An urgent problem in protein science is to understand ion uptake and ion recognition (selectivity) by proteins and polypeptides. This impacts proteins ranging from ion channels to ion sensors to metalloregulatory proteins to metallo-enzymes. Why and how are these bio-nanostructures so exquisitely sensitive to particular ions? How do local changes in the binding pockets lead to global conformational change? These questions have major implications for biology, and they need an answer from physical chemistry. In a separate field, that of green chemistry, there is another pressing problem to understand structural and dynamical heterogeneity in ionic liquids. What does this proposed heterogeneity imply about the solvation properties of these new "designer solvents''? Can we measure it? Can we use it to tune the solvent's properties? Better understanding the chemical physics of these systems will aid the rational design of new solvents, which in turn will have industrial consequences. There is an underlying connection between these biophysical and chemical physics questions – to really probe the mechanisms in operation, one must be able to separate static and dynamic heterogeneity. The nonliear spectroscopies developed in the Garrett-Roe lab can do exactly this. Multidimensional infrared spectroscopy can reveal structural dynamics on timescales spanning femtosecond–microseconds, and make molecular movies as reported by vibrational frequencies. These techniques will clarify
- The mechanism of ion selectivity in selectivity filter of an archetypal biological ion channel (KcsA).
- The conformational dance of guest and host in the molecular recognition of ionophores such as valinomycin.
- The binding of calcium ions in a biological ion sensor, EF hand, in a time- and reside-resolved way. Calcium uptake is a key step of many cellular signalling processes and is unexplored on a submicrosecond timescale.
- The structural and dynamical heterogeneity of ionic liquids. These fluids are a fascinating arena to move towards a deeper understanding of complex fluids.
Each of these experiments requires a combination of experimental expertise in the non-linear spectroscopy as well as skill modelling stochastic dynamics on a complex free energy landscape.
- "Electron Solvation in Two Dimensions," A. D. Miller, I. Bezel, K. J. Gaffney, S. Garrett-Roe, S. H. Liu, P. Szymanski, C. B. Harris, Science 297, 1163 (2002)
- "Time- and angle-resolved two-photon photoemission studies of electron localization and solvation at interfaces," P. Szymanski1, S. Garrett-Roe, C.B. Harris, Progress in Surface Science 78, 1 (2005)
- "Intermolecular zero-quantum coherence imaging of the human brain," Rahim R. Rizi, Sangdoo Ahn, David C. Alsop, Sean Garrett-Roe, Marlene Mescher, Wolfgang Richter, Mitchell D. Schnall, John S. Leigh, Warren S. Warren, Magnetic Resonance in Medicine 43, 627 (2000)
- "Purely absorptive three-dimensional infrared spectroscopy," Sean Garrett-Roe and Peter Hamm, J. Chem. Phys. 130, 164510 (2009)
- "Numerical studies of intermolecular multiple quantum coherences: high-resolution NMR in inhomogeneous fields and contrast enhancement in MRI", Sean Garrett-Roe, Warren S Warren, Journal of Magnetic Resonance, 146, 1 (2000)
- "Temperature and chain length dependence of ultrafast vibrational dynamics of thiocyanate in alkylimidazolium ionic liquids: A random walk on a rugged energy landscape", Thomas Brinzer, and Sean Garrett-Roe, The Journal of Chemical Physics 147, 194501 (2017)
- "Sub-10 Nanometer Feature Size in Silicon Using Thermal Scanning Probe Lithography", Yu Kyoung Ryu Cho, Colin D. Rawlings, Heiko Wolf, Martin Spieser, Samuel Bisig, Steffen Reidt, Marilyne Sousa, Subarna R. Khanal, Tevis D. B. Jacobs, and Armin W. Knoll, ACS Nano (2017)
- "Ultrafast dynamics of ionic liquids in colloidal dispersion", Zhe Ren, Jordan Kelly, Chaminda Prasad Gunathilaka, Thomas Brinzer, Samrat Dutta, Clinton A Johnson, Sunayana Mitra and Sean Garrett-Roe, Phys. Chem. Chem. Phys. (2017)
- "Reorientation-induced spectral diffusion of non-isotropic orientation distributions," Zhe Ren, and Sean Garrett-Roe, The Journal of Chemical Physics 147, 144504 (2017)
- "Modeling Carbon Dioxide Vibrational Frequencies in Ionic Liquids: I. Ab Initio Calculations," Eric J. Berquist, Clyde A. Daly Jr., Thomas Brinzer, Krista K. Bullard, Zachary M. Campbell, Steven A. Corcelli, Sean Garrett-Roe, and Daniel S. Lambrecht, J. Phys. Chem. B, 121, 208 (2017)