Document Type

Dissertation - Open Access

Award Date

2022

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

Douglas Raynie

Abstract

In the design of greener chemicals, deep eutectic solvents (DESs) are considered as one of the most versatile alternative solvents with widespread applications. DESs have the advantages of being nonflammable with negligible vapor pressure compared to traditional solvents. They share many characteristics of ionic liquids, but DESs are cheaper to formulate, typically nontoxic, recyclable, biodegradable, and are suitable for use with biological systems. In my Ph.D. research, three types of emerging and unconventional types of DESs, namely therapeutic DES (THEDES), amino acid-based DES (AADES), and water-based DES (WDES), have been investigated. To formulate these DES easily available and cheaper chemicals, such as water, choline chloride, menthol, aspirin, glutamic acid, arginine, and glycerol, were used. Besides formulation, experimental structural characterization, and rigorous computational studies, some of their preliminary applications have been explored to understand their potential area of applications. Formulation for poorly soluble drugs as THEDESs could enhance their solubility significantly and AADES were used to selectively depolymerize lignin. A complete characterization of WDES and solubility of salt or drug was explored. The structures and structural properties of the DES studied were explored rigorously, as these insights can help to make them more effective. The major aim of the research projects was to find out the gaps of the DES research and provide a solid background for future research. Combining the molecular dynamics (MD), density functional theory (DFT), spectroscopic (Raman, IR, and VCD) techniques, solvatochormism, cheminformatics, and chromatographic techniques helped to understand the behavior and potential of the studied formulations. For example, atom-atom radial distribution functions (RDFs) based on MD simulation reveal that hydrogen bonds are formed between Cl-…HOCh+ and Cl- …HOCOOH of the THEDES, where Cl- works as a bridge between ASA and Ch+. Cationanion electrostatic attractions are disrupted by highly interconnected hydrogen bonds. Nonsalt HBA-HBD THEDES (1:1 L-Menthol: acetic acid) is also explored and found that their depression of melting point is mainly because of long network of hydrogen bond. Since menthol is a chiral molecular, VCD was found as a good tool to understand the behavior of chiral molecule-based DES. Melting points of WDESs (1:3 and 1:4 choline chloride: H2O) were found significantly low, -79.21 and -79.25 °C, respectively. TGA study proved that water could be relatively stable at a higher temperature when it forms the DESs. Solvent selectivity triangle (SST) of Kamlet-Taft parameters proved that the DESs possess similar solvatochromic properties to ionic liquids. A simple analytical method was developed employing ion chromatography and atomic absorption spectroscopy to investigate the solubility of sodium halides, alkali chlorides, and cobalt chloride in the studied water-based DESs. Solubility trends of the metal halides in both DESs were found same, NaCl > NaBr > NaI > NaF for sodium halides and LiCl > NaCl > KCl for alkali metal chlorides. Solubilities of the studied drug molecules such as aspirin were found to be 1.3 to 6.7 times higher in the solvents than their solubilities in water. Cell viability assay of the WDES1 (1:3 ChCl:H2O) compared to dimethyl sulfoxide (DMSO) against HEK293 cell line proved that the solvent is applicable to the biological system. The eutectic points of the formulated AADESs were -0.14°C for Glu-Gly and -1.36°C for Arg-Gly. FT-IR, 1HNMR spectroscopy, and mass spectrometry studies found that Glu-Gly formed ester impurities. However, mass spectrometry showed that the impurities are negligible. TGA revealed that both DESs could be applied up to 150-160°C without losing weight, while Glu-Gly could be used up to 200°C. AADESs are excellent pretreatment media for biomass, lignin was treated as a model biomass in this study with the formulated AADESs to determine their reaction products. It was found that Arg-Gly can isolate only one monomeric compound (4-methyl benzaldehyde), while Glu-Gly can isolate three monomeric compounds. Oxidative depolymerization of the lignin residues validated the outcomes obtained from the AADES-lignin reactions. Overall, this work helped to understand how to formulate novel DESs, their wide variety of characterizations, and possible application.

Number of Pages

217

Publisher

South Dakota State University

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Rights Statement

In Copyright