ORCID

https://orcid.org/0009-0003-5847-6677

Date of Award

2026

Document Type

Thesis

Degree Name

MS in Chemistry

Department

Chemistry

First Advisor

Anne Vazquez

Second Advisor

Enju Wang

Third Advisor

Joseph Serafin

Abstract

The environmental persistence of naphthenic acids (NAs), a class of toxic organic acids generated during oil sands extraction, presents a significant challenge to remediation efforts in aquatic and soil systems, particularly in Alberta, Canada. The presence of dissolved organic matter (DOM), primarily composed of humic acid, has been shown to enhance the solubility and mobility of NAs. Yet, the molecular-level mechanism governing interactions between DOM and NAs remains unclear. This study aims to elucidate the mechanism and strength of NA binding to humic acid in order to inform the development of more effective remediation strategies. To investigate structure–function relationships, a series of model compounds representing common NA functional groups and structural motifs was selected, including benzoic acid, cyclohexane carboxylic acid, decanoic acid, benzaldehyde, and 2-phenylethanol. Fluorescence quenching spectroscopy was employed as the primary analytical technique, leveraging the intrinsic fluorescence of humic acid. Binding interactions were analyzed using Stern–Volmer relationships to determine quenching constants (KSV) and differentiate between static and dynamic quenching mechanisms through temperature-dependent studies. Complementary fluorescence anisotropy measurements were conducted to assess changes in molecular rotational freedom upon binding, providing additional evidence of complex formation. Results indicate that most NA model compounds exhibit weak static quenching behavior, consistent with the formation of ground-state complexes with humic acid, while benzaldehyde and decanoic acid display predominantly dynamic quenching, suggesting minimal binding. The data further suggest that binding is governed by a combination of weak intermolecular forces, including hydrogen bonding and London dispersion interactions, with limited contribution from π–π interactions. Additionally, molecular size, polarity, and hydrogen bonding capability were found to influence binding strength. These findings provide mechanistic insight into NA–DOM interactions, contributing to a better understanding of NA transport and persistence in environmental systems. Ultimately, the findings of this study provide mechanistic insight that may inform the future development of remediation strategies for oil sands-impacted ecosystems.

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