The main objectives of the research presented in this thesis were to understand mechanistic aspects of the photochemistry of ferritin (Ftn) and bioconjugates that consisted of Ftn linked to gold nanoparticles (AuNPs). The photochemistry investigated in this thesis repurposed Ftn from its role in biological systems as an iron-sequestration protein to potential applications in photocatalysis and nanobiomedicine. The first phase of the thesis research developed a mechanistic understanding of the underlying mechanisms involved in the photochemistry of Ftn with relevance to photocatalysis. In particular, research was designed to determine whether the light-induced bandgap excitation of the semiconductor core of horse-spleen ferritin (HSFtn) resulted in electron transfer from the inorganic core to aqueous redox active reactant via electron transport through the 2 nm thick shell of HSFtn. To investigate this mechanistic pathway, 4-5 nm copper (hydr)oxide nanoparticles were mineralized within the internal volume of HSFtn (CuFtn). It was shown that, unlike the native iron oxyhydroxide-bearing (Ferrihydrite; Fh) Ftn, the visible light photoexcitation of the inorganic core of CuFtn (measured optical bandgap to be 3.65 eV) did not exhibit any release of redox-active metal cation from the HSFtn cage into solution. By photoexciting CuFtn in the presence of aqueous chromate (Cr(VI)) it was shown that the Cr(VI) underwent reduction to Cr(III) in solution. The research strategy eliminated the possibility that metal cations escaping from the HSFtn during photoexcitation could be responsible for Cr(VI) reduction. Hence, the research showed for the first time that electrons resulting from a photoexcited metal oxide core of Ftn could transfer through the protein shell to reduce an aqueous redox active reactant. The research also investigated the wavelength-dependent photochemistry of CuFtn to show that bandgap excitation was indeed responsible for the electrons that transfer across the protein shell. In a second project, the research investigated the bioconjugation of anisotropic AuNPs—gold nanorods (AuNRs) and gold nanostars (AuNSs)—to human H-type ferritin (HFtn). After attaching the AuNRs or AuNSs to HFtn, it was shown that the near-infrared (NIR) radiation excitation of the localized surface plasmon resonance (LSPR) of the AuNR or AuNS conjugated to HFtn led to the activation of the Fh core of the protein. This NIR photochemistry (λ = 850 nm light) resulted in the release of Fe(II) from the Ftn and also led to the reduction of Cr(VI) when it was present in the aqueous phase. The novel synthetic protocols to synthesize the bioconjugates focused on attaching the AuNRs and AuNSs to the solvent-exposed cysteines (Cys) on HFtn. The research also developed techniques for the removal of colloidal stabilizing surfactants, such as cetyltrimethyl ammonium bromide (CTAB), and TritonX-100 (TX-100), from anisotropic AuNPs (AuNR/AuNS) before their attachment to HFtn. The removal of the surfactant was not only important for attachment to the HFtn, but it also removed a cytotoxic species so that the bioconjugates could be used in research that had applications to biomedicine.
Research also investigated synthetic strategies to form bioconjugates that consisted of spherical gold nanoparticles (AuNSps) attached to HSFtn. In contrast to HFtn, HSFtn contains a few solvent exposed Cys groups. Hence, a challenge that was overcome in this research was to populate the outer surface of HSFtn with thiol groups (-SH) so that AuNSps could be attached. To meet this challenge, the surface primary amine-containing amino acids (Lysine) in HSFtn were modified to active Cys using N-succinimidyl S-acetylthioacetate (SATA). After this chemical modification of HSFtn, it was shown that a relatively high density of AuNSps could be attached to HSFtn. This SATA-modified HSFtn bioconjugate system (AuNSp-HSFtn) exhibited the release of Fe(II) at wavelengths of light where λ > 475 nm. In the absence of AuNSp, HSFtn released Fe(II) during exposure to light at wavelengths of light where λ < 475 nm. The activation of the bandgap at longer wavelengths of light (λ > 475 nm) was due to the excitation of the 532 nm plasmon resonance of AuNSp and the presumed transfer of hot electrons to the inner Fh core of HSFtn.
A final project investigated the use of the AuNR-HFtn bioconjugates as a photodynamic strategy utilizing NIR to suppress the growth of cancer cells with the expectation that this process will occur through the mechanism of ferroptosis. We carried out experiments that exposed prostate cancer cells (PC3) to AuNR-HFtn, and during NIR irradiation, they showed the ability to limit the growth of the cells compared to experiments where the cells were exposed to just HFtn or AuNRs. The results suggested that Fe(II) released from the HFtn led to cancer cell death through a process that might be ferroptosis. Future studies will need to investigate this possibility and whether the bioconjugates developed in this thesis will offer a novel therapeutic strategy for cancer/tumor suppression. / Chemistry
| Identifer | oai:union.ndltd.org:TEMPLE/oai:scholarshare.temple.edu:20.500.12613/9508 |
| Date | 07 1900 |
| Creators | Dunuweera, S.P, 0000-0003-0197-423X |
| Contributors | Strongin, Daniel R., Valentine, Ann M., Sun, Yugang, Dmochowski, Ivan J. |
| Publisher | Temple University. Libraries |
| Source Sets | Temple University |
| Language | English |
| Detected Language | English |
| Type | Thesis/Dissertation, Text |
| Format | 275 pages |
| Rights | IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available., http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | http://dx.doi.org/10.34944/dspace/9470, Theses and Dissertations |
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