Exoreceptors

Because of the peculiar electrochemical behavior (a single cyclic voltammetric wave characterized by remarkable electrochemical and chemical reversibility), dendrimers terminated with ferrocene-type units can be profitable used as exoreceptors, provided that they contain a group able of interacting through noncovalent bonds with the species to be recognized. Furthermore, such a group has to be located near the ferrocene units to sufficiently perturb their electrochemical response as a consequence of the interaction with the guest species. 

The electrochemical properties of the two types of iron-cluster-derivatized AuNPs resemble that of the monomeric tetrairon cluster, except that they additionally show adsorption due to their large size, and evidence that all the Fe4 clusters are active at about the same potential, thereby indicating that they are sufficiently remote from one another to behave independently. The changes in the cyclic voltammetric pattern caused by the addition of H2P04 and ATP2- oxoanions evidence recognition features that are very different from those obtained with dendritic ferrocene exoreceptors. In particular, the results show that with these iron-cluster-derivatized AuNPs... 

From Endoreceptors to Exoreceptors. Molecular Recognition at Surfaces... 

The design of exoreceptors requires a means of generating defined external molecular shapes. This may be achieved by the stepwise synthesis of molecular architectures via covalent bond formation (covalent or molecular morphogenesis). The polymerization of oriented systems in molecular assemblies may also serve this end [7.10]. 

As cheaper and readily accessible alternatives to regular dendrimers, hyper-branched polymers are increasingly being used as catalyst platforms. Rainer Haag has been one of the leaders in this field. He and C. Hajji provide an overview of an area for which commercial applications are most likely. Finally, all of these catalysis-related topics are complemented by a review of metallo-dendritic exoreceptors for the redox recognition of oxo-anions and halides, written by D. Astruc. This field offers new perspectives both for catalytic transformation and the development of molecular sensors. 

Endoreceptors and Exoreceptors Host molecules with surface receptor sites are called exoreceptors, while hosts with receptor sites inside cavities are called endoreceptors. Exoreceptors yield a wide array of possibilities when constructing host systems. 

Astruc and co-workers have also isolated dendrimers using a tetrairon cluster [ CpFe(p,3-CO) 4], 302.355 Dendrimer 303, with nine organoiron clusters at the peripheries, was prepared via the reaction of the tetrairon cluster with dendrimer 301 (Scheme 2.78). These types of dendrimers were air-stable, and electrochemistry studies showed that the iron clusters were separated enough from each other to prevent any electrostatic interaction. These dendrimers are potential exoreceptors, which are generally confined to dendrimers containing metallocene units.355... 

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