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5. The Peptide Environment:
A Critical Component of Photosynthetic Units
Based on our success with the metalloreceptors outlined in section
3, we are interested in the development of synthetic routes to model
peptide environments. These environments are critical to PSII, from the
assembly of the LHC, to the recognition and binding of quinones. Modelling
how peptides affect the nano-environment of small molecules may aid in
developing artificial environments without the need for complete encapsulation.
Thus, we have developed "peptide shrouds", nano-environments
enshrouded by peptide chains. While these systems may be developed without
metal binding units, we propose their incorporation in order to study
substrate binding in the core. Although 1H NMR will provide a wealth of
information about substrate binding, changes in metal-based UV/vis, electrochemistry,
luminescence and magnetic properties may allow more in-depth analysis.
These complexes serve as structural and functional models for enzymes
by varying the metal ion(s) and functional groups near the active site.
Our design incorporates a metal-binding domain surrounded by stereochemically
pure amino acids. To access the vacant metal coordination site, substrate
must pass through this "peptide shroud". Substrate selectivity
will be enforced by non-covalent interactions between the substrate and
the amino-acids. Very specific modifications may be made to each ligand
in order to mimic specific enzyme active sites (e.g., number of
"arms" and the amino acid sequence).
To be viable, the methodology must be compatible with different metal-binding
domains (e.g., variations in coordination geometry and donor atoms,
number of metal ions, and oxidation states) and, most importantly, allow
facile modification of the active-site environment. As amino acids are
readily available in enantiomerically pure form, they were the first choice
for functionalizing the core building block,
although extensions to include other building blocks can easily be envisaged.
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