Title

Switchable bimodal cyclodextrin complexation of ferrocene derivatives for supramolecular assemblies

Date of Award

1992

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

Part I. The complexation of alkyldimethyl(ferrocenylmethyl)ammonium salts, where the alkyl group is methyl (4), heptyl (5), and hexadecyl (6), by $\alpha$-, $\beta$- and $\gamma$-cyclodextrin was studied by electrochemical methods and $\sp1$H-NMR spectroscopy. The apparent diffusion coefficients of all the ferrocene derivatives were found to decrease upon the addition of any cyclodextrin, however, the oxidation potential of the ferrocene derivatives was substantially shifted to more positive values only in the presence of $\beta$-CD. Compound 4 and 5 form 1:1 complexes with all three cyclodextrins. Compound 6 forms a 1:2 complex with $\alpha$-CD and 1:1 complexes with $\beta$-CD and $\gamma$-CD. $\alpha$-CD interacts with the aliphatic region of the derivatives, while $\beta$-CD and $\gamma$-CD interact with the ferrocene subunit. The dual mode of CD binding with these derivatives was used to build small supramolecular aggregates such as the ternary complex, 5$\cdot\alpha$-CD$\cdot\beta$-CD and quaternary complex 6$\cdot$(2 $\alpha$-CD)$\cdot\beta$-CD. In addition, the interaction of the ferrocene subunit with $\beta$-CD is governed by its oxidation state, while the interaction of $\alpha$-CD with the alkyl chain is governed by the polarity of the alkyl terminus. (Ferrocenylmethyl) 8-octanoyldimethylammonium bromide (7) possesses both structural features that can act as switches for $\alpha$-CD and $\beta$-CD binding.Part II. The synthesis and properties of a new class of asymmetric zwitterionic CD-based rotaxanes are described. The synthetic method is based on the formation of stable inclusion complexes between $\alpha$-CD and the aliphatic chain of the (Ferrocenylmethyl) 8-octanoyldimethylammonium bromide or (Ferrocenylmethyl) 12-dodecanoyldimethylammonium bromide, followed by the capping of the open end via mild amidation reaction of the carboxylic functional group with potassium 5-amino-2-naphthalenesulfonate. The asymmetric nature of these rotaxanes leads to the observation of isomerism due to the possible orientations of the threaded CD receptors. The separated isomers exhibit different stability towards unthreading of $\alpha$-CD.

Keywords

Chemistry, Physical

Link to Full Text

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