In this dissertation, I used Fourier transform ion cyclotron resonance mass spectrometry (FTICR) and ion mobility spectrometry (IMS) to study the structure and energetics of supramolecular complex ions in the gas phase. Using the CRAFTI (cross sectional areas by Fourier transform ion cyclotron resonance) technique developed by Dearden’s lab we observed that complexes with alkali cations capping the portals of cucurbit[5]uril (CB[5]) bind halide anions size-selectively in the gas phase. Our data suggest that Cl– binds inside the CB[5] cavity, Br– binds both inside (with Na+ions capping the portals of CB[5]) and outside (when K+caps CB[5]), and I– binds weakly outside. Although geometry optimization at the M06-2X/6-31+G* level of ab initio theory suggests internal anion binding is energetically favored over external binding, we believe the externally-bound complexes observed experimentally must be due to large energetic barriers hindering the passing of large anions through the CB[5] portal, preventing access to the interior. Calculation of the barriers to anion egress using MMFF//M06-2X/6-31+G* theory supports this idea. Collision cross section (CCS) measurements using the CRAFTI method for CB[5] complexes with various alkali metals and different neutral guests (methanol, ethanol, formic acid, and acetonitrile) along with the results of mass spectra from FTICR show that both the sizes and the resulting charge densities of the alkali metal ions affect the relative tendency of the guests to bind inside CB[5]. The CCS values suggest that methanol, formic acid, and acetonitrile are internally bound CB[5] while ethanol is bound outside the CB[5] host. The relative abundances of the paired peaks in the obtained mass spectra indicate that the inclusion of formic acid and methanol are enhanced when K+ ions cap the complexes, whereas the inclusion of acetonitrile is enhanced when Cs+ ions cap the complexes. The relative abundance of ethanol complexes increases when Na+ ions cap the complexes. CRAFTI CCS values for singly- and doubly-charged cucurbit[n]uril (n = 5, 6, and 7), decamethylcucurbit[5]uril (mc5), and cyclohexanocucurbit[5]uril (CB*[5]) complexes of alkali metal cations (Li+-Cs+) show +2 complex ions have CCS values ranging between 94-105% of those of their +1 counterparts (increasing with metal ion size). These results are consistent with CCS values were calculated using the projection approximation (PA). Ion mobility measurements of the same complexes find the CCS of +2 complexes to be in all cases 9-12% larger than those of the corresponding +1 complexes, with little metal ion dependence. Trajectory method (TM) calculations of CCS for the same structures consistently yield values 7-10% larger for the +2 complexes than for the corresponding +1 complexes and little metal ion dependence which agrees with experimental values.
| Identifer | oai:union.ndltd.org:BGMYU2/oai:scholarsarchive.byu.edu:etd-10718 |
| Date | 08 August 2022 |
| Creators | Heravi, Tina |
| Publisher | BYU ScholarsArchive |
| Source Sets | Brigham Young University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | https://lib.byu.edu/about/copyright/ |
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