Host-guest properties cationic guests

Owing to the unique host-guest properties of calixarene macrocycles, calixarene-functionalized silica particles were used as cation-selective receptor colloids [81], and separator of lanthanides and actinides [82]. Calixarenes were also used for the syntheses of Ru, Pt and Pd NPs [83-85]. Furthermore, photoluminescence and charge-transfer complexes of calixarenes and calix[4]arene-based glycoclusters were grafted onto the surface of Ti02 NPs [64, 86]. 

Zeolites have increasingly found applications as catalysts, adsorbents and ion exchangers [1]. Their microporous properties of the inorganic host-guest systems are based primarily on the structure of the tetrahedral framework built from the TO4 tetrahedral and the possible variation of T atoms (Si, Al, P, Zr, Sn, Ti, 621, B, etc.). The guest species such as organic and/or inorganic cations fill the pore space of the framework to achieve electroneutrality. 

In 1967, Pedersen described the preparation and properties of crown ethers,3 which are macrocyclic polyethers capable of sequestering metal cations. These catalysts can enhance the solubility and reactivity of salts in nonpolar solvents. For example, 18-crown-6, i.e., yxo-anhydro-hexaethylene glycol, forms a host-guest complex with potassium cation (K+) (Equation (1)). This association enables ionic potassium fluoride (KF) to dissociate in nonpolar benzene. And since the nucleophilic F counterions are not complexed,4 the yield of the Finkelstein reaction,5 i.e., halide-halide exchange, is increased 6... 

Host/guest interactions of benzene, p-xylene,p-chlorotoluene and chlorocyclo-hexane with ZSM-5 were investigated by Huang et al. [832]. These authors used FT-Raman spectroscopy and utilized the excitation by an NIR laser (A=1064 nm), which considerably reduced the fluorescence background. The effect of loading on the framework and OH stretching vibrations was determined as well as sor-bate-induced phase transitions, conformational properties of the guest molecules, their location and sorbate/cation interactions. 

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