| Proton-coupled electron transfer (PCET) reactions are essential for many biological systems such as photosynthesis and respiration. In this thesis, the role of H-bonding in PCET is investigated in two different systems. The first involves a urea that contains a redox-active phenylenediamine, U(H)H, with a basic guest, 1,8-naphthyridine, naph, that forms a hostguest complex through H-bonding. Cyclic voltammetry (CV) experiments with both platinum (Pt) and poorly polished glassy carbon (GC) working electrodes show inconsistent CV overlays. Electrode fouling could be involved where a nucleophile on the electrode surface can react with the quinoidal cation, U(H)+. With a carefully polished GC electrode and shortening the potential window, reproducible data was achieved where the current height increases as the concentration of naph increases, meaning naph is a strong enough base to deprotonate U(H)H. An oxidation peak more positive than the U(H)H redox wave is observed and suspected to be the oxidation of the U(H)H-naph+ complex. DFT calculations revealed that U(H)H and naph bind in a twisted conformation due to steric hindrance. A binding constant of 30 M-1 was calculated through NMR titration experiments. A mechanism was proposed and simulated which provides good fitting of the data implying the mechanism is plausible. The second involves the synthesis and voltammetry studies of UPy(MeP), an ureidopyrimidone containing a pyridinium redox center. The initial synthetic procedure went smoothly until solubility issues started occurring. Another synthetic route was created yielding the product, UPy(MeP), which forms two tautomers, pyrimidinol and pyrimidinone, in equilibrium. Two compounds, 4-acetylpyridinium (AcP+) and N-methyl-4,4'-bipyridinium (MeV +), were synthesized and investigated to better understand the electrochemistry of UPy(MeP) tautomer states. The voltammetry of UPy(MeP) present two redox waves with two oxidation peaks further positive. The first redox wave is believed to be the reduction of the pyrimidinol dimer where 1e- is gained per redox center. The second redox wave may likely be the second 2e- reduction of the dimer. The lack of chemical reversibility in the redox waves could reflect the formation of other tautomers after the second reduction where the proton does not transfer through the H-bond and is instead transferred to a neighboring H-acceptor. |
