Mass spectrometry methyl groups

The behaviour under electron impact of IV- and C-trimethylsilylpyrazoles (mono-, di-and tri-substituted) has been studied by Birkofer et al. (740MS 8)347). Loss of a methyl radical followed by loss of HCN is the most common fragmentation feature of these compounds. When more than one trimethylsilyl group is present, a neutral fragment CaHgSi is expelled. Mass spectrometry of pyrazolium salts has been studied by Larsen etal. (8i OMS377, 830MS52). 

The present work involves the study of methyl glycosides and O-isopropylidene ketals of various isomeric deoxy sugars by mass spectrometry. Several of the compounds selected for the present study have free hydroxyl groups, and interpretation of their mass spectra shows the scope of the study of these and related deoxy sugar derivatives by mass spectrometry without prior substitution of all hydroxyl groups. Some of the candidates (compounds 4, 7, 8 and 10) are structurally related to biologically-derived deoxy sugars. 

Laali and Lattimer (1989 see also Laali, 1990) observed arenediazonium ion/crown ether complexes in the gas phase by field desorption (FD) and by fast atom bombardment (FAB) mass spectrometry. The FAB-MS spectrum of benzenediazonium ion/18-crown-6 shows a 1 1 complex. In the FD spectrum, apart from the 1 1 complex, a one-cation/two-crown complex is also detected. Dicyclo-hexano-24-crown-6 appears to complex readily in the gas phase, whereas in solution this crown ether is rather poor for complexation (see earlier in this section) the presence of one or three methyl groups in the 2- or 2,4,6-positions respectively has little effect on the gas-phase complexation. With 4-nitrobenzenediazonium ion, 18-crown-6 even forms a 1 3 complex. The authors assume charge-transfer complexes such as 11.13 for all these species. There is also evidence for hydride ion transfer from the crown host within the 1 1 complex, and for either the arenediazonium ion or the aryl cation formed from it under the reaction conditions in the gas phase in tandem mass spectrometry (Laali, 1990). 

Xu, M. Basile, F. Voorhees, K. J. Differentiation and classification of user-specified bacterial groups by in situ thermal hydrolysis and methylation of whole bacterial cells with tert-butyl bromide chemical ionization ion trap mass spectrometry. Anal. Chim. Acta 2000, 418,119-128. 

Tandem mass spectrometry has been used to demonstrate that M+ as well as MH+ of substituted A-(ort/zo-cyclopropylphenyl)benzamides isomerizes before the fragmentation, with formation of 3-aryl-1-ethyl-lH-benzoxazines and 5-ethyl-2-oxodi-benzoazepines (Scheme 5.14). The methyl group in /V-[ortho-( 1 -methylcvclopropyl )-phenyl]benzamides quenches the latter process, leaving the formation of benzoxazines as the only cyclization reaction. A subsequent chemical experiment in solution confirmed the mass spectral predictions [24]. A similar study confirmed the analogy of cyclization of substituted A-(ort/zo-cyclopropylphenyl)-A -aryl ureas and N- ortho-cyclopropylphenyl)-A -aiyl thioureas in the ion source of mass a spectrometer and in solution [25]. 

To examine variation in the quality of methyl ketones expressed by females and newly-emerged males, we determined the number of unique methyl ketones expressed by individual snakes and compared the relative concentrations of individual methyl ketones comprising the overall pheromone profiles for the two groups. The methyl ketones present in the pheromone extracts were identified by gas chromatography / mass spectrometry (Hewlett Packard 5890 Series II gas chromatograph coupled with a Hewlett Packard 5971 Series mass selective detector— see LeMaster and Mason 2003 for full description of the GC/MS platform and methods). 

The strong interaction of methanol with the surface hydroxyl groups leads to a methylated surface which is clearly shown by Figure 3. The CP/MAS C-NMR line of 59.9 ppm is attributed to surface methyl groups (10). On a NaGeX zeolite, the amount of these groups was computed from the comparison of the relative amounts of CH3OH and of (CI O obtained from either mass spectrometry data or C-NMR measurements (45). ... 

Desferrimaduraferrin is a Fe " complexing metabolite of Actinomadura madurae 185). It consists of salicylic acid, p-Ala, Gly, L-Ser and 77 -hydroxy-77 -methyl-L-Om, with the latter incorporated in a heterocyclic system (Fig. 4, 13). From the same species the madurastatin group was obtained 136). The main representative A1 shows the sequence salicylic acid, o-azaridine carboxylic acid, L-Ala, p-Ala, 77 -hydroxy-77 -methyl-Om, L-cOHOm (Fig. 4, 14). In A2 the azaridine ring is opened giving a Ser residue, A3 is an isomer of the open form with the salicylic acid bound to the hydroxy group of Ser. B1 and B2 are the precursors A-salicyloyl-azaridine carboxylic acid and A-salicyloyl-Ser. The madurastatin species A1 forms a 1 1 Fe " complex as shown by mass spectrometry. 

The same group studied the lithium cation basicities of a series of compounds of the general formula R R R PO, i.e. phosphine oxides, phosphinates, phosphonates and phosphates, by using Fourier Transform Ion Cyclotron Resonance (FTTCR) mass spectrometry. A summary of their results is shown in Figure 4. The effect of methyl substitution on LCA as well as the correlation between LCA and PA was also investigated by Taft, Yanez and coworkers on a series of methyldiazoles with an FTICR mass spectrometer. They showed that methyl substituent effects on Li binding energies are practically additive. 

Some information has been obtained on the fragmentation patterns of 1,4-thiazine derivatives. A group of 2- and 3-substituted A-methylated benzothiazines with the general structure 2 (R = Me) lost a methyl radical in electron impact mass spectrometry at 70eV (Scheme 2) <1982J(P1)831>. 

Lemberger et al. used gas chromatography/mass spectrometry and reported that the hydroxymethyl metabolite represents only two minor metabolites produced by rat liver microsomes this suggests that with DMHP the methyl group at C-ll is not active and therefore that the 11-hydroxy DMHP would not be a major metabolite, Lemberger et al. have given evidence that the hydroxylation occurs primarily on one of the methyl groups of the side chain. 

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