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Photosensitizer/electron acceptor molecular cross-linked Au-nanoparticle arrays are assembled on indium-doped tin oxide (ITO) electrodes by a layer-by-layer deposition process. A Ru(II)-tris-(2,2′-bipyridine)cyclobis(paraquat-p-phenylene) catenane (1) or Zn(II)-protoporphyrin IX-bis(N-methyl-N′-undecanoate-4,4′bipyridinium) (2) are used as molecular cross-linkers for the generation of Au-nanoparticle (13 ( 1 nm) arrays of a controlled number of layers. The Au-nanoparticle arrays are characterized by absorbance spectroscopy and by electrochemical means. The electrodes functionalized with 1-or 2-cross-linked Au-nanoparticle arrays are used in photoelectrochemical experiments. The resulting action spectra of the photocurrents follow the absorbance spectra of the respective chromophores. Mechanistic studies indicate that the photocurrents originate from intramolecular electron-transfer quenching of the photoexcited state of the photosensitizer by the electron acceptor units, leading to the formation of intermediate redox species. The oxidized photoproduct oxidizes the sacrificial electron donor, Na 2 EDTA, whereas the reduced bipyridinium radical cations transfer the electrons to the bulk electrode support.

A four-helix bundle de novo synthesized protein is assembled as a monolayer onto a Au electrode. Two of the helices include each two histidine units. This allows the reconstitution of the de novo protein with two Fe(III)-protoporphyrin IX units. Electrochemical characterization of the bis-heme-functionalized de novo protein, surface coverage 2.5 × 10 -11 mol‚cm -2 , reveals that the heme site close to the electrode surface exhibits a redox potential, E°) -0.43 V (vs SCE), whereas the heme center in the remote position with respect to the electrode exhibits a more positive potential, E°) -0.36 V (vs SCE). This enabled the use of the de novo protein as a rectifier element in which rapid vectorial electron transfer occurs. The bis-hemefunctionalized de novo protein assembled onto the electrode forms an affinity complex with the cytochrome b 1 -dependent nitrate reductase (NR, E.C. 1.9.6.1). The affinity complex was cross-linked with glutaric dialdehyde to yield an integrated, electrically contacted, enzyme electrode for the effective bioelectrocatalyzed reduction of NO 3 -, current yield 80%. Similarly, the bis-heme-reconstituted de novo protein assembly forms an affinity complex with Co(II)-protoporphyrin-reconstituted myoglobin, Co(II)-Mb. Cross-linking of the affinity complex between the de novo synthesized hemoprotein and Co(II)-Mb with glutaric dialdehyde results in an integrated bioelectrocatalytic electrode for the electrocatalyzed hydrogenation of acetylene dicarboxylic acid (3) to maleic acid (4), current yield 85%.