Redox enzymes - tuning and design

项目总结

PROJECT SUMMARY Enzymes exhibit superb catalytic efficiencies and reaction selectivity. Local electric field (electrostatic) effects have been proposed as critical factors, providing stability and regulation of enzyme function and redox behavior. Within a protein, these effects are difficult to detect and control. However, molecular transition metal complexes with incorporated electrostatic interactions offer spectroscopic signatures, making these effects easier to study. In contrast to other noncovalent interactions, such as H-bonding, experimental examples of local electric field effects have been minimally explored despite theoretical studies supporting their potential to improve reaction rate, regioselectivity, and stereoselectivity at molecular systems. Of the existing state-of-the-art experimental examples of designed electric fields, several practical challenges currently limit the scalability and generality of these techniques. Therefore, the broad objective of this proposal is to develop transition metal complexes with local electric field effects and to study how modulation of the electrostatic interaction can be used to control reactivity. This research is based on the central hypothesis that incorporating cationic or anionic moieties proximal to a transition metal center will result in defined and measurable electric field effects, which can then be harnessed to tune the proton- and electron-transfer reactivity of the transition metal complex. The following specific aims will be explored: 1) Develop correlations between electric field effects at Mn, Cr and V Schiff base complexes to proton, electron, and hydrogen atom transfer reactions; and 2) Demonstrate stoichiometric O- and N-atom transfer reactions. We will use the straightforward synthesis and broad reactivity of Schiff base complexes to our advantage to study these electrostatic effects. Cyclic voltammetry, X-ray diffraction, and vibrational spectroscopy will be used to quantify the magnitude of the electric field present at the transition metal complex. Further, reactivity studies will employ electron paramagnetic resonance and UV-vis absorption spectroscopies. The product of this research will be a fundamental understanding of how electric fields play key roles in modulating reactivity of transition metals. This model will build our understanding of how enzymes exploit similar effects to achieve reaction selectivity and rate-enhancement for biosynthetic processes.