Controlling catalytic properties via protein engineering and nanoscale synthesis

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biological Engineering, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 136-146).From the fabrication of fine chemicals, to the increasing attainability of a non-petrochemical based energy infrastructure, catalysts play an important role in meeting the increasing energy and consumable demands of today without compromising the global health of tomorrow. Development of these catalysts relies on the fundamental understanding of the effects individual catalyst properties have on catalytic function. Unfortunately, control, and therefore deconvolution of individual parameter effects, can be quite challenging. Due to the nanoscale formfactor and wide range of available surface chemistries, biological catalyst fabrication affords one solution to this challenge. To this end, this work details the processing of M13 bacteriophage as a synthetic toolbox to modulate key catalyst parameters to elucidate the relationship between catalyst structure and performance. With respect to electrocatalysis, a biotemplating method for the development of tunable 3D nanofoams is detailed. Viral templates were rationally assembled into a variety of genetically programmable architectures and subsequently templated into a variety of material compositions. Subsequently, this synthetic method was employed to examine the effects of nanostructure on electro-catalytic activity. Next, nanoparticle driven heterogeneous catalysis was targeted. Nanoparticle-protein binding affinities were leveraged to explore the relationship between nanoparticles and their supports to identify a selective, base free alcohol oxidation catalyst. Finally, the surface proteins of the M13 virus were modified to mirror homogeneous copper-ligand chemistries. These viruses displayed binding pocket free copper complexation and catalytic efficacy in addition to recyclability and solvent robustness. Subsequently, the multiple functional handles of the viron were utilized to create catalytic ensembles of varying ratios. Single and dendrimeric TEMPO (4-Carboxy-2,2,6,6-tetramethylpiperidine 1-oxyl) were chemically conjugated to the surface of several catalytically active phage clones further tailoring catalytic function. Taken together, these studies provide strong evidence of the utility of biologically fabricated materials for catalytic design.by Jacqueline Ohmura.Ph. D

Virus-templated Pt–Ni(OH)₂ nanonetworks for enhanced electrocatalytic reduction of water

Clean hydrogen production via water electrolysis is incumbent upon the development of high-performing hydrogen evolution reaction electrocatalysts. Despite decades of commercial maturity, however, alkaline water electrolyzers continue to suffer from limitations in electrocatalytic activity and stability, even with noble metal catalysts. In recent years, combining platinum with oxophilic materials, such as metal hydroxides, has shown great promise for improving performance potentially by enabling stronger water dissociation at the surface of electrocatalysts. In this work, we leveraged the nanoscopic proportions and surface programmability of the filamentous M13 bacteriophage in the design, synthesis, and exceptional performance of 3D nanostructured biotemplated electrocatalysts for alkaline hydrogen evolution. We developed a facile synthesis method for phage-templated, Pt–Ni(OH)₂ nanonetworks, relying on scalable techniques like electroless deposition. After optimization of the platinum content, our materials display –4.9 A mg⁻¹Pt at −70 mV versus the reversible hydrogen electrode, the highest reported mass activity in 1 M KOH to date, and undergo minimal changes in overpotential under galvanostatic operation at −10 mA cm⁻²[subscript geo]. Looking forward, the performance of these catalysts suggests that biotemplating nanostructures with M13 bacteriophage offers an interesting new route for developing high-performing electrocatalysts. Keywords: Hydrogen evolution reaction; Electrocatalysis; M13 bacteriophage; 3D nanostructure; BiotemplatingUnited States. Defense Advanced Research Projects Agency (Award HR0011835402)Shell International Exploration and Production B.V. (Award 4550155123

Highly adjustable 3D nano-architectures and chemistries

Porous metal nanofoams have made significant contributions to a diverse set of technologies from separation and filtration to aerospace. Nonetheless, finer control over nano and microscale features must be gained to reach the full potential of these materials in energy storage, catalytic, and sensing applications. As biologics naturally occur and assemble into nano and micro architectures, templating on assembled biological materials enables nanoscale architectural control without the limited chemical scope or specialized equipment inherent to alternative synthetic techniques. Here, we rationally assemble 1D biological templates into scalable, 3D structures to fabricate metal nanofoams with a variety of genetically programmable architectures and material chemistries. We demonstrate that nanofoam architecture can be modulated by manipulating viral assembly, specifically by editing the viral surface coat protein, as well as altering templating density. These architectures were retained over a broad range of compositions including monometallic and bi-metallic combinations of noble and transition metals of copper, nickel, cobalt, and gold. Phosphorous and boron incorporation was also explored. In addition to increasing the surface area over a factor of 50, as compared to the nanofoam's geometric footprint, this process also resulted in a decreased average crystal size and altered phase composition as compared to non-templated controls. Finally, templated hydrogels were deposited on the centimeter scale into an array of substrates as well as free standing foams, demonstrating the scalability and flexibility of this synthetic method towards device integration. As such, we anticipate that this method will provide a platform to better study the synergistic and de-coupled effects between nano-structure and composition for a variety of applications including energy storage, catalysis, and sensing.United States. Army Research Office (Grant W911NF-09-0001)National Science Foundation (U.S.) (Grant DMR-0819762)National Science Foundation (U.S.). Graduate Research Fellowship (NSFGRFP