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The synthesis of porphyrins for the study of self-replication and supramolecular assemblies

Clixby, Gregory David (2017) The synthesis of porphyrins for the study of self-replication and supramolecular assemblies. PhD thesis, University of Sheffield.

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Abstract

The research conducted into porphyrin interactions and assemblies has been explored for several applications and functions. The concept of self-replication and a brief overview of porphyrin materials form the basis of the main introduction to the research, while further introductory sections are found at relevant sections, corresponding to the area of study investigated. The primary area of study focused on the synthesis of a porphyrin dimer, which, along with chaperone ligands, would be capable of acting as a self-replicating template for active monomeric porphyrin building blocks. Linear and non-linear porphyrin dimers were synthesised from their corresponding monomer porphyrin feedstock, and zinc centres inserted to facilitate binding to the ligands. UV titration studies with the porphyrin dimers and ligands determined that the binding for complex formation was non-cooperative, and diffusion NMR confirmed the presence of small complexes in solution of a size corresponding to a porphyrin-ligand duplex: roughly twice the size of porphyrin dimer alone. Self-replicating and templating reactions revealed no increase in reaction rate or product yield, relative to uncatalysed bimolecular reaction. Despite this, the research in this project provided valuable insight into the requirements for designing a successful porphyrin replicating system. Some preliminary studies into these ideas were initiated, leading to interesting results for future exploration. A further field of investigation examined the binding between a linear porphyrin dimer and polydentate pyridyl ligands of differing geometries. This work aimed to determine the most favourable complex formed between a trigonal pyridyl ligand and porphyrin dimer. The association of the porphyrin-ligand complex was probed by UV binding studies, and displayed a small increase in Ka for bidentate and tridentate trigonal pyridyl moieties, relative to the binding of a mono-pyridyl ligand. Analysis of the complex by diffusion NMR determined the most stable complex present was a supramolecular hexamer approximately three times the size of porphyrin dimer alone. The final area of research, conducted alongside other members of the group, targeted the self-assembly of a multiporphyrin-macromolecular scaffold complex. This aspect of the project focused on confirming the complex assembly using dimeric and monomeric porphyrins coordinating to the multiple pyridyl sites at the periphery of the hyperbranched polymer scaffold. UV titrations showed an increase in binding to polymer using porphyrin dimer relative to monomer, further suggesting pyridine sites are located at the polymer termini. In addition, diffusion NMR results determined that the complex had a slightly slower rate of diffusion than hyperbranched polymer alone.

Item Type: Thesis (PhD)
Keywords: Porphyrin, self-replication, supramoleculer assembly, ligand, light-harvesting
Academic Units: The University of Sheffield > Faculty of Science (Sheffield) > Chemistry (Sheffield)
Identification Number/EthosID: uk.bl.ethos.739863
Depositing User: Mr Gregory David Clixby
Date Deposited: 30 Apr 2018 10:54
Last Modified: 12 Oct 2018 09:53
URI: http://etheses.whiterose.ac.uk/id/eprint/20125

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