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Abstract

By mixing 1,2,4-triazolium salts (precursors of N-heterocyclic carbenes 1–6) with mercury acetate, a number of complexes have been obtained under electrospray ionization condition. Carbenes 1 and 2 contain one carbene center; therefore, they are able to bond only one mercury cation. Carbenes 3–5 contain two carbene centers; therefore, they can bond two mercury cations. Mercury complexes of 1–5 always contain an acetate anion attached to a mercury cation. Carbene 6 also contains two carbene centers; however, its structure allows formation of a complex containing mercury bonded simultaneously to both centers, therefore, the complex that does not contain an acetate anion. The MS/MS spectra taken for complexes of carbenes 1–5 have shown formation of a cation corresponding to N1 substituent (adamantyl or benzyl), and those of complexes of carbenes 3–5 (doubly charged ions) have also shown the respective complementary partner ions. Mercury complex of 2 has yielded some other interesting fragmentation pathways, e.g. a loss of the HHgOOCCH3 molecule. The fragmentation pathway of the mercury complexes of 6 was found to be complicated.

characterization of two novel inflammatory peptides from the venom of the social wasp Polybia paulista”, Rapid Commun. Mass Spectrom., Vol. 18, (2004), pp. 1095–1102. http://dx.doi.org/10.1002/rcm.1452 [4] W. Qi, C.X. Jia, Z.M. He and B. Qiao: “Analysis of racemization products of synthetic heptapeptide by reversed phase high performance liquid chromatography/mass spectrometry”, Chinese J. Anal. Chem., in press. [5] B. Paizs and S. Suhai: “Fragmentation pathways of protonated peptides”, Mass Spec. Rev., Vol. 24, (2005), pp. 508–548. http://dx.doi.org/10.1002/mas.20024 [6] V

ionization techniques in the mass spectrometry of free dipeptides can be used to obtaine informations about primary structure and molecular weight. Characteristic fragmentation pathways of dipeptides are discribed and the mechanism of diketopiperazine formation is discussed. Einleitung Über das Fragmentierungsverhalten von freien und geschützten Dipeptiden im Elektronenstoß(EI)- Massenspektrometer wurde bereits mehrfach be- richtet [1-3]. Während für freie Dipeptide Molekül- ionen nicht oder nur in sehr geringen Intensitäten nachgewiesen wurden [1, 2], lassen sich

used to determine molecular weights. The negative ion spectra provide more detailed structural information through an (M-H)- ion as well as a variety of fragment ions. The collisional dissociation spectra of these negative ions give detailed structural information which is determined by possible resonance structures for the specific ions. Deuterium exchange reactions were found to be quite useful to define fragmentation pathways. Key words: Underivatized pterins, Laser desorption, . Mass spectrometry Introduction Mass spectrometry may be used for

ions and background gas atoms/molecules can increase the internal energy of the ions by thermal heating [ 37 ]. Such collisional activation results in collision induced dissociation (CID) [ 38 ], [ 39 ] which is widely utilized in mass spectrometry, e.g. for protein sequencing [ 40 ], [ 41 ]. In the context of transition metal complexes, CID is very useful to investigate activation barriers of catalyst precursors [ 42 ], [ 43 ], ligand binding energies [ 44 ], [ 45 ], [ 46 ] and intramolecular fragmentation pathways [ 47 ]. We have previously investigated N 2

Abstract

The complementary informations from field desorption and electron impact mass spectra of free tripeptides and thyrotropine releasing hormone derivatives can be used to determine primary structure and molecular weight. Characteristic and diagnostic fragmentation pathways, the formation of diketopiperazines and the temperature-dependent tendency to form amine fragments and diketopiperazines will be discussed.

Abstract

In this paper we are focused on analysis of hydroxychalcones, i.e. 2’-hydroxychalcone, 3’-hydroxychalcone and 4’-hydroxychalcone, by the Flowing Atmospheric Pressure Afterglow mass spectrometry (FAPA-MS), and on comparison of the obtained data with other classical methods including ESI-MS, APCI, MALDI, and GC/EI-MS. The paper is presenting fragmentation pathways of both positive-, and negative hydroxychalcone ions. Tested compounds were characterized by comparison of the results (signals m/z and relative intensities) from the five mass spectrometry techniques, showing very good utility of FAPA method for fast and easy analysis of the low molecular weight compounds. Moreover, FAPA does not require a time-consuming derivatization, nor search for a suitable solvent or matrix, often incompatible with various ion sources.

Abstract

Electrospray ionization mass spectrometry was used to study the complexes of ligands containing two bipyridine units, namely 3,5-bis(2,2-bipyridin-4-ylethynyl)benzoic acid (1) and its methyl and ethyl esters (2, 3), with copper cation, with CuCl2 as a source of copper. It was found that the type of complexes formed strongly depends on CuCl2 concentration. At lower CuCl2 concentration, the detected complexes were rather simple and some of them were formed upon electrospray ionization conditions e.g. ions [22+Cu2]2+ and [32+Cu2]2+ (complexes ligand-Cu(I) of stoichiometry 2:2) which are analogical to the well known, for quaterpyridine, helical complexes. At higher CuCl2 concentration, the detected complexes were more complicated, and most of them contained copper cations bridged by chlorides. The largest ions were [L2+Cu4Cl6]2+. The CID MS/MS spectra of these ions allowed determination of their mass spectrometric fragmentation pathways and as a consequence their structure elucidation.

Abstract

In this study maltose, maltotriose and maltotetraose were for the first time, coupled to 4,4′-methylenedianiline (MDA). The aim of this preliminary work was to test the feasibility of oligo- and polysaccharide coupling to MDA and the characterization of the coupling products by high resolution mass spectrometry (MS). (+) nanoESI in combination with a quadrupole time of flight (QTOF) MS in full scan (MS) and MS/MS was optimized first on underivatized maltose, maltotriose and maltotetraose. The optimal screening and sequencing conditions were further applied to the MDA-functionalized oligosaccharides. The obtained results revealed a straightforward MS detection of the functionalized oligomers, high sequence coverage and a fragmentation pathway with the formation of B and Y ions as well as the complementary C and Z ions along with a typical cleavage of the aglycon. We consider that this methodology is fully applicable also to polydisperse mixtures of long chain polysaccharides, which due to the large number of components and their size require a systematic method of development and testing.

was further confirmed by reference substance. Figure 2: Mass spectrum and proposed fragmentation pathway of schizandrin B ( L34 ). 3.2.2 Identification of triterpenesaponins As shown in Table S2, 19 peaks detected in DWYG were identified or tentatively characterized as triterpenesaponins. Chemical structures of identified compounds are displayed in Figure S1, and all of them were derived from Gan-Cao . By comparing the retention times and MS data with standard compounds, they were unequivocally identified as licoricesaponin J 2 ( T1 ), 24-hydroxyllicoricesaponin E