Scientists have combined two molecules that occur naturally in blood to engineer a molecular complex that uses solar energy to split water into hydrogen and oxygen. The research is published today in the Journal of the American Chemical Society.
Professors Tsuchida and Komatsu from Waseda University, Japan, in collaboration with Imperial College London, synthesized a large molecular complex from albumin (a protein molecule that is found at high levels in blood serum) and porphyrin (a molecule which is used to carry oxygen around the body and gives blood its deep red color).
Porphyrin molecules are normally found combined with metals, and in their natural state in the blood they have an iron atom at their center. The scientists modified the porphyrin molecule to swap the iron for a zinc atom in the middle, which completely changed the chemistry and characteristics of the molecule.
This modified porphyrin molecule was then combined with albumin; with the albumin molecule itself being modified by genetic engineering to enhance the efficiency of the process. The resulting molecular complex was proven to be sensitive to light, and can capture light energy in a way that allows water molecules to be split into molecules of hydrogen and oxygen.
The efficiency of the photoproduction of H2 was greater than that of the system using the well-known organic chromophore, tetrakis(1-methylpyridinium-4-yl)porphinatozinc(II) (ZnTMPyP4+), under the same conditions.
This work has shown that it is possible to manipulate molecules and proteins that occur naturally in the human body by changing one small detail of their make-up, such as the type of metal at the heart of a porphyrin molecule, as we did in this study.
It’s very exciting to prove that we can use these biological structures as a conduit to harness solar energy to separate water out into hydrogen and oxygen. In the long term, these synthetic molecules may provide a more environmentally friendly way of producing hydrogen, which can be used as a “green” fuel.—Dr Stephen Curry, Imperial College London
“Photosensitized reduction of water to hydrogen using human serum albumin complexed with zinc protoporphyrin IX”; Teruyuki Komatsu, Rong-Min Wang, Patricia A Zunszain, Stephen Curry, Eishun Tsuchida; Journal of the American Chemical Society ASAP Article 10.1021/ja0656806 S0002-7863(06)05680-0