I. Synthesis of electron transfer complexes and their transient dynamic behaviors. II. Design and synthesis of near-infrared fluorophores for biomedical imaging

The first portion of this thesis is concerned with the characterization of electron transfer model complexes designed with amphiphilic moieties rendering them amenable for further synthetic manipulations or solubility in aqueous environments. Specifically, a meso-to-meso ethyne-bridged (porphinato)zinc(II)-(porphinato)iron(III) complex with hydrolizable ester groups was synthesized and their photoinduced electron transfer dynamics were investigated via optical pump-probe transient spectroscopy. These studies show that the electronic environment exerted by the iron axial ligand does not dictate the electron transfer dynamics of the bis(porphyrin) complex. Geometric constraints imposed by the chromophore's surroundings have profound impacts on its ET kinetics. To probe proton-coupled electron transfer events in biological milieu, a phenyl-linked (porphinato)zinc(II)-naphthalene diimide donor-spacer-acceptor complex with amphiphilic polyethylene glycol was also synthesized. Its solubility in both non-polar organic solvents and aqueous media makes it suitable for manipulations in peptidic environments.; The spectroelectrochemical characterization of a de novo designed tetra-alpha-helical peptide bundle that only binds an abiological cofactor is also described. Like natural proteins, the synthetic peptide construct is highly selective for a specific ferric porphyrin. An optically-transparent thin layer electrode whose gold mesh working electrode can be modified for mediator-free protein spectroelectrochemical experiments was assembled. The redox potential of the peptide-bound metalloporphyrin is one of the highest determined for synthetic proteins. This new (porphinato)iron-peptide matrix represents a new platform towards mimicking the wide redox potential range observed in natural cytochromes.; The last chapter of this thesis focuses on the design and synthesis of a family of near-infrared emissive chromophores and their delivery to melanoma cells via the low-density lipoprotein receptor pathway. By modulating the lipophilicity of the tris[(porphinato)zinc(II)] species, we have successfully incorporated them into the hydrophobic core of LDL and visualized murine melanoma cells with NIR fluorescence using a low dose (∼pM) of contrast agents. Given the low cytotoxicity profiles of the contrast agents and their LDL-reconstituted solutions, these compounds and their delivery platform are promising candidates for the non-invasive in vivo imaging of tumor tissue.