Dissertation
Axial Ligation of Surface Confined Porphyrins: Thermodynamics, Kinetics, and Cooperativity
Washington State University
Doctor of Philosophy (PhD), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004530
Handle:
https://hdl.handle.net/2376/124617
Abstract
This work presents a detailed investigation of the influence of solid supports on the axial ligand binding properties of cobalt porphyrins. Molecular resolution scanning tunneling microscopy (STM) imaging combined with theoretical computations reveal how the substrate and intermolecular interactions influence ligand binding affinity, cooperative affects (positive or negative) in the binding affinity of adjacent molecules, and ligand binding kinetics. The results are presented as two main cases studies comparing the binding of 4-methoxypyridine (MeOPY) and 3-phenylthiophene (PhTh), ligands to Co(II)octaethylporphyrin (CoOEP) at the phenyloctane/graphite interface and in solution. Both ligands reversibility bind to CoOEP adsorbed on graphite, but only the MeOPy complex is observed in solution. Ligand affinities (or ΔG) for the different binding processes were determined from the respective equilibrium constants. The free energy value of -13.0±0.3 kJ/mole for the ligation reaction of MeOPy to CoOEP at the solution/graphite interface is less negative than the ΔG for the reaction in solution, -16.8±0.2 kJ/mole. Meaning the MeOPy complex is more stable in solution phase. The graphite was necessary to observe the ligation of CoOEP by PhTh with a free energy value of -4±1 kJ/mole. At the solution/solid interface, the MeOPy system follows a simple Langmuir isotherm whereas the PhTh system follows a Temkin isotherm. The Langmuir isotherm is appropriate from systems with non-interacting surface sites while the Temkin isotherm accounts for cooperative interactions. Nearest neighbor analysis of the ligation products in the STM images revealed positive cooperative ligand binding behavior for the PhTh-CoOEP at all ligand concentrations, but for MeOPy only at the highest concentration. Density functional computational methods were also employed to explore the energetics of both the solution and surface reactions. Stochastic kinetic analysis of CoOEP oxygenation is also presented. Image movies were used to determine the rate constants for the oxygenation reaction by monitoring the lifetime of the oxygenated state. The rate constants for CoOEP oxygenation are ka = 4.4×10-4 s-1∙torr-1 and kd = 0.017 s-1. Results showed good agreement with previous thermodynamic properties. The work brings new insights to the general principles of affinity and cooperativity in the ligand-receptor interactions at the solution/solid interface.
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Details
- Title
- Axial Ligation of Surface Confined Porphyrins
- Creators
- Kristen Nicole Johnson
- Contributors
- Ursula Mazur (Advisor)Kerry W. Hipps (Advisor)James A Brozik (Committee Member)Qiang Zhang (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Chemistry, Department of
- Theses and Dissertations
- Doctor of Philosophy (PhD), Washington State University
- Publisher
- Washington State University
- Number of pages
- 171
- Identifiers
- 99900882927401842
- Language
- English
- Resource Type
- Dissertation