Raman Group

Our side of the research group uses a variety of spectroscopic techniques, primarily Raman spectroscopy, to elucidate condensed phase photochemical reaction dynamics. A major focus of our research is the photochemistry of rhodopsin, the visual pigment that allows animals to see. We have used femtosecond to millisecond time-resolved techniques and a variety of mutagenesis studies to elucidate both the primary photochemistry and the secondary protein changes that are responsible for color vision. We are also currently investigating the femtosecond time-resolved dynamics of a multitude of photochemically relevant systems using a recently developed technique, Femtosecond Stimulated Raman Spectroscopy, as well as the fundamental solvation dynamics of the solvated electron in water.

Heme-Nitric Oxide/Oxygen Binding Proteins

In collaboration with the Marletta lab, we are using resonance Raman spectroscopy to probe the heme pocket of several H-NOX domains. A major characteristic of this family is that some proteins tightly bind oxygen whereas others do not. By combining RR with site-directed mutagenesis, we hope to better understand the structural determinants that govern ligand binding and downstream signal transduction.

Rosalie Tran (Alumnus: Douhai Pan)

Femtosecond Stimulated Raman Spectroscopy (FSRS)

We have developed a spectroscopic system to acquire Raman vibrational spectra on the femtosecond time-scale. We avoid the traditional limitations of the uncertainty principle by using a stimulated Raman technique with femtosecond and picosecond pulses. Femtosecond Stimulated Raman Spectroscopy has produced a new way to study transition state structures in photochemical reactions. Currently we are studying the ultrafast dynamics of a variety of relevant photochemical reactions, including solar cell sensitizers, rhodopsins, and phytochromes. Check out our recent Science publication on rhodopsin dynamics here.

Mark Creelman Dr. Jyotishman Dasgupta Renee Frontiera Dr. Sangdeok Shim Katelyn Spillane (Alumni: Dave McCamant Phil Kukura)

Above is an illustration of the vibrational probing scheme used in FSRS. The Raman pulse is a narrow bandwidth picosecond pulse, and the probe is a broadband femtosecond pulse. When the pulses are spatially and temporally overlapped, photons are transferred from the high intensity Raman pulse to the weak probe pulse at the vibrational resonances of the sample. A single shot spectrum for cyclohexane is depicted. Division of the probe spectra in the presence (black) and absence (red) of the Raman pulse gives a traditional Raman spectrum (blue).

If you're interested in setting up a FSRS table, check out our frequently asked questions.



Recombinant Rhodopsins

In collaboration with Professor Tom Sakmar at The Rockefeller University in New York, we are using recombinant DNA techniques to develop a variety of novel rhodopsins. Current projects include site-directed mutagenesis of the native rhodopsin binding pocket, studies of the mechanism of spectral tuning in visual pigments, and reconstruction of ancient (dinosaur) rhodopsins.

Katelyn Spillane (Alumnus: Elsa Yan)

Modeling the Rhodopsin Binding Pocket

The publication of the x-ray structure of rhodopsin has allowed us to look in detail at the chromophore-protein interaction that give rise to rhodopsin's amazingly fast and efficient photochemistry. These investigations are used to motivate our site-directed mutagenesis studies and to elucidate the dynamics observed in the microflow resonance Raman studies.

(Alumnus: Ziad Ganin, Dan Wandschneider)