Paul Champion Professor PhD University of Illinois at Urbana-Champaign, 1975 (617)373-2918 champ@neu.edu

Research Summary:

Biomolecules form a class of complex systems that are fundamental to the existence of life. We study the structure  and dynamics of such systems in order to better understand the microscopic aspects of their crucial and varied functions. We use a variety of optical-based methods such as inelastic (Raman) and quasi-elastic (Rayleigh) laser light scattering, as well as the complementary techniques of femtosecond coherence, infrared, and ultraviolet absorption spectroscopies, to probe heme containing proteins (e.g. hemoglobin, myoglobin, cytochrome c, cytochrome P450) and photosynthetic complexes (reaction centers, light harvesting antenna). Resonance effects are exploited by tuning the laser frequency to energies ~1-4 eV that coincide with the electronic excitations of various biological chromophores. In the case of Raman scattering, the resonance enhancement effects are enormous ~10E6 and allow us to selectively interrogate specific regions within the complex biological macromolecule. Measurements of absolute scattering cross-sections are emphasized, and the intensity of the scattering as a function of excitation frequency is used to obtain the electron-nuclear coupling parameters as well as other information pertinent to the structure and function of these materials. Samples are studied in the solution, crystalline and frozen states.

Additional experiments utilize pulsed laser excitation and allow time-resolved dynamic information to be obtained. In particular, unstable catalytic intermediates involving enzyme-substrate complexes are being studied using sophisticated optical detection systems, which are gated to accept short bursts of scattered light over broad spectral regions. High resolution transient absorption studies are also being used to characterize kinetic processes taking place over a wide dynamic range of timescales. These processes involve diatomic ligand binding, rapid (local) structural relaxations, and more global protein conformational interconversions. Other experiments involve studies of photon induced perturbations, such as photoreduction and local chromophore heating (monitored using the Stokes and anti-Stokes Raman scattering cross-sections), which may turn out to be important in understanding photon induced biological processes involving isomerization, charge separation, and energy transport.

With the introduction of a self mode-locked Ti:sapphire laser, the laboratory has now developed the capability of following the dynamics of biomolecular systems on both the femtosecond and picosecond timescales. Current studies are focusing on the technique of "femtosecond coherence spectroscopy" which has allowed us to detect very interesting, functionally important, low frequency biomolecular oscillations. Future work will be directed toward other classes of four wave mixing experiments that exploit the capability of ultrafast laser pulses.

Recent Publications :

• Dan Ionascu, Florin Rosca, Florin Gruia, Anchi Yu, and Paul M. Champion, "Optical Scanning Instrument for Ultrafast Pump-Probe Spectroscopy of Biomolecules at Cryogenic Temperatures", Rev. Sci. Instrum. 77, 064303 (2006).
• Xiong Ye, Anchi Yu, and Paul M. Champion, "Dynamics of Nitric Oxide Rebinding and Escape in Horseradish Peroxide" J. Am. Chem. Soc. 128, 1444 (2006).
• Anchi Yu, Xiong Ye, Dan Ionascu, Wenxiang Cao, and Paul M. Champion, "Two-color Pump-probe Laser Spectroscopy Instrument with Picosecond Time-resolved Electronic Delay and Extended Time Range", Rev. Sci. Instrum. 76, 114301 (2005).
• Dan Ionascu, Florin Gruia, Xiong Ye, Anchi Yu, Florin Rosca, Chris Beck, Andrey Demidov, John Olson, and Paul M. Champion, “Temperature Dependent Studies of NO Recombination to heme and Heme Proteins”, J. Am. Chem. Soc. 127, 16921 (2005).
• Paul M. Champion, "Following the Flow of Energy in Biomolecules", Science 310, 980 (2005).

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