A Study of structures and the binding in cationized host-guest complexes in the gas phase

Chen, Yanyang (2025) A Study of structures and the binding in cationized host-guest complexes in the gas phase. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Studying host-guest complexes in the gas phase provides a way to understand the intrinsic properties of the non-covalent interactions between hosts and guests. Two hosts were studied in the current thesis. One is 1,1,n,n-tetramethyl[n](2,11)teropyrenophane (TMnTP, n=7, 8 ,9), synthesized by Dr. Bodwell’s group, in which the non-planar teropyrene of TMnTP molecules allow alkali metal cations and protonated glycine to associate. The other types of hosts are ethers, including ortho-, meta-, para- and bridge- tetra anisole (TA) substituted anthraquinodimethane (AQ), namely o-TAAQ, m-TAAQ p-TAAQ and b-TAAQ, synthesized by Dr. Zhao’s group. The oxygen atoms, as well as the π electrons enable complexation with alkali metal cations. These cationized host-guest complexes were electrosprayed and isolated in the Fourier-transform ion cyclotron resonance (FT-ICR) cell, which allowed tandem mass spectrometry to be performed in order to explore the structures and unimolecular dissociation chemistries of host-guest complexes. Along with experiments, computational methods were also used to obtain proposed structures and energy information to compare with experimental results. Fragments of the host-guest complexes under sustained off-resonance irradiation collision induced dissociation (SORI-CID) were analyzed. The fragments of M⁺(TMnTP) (M = K, Rb, Cs) complexes are alkali metal cations and TMnTP, whereas the fragments of protonated glycine (GlyH⁺)/TMnTP complexes were Gly and protonated TMnTP. Energy resolved SORI-CID provided relative gaseous stabilities of the host-guest complexes. Two species (endo- and exo- guests/hosts) were observed in both the M⁺(TMnTP) and GlyH⁺/TMnTP by the means of blackbody infrared radiative dissociation (BIRD). Structures with guests associating the host at different sites were proposed and computed using density functional theory (DFT). In this research, only M⁺(TMnTP) dissociated under infrared multiphoton dissociation (IRMPD) in the range of 3150 cm⁻¹ to 2700 cm⁻¹. The experimental IRMPD spectra of M⁺(TMnTP) agreed well with the computed infrared (IR) spectra of endo-M⁺(TMnTP). Additionally, the non-covalent interactions between GlyH⁺ and TMnTP were a little more complicated thus they were visualized using the independent gradient model based on Hirshfeld partition (IGMH), and the nature of these non-covalent interactions were analyzed by natural energy decomposition analysis (NEDA). It showed a strong ion-induced dipole interaction within endo-protonated glycine TMnTP complexes. As for M⁺(TAAQ) complexes (M = Na, K, Rb, and Cs), they decompose to M⁺ and TAAQ under SORI-CID experiments except lithiated TAAQ and sodiated o-TAAQ. The relative gas phase stabilities of M⁺(TAAQ) were determined both experimentally resulting in the following series Na⁺(TAAQ) > K⁺(TAAQ) > Rb⁺(TAAQ) > Cs⁺(TAAQ). This agreed with the results of NEDA analysis that the interactions between alkali metal cations and TAAQ are electrostatic. The structures of M⁺(TAAQ) complexes were explored using DFT method.

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