Degree Type

Dissertation

Date of Award

2006

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Marc D. Porter

Abstract

Electroanalytical chemistry is often utilized in chemical analysis and fundamental studies. Important advances have been made in these areas since the advent of chemically modified electrodes: the coating of an electrode with a chemical film in order to impart desirable, and ideally, predictable properties. These procedures enable the exploitation of unique reactivity patterns. This dissertation presents studies that investigate novel reaction mechanisms at self-assembled monolayers on gold. In particular, a unique electrochemical current amplification scheme is detailed that relies on a selective electrode to enable a reactivity pattern that results in regeneration of the analyte (redox recycling). This regenerating reaction can occur up to 250 times for each analyte molecule, leading to a notable enhancement in the observed current. The requirements of electrode selectivity and the resulting amplification and detection limit improvements are described with respect to the heterogeneous and homogeneous electron transfer rates that characterize the system. These studies revealed that the heterogeneous electrolysis of the analyte should ideally be electrochemically reversible, while that for the regenerating agent should be held to a low level. Moreover, the homogeneous reaction that recycles the analyte should occur at a rapid rate. The physical selectivity mechanism is also detailed with respect to the properties of the electrode and redox probes utilized. It is shown that partitioning of the analyte into/onto the adlayer leads to the extraordinary selectivity of the alkanethiolate monolayer modified electrode. Collectively, these studies enable a thorough understanding of the complex electrode mechanism required for successful redox recycling amplification systems. Finally, in a separate (but related) study, the effect of the alkyl chain length on the heterogeneous electron transfer behavior of solution-based redox probes is reported, where an odd-even oscillation (with respect to the number of methylene units in the alkyl chain) was observed. Characterization of the adlayers by infrared reflection spectroscopy, ellipsometry, and wetting revealed odd-even effects in the orientation of the terminal methyl group and hydrophobic character of the adlayers. Using these structural characterizations as a basis, several possible mechanisms that can account for the odd-even effect in the heterogeneous electron transfer rates of solution-based redox couples are discussed.

DOI

https://doi.org/10.31274/rtd-180813-15421

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Adam Johan Bergren

Language

en

Proquest ID

AAI3217254

File Format

application/pdf

File Size

206 pages

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