FABMS characteristics

Analogous to the previously synthesized dicopper(I) knots [97], Cu2(K-84)p+ gives characteristic 1H NMR and FABMS spectroscopy data [102], In particular, some of the aromatic protons of the bis-chelates are strongly shielded, which indicates that Cu2(K-84)p is compact and that its helical core is geometrically very similar to that observed in 32. This was fully confirmed by subsequent X-ray structure determination. 

Several guns have been used to produce the primary beam to bombard the FABMS target (12). These beams are composed of fast neutral atoms or ions, or a mixture of the two. It does not appear that the charge state is critical, because desorption is produced by momentum transfer. Some of the guns and the characteristics of the beams are examined in this section. 

Finally, an alkaloid of undetermined structure was studied to demonstrate the utility of these methods. The FABMS of the alkaloid was first determined, followed by derivitization of the alkaloid to its bismethiodide (MeI/Me2CO - room temperature), and subsequent determination of the FABMS of the derivative. The unknown alkaloid exhibited fragmentation characteristic of a type A aporphine-benzylisoquinoline alkaloid with one methoxy and one hydroxy group in... 

The group of compounds amenable to FABMS analysis is similar to that analysed by FD that is non-volatile polar sohds, however, FAB is more suited to high molecular weight very polar sohds and FD to compounds of lower polarity. The characteristic feature of FABMS spectra is the presence of intense [M -t-H]+ ion in addition to considerable number of characteristic fragment ions that are useful for structure analysis. 

FABMS has been employed to identify and quantify dansyl amino acids (8) formed in a procedure for the N-terminal analysis of proteins (57). This sensitive method involves the reaction of the protein with dansyl chloride, followed by acid hydrolysis. Previously the characteristic involatile N-terminal amino acid derivative (8) was analyzed either by TLC or high-voltage electrophoresis but FAB ionization now permits rapid identification of the protonated molecular ion. The responses of this and other characteristic ions were monitored employing dansyl amino butyric acid as an internal standard, enabling the dansyl derivatives (8) to be determined quantitatively at a level of 0.1 nmol. 

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