Edge functionalisation of graphene nanoribbons with a boron dipyrrin complex : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nanoscience at Massey University, Manawatū, New Zealand

Chemical modification can be used to tune the properties of graphene and graphene nanoribbons, making them promising candidates for carbon-based electronics. The control of edge chemistry provides a route to controlling the properties of graphene nanoribbons, and their self-assembly into larger structures. Mechanically fractured graphene nanoribbons are assumed to contain oxygen functionalities, which enable chemical modification at the nanoribbon edge. The development of graphene nanoribbon edge chemistry is difficult using traditional techniques due to limitations on the characterisation of graphene materials. Through the use of a chromophore with well-defined chemistry, the reactivity of the edges has been investigated. Small aromatic systems were used to understand the reactivity of the boron dipyrrin Cl-BODIPY, and with the aid of spectroscopic and computational methods, the substitution mechanism and properties of the compounds have been investigated. The synthetic procedure was then applied to graphene nanoribbons. Results from infrared and Raman spectroscopy studies show that edge-functionalisation of graphene nanoribbons with BODIPY was successful, and no modifications to the basal plane have been observed

New AMD3100 derivatives for CXCR4 chemokine receptor targeted molecular imaging studies: synthesis, anti-HIV-1 evaluation and binding affinities

CXCR4 is a target of growing interest for the development of new therapeutic drugs and imaging agents as its role in multiple disease states has been demonstrated. AMD3100, a CXCR4 chemokine receptor antagonist that is in current clinical use as a haematopoietic stem cell mobilising drug, has been widely studied for its anti-HIV properties, potential to inhibit metastatic spread of certain cancers and, more recently, its ability to chelate radiometals for nuclear imaging. In this study, AMD3100 is functionalised on the phenyl moiety to investigate the influence of the structural modification on the anti-HIV-1 properties and receptor affinity in competition with anti-CXCR4 monoclonal antibodies and the natural ligand for CXCR4, CXCL12. The effect of complexation of nickel(II) in the cyclam cavities has been investigated. Two amino derivatives were obtained and are suitable intermediates for conjugation reactions to obtain CXCR4 molecular imaging agents. A fluorescent probe (BODIPY) and a precursor for 18F (positron emitting isotope) radiolabelling were conjugated to validate this route to new CXCR4 imaging agents

Boron Dipyrromethenes: Synthesis and Computational Analysis

Recently, there has been a growing interest in the boron dipyrromethene (BODIPY, 4,4′- difluoro-4-bora-3a,4a-diaza-s-indacene) compounds. BODIPY compounds have fascinating properties that allow for the absorption and emission of light in the near infrared region of the electromagnetic spectrum. These molecules are highly modifiable making them ideal chemicals for the use of photoelectric energy conversion such as for commercial use in dye sensitized solar cells (DSSCs). It has been previously shown that different meso compounds have only a slight effect on the absorptive capabilities of these BODIPY compounds. We believe that the BODIPY compounds’ lack of planarity is one of the major obstacles in more efficient absorption in the NIR and IR regions. Because of this, we focused on modifying recently synthesized BODIPY compounds in an attempt to align their meso group with the rest of the compound’s framework. Synthesis of various BODIPY compounds was attempted in order to perform the ring fusion reaction between the meso group and the body of the compound. Computational analysis on several BODIPY compounds was performed with several setups and the results were compared to x-ray crystallography from the literature

Prolonged and tunable residence time using reversible covalent kinase inhibitors.

Drugs with prolonged on-target residence times often show superior efficacy, yet general strategies for optimizing drug-target residence time are lacking. Here we made progress toward this elusive goal by targeting a noncatalytic cysteine in Bruton's tyrosine kinase (BTK) with reversible covalent inhibitors. Using an inverted orientation of the cysteine-reactive cyanoacrylamide electrophile, we identified potent and selective BTK inhibitors that demonstrated biochemical residence times spanning from minutes to 7 d. An inverted cyanoacrylamide with prolonged residence time in vivo remained bound to BTK for more than 18 h after clearance from the circulation. The inverted cyanoacrylamide strategy was further used to discover fibroblast growth factor receptor (FGFR) kinase inhibitors with residence times of several days, demonstrating the generalizability of the approach. Targeting of noncatalytic cysteines with inverted cyanoacrylamides may serve as a broadly applicable platform that facilitates 'residence time by design', the ability to modulate and improve the duration of target engagement in vivo

Synthesis and Biological Characterization of a New Norbormide Derived Bodipy FL-Conjugated Fluorescent Probe for Cell Imaging

Background: Norbormide (NRB) is a selective rat toxicant endowed with vasoconstrictor activity confined to the rat peripheral arteries. In a recent work we used a fluorescent derivative of NRB (NRB-AF12), obtained by coupling the NBD fluorophore to the parent molecule via a linker, in order to gain information about the possible site of action of the unlabeled compound. We found that NRB-AF12 labeled intracellular organelles in both NRB-sensitive and -insensitive cells and we accordingly proposed its use as a scaffold for the development of a new class of fluorescent probes. In this study, we examined the fluorescent properties of a BODIPY FL-conjugated NRB probe (MC009) developed: (A) to verify if NRB distribution could be influenced by the attached fluorophore; (B) to improve the fluorescent performance of NRB-AF12. Methods: MC009 characteristics were investigated by confocal fluorescence microscopy, in freshly isolated rat caudal artery myocytes (FIRCAM) and in LX2 cells, representative of NRB-sensitive and insensitive cells, respectively. Main results: In both FIRCAM and LX2 cells MC009 stained endoplasmic reticulum, mitochondria, Golgi apparatus and lipid droplets, revealing the same intracellular distribution as NRB-AF12, and, at the same time, had both improved photostability and gave a more intense fluorescent signal at lower concentrations than was possible with NRB-AF12, which resulted in a better and finer visualization of intracellular structures. Furthermore, MC009 was effective in cellular labeling in both living and fixed cells. At the concentration used to stain the cells, MC009 did not show any cytotoxic effect and did not affect the regular progression of cell cycle and division. Conclusions: This study demonstrates that the distribution of fluorescently labeled NRB is not affected by the type of fluorophore attached to the parent compound, supporting the idea that the localization of the fluorescent derivatives may reasonably reflect that of the parent compound. In addition, we observed a marked improvement in the fluorescent properties of BODIPY FL-conjugated NRB (MC009) over its NBD-derived counterpart (NRB-AF12), confirming NRB as a scaffold for the development of new, high performance, non-toxic fluorescent probes for the labeling of intracellular structures in both living and fixed cells

Novel photobase generators for photoinduced polymerization and pH regulation

Photochemistry encompasses the investigation of chemical processes instigated by light absorption. As important branches of photochemistry, photosensitive and optical materials have attracted extensive research interests in both academia and industry. Photosensitive and optical materials are composed of polymers / small molecules with photo-responsive properties. These materials not only can absorb light in the desired energy spectrum, but also exhibit chemical / physical reactions, which can be applied to different fields such as photoredox, photo-heat, phototherapy, solar cells, diodes, etc. Among them, photobase generators (PBGs) are a series of photosensitive compounds, which absorb the incident light, then release the basic species that can trigger the consequent reactions such as thiol-Michael reaction and ring-opening polymerization reactions. Boron-dipyrromethene (BODIPY)-based chromophores have emerged as highly intriguing moieties within the realm of chromophores. The prominence is attributed to its remarkable properties, including a high fluorescent quantum yield, pronounced chemical stability, and minimal Stokes shift. The core structures of BODIPY have been subject to thorough investigations and refinements, resulting in the development of a spectrum of BODIPY derivatives that find applications within the domain of chemical synthesis and biological science. In this work, three projects about BODIPY-based photobase generators are included with demonstration and discussion of their bio-applications. Firstly, BODIPY based PBGs are synthesized and the photochemical/photophysical properties are characterized. Secondly, the applications of BODIPY based PBGs in photoinduced thiol Michael reaction and ring-opening reaction are explored. Thirdly, the feasibility of using PBGs in lysosome pH regulation light is demonstrated and the potential usage in cancer therapy is discussed

Synthesis and Characterization of Alkynyl-Substituted Boron Formazanate Dyes

This thesis outlines the synthesis and characterization of the first alkynyl-substituted boron formazanate complexes and explores the electronic and structural changes that occur in these systems as a result of chemical modification at the boron centre. An alkynyl-substituted complex appended with a redox-active handle is also described, and the chemical reduction and oxidation of this system is explored. Finally, a model reaction is examined as a proof of concept toward the post-synthetic modification of these boron formazanate systems through copper(I)-assisted alkyne-azide cycloaddition chemistry. Exploiting chemistry at the boron centre opens up new possibilities toward incorporating function onto the boron formazanate scaffold

Synthesis and characterization of new light emitting probes for sensitive detection of bio-molecules and live cells

A variety of contemporary analytical platforms in technical and biological applications take advantage of labeling the objects of interest with fluorescent or luminescent tracers. Luminescent tracers take advantage of the unique property of some lanthanide metals to absorb and emit light. Long lifetime of lanthanide emission allows temporal gating of the signal, which avoids the short-lived background of interfering sample components. This property in combination with large Stokes shift contributes to extreme sensitivity of detection (ca. 10-13-10-14 M), which makes lanthanide-based probes suitable for large variety of challenging tasks ( e.g., intracellular detection of single DNA/RNA, or protein molecules, microbial pathogen detection in human specimens, tracing analysis, etc.). Luminescent probes include antenna fluorophore that absorbs light and transfers the excitation energy to a lanthanide metal tethered to antenna through chelation. The probe also contains crosslinking group that allows covalent labeling of the molecule of interest. Despite great potentials of lanthanide-based tracers the wide spread of the technology is impeded by very high price of commercially available probes to their complex structure. The goal is to develop novel approaches for the synthesis of lanthanide probes with improved quantum efficiency. This work discusses development of new strategies for synthesis of antena-fluorophores, development of new methods for introduction of the crosslinking groups in the luminescent probes and elucidates the mechanisms of chemical reactions leading to principal synthetic intermediates. New quinoline and quinolone based fluorescent compounds were synthesized, whose light emission can be conveniently tuned by simple structural modifications. Developed probes represent high-quantum yield, large Stokes shift fluorophores with amine-reactive and click-reactive groups convenient for conjugation. Some of these compounds can be used as sensitizers for lanthanide emission in design of highly sensitive luminescent probes. Obtained probes demonstrate efficient derivatization reactions allowing introduction of amine- or click-reactive crosslinking groups into the fluorophores. The reactivity of synthesized compounds is confirmed in reaction with low molecular weight nucleophiles as well as with click-reactive DNA-oligonucleotide counterparts. These reactive derivatives can be used for covalent attachment of the fluorophores to various biomolecules of interest including nucleic acids, proteins, live cells and small cellular metabolites. Synthesized compounds were characterized using N MR, steady-state and time-resolved fluorescence spectroscopy, as well UV absorption spectroscopy. This work also discusses the development of fluorescent derivatives of the antifungal drugs, posaconazole and caspofungin, for diagnostic imaging of fungal cells. Invasive fungal infections (IFI’s) are a growing threat to human health particularly, with increase in the number of immune-compromised patient population, such as organ transplant recipients, al logeneic B MT, hematologic cancers; AIDS etc. The diagnosis of fungal infections is a complicated task and requires a combination of clinical observations, laboratory investigation, and radiological or other diagnostic imaging methods. Only 25% of I FI cases are diagnosed pre-mortem due to the current diagnostic challenges, which justifies the development of express diagnostic procedures. To address the issue fluorescent derivatives of the antifungal drugs, posaconazole and caspofungin, were synthesized. The fluorescent derivatives retained strong and highly specific binding to their cellular targets rendering the cells fluorescent. This new affinity-based approach strongly facilitates the detection of fungal pathogen thereby overcoming the current diagnostic challenges and can be used for clinical diagnostics. The power of this approach is not limited to fungal pathogens, but in fact represents a broader platform useful for detection of other classes of infections, both in the biological specimens and in the whole body using contemporary 3-D imaging approaches like fluorescence based in vivo imaging, luminescence imaging, positron emission tomography approach, and computer-assisted X-ray tomography

DDAO Controlled Synthesis of Organo-Modified Silica Nanoparticles with Encapsulated Fluorescent Boron Dipyrrins and Study of Their Uptake by Cancerous Cells

The design of cargo carriers with high biocompatibility, unique morphological characteristics, and capability of strong bonding of fluorescent dye is highly important for the development of a platform for smart imaging and diagnostics. In this paper, BODIPY-doped silica nanoparticles were prepared through a "one-pot" soft-template method using a sol-gel process. Several sol-gel precursors have been used in sol-gel synthesis in the presence of soft-template to obtain the silica-based materials with the most appropriate morphological features for the immobilization of BODIPY molecules. Obtained silica particles have been shown to be non-cytotoxic and can be effectively internalized into the cervical cancer cell line (HeLa). The described method of synthesis allows us to obtain silica-based carriers with an immobilized fluorescent dye that provide the possibility for real-time imaging and detection of these carriers

Near infrared fluorescence probes : towards applications in fluorescence guided surgery

Surgery has been a popular method for the treatment of cancers, in particular solid tumours; but the surgical margins for cancerous tissues are often indistinct and in most cases, the poor identification of residual cancer tissues can result in re-excision. Therefore, near infrared (NIR) fluorescence-guided surgery (FGS) is being developed as a real time intra-operative imaging technique to assist surgeons by improving the accuracy and precision of the removal of tumours.However, current FDA approved fluorophores suffer from poor chemical stability, limited water-solubility, and lack selectivity toward neoplastic tissue, limiting their clinical application. These current challenges have led to the development of new and improved fluorophores capable of absorbing and emitting light at NIR wavelengths, negating autofluorescence and improving deeper light transmission.Throughout this project, a series of BODIPYs, aza-BODIPYs and bacteriochlorins were synthesised and developed for bioimaging applications. Despite many of them showing interesting fluorescence properties, the investigation suggested aza-BODIPYs were the most promising red / NIR fluorophores (λem 600-700 nm) due to their excellent photostability. Methods have been developed to incorporate functionalities suitable for bioconjugation.Different bioconjugation strategies have been explored to covalently conjugate the NIR fluorophores to a clinically relevant protein, peptide and antibody under mild conditions. The viability of aza-BODIPY conjugates against biological targets were investigated and a range of other novel targeted NIR fluorophores were successfully developed. In vitro fluorescence imaging was subsequently carried out to demonstrate the enhanced selectivity of the targeting NIR fluorophores toward overexpressed receptors on various cancer cells lines.This project has demonstrated the potential of aza-BODIPY in biological imaging and developed targeted NIR fluorophores. Further biological evaluation is progressing with the eventual aim of developing a pre-clinical model for NIR FGS in oncology