Electrospray mass spectrometry and tandem mass spectrometry of bimetallic oxovanadium complexes

Abstract

A series of six bimetallic oxovanadium complexes (1-6; only one was purified) were investigated by electrospray quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in negative-ion mode. Radical molecular anions [Ml-were observed in MS mode. Fragmentation patterns of [Ml-were proposed, and elemental compositions of most of the product ions were confirmed on the basis of the high-resolution ESI-CID-MS/MS spectra. A complicated series of low-abundance product ions similar to electron impact (EI) ionization spectra indicated the radical character of the precursor ions. Fragment ions at m/z 214, 200, and 182 seem to be the characteristic ions of bimetallic oxovanadium complexes. These ions implied the presence of a V-D-V bridge bond, which might contribute to stabilization of the radical. To obtain more information for structural elucidation, three representative bimetallic oxovanadium complexes O xovan ad iu m complexes have played active roles in the fields of pharmaceutical research and organic synthesis. These complexes exhibit attractive promise as orally available treatments for diabetes mellitus and also have a number of applications as catalysts in various oxidation reactions [1][2][3][4][5][6][7][8][9][10]. Recently, some oxovanadium complexes, especially bimetallic oxovanadium complexes of chiral Schiff bases reported by Gong's group, were shown to provide high enantioselectivity for the oxidative coupling of 2-naphthols, which play very important roles in the history of asymmetric synthesis [11][12][13][14][15][16][17].Structural characterization of the bimetallic oxovanadium complexes is key to the further development of their functions. Nuclear magnetic resonance (NMR) spectroscopy eH and SlV) can provide abundant information for structural analyses of bimetallic oxovanadium complexes. Unfortunately, NMR measurements Address reprint requests to Dr. Z.-J. Wu, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China. E-mail: wuzhijunyinger@ 163.com require pure samples, which are difficult to obtain for most bimetallic oxovanadium complexes [17]. X-ray crystallographic analyses require the production of monocrystals, which limits the applicability of this technique for structural characterization. Furthermore, UV, IR, and ESR spectroscopy offer only limited structural information [18]. Obviously, a method that provides abundant structural information without laborious purification would be highly desirable for the structural characterization of the bimetallic oxovanadium complexes.Mass spectrometry (MS) has greatly benefited from the development of electrospray ionization (ESI) and has been applied successfully in various fields. A series of simple oxovanadium complexes has been studied by . Recently, Zeng et al. reported the fragmentation study of monometallic oxovanadium Schiff base complexes by ESI-IT-MS n [25]. However, it seems not to obtain the information of uniform fragmentation patterns, except for the loss of CO 2 , Surprisingly, in our recent work, the [Ml...

Evaluation of Differences in MS/MS Spectra from Two Differentgeneration Q-TOF Instruments: Implications for Metabolomic Database Use

“…These spectra were derived resulted from epipolythiodioxopiperazines, sesterterpenoids, caffeic acidderivatives, longipedlactones, cinchona alkaloid derivatives, and bimetallic oxovanadium complexes. The spectra from epipolythiodioxopiperazines, sesterterpenoids, caffeic acidderivatives, longipedlactones, and bimetallic oxovanadium complexes obtained by BioTOF-Q were reported in our previous study [30][31][32].…”

ESI–IT–MS n and DFT calculation for electron affinities of bimetallic oxovanadium complexes

“…Both 1 and 3 contain a bridging V-O-V bond, which is the fundamental structural difference between mono-and bimetallic oxovanadium complexes. To support the previous assumption that the bridging V-O-V bond contributes to the stabilization of the radical [21], a monometallic oxovanadium complex similar to complex 1 was selected for parallel analysis. Bimetallic oxovanadium complexes 1 and 3 were found to have about 0.6 eV higher EAs than the monometallic oxovanadium (Fig.…”

“…It is necessary to point out that the fragment ion at m/z 484, which was considered to derive from the ion at m/z 552 [21], is more likely formed directly from the ion at m/z 570. The formation of the fragment ion at m/z 552 might involve a rearrangement of the ion at m/z 570 via a six-membered transition state and a retro-1,1-insertion reaction [21]. The fragment ion at m/z 552 readily lost a hydrogen atom to produce an ion at m/z 551 (Fig.…”

“…Nevertheless, there are very few reports on the observation of radical ions of vanadium complexes by ESI-MS [20] and none on the radical ions of mononuclear oxovanadium(V) complexes using this method [16]. Surprisingly, we detected radical ions of bimetallic oxovanadium complexes by electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS) [21]. In order to understand the structural features of bimetallic oxovanadium complexes leading to the formation of radical ions, electron affinities (EAs) of both mono-and bimetallic oxovanadium complexes were calculated by density functional theory (DFT).…”

“…In order to understand the structural features of bimetallic oxovanadium complexes leading to the formation of radical ions, electron affinities (EAs) of both mono-and bimetallic oxovanadium complexes were calculated by density functional theory (DFT). On the other hand, to verify the previously postulated fragmentation pathway of radical anions by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) [21], three bimetallic oxovanadium complexes 1-3 ( Fig. 1) were analyzed by electrospray ionization ion trap multi-stage mass spectrometry (ESI-IT-MS n ) and ESI-QTOF-MS/MS.…”