Professor of Chemistry
Professor Hammes-Schiffer received her B.A. degree in Chemistry from Princeton University in 1988 and her Ph.D. in Chemistry from Stanford University in 1993. After working as a postdoctoral fellow at AT&T Bell Laboratories, she was a faculty member at the University of Notre Dame from 1995-2000 and at The Pennsylvania State University from 2000-2012. In August 2012, Professor Hammes-Schiffer joined the faculty of the Department of Chemistry at the University of Illinois. She is also a Deputy Editor for The Journal of Physical Chemistry.
Our research centers on the development and application of theoretical and computational methods for describing chemical reactions in condensed phases and at interfaces. The group is divided into three general areas: proton-coupled electron transfer reactions, enzymatic processes, and non-Born-Oppenheimer electronic structure methods. Our overall objective is to elucidate the fundamental physical principles underlying charge transfer reactions. Our theories also assist in the interpretation of experimental data and provide experimentally testable predictions.
Proton-coupled electron transfer
Proton-coupled electron transfer (PCET) reactions play a critical role in a wide range of chemical and biological processes. We have developed a general theoretical formulation for PCET and have applied this theory to experimentally studied reactions in solution, proteins, and electrochemistry. This theory treats the electrons and transferring proton(s) quantum mechanically and includes the solvent and solute reorganization as well as the proton donor-acceptor motion. We have derived a series of analytical expressions for the rate constants of PCET reactions and for the current densities of electrochemical PCET processes. We have also developed methodology to simulate the nonadiabatic ultrafast dynamics of photoinduced PCET reactions. Applications of this theory have provided explanations for the experimental trends in the rates and deuterium kinetic isotope effects, and in some cases the temperature and pH dependences. Current applications focus on the design of molecular electrocatalysts and photocatalysts for hydrogen oxidation and production in energy conversion devices such as solar cells.
We have developed a hybrid quantum/classical molecular dynamics approach for simulating proton and hydride transfer reactions in enzymes. This hybrid approach includes electronic and nuclear quantum effects, as well as the motion of the entire solvated enzyme. The methodology provides detailed mechanistic information at the molecular level and allows the calculation of rate constants and kinetic isotope effects. Applications of this methodology have led to the concept of a network of coupled equilibrium motions extending throughout the enzyme and representing conformational changes that facilitate the chemical reaction. Mutations distal to the active site can significantly impact the catalytic rate constant by altering the conformational motions of the entire enzyme and thereby changing the probability of sampling conformations conducive to the catalyzed reaction. Currently we are developing methods for calculating the vibrational Stark effect in enzymes to further probe the roles of hydrogen bonding, electrostatics, and conformational motions in enzyme catalysis. We are also extending our studies to ribozymes (RNA enzymes) as well as protein enzymes.
Non-Born-Oppenheimer electronic structure methods
We have developed the nuclear-electronic orbital (NEO) method for the incorporation of nuclear quantum effects into electronic structure calculations. In the NEO approach, specified nuclei are treated quantum mechanically on the same level as the electrons, and mixed nuclear-electronic wavefunctions are calculated variationally with molecular orbital methods. Correlation among electrons and nuclei can be included with multiconfigurational methods, perturbation theory, or density functional theory. For hydrogen transfer and hydrogen bonding systems, typically the key hydrogen nuclei and all electrons are treated quantum mechanically. The advantages of the NEO approach are that the Born-Oppenheimer separation between electrons and specified protons is avoided, nonadiabatic effects are inherently included, and excited electron-proton vibronic states may be calculated. Current efforts are directed toward including electron-proton correlation with explicitly correlated wavefunction methods and multicomponent density functional theory.
A. Hazra, A. V. Soudackov, and S. Hammes-Schiffer, “Isotope effects on the nonequilibrium dynamics of ultrafast photoinduced proton-coupled electron transfer reactions in solution,” J. Phys. Chem. Lett. 2, 36-40 (2011).
A. Sirjoosingh and S. Hammes-Schiffer, “Proton-coupled electron transfer versus hydrogen atom transfer: Generation of charge-localized diabatic states,” J. Phys. Chem. A 115, 2367- 2377 (2011).
N. Veeraraghavan, A. Ganguly, J.-H. Chen, P. C. Bevilacqua, S. Hammes-Schiffer, and B. L. Golden, “Metal binding motif in the active site of the HDV ribozyme binds divalent and monovalent ions,” Biochemistry 50, 2672-2682 (2011).
S. Hammes-Schiffer, “Current theoretical challenges in proton-coupled electron transfer: Electron-proton nonadiabaticity, proton relays, and ultrafast dynamics,” J. Phys. Chem. Lett. 2, 1410-1416 (2011).
B. Auer, L. E. Fernandez, and S. Hammes-Schiffer, “Theoretical analysis of proton relays in electrochemical proton-coupled electron transfer,” J. Am. Chem. Soc. 133, 8282-8292 (2011).
S. Hammes-Schiffer, “When electrons and protons get excited,” Proc. Nat. Acad. Sci. USA 108, 8531-8532 (2011).
N. Veeraraghavan, A. Ganguly, B. L. Golden, P. C. Bevilacqua,and S. Hammes-Schiffer, “Mechanistic strategies in the HDV ribozyme: Chelated and diffuse metal ion interactions and active site protonation,” J. Phys. Chem. B 115, 8346-8357 (2011).
C. Ko, M. V. Pak, C. Swalina, and S. Hammes-Schiffer, “Alternative wavefunction ansatz for including explicit electron-proton correlation in the nuclear-electronic orbital approach,” J. Chem. Phys. 135, 054106 (2011).
P. Hanoian and S. Hammes-Schiffer, “Water in the active site of ketosteroid isomerase,” Biochemistry 50, 6689-6700 (2011).
A. Sirjoosingh and S. Hammes-Schiffer, “Diabatization schemes for generating charge-localized electron-proton vibronic states in proton-coupled electron transfer systems,” J. Chem. Theory and Comput. 7, 2831-2841 (2011).
A. Sirjoosingh, M. V. Pak, and S. Hammes-Schiffer, “Derivation of an electron-proton correlation functional for multicomponent density functional theory within the nuclear-electronic orbital approach,” J. Chem. Theory and Comput. 7, 2689-2693 (2011).
B. H. Solis and S. Hammes-Schiffer, “Theoretical analysis of mechanistic pathways for hydrogen evolution catalyzed by cobaloximes,” Inorg. Chem. 50, 11252-11262 (2011).
A. V. Soudackov, A. Hazra, and S. Hammes-Schiffer, “Multidimensional treatment of stochastic solvent dynamics in photoinduced proton-coupled electron transfer processes: Sequential, concerted, and complex branching mechanisms,” J. Chem. Phys. 135, 144115 (2011).
B. H. Solis and S. Hammes-Schiffer, “Substituent effects on cobalt diglyoxime catalysts for hydrogen evolution,” J. Am. Chem. Soc. 133, 19036-19039 (2011).
G. G. Hammes, S. J. Benkovic, and S. Hammes-Schiffer, “Flexibility, diversity, and cooperativity: Pillars of enzyme catalysis,” Biochemistry 50, 10422-10430 (2011).
A. Ganguly, P. C. Bevilacqua, and S. Hammes-Schiffer, “Quantum mechanical/molecular mechanical study of the HDV Ribozyme: Impact of the catalytic metal Ion on the mechanism,” J. Phys. Chem. Lett. 2, 2906-2911 (2011).
L. E. Fernandez, S. Horvath, and S. Hammes-Schiffer, “Theoretical analysis of the sequential proton-coupled electron transfer mechanisms for H2 oxidation and production pathways catalyzed by nickel molecular electrocatalysts,” J. Phys. Chem. C 116, 3171-3180 (2012).
S. Hammes-Schiffer, “Proton-coupled electron transfer: Classification scheme and guide to theoretical methods,” Energy and Environ. Sci. 5, 7696-7703 (2012).
S. Horvath, L. E. Fernandez, and S. Hammes-Schiffer, “Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production,” Proc. Nat. Acad. Sci. USA (in press).
C. Swalina, M. V. Pak, and S. Hammes-Schiffer, “Analysis of electron-positron wavefunctions in the nuclear-electronic orbital framework,” J. Chem. Phys. 136, 164105 (2012).
A. Sirjoosingh, M. V. Pak, and S. Hammes-Schiffer, “Multicomponent density functional theory study of the interplay between electron-electron and electron-proton correlation,” J. Chem. Phys. 136, 174114 (2012).
B. Auer, A. V. Soudackov, and S. Hammes-Schiffer, “Nonadiabatic dynamics of photoinduced proton-coupled electron transfer: Comparison of explicit and implicit solvent simulations,” J. Phys. Chem. B 116, 7695- 7708 (2012).
B. H. Solis and S. Hammes-Schiffer, “Computational study of anomalous reduction potentials for hydrogen evolution catalyzed by cobalt dithiolene complexes,” J. Am. Chem. Soc. 134, 15253-15256 (2012).
Member of American Academy of Arts and Sciences, 2012
Fellow of the American Chemical Society, 2011
NIH MERIT Award, 2011
Fellow of the American Physical Society, 2010
American Chemical Society Akron Section Award, 2008
Iota Sigma Pi Agnes Fay Morgan Research Award, 2005
International Academy of Quantum Molecular Science Medal, 2005
Alexander M. Cruickshank Lecturer, Gordon Research Conferences, 2004
NSF Creativity Extension Award, 2003
Camille Dreyfus Teacher-Scholar Award, 1999
Alfred P. Sloan Research Fellowship, 1998
Ralph E. Powe Junior Faculty Enhancement Award, Oak Ridge Associated Universities, 1998
NSF CAREER Award, 1996