Artificial metalloproteins: photochemical and electrochemical approaches for understanding mechanism and catalysis

点击翻译按钮获取中文摘要

Accelerating climate change demands the development of new technologies that enable access to renewable chemical fuels and feedstocks. Despite the many approaches currently being pursued, catalysis using proteins remains an unrealized resource, especially for redox transformations (e.g., carbon dioxide to methanol). Redox enzymes are ideal candidates for catalysis because they naturally exert exquisite control over the energetic electrons required for complex transformations. Recent advances in our understanding of multistep electron transfer reactions, as well as protein design, open new avenues for investigations of artificially modified protein catalysts. To that end, a long-term goal of my bioinorganic chemistry research program is to develop a new generation of biocatalysts that can compete with “state-of-the-art” industrial approaches. Further, as we design, synthesize, and investigate new protein-based catalysts we will also develop a comprehensive set of metrics that can be used to assess and improve redox functions. We will address fundamental questions about how electrons move in artificial proteins and how we can best exploit biological redox machinery for essential chemical transformations. The proposed research will focus on the following three short-term objectives over the next 5 years: (1) to demonstrate photoelectrochemical catalysis by novel protein + indium tin oxide electrodes; (2) to selectively oxidize organic biopolymers with engineered heme proteins; and (3) to modify metalloproteins for renewable energy redox catalysis. These three complementary research objectives address key hurdles to using enzymes on large scales: constructing devices, optimizing protein catalysis, and elucidating design criteria for new, targeted catalysts. In Objective 1 we will establish methods for immobilizing functional proteins on electrode surfaces (device development). This opens the way for electrochemical- and photo-catalysis. In Objective 2 we focus on careful modifications to the easily obtained protein cytochrome c peroxidase to elicit new redox functions (catalyst optimization). A conservative and systematic approach will provide specific information about structure-function relationships. Ideally, these new systems will be amenable to immobilization strategies developed through Objective 1. Finally, our work on Objective 3 will take a more ambitious tact (designing new catalysts). Starting from very stable, heat tolerant metalloproteins, we will generate proteins with exposed (coordinatively unsaturated) metal sites. Hydrogen bonding and steric constraints make proteins exceptional “ligands” for supporting unusual coordination geometries and imparting unique reactivity upon first-row transition metals. However, few studies have taken advantage of this control to build proteins with reactivity that mirrors or improves upon that of small molecule catalysts. We will produce and extensively characterize artificial proteins to establish design elements, and then investigate the reactivity of the metal sites toward substrates (e.g., reduction of protons to dihydrogen). Taken together, the knowledge gained from this research program will provide new ways to approach our growing need for renewable chemical catalysis as we accelerate a global transition away from fossil fuels. Our work ranges from the development of photoelectrochemical devices (Objective 1) to design and optimization of protein redox catalysts (Objectives 2 and 3). The range of projects in my program will enable new approaches and technologies for catalysis using artificial proteins, while providing fruitful opportunities for the intellectual and professional development of highly qualified personnel in biological inorganic chemistry and catalysis.