Structures of metal-dication/Uracil complexes in the gas phase and matrix isolated-hydrogen bonded complexes

Ali, Osama Yousef (2012) Structures of metal-dication/Uracil complexes in the gas phase and matrix isolated-hydrogen bonded complexes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Ionic complexes have long been studied by mass spectrometry while leisurely spectroscopic studies of neutral complexes can be studied using matrix isolation spectroscopy. Experimental results aiming to elucidate the structures of neutral and ionic complexes are often complemented by electronic structure calculations as has been done in this work. -- Complexes of divalent metal ions and uracil have been investigated using FTICR mass spectrometry. Positive ion electrospray mass spectra show that [M(Ura-H)(Ura)]⁺, where M is formally a divalent metal ion, are the most abundant ions even at low concentrations of uracil. MS/MS experiments show that the lowest energy decomposition pathway for [M(Ura-H)(Ura)]⁺ complexes is loss of HNCO for all metals studied with the exception of Sr, Ba and Pb which do lose a molecule of uracil. The computed binding energies between neutral uracil and [M(Ura-H)]⁺, M= Zn, Cu, Ni, Fe, Cd, Pd , Mg, Ca, Sr, Ba, and Pb have also been calculated and are consistent with the experimentally-observed differences in fragmentation pathways. The potential energy surfaces associated with the fragmentation pathways of [Cu(Ura-H)(Ura)]⁺ were computed to help explain the collision induced dissociation spectra. -- Complexes of uracil and Pb²⁺, as well the water-solvated complexes have been studied by infrared multiple photon dissociation (IRMPD) spectroscopy in the N-H and O-H stretching region. The computed IR spectra for the lowest energy structures are consistent with the experimental IRMPD spectrum. The experimental spectra for [Pb(Ura-H)(H₂O)n]⁺ (n=1-2) revealed that the first water molecule binds to the lead ion and indicates the presence of intramolecular hydrogen bonding to a carbonyl of uracil. The second molecule of water also attaches directly to the lead ion, but does not participate in any hydrogen bonding. -- The infrared absorption spectra of hydrogen-bonded complexes of propylene oxide with either ethanol or 2-fluoroethanol have been recorded in neon matrices. The results indicate that hydrogen-bonded complexes were formed with propylene oxide as the hydrogen bond acceptor and either ethanol or 2-fluoroethanol as the hydrogen bond donors. The features assigned to the O-H stretch were red-shifted by 175 cm⁻¹ and 193 cm⁻¹ for ethanol and 2-fluoroethanol containing complexes. From the peak shifts and the comparison with the calculations, a 1:1 propylene oxide/ethanol and propylene oxide/2-fluoroethanol complexes are formed.

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