Spectroscopic Studies of Pharmaceutically and Biologically Relevant Ions using Laser Interfaced Mass Spectrometry

This thesis reports results obtained from laser induced photodissociation spectroscopy experiments performed on isolated biologically and pharmaceutically relevant molecules and cluster ions within a commercial adapted quadrupole ion-trap mass spectrometer.
Laser photodissociation spectroscopy has been used to measure the dissociative photochemistry of 2-thiouracil. This was the first study to investigate the effect of protonation/deprotonation, i.e pH at the molecular level on the photochemical and photophysical properties of thionucleobases. It is shown that the deprotonated and protonated forms decay by production of free radicals, with the major pathways being electron detachment and production of cationic specie, which is a product from direct excited state decay, respectively.
The effect of intra-cluster electron transfer and excited state modifications as a function of sulphur atom substitution on complexes of iodide with 2-thiouracil (2-TU), 4-thiouracil (4-TU) and 2,4-thiouracil (2,4-TU) were studied to better understand electron capture by thionucleobases, which are used in photo-radiation therapy. It was shown that electron detachment is the dominant decay pathway for all clusters with the respective stable valence molecular anions being formed for the 4-TU and 2,4-TU complexes. The 2-TU complex shows a near-threshold dipole-bound excited state, while the spectral profiles of the 4-TU and 2,4 TU complexes display strong chromophore excitations. Extending the phenomena of this work to the complex of a relatively large biological molecule, I-·RF where RF = riboflavin, the photochemistry strongly resembles that of the I-·4-TU and I-·2,4-TU complexes. We observed the formation of the RF- anion, which is the first observation of the intact molecular anion for this important specie.
Finally, photodissociation spectroscopy has been used to study the effect of complexation on iron III metalloporphyrin (FeTPP+) and N-aromatic molecules (pyridine, quinoline and iso-quinoline), compared to the uncomplexed molecule. This is important because of MP’s biological, pharmaceutical, and other scientific applications. The spectra revealed that their absorption strength is not reduced as a function of complexation, and both the ground-state and the excited-state properties are highly influenced by the intrinsic properties of the different ligand.