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SHG from a Single Monolayer of the RuPZn Cofactor within the 4-Helix Bundle AP0

Grazia Gonella, Venkata Krishnan, Joseph Strzalka, Andrey Tronin, Hai-Lung Dai, Michael J. Therien & J. Kent Blasie

image 1

Electron density profiles for the AP0 peptide monolayer vectorially oriented at the water-air interface in the presence and absence of the bound cofactor RuPZn. The difference profile (inset) reveals the location of the cofactor within the hydrophilic domain of the bundle.

image 2

Polarization dependent SHG from a single monolayer of the vectorially oriented RuPZn-AP0 complex on a fused silica substrate.

Extended chromophores can be designed to possess extraordinary non-linear optical properties. When incorporated into designed n-helix bundle peptides, the peptide can control the microscopic properties of the cofactor and allow for the vectorial-orientation of the peptide-cofactor complex at interfaces, including on surfaces. Together, they can provide for the translation of the cofactor’s microscopic property into a potential device application, either single-molecule based or ensemble-based. Here, we demonstrate that the design of an amphiphilic 4-helix bundle peptide AP0 can be used to vectorially incorporate the non-linear optical cofactor RuPZn, based on an ethyne-bridged zinc-porphyrin polypyridyl-ruthenium. The designed amphiphilicity of the peptide has allowed the covalent attachment of the peptide-cofactor complex to the surface of inorganic substrates, e.g., silicon. As a result, highly efficient second harmonic generation (SHG) from a monolayer ensemble of the complex has been observed, preserving the designed large hyperpolarizability of the cofactor as the incoherent sum, in the absence of undesirable interactions between cofactors.

 

 

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