Fragmentation characteristics

Pyrolysis mass spectrometry, which does not require a volatile derivative, has been applied to various penicillins (78MI51100). These spectra contained fragments arising from the bicyclic ring system (4,5-dihydro-5,5-dimethylthiazole at mje 115, 1- and 2-methylpyrrole at mje 81 and unidentified peaks at m/e 100 and 125) as well as a series of fragments characteristic of the C(6) side chain. 

As emphasized above, neither statistical or theoretical methods for determining fragment characteristics are fully adequate, and it is sometimes difficult to decide... 

Figure 9.6. Decision diagram for determining fragment characteristics.

The Mass Spectra of O-Isopropylidene Ketals 9 (Figure 6), 10, (Figure 7), and 11 (Figure 8). Three fragmentations characteristic of O-isopropylidene ketals are loss of a methyl radical from the ketal ring, cleavage of bonds adjacent to the ketal ring, and loss of acetone (12). 

As each functional grotip is discussed in future chapters, mass-spectral fragmentations characteristic of that group will be described. As a preview, though, we Jl point out some distinguishing features of several common functionaj groups. 

Fragmentation Characteristic losses from the molecular ions areas follows ... 

Fragmentation Characteristic losses from the molecular ion include 26, 33, and 44 (C=S) Daltons. Ions characteristic of the phenyl group are also observed. 

Fragmentation Characteristic fragments of aliphatic isocyanates include m/z 56 (CH2NCO), 70 (CH2CH2NCO), 84 (CH2CH2CH2NCO), and so forth. 

The MAB ion source offers several advantages over El for PyMS. By eliminating excessive fragmentation, characteristic of electron ionisation, and by producing highly reproducible mass spectra MAB (Kr) greatly simplifies the analysis of pyrolysis data. Furthermore, MAB ionisation, when combined to MS/MS, provides a useful tool for structural elucidation of pyrolysis products. The ability for selective ionisation can be very useful to reduce the background combination in techniques such as GC-MS, LC-MS or SFC-MS. 

The mass spectrum of triprolidine hydrochloride is shown in Figure 4. It was obtained with a Varian MAT CH5-DF mass spectrometer. The electron energy was 70 eV and the sample was introduced via direct probe at 120°C.5 The characteristic fragments are in agreement with those found by Kuntzman and co-workers.6 The major fragments characteristic of triprolidine are shown in Figure 5. 

Priming Fragment Characteristics and Impact Effects on Protective Barriers, Picatinny Arsenal, Dover, New Jersey, Technical Report 4903, December 1975. 

The fragmentation characteristics of the CH3NC>2 isomers have been studied by a number of investigators and the system constitutes one of the most well-decribed within the field of mass spectrometry. Apparently intricate inter-relations between the isomers do exist. 

There is an exception in addition to the expected normal arachno nine-vertex fragment characteristic of w-BqHis (XI-A19) (75, ISO), there is a fragment generated by the removal of a low coordination vertex which is reflected in the structures of both i-ByHis (I-A19) 21) and its isoelectronic analog i-C2B7Hi3 (II-A19) 1S6). 

SCHEME 7. Fragmentation characteristic of the substituents present in either aglycone or sugar parts of the molecule ... 

Mesoionic 1,3-thiazole -ones of type 34 are known as thioisomiinchnones. As one of the mesomeric structures demonstrates, these species contain the structural fragment characteristic of thiocarbonyl ylides (61). A convenient access to thioisomiinclinones involves the reaction of A(-arylthiobenzamides with a-bromo-phenylacetyl chloride (62). 

Fragmentation Characteristics. As a manifestation of expl output fragmentation is characterized by velocity and size distribution of fragments. For some purposes, die size and shape of.fragments are predetermined either by preforming or by modifications of the case or chge design which predisposes it to break as desired... 

The initial velocity of fragments is quite accurately predicted by the Gumey formulas described by us under "Gurney Constant and Gumey Formulas" in Vol 6 of Encycl More detailed discussion on "Fragmentation Characteristic " is given in ... 

Figure 5 shows the HPLC separation of Fraction A spiked with LS27D. The peak at 16.9 min in Fraction A (unspiked) was collected, but mass spectrometry gave its molecular weight as 326 daltons. No fragments characteristic of LS270 were present in its mass spectrum. 

Mixtures of more complex nitrogen-containing compounds such as amine oxides and ethoxylated quaternary amines are also amenable to the type of Investigation described above ( ). The CAD spectra of these substances are dominated by a few informative ions which result from specific fragmentations characteristic of the class of compounds. The Crfi2n+2 1099 series also occurs but at a less abundant level for the ethoxylated compounds, and the series is of low abundance for the amine oxides. 

E. Stephens, S. L. Maslen, L. G. Green, and D. H. Williams, Fragmentation characteristics of neutral V-linked glycans using a MALDI-TOF/TOF tandem mass spectrometer, Anal. Chem., 76 (2004) 2343-2354. 

Molecules such as amphetamine and methamphetamine are different in their amino substitutions on nitrogen and, following the fragmentation pattern seen above, it is clear how these molecules have a common fragment of m/z 119 amu as can be seen in Fig. 6. The other fragment that appears in the CID spectra of these two substances falls at m/z of 91 amu, due to tropylium ion fragment, characteristic... 

For determination of peptide sequences as well as protein modifications, MS/MS has become the definitive approach. However, for database searches MS/MS spectra have to be perfect. This is not always given because there are differences in tendencies of peptide bonds to fragment and certain amino acids show unique fragmentation characteristics. 

The indole alkaloids so far discussed all have a tetrahydro-/ -carboline system. The main fragments of these alkaloids contain the indole part of the molecules. This situation is changed in alkaloids which have a larger ring C or an indoline system, permitting the production of fragments characteristic of both the indole and piperidine moieties. 

Petes, J., "Blast and Fragmentation Characteristics," Annals of the New York Academy of Sciences, Vol. 152, Article 1, October I968, pp. 283-517 UH... 

Sustained elevations in intracellular Ca levels promote mitochondrial Ca uptake, which decreases the mitochondrial membrane potential and blocks the electron transport chain leading to ATP depletion. Large increases in mitochondrial Ca uptake also increase mitochondrial membrane permeability (Dubinsky and Levi, 1998) resulting in the release of proapoptotic factors such as cytochrome c and apoptosis inducing factor (AIL) (Luetjens et al, 2000). Cytochrome c binds to apoptotic protease-activation factor 1 (APAFl) and procaspase-9, forming a multiprotein complex known as the apoptosome that activates the caspase cascade. The apoptosome activates caspase-9, which in turn activates caspase-3. Caspase-3 activates caspase-activated DNase (CAD), resulting in DNA fragmentation, characteristic of apoptosis. 

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