A main focus is on the dynamics of structural change.Methods are sought that can determine the atomic level structure of molecules in the solution phase while they are undergoing conformational motions or chemical reactions. Such research involves nonlinear infrared spectroscopy and properties of single molecules. Femtosecond lasers are used to explore new linear and nonlinear properties of molecular systems. Processes such as electronic and vibrational energy transfer, electron and proton tunneling and phase relaxation in solids, ultrafast conformational processes in liquids and vibrational energy relaxation in condensed phases are studied. New laser techniques are also used to study protein dynamics, especially of peptides, small proteins, including those whose functions can be triggered by optical pulses. The research uses femtosecond pulsed lasers and high power tunable lasers for nonlinear studies. These and other modern techniques are used for studies of optical processes undergone by molecular systems of many types. An important goal is to bring the new experimental results into relationship with theory such as molecular dynamics simulations and quantum mechanics.
Two-Dimensional Infrared Spectroscopy
Infrared analogues of 2D NMR experiments are being developed in which the coupling between the vibrations mimics the coupling between the spins in NMR. Nonlinear spectroscopies such as the photon echo, facilitate experiments in which these couplings show up as cross peaks in a 2D spectrum. The magnitudes of the couplings can be used to determine the structure of the network of vibrators giving rise to the signal. Most importantly the 2D spectral dynamics yields properties of water local to proteins and peptides. See the RLBL homepage for more information (http://rlbl.chem.upenn.edu).
Tucker MJ, Gai XS, Fenlon EE, Brewer SH, Hochstrasser RM. "2D IR photon echo of azido-probes for biomolecular dynamics", Phys. Chem. Chem. Phys. ASAP (2010).
Urbanek DC, Vorobyev DY, Serrano AL, Gai F, Hochstrasser RM. "The two-dimensional vibrational echo of a nitrile probe of the villin HP35 protein", J. Phys. Chem. Lett. 2010(1):3311-3315 (2010)
Tucker MJ, Courter JR, Chen J, Atasoylu O, Smith AB III, Hochstrasser RM. 'Tetrazine phototriggers: probes for peptide dynamics', Angew. Chem. Intl. Ed. 49(21):3612-3616 (2010)
Vorobyev DY, Kuo CH, Kuroda DG, Scott JN, Vanderkooi JM, Hochstrasser RM. "Water-induced relaxation of a degenerate vibration of guanidinium using 2D IR echo spectroscopy", J. Phys. Chem. B 114(8):2944-2953 (2010)
Kuroda DG, Vorobyev DY, Hochstrasser RM. "Ultrafast relaxation and 2D IR of the aqueous trifluorocarboxylate ion", J. Chem. Phys. 132(4):044501/1-044501/10 (2010)
Kim YS, Liu L, Axelsen PH, Hochstrasser RM. "2D IR provides evidence for mobile water molecules in amyloid fibrils", Proc. Natl. Acad. Sci. USA 106(42):17751-17756 (2009)
Fang C, Bauman JD, Das K, Remorino A, Arnold E, and Hochstrasser RM. "Two-dimensional infrared spectra reveal relaxation of the nonnucleoside inhibitor TMC278 complexed with HIV-1 reverse transcriptase", Proc. Natl. Acad. Sci. USA 105(5):1472-1477 (2008)
Hochstrasser RM. "Two-dimensional spectroscopy at infrared and optical frequencies", Proc. Natl. Acad. Sci. USA 104(36):14190-14196 (2007)