The synthesis and characterisation of inorganic and organic luminophores suitable for biomolecule conjugation

Inorganic transition metal complexes have been under extensive investigation for many years in supramolecular assemblies due to their favourable photophysical and redox properties including; absorbance and emission in the visible region of the spectrum, large stokes shifts, long lifetimes, intense luminescence, good photostability and useful photosensitising properties for photodynamic therapy. Their properties make them potentially very valuable biological probes but to date relatively little application of transition metals in this area have been made. This thesis focuses on a range of novel ruthenium and iridium luminophores, their bioconjugates and nanoparticle conjugates which were prepared for applications in cell imaging. A key aim of this thesis was the synthesis, characterisation and identification of novel bioconjugates suitable for applications in cellular imaging. Some preliminary studies of their application in cell imaging are also presented. Chapter 1 outlines how metal complexes have been used previously in cellular imaging and how conjugation of these transition metal complexes to biomolecules has lead to more targeted and improved applications in medical diagnostics, photodynamic therapy, cellular imaging and pharmaceutical drug delivery. Chapters 3 & 4 detail the synthesis and photophysical characterisation of a series of Raman and oxygen sensitive, water soluble and water insoluble ruthenium (II) and novel iridium (III) polypyridyl complexes suitable for biomolecule coupling. Following conjugation of these luminophores to gold nanoparticles in Chapter 3 and cell penetrating peptides in Chapter 5, the dye-conjugates were shown to transport efficiently across the cellular membrane of mammalian SP2 and CHO cells and locate throughout the cell’s organelles. Whereas, using confocal fluorescence microscopy, the parent complexes were shown not to internalise within the cellular structures. The inherent properties of the dyes, such as Raman and lifetime sensitivity, may then be used to determine pH and oxygen levels inside the cell. This could provide critical information for the early detection of certain diseases, as abnormal pH and oxygen levels are indicative of cancerous tumours. Furthermore, the generation of singlet oxygen following light absorption by the luminophores is known to cause additional cell apoptosis. Finally, Chapter 6 describes attempts to functionalise the nucleobase guanine with a fluorescent fluorescein molecule through a short and rigid linker. A range of synthetic techniques such as Suzuki coupling, Sonogashira coupling, click chemistry and Buchwald-Hartwig coupling were used in an effort to achieve this. Using DNA as a scaffold for the first time, the modified nucleoside may be incorporated into the sequence of DNA which may be surface immobilised. Thus, providing an efficient light harvesting supramolecular assembly for the conversion of solar energy into electrical potential