Mass Spectrometry Studies on the Dissociation of Metal-Adducted Oligosaccharides, Glycopeptides, and Fatty Acids

Analyzing oligosaccharides, glycopeptides, and fatty acids poses a significant analytical challenge due to their structural complexity and diversity. Structural alterations in these biomolecules have direct implications for health and diseases, necessitating the development of analytical methods capable of providing comprehensive structural information. Mass spectrometry (MS) stands out as a leading technique for this purpose, although its efficacy is hindered by poor ionization and dissociation of these biomolecules. Consequently, derivatization is commonly employed to enhance ionization and dissociation efficiency.This dissertation focuses on exploring the use of in-source decay (ISD) and high-energy collision-induced dissociation (HE-CID) performed on a matrix-assisted laser desorption ionization (MALDI)/tandem time-of-flight (TOF-TOF) mass spectrometer to obtain complete structural information on underivatized oligosaccharides, glycopeptides, and fatty acids. Extensive experimentation with various MALDI matrices and metal cations led to the identification of optimal conditions for ionization and dissociation.Dissociation of the metal-adducted underivatized biomolecules by HE-CID generated extensive fragmentation and structural information not attainable through dissociation of the protonated biomolecule, or collision-induced dissociation (CID) performed on quadrupole-based mass spectrometers. The glycosidic bond cleavage, cross-ring cleavage, and internal cleavage ions generated by HE-CID of metal-adducted oligosaccharides and glycopeptides provided valuable information on sequence, linkage type, and monosaccharide ring content. Also, HE-CID of the structural isomeric tetrasaccharides studied produced distinct mass spectra and product ions necessary to distinguish between the isomers. In addition, HE-CID of metal-adducted unsaturated fatty acids facilitated the determination of double bond positions, distinguished double bond positional isomers, and cis/trans isomers. While ISD proved less useful for fatty acids and glycopeptides, ISD complemented HE-CID in providing structural information for metal-adducted oligosaccharides.Remarkably, derivatization of oligosaccharides through permethylation was unnecessary for obtaining good ionization and structural information. Metal ions, particularly lithium (Li+), significantly enhanced the ionization and structural characterization of oligosaccharides, glycopeptides, and fatty acids. The choice of metal ions influenced the type and intensity of product ions, with lithium (Li+) consistently producing the most structural information. Furthermore, trihydroxyacetophenone (THAP) emerged as the optimal MALDI matrix for ionization and HE-CID, 2,5-dihydroxybenzoic acid (DHB) for ISD and HE-CID of long-chain oligosaccharides, and 4-dimethylaminobenzaldehyde (DMABA) for ISD of tetrasaccharides and pentasaccharides.