An essential issue in the development of materials presenting an accurately functionalized surface is to achieve control of layer structuring. Whereas the very popular method based on the spontaneous adsorption of alkanethiols on metal faces stability problems, the reductive electrografting of aryldiazonium salts yielding stable interface, struggles with the control of the formation and organization of monolayers. Here we report a general strategy for patterning surfaces using aryldiazonium surface chemistry. Calix[4]tetra-diazonium cations generated in situ from the corresponding tetra-anilines were electrografted on gold and carbon substrates. The well-preorganized macrocyclic structure of the calix[4]arene molecules allows the formation of densely packed monolayers. Through adequate decoration of the small rim of the calixarenes, functional molecules can then be introduced on the immobilized calixarene subunits, paving the way for an accurate spatial control of the chemical composition of a surface at molecular level.

The selective recognition of substrates or cofactors is a key feature of biological processes. It involves coordination bonds, hydrogen bonding, charge/charge and charge/dipole interactions. In this Perspective, we describe how the calix[6]arene core can be functionalized and shaped to act as a biomimetic molecular receptor. The strategy relies on the selective introduction of three amino arms on alternate phenolic positions. Upon metal ion binding or self-assembly via multiple ion-pairing and H-bonding, these amino arms are projected towards each other, thus closing the calixarene small rim. The resulting cone-shaped receptors act as molecular funnels displaying high affinities for a variety of neutral guests. Their hosting properties can be finely tuned by changing the small or the large rim or by allosteric effects. Induced-fit processes are also often observed as the cavity can expand for large guests or shrink for small ones. Hence, the different families of calix[6]arene-based receptors presented here highlight the importance of having a flexible and polarized hydrophobic structure to accommodate the guest.

Mono-copper enzymes play an important role in biology and their functionality is based on Cu(II)͞Cu(I) redox processes. Modeling a mono-nuclear site remains a challenge for a better understanding of its intrinsic reactivity. The first member of a third generation of calixarene-based mono-copper ''funnel'' complexes is described. The ligand is a calix[6]arene capped by a tren unit, hence presenting a N4 coordination site confined in a cavity. Its Cu(II) complexes were characterized by electronic and EPR spectroscopies. The x-ray structure of one of them shows a five-coordinated metal ion in a slightly distorted trigonal bipyramidal geometry thanks to its coordination to a guest ligand L (ethanol). The latter sits in the heart of the hydrophobic calixarene cone that mimics the active site chamber and the hydrophobic access channel of enzymes. bioinorganic ͉ supramolecular ͉ electrochemistry ͉ host-guest ͉ enzyme model C opper enzymes such as dopamine ␤-monooxygenase, peptidylglycine ␣-hydroxylating monooxygenase, and nitrate reductase present a mononuclear copper ion buried in their active pocket opened to the external medium through a selective substrate access channel. This organization is responsible for the efficiency and selectivity of their catalytic activity (1-6). A good chemical model for metalloenzymes is a key to the understanding of the fundamental mechanisms involved in the catalytic cycle and to the design of efficient and selective new tools for the synthetic chemist. Most classical models, however, irreversibly lead to dinuclear species because of the propensity of reactive cupric species to undergo dimerization (7-10). Trying to gain insights into the chemical and redox specificity (11-15) resulting from the proteic environment of mono-copper sites, we have developed a supramolecular system that mimics not only the polyhistidine binding core but also the hydrophobic pocket that controls the second coordination sphere of the metal and its binding to an exogenous molecule. The model is based on a calix[6]arene functionalized with a nitrogenous coordination core (16 -24). The first generation of such ligands (calix[6]N 3 , see Fig. 1) (16, 17) presents three amino arms that, upon binding to the copper ion, constrain the calix[6]arene into the cone conformation required to play the role of a host for a guest ligand L. The so-called funnel complexes best stabilize Cu(I) in a tetrahedral N 3 L environment (16, 18 -20), whereas the Cu(II) species adopt a square-based pyramidal geometry N 3 L(S) with the binding of a water molecule (S is H 2 O) as a fifth ligand that is added to the system by an upper access from the outside (21,22). Despite the coordination number change between both redox states, the calixarene cavity acts as a selective funnel for small neutral organic molecules (L) as a result of the innercavity coordination site. Interestingly, the guest ligand L was shown to play the role of a shoetree molecule (23, 24) that shapes the calixarene structure and fixes the global organization of the co...