**2.2.7 Genetic engineering models**

Wydrzynski and co-workers, in a different approach, introduced a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre and a bacterioferretin molecule is being 'coaxed' using genetic engineering to include the chromophores for light absorption and Mn complexes for water oxidation; they could observed oxidation of manganese in this engineered system (Conlan et al., 2007). Recently, Nam and co-workers imtroduced a biologically templated nanostructure for visible light driven water oxidation that uses a genetically engineered virus scaffold to mediate the co-assembly of zinc porphyrins (photosensitizer) and iridium oxide clusters (water oxidizing catalyst) (Nam et al., 2010). Their results suggested that the biotemplated nanoscale assembly of functional components is a promising route to improved photocatalytic water-splitting systems.

Fig. 13. Motif of edge-sharing MnO6 octahedra (di-μ-oxido bridging) in the manganese – calcium oxides (manganese: blue, oxygen: red and calcium: green) (Zaharieva et al., 2011). (Zaharieva et al., 2011). Oxygen evolution formation pathways indicated by 18O-labelling studies showed that water oxidation by these layer manganese oxides in presence of cerium (IV) ammonium or [Ru(bpy)3]+3 is a ''real'' water oxidation reaction and both oxygen atoms of formed dioxygen molecules originated from water (Shevela et al., 2011). In continuation of our efforts to synthesize an efficient and biomimetic catalyst for water oxidation, we synthesized nano - size amorphous calcium - manganese oxides that are very closely related to the WOC in PSII not only because of similarity in the elemental composition, oxidation number of manganese ions and similarity of structure and function to Mn4O*5*Ca cluster in PSII but also because of nearer on the of catalyst particle size as compared to previously reported micro - size amorphous calcium manganese

Wydrzynski and co-workers, in a different approach, introduced a reverse engineering approach to build a simple, light-driven photo-catalyst based on the organization and function of the donor side of the PSII reaction centre and a bacterioferretin molecule is being 'coaxed' using genetic engineering to include the chromophores for light absorption and Mn complexes for water oxidation; they could observed oxidation of manganese in this engineered system (Conlan et al., 2007). Recently, Nam and co-workers imtroduced a biologically templated nanostructure for visible light driven water oxidation that uses a genetically engineered virus scaffold to mediate the co-assembly of zinc porphyrins (photosensitizer) and iridium oxide clusters (water oxidizing catalyst) (Nam et al., 2010). Their results suggested that the biotemplated nanoscale assembly of functional components

is a promising route to improved photocatalytic water-splitting systems.

oxides (Fig. 14.).

**2.2.7 Genetic engineering models** 

Fig. 14. Scanning electron microscope (SEM) (a) and transmission electron microscopy (TEM) (b,c) images of amorphous calcium - manganese oxides. These readily synthesized manganese-calcium oxides are the closest structural and functional analogs to the native the WOC of PSII found so far.

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