Date of Award
Doctor of Philosophy
Ionic Liquids (ILs) are molten organic solvents comprised of unsymmetrical organic cations and inorganic/organic anions with melting points below 100 ˚C. The unique physicochemical properties of ILs including high thermal stabilities, negligible vapor pressures at room temperature, and tunable solubilities and viscosities have tremendously increased their applications in analytical chemistry.
The first part of research work presented in this dissertation focuses on different synthetic strategies that are employed to tailor the physicochemical properties as well as paramagnetic susceptibilities of magnetic ionic liquids (MILs). The developed synthetic methods yielded MILs with low aqueous solubilities (0.1% w/v) and high magnetic susceptibilities. The second part of dissertation describes the self-assembly properties of different classes of ILs in aqueous solutions. The last part of dissertation focuses on the applications of ILs and polymeric ionic liquids (PILs) for analysis of pharmaceuticals and nucleic acids, respectively.
MILs are a special class of ILs with paramagnetic component(s) in their molecular structure. In addition to favorable properties of ILs, MILs exhibit paramagnetic susceptibilities at room temperatures when suspended in aqueous solutions. As a result their molecular motion can be readily controlled by exposure to an external magnetic field. Owing to their structural tunability as well as paramagnetic susceptibilities, MILs demonstrate a remarkable potential to address the challenges associated with liquid liquid extraction (LLE) techniques. Imidazolium-based cations with [FeCl4-]/[FeCl3Br-] anions represents the common class of MILs. The high aqueous solubility of iron (III)-based MILs represents a serious problem for their applicability in liquid liquid microextraction techniques. Three different classes of iron-based hydrophobic MILs including monocationic, dicationic, and tricationic MILs were prepared. The incorporation of long hydrocarbon chains, benzyl groups, and perfluoroalkyl alkyl moieties as substituents within cation framework has significantly improved the hydrophobicity of resulting MILs. A series of dicationic imidazolium cations with weakly coordinating and relatively hydrophobic anions yielded MILs with low melting points and low aqueous solubilities. The paramagnetic susceptibility of MILs is controlled by varying the number of paramagnetic anions in the molecular structure. The developed MILs demonstrated structure-dependent extraction properties for analysis of DNA and polycyclic aromatic hydrocarbons (PAHs) from complex sample matrices.
ILs with long hydrocarbon chains and hydrophilic cations (e.g., imidazolium and pyridinium) exhibit self-assembly properties in aqueous solutions. Similar to conventional surfactants, IL-based surfactants demonstrate concentration dependent properties in aqueous solutions including bulk phase aggregation (micelle formation) and surface adsorption. The interfacial and micellar properties of three dicationic and two tricationic IL-based surfactants in aqueous solutions were examined using fluorescence spectroscopy, conductometry, and tensiometry techniques. In addition, the effects of inorganic and organic salts and organic solvent content on the aggregation properties of IL-based surfactants was investigated. The surface adsorption as well as micellar properties of tricationic IL-based surfactants was compared against the analogous trimeric quaternary ammonium-based surfactants.
The high thermal stability as well as relatively low vapor pressure at high temperatures are some interesting properties of ILs that represent them as new diluent systems in headspace gas chromatography (HS-GC) applications. Two ILs were examined as HS-GC diluents for analysis of residual solvents in pharmaceutical substances. To improve the analytical performance of the developed method, the HS-GC parameters were optimized including HS extraction time and HS incubation temperature. Owing to their favorable physicochemical properties, IL-based HS-GC method yielded low detection limits (LODs), high sensitivities, and better sample throughput compared to conventional organic solvent-based HS-GC method.
Solid-phase microextraction (SPME) is a miniaturized and automated solvent-free sample preparation technique. In contrast to solid-phase extraction (SPE) and LLE methods, SPME streamlines the analytical workflow by combining sampling and sample preparation into a single step. This significantly reduces the overall analysis time. PILs represent as new class of sorbent coatings with tunable solvation properties and high thermal stabilities. The unique extraction properties of PILs were exploited for the purification of nucleic acids from complex sample matrices. Electrostatic and ion–exchange interactions between negatively charged phosphate backbone of nucleic acid and cationic framework of PIL sorbent coating are the main driving force for extraction of nucleic acids by PIL sorbent coatings. The developed PIL-based SPME method purified sufficient quantity and quality of DNA from bacterial cell lysate samples and subsequently used for downstream enzymatic amplification techniques including endpoint polymerase chain reaction (PCR) and quantitative real-time PCR.
Given the success of SPME toward DNA analysis, the applicability of the PIL-based SPME was also investigated for analysis of yeast RNA samples. The PIL-based sorbent coating featuring carboxylic acid groups within IL monomer and halide-based anions extracted the highest amount of mRNA from aqueous samples compared to analogous PIL sorbent coatings. Under similar experimental conditions, the PIL-based SPME method yielded higher quantities of mRNA for real-time reverse transcription quantitative PCR (RT-qPCR) compared to phenol/chloroform LLE method. The selectivity of PIL-based SPME method toward mRNA analysis was improved by modifying the surface composition of a commercial poly acrylate (PA) sorbent coating with oligo deoxythymine (dT) that assist in specific capture of mRNA from total RNA samples. The developed oligo dT modified PA-based SPME method extracted low quantity of mRNA compared to commercial silica-based SP
Nacham, Omprakash, "Synthesis of new classes of ionic liquids and their utilization in biological and pharmaceutical analysis" (2017). Graduate Theses and Dissertations. 15587.