Gas-phase conformations and folding energetics of synthetic polymers

In this dissertation, the gas-phase structures, energies, and folding properties of a group of polyether, polyester, and polyvinyl oligomers cationized by various alkali ions are presented. Oligomer ions were formed by MALDI and their cross-sections measured using ion mobility experiments. Conformational information about the ions was obtained by calculating the cross-sections of theoretical structures (generated by molecular mechanics calculations) and comparing them to the experimental values. Agreement between the experimental and theoretical cross-sections was generally within 1–2%. Temperature dependent experiments and molecular dynamics simulations were used to investigate the energetics and dynamics of the oligomer folding process.; Several types of polymeric systems were studied. The first set that will be discussed is poly(ethylene glycol), poly(propylene glycol), and poly(tetramethylene glycol). These polyethers essentially wrap around the accompanying metal cation forming a crown ether-like complex. Observed structural differences are attributed to changes in metal-oxygen binding energies and changes in the flexibility of the oligomer backbones.; The next two polymeric systems that will be discussed are poly(methyl methacrylate) and polystyrene. Both oligomers have similar CID fragmentation spectra but ion mobility experiments and computer modeling suggest different mechanisms in the two systems. Metal-oligomer binding energies and conformational details were used to propose possible CID fragmentation mechanisms for each system.; The final, and most complex, polymeric systems that will be discussed are poly(ethylene terephthalate), poly(propylene terephthalate), and poly(butylene terephthalate). Two stable conformers with significantly different cross-sections were identified for the 3-mers. The energetics and dynamics for the isomerization between the two forms was system dependent. Information about the barrier height and relative stabilities of the two conformers was obtained by temperature dependent measurements and kinetic theory. A mechanism for the formation of the 3-mer ions in the MALDI source is also proposed. The effects of conformation and oligomer—cation binding energy on the mass spectra of these polyesters are addressed as well.