The Electronic Structure of the Pyranopterin Dithiolene Cofactor and Radical Reporters of Excited State Interactions

Crystal structures of multiple molybdenum enzymes clearly demonstrate interesting structural distortions involving the pyranopterin dithiolene. These distortions can be correlated with pyranopterin oxidation state through the use of DFT geometry optimized structures of the possible oxidation states, and these are correlated with enzyme family. The potential role of the pyranopterin dithiolene in electron transfer in the varied enzyme familes has been explored through the use of non-equilibrium Green's function (NEGF) electron transport calculations. These calculations demonstrate clear differences in electron transport behavior as a function of pyranopterin oxidation state.;The Jahn-Teller effect can strongly impact the geometric and electronic structures of molecules which are Jahn-Teller or pseudo-Jahn-Teller active. An intriguing Jahn-Teller effect has been explored in Cp 2M(bdt) model compounds, which are shown to be useful models for studying pseudo Jahn-Teller effects in metal dithiolenes and pyranopterin molybdenum enzymes. Easily synthesized, flexible architecture, and small size enable for complete spectroscopic and theoretical characterization of these classic Cp2M(bdt) compounds. The three metals studied (M=Ti,V, or Mo) span the d-electron counts from n=0-2, which are the same d electron counts found in molybdenum enzymes. These model systems are shown to be susceptible to either a strong, weak, or no pseudo Jahn-Teller effect, which changes over several orders of magnitude upon oxidation or reduction.;Pendant radicals are shown to be powerful tools probes to better understand the electronic structures of molecules. Radical elaborated square-planar Pt(II) donor-acceptor systems are studied by MCD spectroscopy, even though the parent non-radical elaborated compound is formally diamagnetic. This allows for a level of understanding so far unseen for this well-studied family of molecules. Exchange mixing between the pendant radical and photogenerated open-shell singlet states is shown to be crucial to understanding the complexities associated with the MCD results. This has enabled the determination of many key spectroscopic and electronic structure parameters that are essentially unobtainable by any other methodologies.