Neutron scattering analysis performed at DOE’s Oak Ridge National Laboratory reveals the lamellar structure of a hydrogen-producing, biohybrid composite material formed by the self-assembly of naturally occurring, light harvesting proteins with polymers. Credit: Oak Ridge National Laboratory
Researchers at the Department of Energy’s
Oak Ridge National Laboratory have developed a biohybrid photoconversion system—based
on the interaction of photosynthetic plant proteins with synthetic polymers—that
can convert visible light into hydrogen fuel.
Photosynthesis, the natural process carried
out by plants, algae, and some bacterial species, converts sunlight energy into
chemical energy and sustains much of the life on earth. Researchers have long
sought inspiration from photosynthesis to develop new materials to harness the
sun’s energy for electricity and fuel production.
In a step toward synthetic solar conversion
systems, the ORNL researchers have demonstrated and confirmed with small-angle
neutron scattering analysis that light harvesting complex II (LHC-II) proteins
can self-assemble with polymers into a synthetic membrane structure and produce
The researchers envision energy-producing
photoconversion systems similar to photovoltaic cells that generate hydrogen
fuel, comparable to the way plants and other photosynthetic organisms convert
light to energy.
“Making a, self-repairing synthetic
photoconversion system is a pretty tall order. The ability to control structure
and order in these materials for self-repair is of interest because, as the
system degrades, it loses its effectiveness,” ORNL researcher Hugh
O’Neill, of the lab’s Center for Structural Molecular Biology, said.
“This is the first example of a protein
altering the phase behavior of a synthetic polymer that we have found in the
literature. This finding could be exploited for the introduction of self-repair
mechanisms in future solar conversion systems,” he said.
Small angle neutron scattering analysis
performed at ORNL’s High Flux Isotope Reactor (HFIR) showed that the LHC-II,
when introduced into a liquid environment that contained polymers, interacted
with polymers to form lamellar sheets similar to those found in natural
The ability of LHC-II to force the assembly
of structural polymers into an ordered, layered state—instead of languishing in
an ineffectual mush—could make possible the development of biohybrid
photoconversion systems. These systems would consist of high surface area,
light-collecting panes that use the proteins combined with a catalyst such as
platinum to convert the sunlight into hydrogen, which could be used for fuel.
The research builds on previous ORNL
investigations into the energy-conversion capabilities of platinized
photosystem I complexes—and how synthetic systems based on plant biochemistry
can become part of the solution to the global energy challenge.
“We’re building on the photosynthesis
research to explore the development of self-assembly in biohybrid systems. The
neutron studies give us direct evidence that this is occurring,” O’Neill
The researchers confirmed the proteins’
structural behavior through analysis with HFIR’s Bio-SANS, a small-angle
neutron scattering instrument specifically designed for analysis of
“Cold source” neutrons, in which
energy is removed by passing them through cryogenically chilled hydrogen, are
ideal for studying the molecular structures of biological tissue and polymers.
The LHC-II protein for the experiment was
derived from a simple source: spinach procured from a local produce section,
then processed to separate the LHC-II proteins from other cellular components.
Eventually, the protein could be synthetically produced and optimized to
respond to light.
O’Neill said the primary role of the LHC-II
protein is as a solar collector, absorbing sunlight and transferring it to the
photosynthetic reaction centers, maximizing their output. “However, this
study shows that LHC-II can also carry out electron transfer reactions, a role
not known to occur in vivo,” he
The research team, which came from various
laboratory organizations including its Chemical Sciences Division, Neutron
Scattering Sciences Division, the Center for Structural Molecular Biology and
the Center for Nanophase Materials Sciences, consisted of O’Neill, William T.
Heller, and Kunlun Hong, all of ORNL; Dimitry Smolensky of the Univ. of
Tennessee; and Mateus Cardoso, a former postdoctoral researcher at ORNL now of
the Laboratio Nacional de Luz Sincrotron in Brazil.
“That’s one of the nice things about
working at a national laboratory. Expertise is available from a variety of
organizations,” O’Neill said.
The work, published in the journal Energy & Environmental Science, was
supported with Laboratory-Directed Research and Development funding. HFIR is
supported by the DOE Office of Science.
ORNL is managed by UT-Battelle for the
Department of Energy’s Office of Science.