Document Type

Dissertation - Open Access

Award Date

2023

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Douglas Raynie

Abstract

Deep eutectic solvents (DES) are emerging as a versatile class of solvents, attracting considerable attention for their unique solvent properties and potential applications. This study examines the effects of variations in combinations as well as molar ratios of hydrogen-bond acceptor (HBA) and hydrogen-bond donor (HBD) on the structure of DES. It further explores the structure-activity relationship, measured using the rate of acetylsalicylic acid (ASA) degradation in the solvent. The project is based on the model that variations in HBA/HBD combinations and their relative molar ratios impact the solvent structure (hydrogen bonding), observable in physicochemical measurements, infrared (IR), and nuclear magnetic resonance (NMR) spectra. It is posited that the structure of the solvent influences its activity, as measured using the rate of degradation of ASA in the solvent. Physicochemical measurements, IR and NMR spectra were employed to elucidate the structural changes in the solvents. Clustering analysis was employed to visualize the structural relationship of the solvent studied via systematic variations in HBA and HBD Correlation analysis was also employed to reveal the association between the measured physicochemical parameters and activity. For studies involving the impact of mole ratio variation on the structure and activity of the solvent, choline chloride (ChCl)-water in the ratios 1:2, 1:5 and 1:10 was used. Both physicochemical measurements as well as spectroscopic measurements revealed differences in the structure of the solvent with ChCl-water 1:2 being structurally distinct from ChCl-water 1:5 and 1:10. Activity studies revealed that acetylsalicylic acid (ASA) was most stable in ChCl-water 1:2 and activity negatively correlated with ChCl fraction, density, basicity, and viscosity. Distinct structural differences were also observed when different HBD and HBA were paired. Activity was observed to be lowest in solvents where water was used as HBD as compared to ethanol and methanol. When either water or ethanol was used as HBD, activity was lowest in ChI as compared to ChCl and ChBr. Again, activity negatively correlated with density and positively correlated with basicity. Overall, the data supports the pivotal role of HBA/HBD combinations in shaping DES structure and its subsequent activity. The insights gained are crucial for optimizing solvent selection, especially in applications like enhancing drug stability, using aspirin as a benchmark..

Library of Congress Subject Headings

Aspirin.
Solvents.
Eutectics.
Hydrogen bonding.

Publisher

South Dakota State University

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Chemistry Commons

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Rights Statement

In Copyright