Research: Solar Biofuels
Light-Driven Biofuel Generation – Solar Driven Metabolic Pathways
Photosynthesis, which powers all life on earth, is perhaps the most interdisciplinary field in science, being comprised of biology, chemistry, biochemistry, and quantum physics. Solar energy conversion machines found in nature utilize a number of small molecules, called cofactors, which serve as discrete sites for the binding of a single electron. Charge separation in these proteins is effected via a cascade of several individual electron transfer (ET) events initiated by the absorption of a photon at a central cofactor termed the primary-donor. These proteins typically contain numerous cofactors arranged so as to enable the movement of the electron and the oxidizing equivalent, or ‘hole’, away from the primary-donor in opposite directions. The resultant potential energy is then coupled to some chemical reactions which create storable, diffusable chemical energy in the form of ATP and NAD(P)H.
Replacing the machinery of photosynthesis (top) with improved and simplified parts (bottom).
The longest-running project in our lab, funded by the AFOSR, the NSF, and NYSERDA, centers on artificial photosynthesis. This has involved the design of a number of cofactor-containing light-activated electron transfer proteins and cofactor-containing enzymes with the goal of creating simplified organisms that take in light energy and use it to drive the formation of carbon-neutral biodiesel.
The project involves computational protein design, NMR, ps and ns laser spectroscopy, biological pathway optimization, quantum energy optimization, and microbiology.
Collaborators are: Scott Banta at Columbia University, Shelly Minteer at the University of Utah and Cara Lubner at the National Renewable Energy Laboratory
Significant findings thus far in this work:
We have developed a design method that combines bioinformatics with binary patterning to create proteins that bind the porphyrin-like cofactors heme, chlorophyll, chlorin, and phthalocyanine.
We theoretically derived the optimum energetic and spatial arrangement of cofactors in charge separation proteins and showed that all extant natural proteins follow our rules. The main thing is that the first electron transfer — from the excited state of the primary donor to the first acceptor — must be in the Marcus inverted region to create a ‘quantum kinetic trap’. And then we built a protein that demonstrates this. The theory has been published; the demonstration is in preparation.
We have created a dimanganese hydrogen peroxide oxidase protein. This protein takes two electrons from a toxic cellular waste product (hydrogen peroxide) forming molecular oxygen, and does not catalyze the reverse reaction. There is no natural analogue for this enzyme. We are currently employing it as a source of electrons in reductive metabolic pathways powered by our artificial reaction centers.
(Left) Energetic requirements for long-lived high yield charge separation in the photosynthetic cofactor triad. (Right) Overdriven recombination is in the Marcus inverted region, creating a quantum kinetic trap.