Association and Fragmentation Characteristics of Biomolecules and Polymers Studied by Mass Spectrometry

This dissertation shows the association and fragmentation reactions of synthetic polymers and biopolymers studied by Electrospray Ionization Quadrupole-Ion-Trap (ESI-QIT-MS), Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-ToF) and Electrospray Ionization Fourier Transform Ion Cyclotron Resonance (ESI-FTICR). The fragmentation reactions of protonated oligoalanines (trialanine, tetraalanine and pentaalanine) and the fragments present in the ESI mass spectrum of polyalanine have been studied by collisionally activated dissociation (CAD) mass spectrometry (MS² and MS³ experiments). The MSⁿ experiments provided strong evidence that the m/z 71n + 1 ion series in the ESI mass spectrum of polyalanine is a b_n series. These ions are formed via the b_n-y_m pathway of amide bond cleavage, which results in the formation of a proton-bound complex of an oxazolone and a peptide/amino acid.

Branched polyethylenimines with lower average molecular weights (600, 1200 and 1800 Da) have been studied by ESI and MALDI mass spectrometry. In both, ESI and MALDI mass spectra, the main distribution arises from protonated PEI oligomers with NH₂end groups, [PEI + H]⁺, which are observed at m/z 43n + 18. A trace of sodium contamination in the PEI samples results in the presence of a series that appears at m/z 43n + 40 [PEI + Na]⁺. CAD (MS/MS) of protonated PEI oligomers is shown to yield three fragment ion series b_n, c_n" and K_n.

The association between synthetic polymers (polyalanine, poly(2-vinylpyridine), poly(ethylenimine)) and biomolecules (Arg, betaine, Ala-Arg, Gly-Arg, Leu-Arg, Arg-Val, Gly-Gly-Tyr-Arg, YGGFLK, 2’-CMP, 3’-CMP, 5’-CMP, dCMP, 2’-AMP, 3’-AMP, 5’-AMP) have been studied by ESI-FTMS and Sustained Off Resonance Irradiation-Collision Activated Dissociation (SORI-CAD) mass spectrometry. ESI-FTMS mass and tandem mass spectra confirm the formation of association (non-covalent) complexes between the polymers and biomolecules. Also, the MS/MS data show that the proton affinity of the complex-forming host oligomers is greater than those of the guests. Only Leu-Arg and Arg-Val guests were found to promote cleavages in the polyalanine.

In a separate study, diazeniumdiolates (NONOates) have been analyzed by ESI-MS; the samples used are commercially available and include Diethylamine NONOate, DETA NONOate, Spermine NONOate, MAHMA NONOate, PROLI NONOate, Dipropylenetriamine NONOate, PAPA NONOate, and Sulpho NONOate. NONOates compounds have been found to ionize upon ESI by protonation, deprotonation and sodiation. The MSn experiments provided strong evidence that such ions release NO, HNO, N₂O, NO₂, N₂O₂, N₃O₃, N₄O₃ and N₄O₄ when collisionally activated.

Representative PIBSA (polyisobutylene succinic anhydride) samples have been studied by different MS techniques. Negative ion ESI-FTMS produces the best results. Differences between “mono-succan” and “di-succan” content can readily be observed. The source of the PIBSA (PIBSA-I and PIBSA-II processes) can be easily distinguished. The formation of methyl esters and amide derivatives can provide complementary data.