Photosynthesis

Hierarchical Photosynthetic Systems for Photochemical Energy Conversion

The goal of this program is to identify the mechanisms responsible for optimization of photochemical energy conversion in natural photosynthesis, and to use this information for the development of artificial photochemical systems with enhanced photochemical energy conversion. The project investigates the correlations between sequential electron transfer with static and dynamic structures in natural and artificial systems, and investigates strategies for linking ultrafast, light-induced, one-electron transfer to slower, energy-conserving redox and electrochemical processes in artificial photosynthetic systems using biomimetic, hierarchical molecular architectures.

Novel approaches include the use of isotopic and transition metal ion labeled photosynthetic proteins (Lisa Utschig-Johnson) for analysis of the structure and function of natural photosynthetic systems, time-resolved and spin polarized electron paramagnetic resonance spectroscopies (Oleg Poluektov) for analysis of sequential electron transfer and electron donor/acceptor geometries, time-resolved x-ray absorption spectroscopy (Lin Chen) for analysis of metal ion structure and function in photosynthetic chemistry, and the use of x-ray and neutron scattering techniques (David Tiede) for resolving molecular structure and structural dynamics of photosynthetic assemblies in disordered media.

Specific project areas are described below.

Structure and Light-Induced Structural Dynamics in Natural Photosynthesis

This project investigates fundamental mechanisms for solar energy conversion in natural photosynthesis. Photosynthetic reaction centers (RCs) are investigated as models of molecular systems in which both the cofactors and the surrounding media are tuned for optimized solar energy conversion. The program approach features the resolution of structural dynamics linked to ET reactions by the application of a suite of advanced, multi-frequency, pulsed magnetic resonance, transient optical, and x-ray techniques together with capabilities to prepare isotope and metal ion edited RC samples. The research develops a fundamental understanding of structure-function relationships in biological photosynthesis and establishes principles for the design of biomimetic systems for solar energy conversion.

Structure and Light-Induced Structural Dynamics in Photosynthetic Model Systems

This project investigates fundamental mechanisms for solar energy conversion in biomimetic photosynthetic model systems and complements the project described above by examining mechanisms for solar energy conversion across a broader range of molecular charge carriers and reaction matrices than can be achieved in biology. The subtask highlights the direct detection of atomic reorganization accompanying photochemical charge separation by combining pioneering time-resolved synchrotron x-ray spectroscopy and wide-angle x-ray scattering techniques with transient optical techniques to follow light-activated structural dynamics across multiple time (10-13 sec to 1 sec ) and length (1 Å to 500 Å) scales. This program tests hypotheses and design concepts for solar energy conversion that emerge from natural photosynthesis, and establishes the groundwork for the development of advanced biomimetic artificial photosynthetic systems.

Ultrafast Spatial Imaging of Solar Energy Flow In Photosynthesis

The goal of this project is to image solar energy flow through quasi-crystalline arrays of light-harvesting proteins in natural photosynthetic membranes and in laboratory-produced 2D and 3D crystalline arrays of isolated photosynthetic proteins with ultrafast time resolution and nanometer to molecular scale spatial resolution. This goal will be accomplished by combining ultrafast transient laser spectroscopy with emergent technology in nanophotonics for spatial control and imaging of light at the nanometer scale. This work will resolve the design principles that underlie Nature’s remarkable hierarchical architectures for solar energy conversion, and it will establish approaches for follow-on research on the design and analysis of efficient, molecular-based biomimetic systems for solar energy capture and conversion.

Contact

David M. Tiede, Group Leader
Photosynthesis
Chemical Sciences and Engineering Division
Argonne National Laboratory, Bldg. 200
phone: 630/252-3539
fax: 630/252-9289
e-mail: Tiede@anl.gov