The Synthesis and Applications of Porphyrin Containing Polyion Complexes

In recent years, there has been a rapid increase in the application of polyion complexes in the field of medicinal chemistry including the drug carrier of prominent biopharmaceuticals. The interaction between counter-charged biopharmaceuticals and the ionic blockcopolymer, generates the polyion complex. PDT depends mainly on three factors: light, oxygen and photosensitiser (PS). PSs are insoluble in water, toxic, and can be distributed to healthy tissues. This project investigated a methodology of preparing polyion complexes which can overcome these problems and focuses on carrying and delivering PSs which are soluble for targeting only tumour cells. Polyion complexes can be formed via the electrostatic interactions between molecule bearing negative charges (polyanion) and compounds bearing positive charges (polycation). The first part of the thesis describes the synthesis of a series of amphiphilic block copolymers bearing amino groups (methoxypoly(ethylene glycol)-poly(2-dimethyl amino ethyl methacrylate) block copolymer). Synthesis of mPEG-PDMA was carried out in two steps. The first step involved the preparation of a macroinitiator suitable for ATRP- methoxypoly(ethylene glycol) bromoisobutyrate macroinitiator (mPEG-Br). Thereafter, mPEG-Br was reacted with the monomer 2-(dimethyl amino) ethyl methacrylate to generate the amphiphilic block copolymer, mPEG-PDMA, via atom transfer radical polymerisation (ATRP). Aggregation and self-assembly of mPEG-PDMA was investigated through CAC studies using tetraphenyl porphyrin (TPP) and pyrene as probes. As such, CAC around 0.1 mg/mL were determined. In addition, tetracarboxyphenyl porphyrin (TCPP) was prepared for use as the photosensitiser.
The second part of the study prepared the polyion complex from mPEG-PDMA (DB) (positively charged segment) and TCPP (negatively charged molecule) using 1:1 ratios of DB:TCPP at 1:1 (w/w). UV, DLS and TEM, which were used to determine the formation and size of the DB/TCPP polyion complexes. DLS indicated a solvated size of 200-250nm whilst TEM image showed that the particles had a size of 150-200nm. The third part of the project studied the release of TCPP from the DB/TCPP polyion complex at pH 7.4 and pH 5. The results showed that 2% of TCPP was released in pH 7.4 and 4% at pH 5, indicating stable complexes, even in acidic conditions.
The fourth step of this project was the synthesis of hyperbranched polymers bearing a large number of negative charges terminal carboxy groups for use as the anionic component of the polyion complexes. Initially, unfunctionalised hyperbranched polymers (HBP-COOH) was prepared for use as a control. This was successful and the porphyrin cored hyperbranched polymer (PH-HBP-COOH) was then prepared as a globular photosensitiser with many negative charges. Capability of HBP-COOH and PH-HBP-COOH forms a polyion complexes with the mPEG-PDMA, which was then the focus of study. UV, DLS and TEM indicated the successful formation of poly ion complex. The PH-HBP-COOH release from the polyion complex showed that 9% of HBP was released at pH 7.4 and 11% at pH 5. This was much higher than a TCPP release and is attributed to weaker interactions between the hyperbranched polymer and mPEG-PDMA.
The final part focused on the preparation of iron-functionalised porphyrin containing polyions for use in catalysis. DB/ Fe-TCPP and DB/Fe-HBP polyion complexes were then tested as a catalyst for cyclohexene oxidation in water using iodosylbenzene as an oxygen source. The results showed that no oxygenation occurred in this heterogeneous medium.