Fourier transform infrared spectrometry/matrix isolation of laser desorbed species.

摘要

The recent advances of Matrix Assisted Laser Desorption/Ionization (MALDI) mass spectrometry has pushed the upper limit of mass determinations of large polymers to values in excess of 300 kDa. This technique has been very successful in the characterization of large biomolecules such as oligosaccharides, olignucleotides, peptides and proteins. The future success of MALDI will most likely depend on the understanding of mechanisms characteristic of the laser desorption process. Recent experimental evidence has indicated that the laser desorbed neutrals of the matrix compounds utilized in MALDI may play a significant role in the ionization process. The viability of the MALDI experiment appears to be linked to the photochemical lability of these matrix species. This dissertation describes the development and implementation of Fourier Transform Infrared (FT-IR) spectrometry utilizing matrix isolation (MI) to study neutral molecules of laser desorption processes. The utilization of matrix isolation techniques has minimized bandbroadening due to the hydrogen bonding which is characteristic of MALDI matrices in the solid state. This improvement in spectral resolution has allowed for the identification of degradation products induced by various laser desorption processes. The generation of matrix isolated reference spectra has been accomplished for various MALDI matrices utilizing a CO{dollar}sb2{dollar} laser (10.6 {dollar}mu{dollar}m). FT-IR/matrix isolation and NMR spectroscopy have been utilized to elucidate the covalent dimerization of nitrogen laser (337.1 nm) desorbed 4-hydroxycinnamic acid and 3,5-dimethoxy-4-hydroxycinnamic acid. Trans to cis isomerization has also been demonstrated with UV laser desorption. The identity of these photochemical reactions may aid in a further understanding of the MALDI process.