Ph.D. Dissertation

Calixarenes with quinone or azo groups have been shown ionophoricability depending on their redox states. Thermodynamic characteristicsof quinone-derivatized calixarenes from calorimetric titrationstudy imply that their structures are very flexible, which arereminiscent of typical calixarenes that have been reported asexcellent ionophores. Compared to calixarenes without quinonemoiety, however, incorporation of the quinone results in enlargingthe effective space for sequestration of a cation since calixarenewith quinone moiety is more flexible and thus provides open ionophoricenvironment in the lower rim. Complexation behavior of quinone-derivatizedcalixarenes reflects this structural change where a large conformationalchange makes it possible to encapsulate relatively large cationssuch as NH₄⁺ and primary alkylammonium ions.These phenomena are unequivocally demonstrated by semi-empiricalcalculation, the formation constants determined by ¹HNMR titration in acetonitrile and potentiometric comparison studywith polymeric liquid membranes.

Electrochemical behavior of quinone-functionalized calix[4]arenesis similar to that of spatially constraint 1,4-benzoquinone. Propertiesof redox-dependent ionophores have been checked in the presenceof various hard metal ions and protonated alkylamines includingammonium ions. Cation bound calix[4]arenediquinone produces anew set of redox peaks at positively shifted potentials. Thus,the association constant between cation and calix[4]arenediquinoneis found to be enhanced by the electrochemical reduction of receptormolecule. The electrochemical enhancement depends on the chargeand the size of cations. The magnitude of potential shift canbe explained on the basis of stabilization due to the change ofbinding characteristics from ion-dipole to ion-ion interaction.This change in binding property is originated from the formationof an anionic cavity by electrochemical reduction. NH₄⁺and primary alkylammonium ions exhibit extraordinary voltammetricbehavior due to the fact that they can form hydrogen bonds incontrast to metal ions. The acidity and capability of forminghydrogen bonds are predominant factors among other propertiesof the guest. The cooperative bond-shortening effect between ammoniumion and carbonyl oxygen atoms by hydrogen bonding causes an extraenhancement because it makes the redox center more easily reducibleand also fast proton transfer possible. In addition to quinone-functionalizedcalixarenes, a calixarene with an azo group shows chromogenicresponse to Na⁺ but electrochemical behavior is toocomplicated to be utilized to recognize the cation because ofthe presence of an intramolecular proton source. A resorcin[4]arenewith four legs of alkylthiol groups, on the other hand, was triedas a candidate for annular macrocycles that can form self-assembledmonolayers on gold surface.

In the viewpoint of analytical applications, quinone derivativeswith or without ionophoric cavity-like structure can be used inelectroanalytical chemistry. Using calix[4]arenediquinone insteadof simply modified benzoquinones, the quantitative analysis ofprimary alkylamines is possible by virtue of the structural assistanceeven though they are weaker Bronsted acid than other typical protondonors such as carboxylic acids and phenols. Potentiometric responseis in good agreement with the Nernsian behavior when calix[4]areneswith quinone moiety are employed as neutral carriers in polymericliquid membranes. The incorporation of quinone contributes toenlarge the effective pore size. As a result, ion-selective electrodesbased on calix[4]arenediquinone are found to be preferentiallysensitive to K⁺ rather than Na⁺. A newlydesigned sandwich type K⁺-selective ionophore showsexcellent selectivities comparable to commercialized K⁺-ionophores.This result appears to be attributed to the fairly preorganizedstructure. On the other hand, chemically modified electrode basedon a calix[4]arenediquinone adsorbed directly onto glassy carbonshows the discriminative permeation of dopamine but electrochemicalinterference by ascorbic acid inhibits the voltammetric determinationof dopamine. A water-soluble calix[4]arene gives an unique phenomenonin the presence of alkaline earth metal ions, especially Ca²⁺,which suggests a new example of voltammetric Ca²⁺ assayin aqueous media.

Key words : Redox-dependent ionophore, Quinone,Calixarene, Azo, Alkylamine, Electrochemical enhancement, Hydrogenbond, Ion-selective electrode