Electron-transfer (ET) reactions are key steps in a diverse array of biological transformations ranging from photosynthesis to aerobic respiration. A powerful theoretical formalism has been developed that describes ET rates in terms of two parameters: the nuclear reorganization energy (1) and the electroniccoupling strength (HAB). Studies of ET reactions in ruthenium-modified proteins have probed h and HAB in several metalloproteins (cytochrome c, myoglobin, azurin). This work has shown that protein reorganization energies are sensitive to the medium surrounding the redox sites and that an aqueous environment, in particular, leads to large reorganization energies. Analyses of electroniccoupling strengths suggest that the efficiency of long-range ET depends on the protein secondary structure: sheets appear to mediate coupling more efficiently than a-helical structures, and hydrogen bonds play a critical role in both. CONTENTS

All Rights Reserved iii For my mom iv ACKNOWLEDGEMENTSI would first like to thank Harry for his guidance over the last five years. Harry has supported my growth as a scientist beyond my wildest expectations-in addition to being the most sincere and caring mentor I could have hoped for, he has given me countless opportunities to define myself beyond the confines of the laboratory and gain exposure in the chemistry community. I could not have made it through these projects without his insight and encouragement, and for that I am truly blessed by this graduate experience.Second, I would like to thank Jay for his support and advice, teaching me everything I know about kinetics and spectroscopy, building me a diode array spectrometer, and routinely reminding me of the value of fundamental research. Like the best of mentors, he has challenged me to be an assertive researcher and calmly watched me freak out more than once. This thesis would not be nearly as comprehensive without his guidance.I have had some of the most rewarding scientific discussions of my graduate career with my thesis committee members, Mitchio Okumura, Nate Lewis, and Tom Miller, and I want to thank them for their support over the last five years. I would especially like to acknowledge Nate for giving me the opportunity to cochair the 2009 Renewable Energy: Solar Fuels Gordon-Kenan Graduate Research Seminar. I also want to thank Bruce Brunschwig and Jonas Peters who provided a good deal of guidance on this project.My undergraduate research advisor, Dan Nocera, has continued to support, encourage, and advise me over the five and a half years since I graduated from MIT. It is from Dan that I gained my love for group theory (5.04) and inorganic spectroscopy, and I am grateful for his continued guidance. I have enjoyed collaborating with a great many researchers during my graduate work.Etsuko Fujita, Dmitry Polyanskiy, and Jim Muckerman at Brookhaven National Laboratory have been enthusiastic about my research for many years and welcomed me into their labs for two visits. Etsuko in particular has been a great friend and role model and I look forward to maintaining our relationship for years to come. It has been a pleasure to make progress towards powering the planet with researchers in both the Lewis and Peters groups.Leslie O'Leary, Judy Lattimer, and Emily Warren have all made contributions towards anchoring cobaloxime catalysts to silicon electrodes, and Xile Hu, Louise Berben, Nate Szymczak, and Charles McCrory have all taught me a great deal about electrochemistry, synthesis, and catalytic hydrogen evolution.I have had the opportunity to work with a number of talented undergraduates at Caltech.Carolyn Valdez has been a great friend and I have been truly honored to watch her grow as a scientist over four years at Caltech. She spearheaded the binuclear cobaloxime catalyst project (Chapter 5), helped lead the Blair High School SHArK program, and is hands-down one of the best all-around undergraduates I ever met at Caltech. I am excited that we will b...

Recent investigations have shed much light on the nuclear and electronic factors that control the rates of long-range electron tunneling through molecules in aqueous and organic glasses as well as through bonds in donor-bridge-acceptor complexes. Couplings through covalent and hydrogen bonds are much stronger than those across van der Waals gaps, and these differences in coupling between bonded and nonbonded atoms account for the dependence of tunneling rates on the structure of the media between redox sites in Ru-modified proteins and protein-protein complexes.electron tunneling ͉ hopping ͉ glass ͉ protein

Materials and Methods Figs. S1 to S3 Table S1 References S1 SUPPORTING MATERIAL Materials and Methods Preparation of Re I (CO) 3 (dmp)(H 124)|(W 122)|AzCu I Mutant azurins were expressed and Re I (CO) 3 (dmp)(H 124)|(W 122)|AzCu I was prepared using previously published protocols (S1,S2). Crystal Structure of Re I (CO) 3 (dmp)(H 124)|(W 122)|AzCu II Crystals of Re(4,7-dimethyl-1,10-phenanthroline)(CO) 3 (H 124){T 124 H|K 122 W|H 83 Q}(Cu II)azurin (Re I (CO) 3 (dmp)(H 124)|(W 122)|AzCu II ; space group I222, cell dimensions 63.22 × 69.08 × 68.94 Å 3 ; α = β = γ = 90.00°, one molecule per asymmetric unit) grew from 4 μL drops made from equal volumes of 30 mg/mL Re I (CO) 3 (dmp)(H 124)|(W 122)|AzCu II in 25 mM HEPES pH 7.5 and reservoir by vapor diffusion. The drops were equilibrated against 500 μL of reservoir

Splitting water to hydrogen and oxygen is a promising approach for storing energy from intermittent renewables, such as solar power. Efficient, scalable solar-driven electrolysis devices require active electrocatalysts made from earth-abundant elements. In this mini-review, we discuss recent investigations of homogeneous and heterogeneous hydrogen evolution electrocatalysts, with emphasis on our own work on cobalt and iron complexes and nickel-molybdenum alloys.