Infrared multiple photon dissociation - mass spectrometry of monosaccharides, disaccharides, trisaccharides and their derivatives for isomeric differentiatio

The structural study of carbohydrates and their derivatives remains challenging due to the large number of possible isomers. As they have identical masses, these isomers cannot be differentiated even by high-resolution mass spectrometry (MS). In order to gain more structural information, their dissociation patterns in MS are of great interest. The central goal of our research is to systematically study the infrared multiple photon dissociation - mass spectrometry (IRMPD-MS) of monosaccharides, disaccharides, trisaccharides and their derivatives.;Here, a tunable CO2 laser and a tunable optical oscillator parametric (OPO) were employed to induce IRMPD of mass-selected carbohydrates, taking advantage of their distinct tuning ranges (a CO2 laser: 925-1085 cm-1 and an OPO: 2500-4000 cm-1). The carbohydrate molecules were ionized by electrospray ionization (ESI) and subsequently fragmented by a focused IR beam in an ion trap. A commercial Fourier transform ion cyclotron resonance (FTICR) mass spectrometer was used in conjunction with the CO2 laser, and a quadrupole ion trap - time-of-flight (QIT-TOF) was coupled with the OPO.;In Chapter 3, monosaccharide isomers were probed by wavelength-dependent IRMPD with a tunable CO2 laser. It was shown that isomeric variants of lithiated monosaccharides could be distinguished with this approach, but deprotonated analytes had nearly identical dissociation spectra. Chapter 4 involved the study of hexoses, Nacetylhexosamines, hexosamine sulfates which were structurally elucidated by IRMPD spectroscopy with a tunable OPO. The IRMPD spectra of monosaccharide derivative isomers displayed remarkable differences in the O-H and N-H stretching IR region. The results also suggested that gas-phase conformation, affected by ionization state or chemical modifications, exhibited diagnostic IR absorbances and characteristic photodissociation behavior. In Chapter 5, a top-down approach was employed to characterize isomeric variants of glucose-based trisaccharides. The trisaccharides were fragmented and mass selected to the key disaccharide fragments. The linkage and anomericity of the disaccharide substructures were then differentiated by wavelengthdependent IRMPD using the CO2 laser. On the basis of these results, variablewavelength IRMPD provides a promising method to characterize carbohydrate structures and thus differentiate isomer variants by mass spectrometry.