Hydrogen-bond complexes anion recognition

This chapter is focused on our recent research topics regarding the analysis of complexation reactions at L/L interfaces. We first describe the hydrogen-bond-mediated anion recognition as studied by ion transfer polarography and interfacial tensiometry [22,23], and then alkali metal ion recognition as studied by SHG spectroscopy [24,25]. 

Polyaza macrocycles in their protonated form, either full or partial, are able to interact with anionic species, by establishing noncovalent interactions (both electrostatic and hydrogen bonding). Complexation of anions by synthetic polyammonium molecules has been explored over the past two decades, and several examples of selective recognition of different anionic substrates have been reported [14 22], Some polyammonium macrocycles such as [24]aneN6H6 +, 16, and... 

In nature the selective complexation of anions takes place by hydrogen bonds the selective recognition of phosphate and sulfate in biological systems by transport receptor proteins has recently been described [ret 26]. 

Although non-covalent interactions of anions are one of the most actively explored areas of supramolecular chemistry [15], the anion sensing and recognition have up to now relied primarily on electrostatic binding or hydrogen bonding to the receptor [16,54-61]. However, recent UV-Vis and NMR spectral studies clearly reveal that complex formation takes place in the solutions between halides and neutral olefinic and aromatic it-acceptors such as those in Fig. 3 [23,62],... 

Currently, the only other monoprotonated sapphyrin-monoanion complex to be solved by X-ray diffraction analysis is that of 3-HN,. As expected, in this complex the azide counteranion is bound above the sapphyrin plane by a combination of anisotropic electrostatic interactions and oriented hydrogen bonds (Figure 4). As such, this structure supports the conclusion, reached in the case of 3-HCl, that a single positive charge on the sapphyrin is enough to effect anion recognition of anionic substrates, at least in the solid state. 

Anion recognition in biological systems is achieved via hydrogen bonds by highly preorganized proteins. The complexation properties of these proteins... 

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