Simultaneous binding, cations ditopic receptors

The ditopic receptor 119 has been shown to bind both inorganic anions and alkali metal cations simultaneously (233). Selectivity was observed for HS04-over CP and the binding of alkali metal cations in the crown ethers was proven to substantially enhance the magnitude of anion binding (through electrostatic interaction). 

A further modification saw the introduction of crown ethers at the end of the side arms creating a ditopic receptor (125) (238). This modification imparted the ability to bind cations and anions simultaneously, introducing an additional electrostatic component to the anion-binding interaction. This receptor exhibited significant transport of hydrophilic KH2P04 through a supported liquid membrane. Electrochemical studies indicated that H2PO perturbed the elec-... 

Covalent binding of an anion and a cation receptor to obtain a ditopic receptor and subsequent application in an SLM has been reported by Rudkevich et al. (66). They synthesized a receptor (carrier 14) which is capable of binding a cation and an anion simultaneously. The crown ether part binds Cs, while the salophene moiety can complex Cl. For carrier 14 CsNOj-fluxes (J = 0.89 x 10 mol m s ) and CsCl-fluxes (J = 1.2 X 10 mol m s ) were measured. In the case of cation assisted transport, CsNOj is expected to give a higher flux than CsCl, due to the higher lipophilicity of the NO3 anion. This proves that both the anion and the cation are involved in the complexation of CsCl, and that selective transport of a hydrophilic salt over a lipophilic salt can be obtained with a ditopic receptor. 

Appropriately strapped calixarenes have also been shown to complex anions and cations simultaneously. Such a system is the ditopic, calixarene-based receptor 11 (Scheme 9.4) reported by Tumcharern and coworkers [51[. Receptor 11, in which the strap incorporates two different binding motifs (urea and amide), showed selectivity for the tetrahedral phenylphosphinate anion (PPhH02) over simple Y-shaped anions, such as acetate. After initial screening studies, quantitative analyses were carried out using NMR spectroscopic methods. Specifically, titrations were carried out in CD3CN using the TBA salts of three promising anions, namely acetate, phenylphosphinate, and diphenylphosphate. Standard analyses of the... 

Beer and co-workers have devised a system that can simultaneously detect two different cations. In the presence of and Ba + in CH3CN solution, the ditopic aza-crown receptor 10 produces three new peaks in the voltammo-gram. These correspond to the 10 2Ba +, 10 2Mg +, and 10 Ba +Mg + complexes with anodic shifts (compared to 10 alone) of 150, 395, and 275 mV, respectively. Ferrocene receptor 11, of Martinez-Manez and co-workers, is monofunctionalized with a smaller aza-oxa crown. In this case the binding unit is Hg selective. Electrochemical results in CH3CN solution show that at pH 5 the receptor is selective for Hg over Pb +, Cu +, Cd +, or... 

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