Date of Award
Doctor of Philosophy
Daniel W. Armstrong
R. S. Houk
This dissertation focuses on two different areas of analysis: liquid chromatography (LC) enantiomeric separations and the detection of anions using electrospray ionization mass spectrometry (ESI-MS) and LC-ESI-MS.
Enantiomeric separations of two distinct classes of chiral compounds were investigated. The first class is pterocarpans, which are isoflavanoids with cis-fused benzopyran benzofuranyl structures. In the reverse phase mode of operation, all pterocarpan enantiomers could be separated using cyclodextrin based chiral stationary phases (CSPs) with hydroxypropyl-β-cyclodextrin, acetyl-β-cyclodextrin, and γ-cyclodextrin showing the broadest enantioselectivity. Two macrocyclic glycopeptide CSPs, ristocetin A and vancomycin also proved useful in the reverse phase mode. Not as many separations were achieved in the normal phase mode for either set of CSPs.
Chiral extended metal atom chains (EMACs) were first synthesized by F.A. Cotton and co-workers as the smallest possible molecular wires. It was not possible to resolve these enantiomers by crystallization and derivatization was impossible. The vancomycin macrocyclic glycopeptide stationary phase proved to be the best approach for separating these unusual chiral entities. Partial or baseline separation of 5 helical EMAC racemates was achieved in the polar organic mode or normal phase mode chromatography. In chapter 4, vibrational circular dichroism (VCD) is used to assign the absolute configuration of Ni3(dipyridylamine)4Cl2.
Negative mode ESI-MS of anions can be problematic due to spray stability and background noise issues. The use of a positively charged reagent which pairs with the anion allows for the detection of anions in positive mode ESI-MS. Singly charged anions can be paired with dicationic reagents, while doubly charged anions can be paired with tricationic reagents to result in an overall +1 charged complex. In this dissertation, a variety of linear tricationic reagents were examined to determine which structural features are important for anion detection. The application of linear tricationic reagents and previously reported trigonal tricationic reagents were then applied to the detection of a larger variety of divalent anions (e.g. disulfonates, dicarboxylates) and bisphosphonates, which are a class of drug used to treat bone diseases. The use of MS-MS and LC-ESI-MS are also discussed.
Warnke, Molly, "Enantiomeric separations of natural compounds and metal complexes and the detection of anions using positive mode electrospray ionization mass spectrometry" (2008). Graduate Theses and Dissertations. 11152.