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2D IR spectroscopy is a powerful technique for investigating molecular structures and dynamics. Using pair of pump pulses we "tag" the initial vibrational frequencies in the sample, and then use a probe pulse at some later time to monitor how they evolve. Information about dynamics is contained in 2D IR diagonal lineshapes, and information about molecular structures in diagonal peaks and cross-peaks.

We developed a mid-IR pulse shaper which uses a germanium acousto-optic modulator (AOM) to manipulate the phase and amplitude of our mid-IR pump pulses. Using this shaper, we can control the time delay and phase of the pump pulses on a shot-to-shot basis, dramatically increasing the acquisition speed and the signal-to-noise of our 2D IR spectra, and enabling experiments requiring more complex pump pulses as well.

Vibrational spectroscopy is sensitive to molecular structure and dynamics. This has made it an attractive candidate as a microscopic contrast agent. We are developing wide-field, femtosecond infrared spectroscopic imaging methods that provide temporal and spatial resolution. Using the Ge AOM pulse shaper pioneered by the Zanni group and a state-of-the-art IR focal plane array (FPA), we have successfully collected FTIR images of metal carbonyls absorbed in polystyrene beads.

Two-Dimensional Sum Frequency Generation (2D SFG) spectroscopy is a powerful technique for resolving both structural and dynamical information on surfaces and interfaces. Stemming from the powerful surface technique, SFG spectroscopy, 2D SFG allows us to investigate many interesting systems in surface chemistry. By incorporating our knowledge of 2D IR, we have characterized peptide dynamics on a gold surface.

Two-dimensional white-light spectroscopy (2D-WL spectroscopy) is a powerful tool we have developed to unravel electronic couplings and energy or charge transfer in systems of interest for solar energy. By using a white light continuum for both pump and probe, we map the correlations between electronic states that span almost the entire solar spectrum.

Utilizing 2D IR with 13C=18O isotope-labeling, we follow the structural changes associated with human islet amyloid polypeptide (hIAPP) aggregation at the residue level. We have found that folding initiates with a parallel β-sheet intermediate that spans residues in what ultimately becomes the partially disordered loop in the final fiber. The disruption of this oligomeric β-sheet as the fibers fold creates a free energy barrier that explains the lag phase ubiquitous to amyloid folding kinetics.

We study molecules that inhibit amyloid formation in order to better understand how drugs might help fight amyloid diseases. We use 2D IR and residue-specific isotope labeling to obtain detailed structural information on amyloid-inhibitor complexes. We have found that the interactions in these complexes can be quite complex and evolve with time.

2D IR linewidths are strongly sensitive to environment. By isotope-labeling individual residues within a membrane-bound peptide and monitoring the 2D IR linewidths of the isotope-labeled peak as a function of label location, we are able to probe the residue's location within the membrane and the peptide's structure on the membrane surface.

The eye lens protein γD-crystallin is a major component of cataracts, but its conformation when aggregated is unknown. We uniformly 13C-labeled one of the two domains so that they can be individually resolved in a 2D IR spectrum. When denatured with acid, the C-terminal domain forms amyloid β-sheets, whereas the N-terminal domain becomes disordered. This finding is unexpected because the N-terminal domain is thermodynamically less stable than the C-terminal domain.

We use transient absorption and anisotropy measurements to study energy transfer and the photophysics of carbon nanotube thin films, analogous to nanotube films used in photovoltaic devices. Our work has revealed that there are two time scales for energy transfer in carbon nanotube films, a faster and a slower rate.

We use transient IR, 2D IR, and transient 2D IR to study the structures and electron-transfer kinetics of rhenium-based dyes on TiO2 nanocrystalline films. Previous work using transient 2D IR suggests that different conformations of the dyes have radically different electron-transfer efficiencies. Recent work using 2D IR and DFT calculations show that aggregation is energetically favorable and may play an important role in defining electronic properties of dye-sensitized solar cells.