In this work, monolayers of metal complexes were covalently attached to the surface of carbon electrodes with the goal of binding monolayers of histidine-tagged proteins with a controlled molecular orientation and a maintained biological activity. In this novel method, which is simple, versatile, and efficient, the covalent attachment was accomplished in a single step by the electrochemical reduction of aryl diazonium ions that were substituted with a nitrilotriacetic (NTA) or an imminodiacetic (IDA) ligand at the para position. The transient aryl radicals that were generated in the reduction were grafted to the surfaces of glassy carbon, highly oriented pyrolitic graphite, and graphite-based screen-printed electrodes, producing dense monolayers of the ligands. The NTA- and IDA-modified electrodes were shown to efficiently chelate Cu(II) and Ni(II) ions. The presence of the metal was established using X-ray photoelectron spectroscopy and electrochemistry. Surface coverages of the ligands were indirectly determined from the electroactivity of the copper(II) complex formed on the electrode surface. Studies on the effect of electrodeposition time and potential showed that, at sufficiently negative potentials, the surface coverage reached a saturating value in less than 2 min of electrodeposition time, which corresponds to the formation of a close-packed monolayer of ligand on the electrode surface. Once loaded with a metal ion, the modified electrode was able to bind specifically to histidine-tagged proteins such as the horseradish peroxidase (His-HRP) or to an enhanced, recombinant green-fluorescent protein via its N-terminal hexahistidine tail. In the case of His-HRP, the amount of active enzyme specifically immobilized by metal-chelating binding was determined from the analysis of electrocatalytic currents using cyclic voltammetry. The electrochemical grafting makes it possible to accurately controlled and electronically address the amount of deposited ligand on the conductive surfaces of carbon electrodes with any size and shape.

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A strategy for the elaboration of a halogen-bonded porphyrin network is reported. The progressive introduction of geometric constraints via the modulation of building blocks and self-assembly via strong and directional halogen bonding led successfully to the construction of an open porphyrin network with nano-sized tubular channels.Based on the chemical and structural diversity of molecular building blocks one can nowadays control to a certain degree the self-assembly process in order to systematically alter the composition, topology and functionality of molecular materials. However, the search for porous solids remains an important topic and new strategies for the construction of extended framework architectures are longed for. 1,2 Porphyrins and their metal complexes are particularly useful building blocks because of their thermal and chemical stability and their square planar geometry and multidentate functionality. Since 1990, many groups have been working successfully on the development of porphyrin framework solids. 3 These assemblies are mainly based on thermodynamically labile interactions such as metal coordination, hydrogen bonding or π-π stacking. More recently, non-covalent halogen bonding (XB) has proven to be an alternative powerful tool in crystal engineering. 4,5 The resulting materials promise interesting potential applications in shape-and size-selective sorption (storage and molecular sieves), chemical sensing or catalysis. 4 A recent IUPAC recommendation 6 defines XB, a special case of σ-hole bonding, 7 as a non-covalent attractive interaction involving halogens as electron density acceptors. In analogy to hydrogen bonding, the halogenated binding partner is designated the XB donor, and the involved Lewis base the corresponding XB acceptor. A striking characteristic of this particular interaction is its unambiguous unidirectionality rendering crystal engineering more predictable in the absence of other competitive strong interactions. Only a few examples of porous supramolecular materials are known that are based on XB as the predominant interaction. Besides cage structures, 8 particularly interesting and challenging is certainly the elaboration of open networks containing channels accessible to solvents. Relatively weak type II XB between halogen atoms (C-X⋯X-C) afforded hexagonal channel clathrates. 8a,9 In more recent approaches the self-assembly process was mainly governed by strong and linear C-X⋯A interactions (A = Lewis base). 10,11 The strategy of Rissanen and Metrangolo 11 involved the alignment of cyclophane cavities capable of complexing small solvent molecules such as chloroform or methanol. In previous work we have also used less rigid ferrocenophanes for the self-assembly directed by XB. 12 Neither our structure nor the more recently published study by Goldberg 3c,13 on halogen-bonded porphyrin assemblies have revealed any porous inclusion compounds. Taking into account these results, we chose a more directed approach for the present study. 14 We systematically varied the topicit...

A short and efficient preparation of conjugated oligo(phenylene-ethylene) thiols bearing redox-active ferrocene moieties is described. While minimising the number of synthetic steps, the proposed strategy permits the development of sets of oligomers with varying chain length. The redox properties of the compounds in solution are determined. Preliminary

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