A Study of Formation and Fragmentation of Ionic Complexes of α-Amino Acids and Peptides with Al(III)-Glycerol by Fast Atom Bombardment Mass Spectrometry

Abstract

Complexation of aluminum ions {Al(III) in glycerol} with α-amino acids has been studied by FAB mass spectrometry. Twelve α-amino acids and cysteine methyl ester interact with different Al(III)-containing ions and form several cluster ions such as [M+117]+, [117={A1(III)+glycerol−2H}]; [M+231]+, [231={Al(III)+glycerol+ trifluoroacetic acid−2H}]; [M+233]+, [233={2Al(III)+2glycerol−5H}]; [2M+Al−2H]+ and [2M+117]+. Fragmentation of these adduct ions led to the formation of mainly metal-containing product ions. Fragmentation pathways were demonstrated with the help of the dissociation of Leu-d3, His-d4, Tyr-d4, Ser-d4, Cys-d4 and Cys methyl ester-d3 ion complexes in glycerol-d3. Aliphatic, aromatic and α-amino acids possessing functional side chains show differences in the fragmentation of [M+117]+ ions. Fourteen peptides of different chain lengths (two through six amino acids) also form adducts with Al(III)-glycerol. Dissociation of these complex ions, especially [M+Al−2H]+ ions provides information about side-chain functional groups and some sequence information. The site of the metal-ion interaction is mostly at the amide nitrogens.