Title

Host-guest complexation studies in aqueous solution and at the electrode-solution interface

Date of Award

2000

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

First Committee Member

Angel E. Kaifer, Committee Chair

Abstract

The electrochemical behavior of cobaltocenium (Cob +) and carboxycobaltocenium (Cob+-COO- ) in aqueous solution was investigated by cyclic voltammetry in the presence of beta-cyclodextrin (beta-CD). While Cob+ and Cob+-COO- do not interact significantly with beta-CD, their reduced partners (Cob and Cob-COO-) do form stable inclusion complexes with beta-CD host.The complexation of Cob+ by sulfonated calix[6]arene host was investigated in buffered aqueous solution using cyclic voltammetry and 1H NMR spectroscopy. The results indicate that the sulfonated calix[6]arene forms a 1:2 complex with Cob+, but does not bind the reduced form Cob significantly. In the presence of beta-CD, reduction of the strong 2:1 complex between Cob+ and sulfonated calix[6]arene leads to the formation of 1:1 complexes between Cob and beta-CD.A series of poly(propyleneimine) dendrimers functionalized with 4, 8, 16 and 32 peripheral Cob+ subunits were investigated, placing especial emphasis on their electrochemical properties and binding interactions with beta-CD. These dendrimers in combination with beta-CD constitute novel supramolecular assemblies whose formation is driven by the electrochemical reduction of these dendrimers.The interfacial binding properties of electrodes prepared by the electrostatic immobilization of positively charged beta-aminocyclodextrin (beta-ACD) hosts onto a self-assembled monolayer of thioctic acid on gold were investigated using Osteryoung square wave voltammetry. The results indicate that the water-soluble ferrocenecarboxylate (Fc-COO-) guest was effectively bound by the interfacial beta-ACD hosts, with binding constants in the range 2--5 x 104 M-1. The measured binding constants were found to increase slightly with the surface density of immobilized hosts.The electrochemical behavior on cystamine-modified gold electrodes of three novel dendrimers containing a single, unsymmetrically positioned ferrocene unit and 3, 9 and 27 carboxylic acid groups in their periphery was investigated as a function of solution pH in the range of 3--7. The results constitute the first example of orientation effects on the heterogeneous electron transfer rates of synthetic compounds whose electron transfer behavior is similar to redox proteins.

Keywords

Chemistry, Physical

Link to Full Text

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