Mass spectral fragmentation carboxylic acids

Figure 4 Proposed mass spectral fragmentations of pyrrole carboxylic acids.

Rontani and Aubert [47] studied the El mass spectral fragmentation of hydroxy carboxylic acids and trimethylsilyl derivatives of oxocarboxylic acids. Some fragmentations appeared to be specific to characterize and... 

A comparison of the mass spectral fragmentation patterns of the dimethyl ester of caperatic acid (41) and the corresponding di(trideutero-methyl) ester located the position of the ester function in this molecule and established the structure as methyl 3,4-dicarboxy-3-hydroxyoctadecanoate (41) (25). In a corroborative chemical degradation (41) was oxidized by treatment with sodium bismuthate, whereupon methyl 3-oxo-octadecano-ate (42), the decarboxylation product of the initially formed P-keto-carboxylic acid, was detected (25). 

The mass spectral data is also consistent with [3]. Thus the ion fragments at 367 (all ion fragments given in amu or Daltons) are characteristic of MTX minus two CO2 groups and 322 characteristic of MTX minus the carboxylic acid containing chain. 

The feasibility of on-line electrochemistry mass spectrometry in the study of electrode processes has recently been demonstrated by Heitbaum et al. . We have tested the potential of on-line mass spectrometry in the study of redox reactivity of biological compounds with uric acid as a probe. Electrochemical oxidation of uric acid has been studied extensively . The scheme in Figure 6 shows the electrochemical oxidation pathway of uric acid and indicates intermediates and products which were identified by on-line electrochemistry thermospray mass spectrometry (EC/TSP/MS/MS) . In our studies, tandem mass spectrometry (MS/MS) was used to obtain structurally informative fragmentation patterns (daughter spectra) of standards for comparison to the mass spectra of intermediates and products obtained by EC/TSP/MS/MS. This, for example, allowed identification of allantoin through its characteristic daughter spectrum. It also allowed confirmation of the structural features of the intermediate, bicyclic carboxylic acid, which apparently forms from the imine alcohol in the oxidation of uric acid. The intermediates and products which were identified in this way are indicated in the scheme, and mass spectral results are summarized in Table 1. 

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