Hancock, N.H. Nanotechnologists have recently succeeded in their attempts to build molecular systems based on highly efficient versions of the molecular "machine" that plants use to turn sunlight into energy. Such molecular-assembly machines could be used in many applications, including sensors and other electronic devices.
One recent example is a chemical system devised at Sandia National Laboratory (Albuquerque, N.M.) that creates a wide variety of complex nanostructures from platinum. The system uses the porphyrin molecule, a protein essential to photosynthesis, as a catalyst for depositing platinum on small organic structures called lipids. The process resembles a molecular-scale electroplating technique, except that photons rather than electrons drive the plating operation.
Working with researchers at the University of New Mexico's Center for Microengineered Materials, Sandia scientist John Shelnutt has created convoluted platinum structures that might be used to split hydrogen atoms from water molecules, leading to a light-driven source of hydrogen.
Controlling platinum deposition at the molecular level could be used in such applications as "catalysis, sensors and optoelectronic and magnetic devices," he said.
Porphyrin is only one component in a complex series of molecular stages used by the photosynthetic process to convert light into the chemical ATP, which is the fuel that powers all living cells. Chlorophyll acts as an antenna that resonates with photons, passing the energy along to porphyrin, which responds by donating electrons to a complex molecular configuration that uses them to generate protons inside a cavity. The protons then drive the synthesis of ATP from precursors. The entire process is complex and still not fully understood.
Part of the quest is to find more efficient photosynthetic machines, since the natural variety is highly inefficient.
Molecular systems that mimic photosynthesis also have applications in molecular electronics. Devens Gust, a biochemist at Arizona State University (Tempe, Ariz.), has been working with Michael Kozicki in the university's Department of Electrical Engineering to find a way to connect optical-molecular electronic switches based on photosynthetic components to the completely different material system found in silicon-based electronic circuits.
Gust has also created an artificial ATP synthesis process inspired by photosynthesis. The molecular machine uses carotene as the optical antenna, porphyrin as the electron donor just as in photosynthesis and buckminsterfullerene molecules to field the electrons. This system is attached to a spherical lipid membrane containing ATP precursors. The charges on the carbon-fullerene molecules cause the buildup of protons inside the lipid sphere. This buildup drives the synthesis of ATP.
Scaling up such light-driven molecular machines could make solar energy a viable alternative for industries that depend on fossil fuel by delivering photon energy directly to chemical processes. And, they could also become prototype nanotechnology systems for synthesizing materials.