metal amides with general formula ((CH2SiMe2)[(2,6- IPr2C6H3)N]2)LnN(SiMe3)2(THF) [(Ln = Yb(2), Y (3), Dy (4), Sm (5), Nd (6)] containing a diamido ligand (CH2SiMe2)[(2,6-iPr2C6H3)N]2(2-) with a CH2SiMe2 link were synthesized in good yields via reaction of [(Me3Si)2N]3Ln(III)(mu-Cl)Li(THF)3 with the corresponding diamine (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1). All compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of complexes 2, 3, 4, 5, and 6 were determined by single-crystal X-ray analyses. Investigation of the catalytic properties of the complexes indicated that all complexes exhibited a high catalytic activity on the cyclotrimerization of aromatic isocyanates, which represents the first example of cyclopentadienyl-free rare earth metal complexes exhibiting a high catalytic activity and a high selectivity on cyclotrimerization of aromatic isocyanates. The temperatures, solvents, catalyst loading, and the rare earth metal effects on the catalytic activities of the complexes were examined.     

Liquid chromatography with electrospray ion-trap mass spectrometry for the determination of anatoxins in cyanobacteria and drinking water

Anatoxin-a (AN) and homoanatoxin-a (HMAN) are potent neurotoxins produced by a number of cyanobacterial species. A new, sensitive liquid chromatography/multiple tandem mass spectrometry (LC/MS(n)) method has been developed for the determination of these neurotoxins. The LC system was coupled, via an electrospray ionisation (ESI) source, to an ion-trap mass spectrometer in positive ion mode. The [M+H](+) ions at m/z 166 (anatoxin-a) and m/z 180 (homoanatoxin-a) were used as the precursor ions for multiple MS experiments. MS(2)bond;MS(4) spectra displayed major fragment ions at m/z 149 (AN), 163 (HMAN), assigned to [Mbond;NH(3)+H](+); m/z 131 (AN), 145 (HMAN), assigned to [Mbond;NH(3)bond;H(2)O+H](+), and m/z 91 [C(7)H(7)](+). Although the chromatographic separation of these neurotoxins is problematic, reversed-phase LC, using a C(18) Luna column, proved successful. Calibration data for anatoxin-a using spiked water samples (10 mL) in LC/MS(n) modes were: LC/MS (25-1000 microg/L), r(2) = 0.998; LC/MS(2) (5-1000(microg/L), r(2) = 0.9993; LC/MS(3) (2.5-1000 microg/L), r(2) = 0.9997. Reproducibility data (% RSD, N = 3) for each LC/MS(n) mode ranged between 2.0 at 500 microg/L and 7.0 at 10 microg/L. The detection limit (S/N = 3) for AN was better than 0.03 ng (on-column) for LC/MS(3) which corresponded to 0.6 microg/L.     

Mass spectrometric characterization of toremifene metabolites in human urine by liquid chromatography-tandem mass spectrometry with different scan modes

The metabolism and excretion of toremifene were investigated in one healthy male volunteer after a single oral administration of 120 mg toremifene citrate. Different liquid chromatographic/tandem mass spectrometric (LC/MS/MS) scanning techniques were carried out for the characterization of the metabolites in human urine for doping control purposes. The potential characteristic fragmentation pathways of toremifene and its major metabolites were presented. An approach for the metabolism study of toremifene and its analogs by liquid chromatography-tandem mass spectrometry was established. Five different LC/MS/MS scanning methods based on precursor ion scan (precursor ion scan of m/z 72.2, 58.2, 44.2, 45.2, 88.2 relative to five metabolic pathways) in positive ion mode were assessed to recognize the metabolites. Based on product ion scan and precursor ion scan techniques, the metabolites were proposed to be identified as 4-hydroxy-toremifene (m/z 422.4), 4'-hydroxy-toremifene (m/z 422.4), α-hydroxy-toremifene (m/z 422.4), 3,4-dihydroxy-toremifene (m/z 404.2), toremifene acid (m/z 402.2), 3-hydroxy-4-methoxy-toremifene (m/z 456.2), dihydroxy-dehydro-toremifene (m/z 440.2), 3,4-dihydroxy-toremifene (m/z 438.2), N-demethyl-4-hydroxy-toremifene (m/z 408.3), N-demethyl-3-hydroxy-4-methoxy-toremifene (m/z 438.3). In addition, a new metabolite with a protonated molecule at m/z 390.3 was detected in all urine samples. The compound was identified by LC/MS/MS as N-demethyl-4,4'-dihydroxy-tamoxifene. The results indicated that 3,4-dihydroxy-toremifene (m/z 404.2), toremifene acid (m/z 402.2) and N-demethyl-4,4'-dihydroxy-tamoxifene (m/z 390.3) were major metabolites in human urine.     

Mass spectrometric study of persistent acid metabolites of nonylphenol ethoxylate surfactants

A mass spectrometric study was carried out on two nonylphenoxycarboxylic acids, NP1EC and NP2EC (where 1 and 2 indicate the number of ethoxylate units attached to the nonylphenoxy moiety), that are persistent metabolites of widely used nonionic surfactant nonylphenol ethoxylates. In a gas chromatographic/mass spectrometric (GC/MS) study of the methyl esters of NP1EC and NP2EC, two series of fragment ions were observed in electron ionization (EI) mass spectra; m/z (179 + 14n, n = 0-7) and m/z (105 + 14n, n = 0-4) for NP1ECMe and m/z (223 + 14n, n = 0-7) and m/z (107 + 14n, n = 0-5) for NP2ECMe. Similarity indices were used to compare quantitatively the mass spectra of isomers. The mass spectra of two isomers were found to be similar whereas those of the remaining isomers were readily distinguishable from each other. The abundant fragment ions of the two NPECMes were investigated further by GC/MS/MS; product ions resulting from cleavage in the alkyl moiety, cleavage in the ECMe moiety and cleavage in both moieties were detected. Possible structures of the nonyl groups in the two esters were inferred. GC/chemical ionization (CI) mass spectra of the NPECMes with isobutane as reagent gas showed characteristic hydride ion-abstracted fragment ions shifted by 1 Da from those in the corresponding EI mass spectra. The sensitivity of a selected ion monitoring quantitation method for the NPECMes is enhanced under CI conditions compared with that under EI conditions. With electrospray ionization MS/MS, [M - H](-) ions of NP1EC (m/z 277) and NP2EC (m/z 321) were observed and, upon collision-induced dissociation of [M - H](-) of each of the two acids, fragment ions of m/z 219 corresponding to deprotonated nonylphenol, were observed in each case. Based on this observation, a rapid, simple and reliable selected product ion quantitation method is proposed for NP1EC and NP2EC.     

Reaction of the silylene Si[(NCH2But)2C6H4-1,2] with the alkali metal silylamides M[N(SiMe3)R](M = Li, Na or K; R = SiMe3 or SiMe2Ph)

The thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2] 1 undergoes oxidative addition reactions with the alkali metal silylamides MN(SiMe(3))(2)(M = Li, Na or K) to afford the new alkali metal amides MN(SiMe(3))[(1)SiMe(3)][M = Li (2), Na (3) or K (4)]. Reaction of two equivalents of 1 with LiN(R)(SiMe(3)) leads in a two-step process to the compound LiN[(1)R][(1)SiMe(3)][R = SiMe(2)Ph (5) or SiMe(3) (6)]. Alternatively, 1 reacts with 3 to afford NaN[(1)SiMe(3)](2) (7). The structures of 2-5 and are presented and the formation of 2-7 is discussed.     

Identification of linoleic acid free radicals and other breakdown products using spin trapping with liquid chromatography-electrospray tandem mass spectrometry

Linoleic acid radical products formed by radical reaction (Fenton conditions) were trapped using 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO) and analysed by reversed-phase liquid chromatography coupled to electrospray mass spectrometry (LC-MS). The linoleic acid radical species detected as DMPO spin adducts comprised oxidized linoleic acid and short-chain radical species that resulted from the breakdown of carbon and oxygen centred radicals. Based on the m/z values, the short-chain products were identified as alkyl and carboxylic acid DMPO radical adducts that exhibited different elution times. The ions identified as DMPO radical adducts were studied by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The LC-MS/MS spectra of linoleic acid DMPO radical adducts exhibited the fragment ion at m/z 114 and/or the loss of neutral molecule of 113 Da (DMPO) or 131 Da (DMPO + H2O), indicated to be DMPO adducts. The short-chain products identified allowed inference of the radical oxidation along the linoleic acid chain by abstraction of hydrogen atoms in carbon atoms ranging from C-8 to C-14. Other ions containing the fragment ion at m/z 114 in the LC-MS/MS spectra were attributed to DMPO adducts of unsaturated aldehydes, hydroxy-aldehydes and oxocarboxylic acids. The identification of aldehydic products formed by radical oxidation of linoleic acid peroxidation products, as short-chain product DMPO adducts, is a means of identifying lipid peroxidation products.     

A trigonal bipyramidal uranyl amido complex: synthesis and structural characterization of [Na(THF)2][UO2(N(SiMe3)2)3

The synthesis and structural characterization of a rare example of a uranyl complex possessing three equatorial ligands, [M(THF)2][UO2(N(SiMe3)2)3] (3a, M = Na; 3b, M = K), are described. The sodium salt 3a is prepared by protonolysis of [Na(THF)2]2[UO2(N(SiMe3)2)4], whereas the potassium salt 3b is obtained via a metathesis reaction of uranyl chloride UO2Cl2(THF)2 (4) with 3 equiv of K[N(SiMe3)2]. A single-crystal X-ray diffraction study of 3a revealed a trigonal-bipyramidal geometry about uranium, formed by two axial oxo and three equatorial amido ligands, with average U=O and U-N bond distances of 1.796(5) and 2.310(4) A, respectively. One of the oxo ligands is also coordinated to the sodium counterion. 1H NMR spectroscopic studies indicate that THF adds reversibly as a ligand to 3 to expand the trigonal bipyramidal geometry. The degree to which the coordination sphere in 3 is electronically satisfied with only three amido donors is suggested by (1) the reversible THF coordination, (2) a modest elongation in the bond distances for a five-coordinate U(VI) complex, and (3) the basicity of the oxo ligands as evidenced in the contact to Na. The vibrational spectra of the series of uranyl amido complexes [UO2(N(SiMe3)2)n]2-n (n = 2-4) are compared, to evaluate the effects on the axial U=O bonding as a function of increased electron density donated from the equatorial region. Raman spectroscopic measurements of the nu 1 symmetric O=U=O stretch show progressive axial bond weakening as the number of amido donors is increased. Crystal data for [Na(THF)2][UO2(N(SiMe3)2)3]: orthorhombic space group Pna2(1), a = 22.945(1) A, b = 15.2830(7) A, c = 12.6787(6) A, z = 4, R1 = 0.0309, wR2 = 0.0524.     

Stereochemical analysis of deuterated alkyl chains by MS/MS

Vicinally deuterated sec-alkyl phenyl ethers, CH(3)(CH(2))(m)()CH(OPh)CHD(CH(2))(n)()CH(3), display significant differences in mass spectra between threo and erythro stereoisomers. MS/MS experiments, in which parent ions of a single mass are selected and their fragmentation patterns subsequently measured, show that alkene expulsion represents virtually the only decomposition pathway. Two types of MS/MS experiment are reported: mass-analyzed ion kinetic energy (MIKE) spectroscopy of metastable ions and collisionally activated decomposition (CAD) of stable ions. The expulsion of a deuterated alkene from a monodeuterated precursor yields ionized phenol, PhOH(*)()(+) (m/z 94). The expulsion of an undeuterated alkene yields PhOD(*)()(+) (m/z 95). Without exception, the ratios (PhOD(*)()(+)/PhOH(*)()(+)) from precursors in the threo series have values greater than their diastereomers in the erythro series. The ratio of ratios, r = PhOD(*)()(+)/PhOH(*)()(+) for the threo divided by PhOD(*)()(+)/PhOH(*)()(+) for the erythro, has a value of 1.2 for the 2-phenoxy-3-deuteriobutanes and larger values for all of the higher homologues up through the monodeuterated phenoxyoctanes (m + n = 4). The highest degree of stereoselectivity, r = 5.8, is measured for 3-phenoxy-4-deuteriohexane. Experiments with multiply deuterated analogues show that alkene elimination is highly regioselective, unlike the corresponding decompositions of ionized sec-alcohols or their acetates. The fact that a large fraction of ionized sec-alkyl phenyl ethers undergo stereospecific syn-elimination means that mass spectrometry has a useful capacity to distinguish one isotopically labeled diastereomer from another.     

Determination of glycoalkaloids and relative aglycones by nonaqueous capillary electrophoresis coupled with electrospray ionization-ion trap mass spectrometry

Glycoalkaloids are naturally occurring nitrogen-containing compounds present in many species of the family Solanaceae, including cultivated and wild potatoes (Solanum spp.), tomatoes (Lycopersicon spp.), etc. These compounds have pharmacological and toxicological effects on humans due to their significant anticholinesterase activity and disruption of cell membranes. Herein is reported the development of a capillary electrophoresis (CE) method using nonaqueous (NA) separation solutions in combination with ion trap mass spectrometry (MS and MS/MS) detection for the identification and quantification of glycoalkaloids and their relative aglycones. A mixture 90:10 v/v of MeCN-MeOH containing 50 mM ammonium acetate and 1.2 M acetic acid (applied voltage of 25.5 kV) was selected as a good compromise for the separation and detection of these compounds. The electrospray MS measurements were carried out in the positive ionization mode using a coaxial sheath liquid, methanol-water (1:1) with 1% of acetic acid at a flow rate of 2.5 microL/min. Under optimized experimental conditions, the predominant ion was the protonated molecular ion ([M+H](+)) of solanidine (m/z = 398), tomatidine (m/z = 416), chaconine (m/z = 852), solanine (m/z = 868), and tomatine (m/z = 1034). MS/MS experiments were carried out systematically by changing the relative collisional energy and monitoring the intensities of the fragment ions that were not high enough to allow better quantification than with the mother ions. The method was used for analyzing glycoalkaloids in potato extracts.