## Dissertations from ProQuest

#### Title

Cyclodextrin complexation of several guests in water and water-urea mixtures and studies on the adsorption of organic molecules on bare and modified gold electrodes

1997

Article

#### Degree Name

Doctor of Philosophy (Ph.D.)

#### First Committee Member

Angel E. Kaifer, Committee Chair

#### Abstract

The complexation of several alkyldimethyl(ferrocenylmethyl)ammonium cations by the hosts $\alpha$- and $\beta$-cyclodextrin was investigated in aqueous media using calorimetric and $\sp1$H NMR spectroscopic measurements. The calorimetric results indicate that the complexation of all the ferrocene-containing guests is enthalpically driven.The thermodynamic functions that describe the complexation of a series of four carboxylic acid guests and two related quaternary ammonium derivatives with $\beta$-CD were measured using flow calorimetry at 298 K in aqueous media in the presence and in the absence of large concentrations of urea. The relative differences of the thermodynamic parameters of complexation revealed the existence of specific interactions between urea and the aromatic surfaces of some of the guests.The adsorption of two viologen-containing polyelectrolytes on the surface of carboxylate-terminated, self-assembled monolayers was investigated by voltammetric methods. Both polyelectrolytes were found to adsorb on either Au/SC$\sb2$COOH or Au/SC$\sb7$COOH monolayers at neutral pH. However, the adsorption was optimized by using the more hydrophobic polyelectrolyte and the longer thiol.Self-assembled aggregates of the three modified cyclodextrins (hexakis, heptakis and octakis(2,3-O-hexyl-6-deoxy-G-amino)-$\alpha ,\ \beta$ and $\gamma$-CD) on bare gold, and on the modified gold substrates Au/SC$\sb2$COOH and Au/SC$\sb7$COOH, were investigated by cyclic voltammetric, contact angle, FT-IR and quartz crystal microbalance measurements in neutral aqueous media. The level of organization of the CD derivatives on the negatively charged surface of the modified gold electrodes, proved to be substantially better than that on bare gold electrodes. Exposure of the CD-modified electrodes to solutions containing micromolar levels of ferrocene showed that binding of the organic substrate took place inside the hydrophobic aggregates.The binding constants for hexafluorophosphate, perchlorate and triflate with $\alpha$- and $\beta$-cyclodextrins were studied using calorimetry, fluorescence spectroscopy and molecular orbital calculations. In particular, the binding constant of hexafluorophosphate and $\beta$-cyclodextrin was measured to be ten times larger than the previously reported value.The complexation of phosphate ion by $\beta$-amino-cyclodextrin was detected by voltammetric methods through the competitive displacement of ferrocene methanol and ferrocenecarboxylate in neutral aqueous media. Using the RDV technique and a commercial simulation software, the stability constants between $\beta$-amino-CD and the three guests were determined.

#### Keywords

Chemistry, Physical