H N M R spectrum even in [D,]DMSO as a solvent. since the N -H signals of the free and complexed 3 appear at 6 = 10.47 and 11.21. respectively.
Complexation of Kions by receptor 3 was studied by picrate (Pic) extraction[*] experiments. For the 1 : 1 complex 3 K'Pica value of Ig K,, = 5.3 was obtained in chloroform.['01
The complexation of K + and H,PO, ions by 3 was also investigated by cyclic voltammetry in DMSO with 2% H,O and with tetrabutylammoniuin tetraphenylborate as a supporting electrolyte. Addition of Bu4N+ H,PO, to a solution of 3 causes a clear shift of both cathodic and anodic peaks toward more negative potentials. This effect is accompanied by a systematic increase in the peak separation, from 85 to 100 mV, and by a decrease of the normalized peak heights. These results suggest that a labile. redox-inactive complex is formed with H,PO;. Assuming the formation of a 1 : 1 complex, a K,,, value of I .3 x 103 M-' for H,PO; is obtained, which is in a good agreement with the 'H NMR measurements.
Upon addition of potassium tetraphenylborate to a solution of receptor 3 in DMSO the electrochemical behavior did not change, probably since the crown ether moieties in 3 are situated rather far from the redox-active U 0 2 center. However, an indirect procedure for the determination of complexation constants[' 'I based on competition between TI' and K + ions gave a K,,, value of 1 .0 x 10, M -' for K '.
Finally, we used FAB-MS, an established technique for investigation of complexes in which cations1I2l and anions are bound non~ovalently.[~. I ' I In the FAB + mass spectrum (m-nitrobenzyl alcohol as matrix) of the 1 : 1 complex[141 of receptor 3 and KH,PO,, prepared by mixing the host and guest in acetonitrile with 10% water and evaporating the solvent. an intense peak corresponding to [3 + K ' 1' was observed. The corresponding FAB-mass spectrum of the same sample yielded an intense peak for [3 + H,PO,]-. while a signal for [3 + H,PO, + K f ]is also present, which clearly proves the complexation ofthe salt.
Previously in our laboratory cation carrier assisted transport of lipopizilic potassium salts was studied.[15' Now preliminary investigations have shown a significant transport of KH,PO, as a hydrophilic potassium salt through a supported liquid membrane with receptor 3.
In conclusion, we have demonstrated that the combination of binding sites for both cations and anions in a neutral receptor molecule leads to hosts with unique, multifunctional complexation behavior.
Esperimentul Procedure
A solution of aldehqde 2 (1.3 mmol) and [~i.r-l.2-cyclohexanediamine 116) (0.65 mmol) in MeOH (100 mL) was refluxed for 1 h. Subsequently a solution of UO,(OAc), ' 2 H 2 0 (0.65 mmol) in MeOH (10 mL) was added and refluxing was continued for 1 h. After cooling. the precipitate that formed was filtered ofT and washed with MeOH (2 x 10 mL) to give 3 as a red solid in 76% yield. M.p. 1x5