Mass spectral behavior of some homoleptic and mixed aryldichalcogenide bis(diphenylphosphino)ferrocenenickel(II), palladium(II), and platinum(II), and bis(diisopropylphosphino)ferrocenepalladium(II) complexes

The mass spectral behavior of a number of organometallic complexes containing the Group 10 metals Ni, Pd, and Pt, together with various thiolate ligands were studied. For Pd, two main types of complexes, differing by the substituents on the phosphorus atom were studied. Types I and II were substituted with bis(diphenylphosphino)ferrocene and bis(diisopropylphosphino)ferrocene ligands, respectively. The Ni complexes, except for one, and the Pd Type I complexes had no molecular radical cations (M(+.)) in their EI spectra. On the other hand, all the Pt complexes showed intense M(+.) ions in their EI spectra indicating that these complexes were more stable as radical cations than those of Ni and Pd. The FAB and MALDI spectra of all the complexes displayed intense quasi-molecular ions (MH(+)) and the fragmentations in both modes were similar. The MALDI spectra of several complexes displayed only M(+.) ions while one gave evidence of both MH(+) and M(+.) ions. Several Pd Type II complexes yielded intense M(+.) in their EI spectra.     

Enhancement of mass spectrometric detection of LTC4, LTD4, and LTE4 by derivatization

Several acylating reagents are synthesized and used to introduce quatemary phosphonium or ammonium or ternary sulfonium functions into a simple model of a peptido leukotriene (PLT). One of these reagents was selected for further study with LTE₄, LTD₄, and LTC₄. We demonstrate that acylation of the free amine function of PLTs to produce the 5-triphenylphosphoniumvaleryl-amide (TPPV) derivatives enhances chemical stabilities and significantly increases responses in fast-atom bombardment and continuous-flow liquid secondary ion mass spectrometry (CF-LSIMS) relative to the native PLTs. With high-performance liquid chromatography inlet to CF-LSIMS, we demonstrate the facile detection in selected ion monitoring of the TPPV derivative of 3 pg of LTD₄.     

Collision-induced oxygen addition to chloroaromatic compounds

The reactions of chloroaromatic radical anions with oxygen were studied with a triple quadrupole mass spectrometer. Two chlorobenzenes and eight polychlorinated biphenyls were analyzed by gas chromatography-tandem mass spectrometry under negative ion chemical ionization. The molecular radical anions were selected with the first quadrupole and reacted with oxygen in the collision cell. Under these conditions, [M+O ? Cl] ions were obtained with intensities similar to those of the transmitted precursor ions. This dechlorination reaction was not affected by a detectable chlorine isotope effect. The intensities of the [M+O ? Cl] ions vary with the nature of the chloroaromatic compounds and with the oxygen pressure and collision energy. Charge transfer reactions are also observed, and the relative amount of O ₂ ^?. produced is controlled by the relative electron affinity of the organochlorine. At high collision energies, collision-induced fragmentation of the molecular ion competes for the production of Cl^?.     

5-epi-Canadensene and other novel metabolites of Taxus canadensis

The Canadian yew distinguishes itself from other yews by the nature of its taxane metabolites. We are now reporting a new canadensene taxane whose stereochemistry is rigorously established. The three-dimensional structures of canadensene, 5-epi-canadensene and three other related bicyclic taxanes isolated from other yews were calculated using distance constraints derived from NMR data. The stereochemistry of the substituents, the polar acetate groups and the double bonds determine the 3D models. In addition, three new taxanes were also characterized and some biosynthetic speculations are presented.     

Mass spectral and pyrolytic fragmentation paths for o-nitroanisole

The mass spectral and pyrolytic dissociations of o-nitroanisole are reported. The parent ion dissociates by two pathways, principally through loss of CH₂O, but a significant fraction through loss of NO. The parent-less-30 peak is therefore a doublet, as shown by high resolution measurements. The thermal decomposition at 600°C and above proceeds also by two pathways, but these are the loss of HNO and HNO₂, to form 1,2-methylenedioxybenzene and benzaldehyde respectively.     

Dechlorination of polychlorinated biphenyls in electron-capture negative-ion chemical ionization mass spectrometry

The electron-capture negative-ion chemical Ionization mass spectra of 36 ³⁵Cl mono- and di-labelled penta- and hexachlorobiphenyls were studied. Under the conditions of the analyses, the dechlorination of these congeners probably proceeds through electrophilic hydrogen atom attachment followed by rapid loss of the chlorine atom at the same position. These dechlorination reactions occur regioselectively. When present, ortho-chlorines are lost preferentially to meta- and para-chlorines. The extent of the dechlorination reaction, as seen by the relative abundance of the [MH ? Cl]^? ions, decreases with increasing number of ortho-chlorines.     

Metabolites from the biodegradation of 1,6‐hexanediol dibenzoate,a potential green plasticizer,by Rhodococcus rhodochrous

Metabolites from the biodegradation of a potential plasticizer 1,6‐hexanediol dibenzoate in the presence of n‐hexadecane as a co‐substrate by the common soil organism Rhodococcus rhodochrous were identified using GC/MS and Fourier transform mass spectroscopy (FTMS) techniques. Trimethylsilylation of compounds from the biodegradation broth permitted detection of the following metabolites: 1‐hexadecyl benzoate, 6‐benzoyloxyhexanoic acid, 4‐benzoyloxybutanoic acid, 6‐benzoyloxyhexan‐1‐ol and benzoic acid. The presence of these metabolites was confirmed by repeating the biodegradation with 1,6‐hexanediol di[²H₅]benzoate, by measurement of their exact masses in FTMS and by comparison with available authentic materials. The results show that biodegradation of 1,6‐hexanediol dibenzoate by R. rhodochrous does not lead to the accumulation of persistent metabolites as has been reported for commercial dibenzoate plasticizers. Copyright © 2009 John Wiley & Sons, Ltd.     

A novel liquid–liquid extraction and stable isotope dilution NCI‐GC‐MS method for quantitation of agmatine in postmortem brain cortex

The group of biologically important amines includes putrescine, spermidine and spermine, as well as agmatine, which is a guanidino‐amine. There is considerable evidence supporting a role of these amines in the etiology and pathology of mental disorders. We have previously developed a quantitative GC‐MS method for simultaneous measurement of three major polyamines to support our studies linking polyamines to mental disorders. However, a unique GC‐MS method is required for agmatine. To efficiently extract agmatine from postmortem brain tissues, we developed an isopropanol based liquid–liquid extraction protocol using potassium carbonate as a salting‐out agent which showed a much greater recovery than n‐butanol used in earlier methods. The GC‐MS analysis employed hexafluoroacetylacetone as derivatization reagent and was carried out using negative chemical ionization with total ion and selected ion monitoring. ¹⁵N₄‐Agmatine was synthesized from ¹⁵N₄‐L ‐arginine and used as internal standard in a conventional stable isotope dilution assay. This method accurately measures the level of agmatine from very small quantities (10–20 mg) of postmortem brain tissue, with a quantitation limit down to 1 ng/g of wet tissue. The limit of detection is 0.01 ng/g of wet tissue. Copyright © 2010 John Wiley & Sons, Ltd.     

Collision of molecular anions of benzenedicarboxylic esters with oxygen in a triple quadrupole mass spectrometer

A series of symmetrical phthalate, isophthalate, and terephthalate ester molecular anions were reacted with oxygen in the collision cell of a triple quadrupole mass spectrometer to produce characteristic [M − R]⁻ fragments that can be used to identify these compounds. The [M − R]⁻/M^−· intensity ratios decreased for homologous esters in the following order: phthalates > isophthalates terephthalates. Based on the [M − R]⁻ ion intensities for different alkyl substituents, on ¹⁸O₂ labeling experiments, and on the reactivity of bis(t-butylcyclohexyl)phthalates, it was concluded that M − R anions are generated through an S_N2 nucleophilic displacement at the alpha carbon of the saturated alkyl substituent. For the phenyl ester, the reaction proceeds through attack at the carbonyl carbon.