Researchers at the Argonne National Laboratory’s Center for Nanoscale Materials have recently published a paper in ACS Nano describing the potential of a synthetic nanocatalytic photon to hydrogen converter to be used as an efficient source for hydrogen fuel. Elena Rozhkova’s team utilized a cell free approach using a “synthetic purple membrane.” This membrane is comprised of nanodiscs, titanium dioxde (TiO2) and platinum (Pt) nanoparticles, all of which are used to harvest sunlight into hydrogen fuel.
This human-made, environmentally friendly nano-architecture does not require the extensive process of in vitro cell culturing, therefore allowing this method to present as a very useful alternative clean energy source in the future.
The Synthetic Purple Membrane
A naturally occurring-retinal bearing proton pump called bacteriorhodopsin (BR), also known as the purple membrane (PM), is present in the single celled organism Halobacterium salinarum. BR is known to be very robust and efficient in harvesting light energy into hydrogen.
The Argonne Researchers used a nanodisc artificial lipoprotein membrane template and a vector containing synthetic DNA to construct the synthetic purple membrane (PMsyn) to mimic the function of the naturally occurring BR pump. High-resolution atomic force microscopy (AFM) of the transmembrane bRsyn revealed a disc shaped topography, which resembled the thickness of the two-dimensional (2D) lattice of the natural crystalline PM patches.
Following purification by nickel affinity chromatography, the expressed bRsyn was placed on the surface of TiO2 semiconductor nanoclusters, which were decorated with Pt catalyst dots, which measured at 3 nm in diameter, to form the final structure of cell-free synthetic Pt/TiO2-bRsyn nano-bio architecture.
H2 Turnover Efficiency
While other Researchers have employed the use of Pt/TiO2bR systems for photocatalytic hydrogen evolution, the synthetic Pt/TiO2-bRsyn nano-bio architecture described in the present research appeared to be much more efficient than others. At a neutral pH and in the presence of green light, whose wavelength measured at approximately 560 nm, the Pt/TiO2-bR pump that is naturally present within H. salinarium demonstrated a turnover rate of 240 mmol of H2. By exposing the synthetically produced Pt/TiO2-bRsyn reached a turnover rate of 17.74 mmol of H2, which was 74 times greater than its natural counterpart.
While the synthetic bRsyn membrane produced such remarkable hydrogen turnover rates, its overall lifetime was much less as compared to that of natural bR. The decay of the bRsyn membrane was recorded at a time constant of approximately 0.32 picoseconds (ps), whereas the natural bR decay constantly is about 1.0 ps. The explanation for this 3-fold decrease in the bRsyn lifetime as compared to that of natural bR is not entirely understood, however the Researchers believe that various influences including the lipid environment, increased presence of double bonds and possible alteration of the transmembrane protein confirmation could play a role in the more rapid decay of the bRsyn.
The Cell-Free Expression Technique
Previous use of the cell-free expression technique that was utilized in this study has found success for the rapid high-fidelity production of membrane proteins for functional studies. The uniqueness of this study to be a completely synthetic process, devoid of any cellular components or additives, presents a promising technique for future research endeavors.
The Argonne Researchers believe that further optimization of this process can lead to large scale protein production, improve biomimetic membrane technologies, higher complexity hierarchical artificial systems, biomimetic catalytic reactors, enhanced drug development processes and much more. Additionally, the Researchers foresee the integration of such a systemic manipulation technique with semiconductor nanoparticles to advance energy nanosystems and various other networks of the future.
- “Cell-Free synthetic Biology Chassis for Nanocatalytic Photon-to-Hydrogen Conversion” P. Weng, A. Chang, et al. ACS Nano. (2017). DOI: 10.1021/acsnano.7b01142.