Dendrimers anion recognition

Many aspects of anion recognition by metal-based receptors have been covered in previous reviews [1-5]. This review is not intended to be comprehensive rather, it provides an overview of the subject with particular reference to the specific properties that metal-containing sub-units impart to this class of anion sensor. The most recent advances in the field are also detailed including the use of metallo-receptors in dendrimer, functionalised nanoparticle and surface-bound anion sensors. 

The first ferrocenyl dendrimers suitable for redox recognition contained amido groups attached to the ferrocenyl moiety [23,24], so that the H-bonding interaction with oxo-anions, known from Beer s work with endo-receptors [8-14], would be efficient. At this point, it is essential to point out that mononuclear amidoferrocenes that contain a linear substituent without any special topological requirement for anion recognition display no specific effect [23,24],... 

Some of the materials highlighted in this review offer novel redox-active cavities, which are candidates for studies on chemistry within cavities, especially processes which involve molecular recognition by donor-acceptor ii-Jt interactions, or by electron transfer mechanisms, e.g. coordination of a lone pair to a metal center, or formation of radical cation/radical anion pairs by charge transfer. The attachment of redox-active dendrimers to electrode surfaces (by chemical bonding, physical deposition, or screen printing) to form modified electrodes should provide interesting novel electron relay systems. 

Application of Ferrocenyl-Containing Dendrimers in the Electrochemical Recognition of Anions and as Electron Transfer Mediators in Amperometric Biosensors... 

The molecular recognition of anionic guest species by positively chaiged or neutral receptors is a relatively new area of research of growing interest in view of the key roles that these anions play in biochemical and chemical processes. For this reason, as part of the electrochemical studies, we decided to examine the use of the redox-active ferrocenyl dendrimers 3 and 4 that contain multiple N-H linkages capable of participating in H-bonding, as well as characteristic internal cavities,... 

More recently, recognition of H2PO and ATP2- anions has been observed with dendrimers obtained by condensation of ferrocene-terminated dendrons on octahedral Moe cluster27 (compound 3 in Fig. 6.3) or Au nanoparticles28 cores. 

Chart 1 Factors responsible for the recognition of oxo-anions HS04-, H2P04- and ATP2-by polyamidoferrocenyl dendrimers... 

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. 

Supramolecules containing metal-polypyridine units, especially the Ru(dpp)-based dendrimers, could be used as electron reservoirs or components of molecular-electronic devices. Supramolecules in which an electroactive M(N,N) group is attached to a receptor capable of molecular recognition (crown ethers, calixarenes, cryptands etc.) can work as electrochemical sensors. Electrochemical recognition of cations as well as anions has been reported [33-35, 257, 263]. 

Valerio C, Fillaut J-L, Ruiz J, Guittard J, Blais J-C, Astruc D (1997) The dendritic effect in molecular recognition ferrocene dendrimers and their use as supramolecular redox sensors for the recognition of small inorganic anions. J Am Chem Soc 119 2588-2589... 

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