Browsing by Author "Silva, C. R. De"

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    Europium-doped calcium fluoride nanoparticles coated with melanocortin stimulating hormone-4 for potential biomedical imaging
    (2021) Silva, C. R. De; Fratarcangeli, M.; Rathbone, M. R.; Hendren, S.
    Lanthanide-based nanomaterials have promising applications including high throughput drug screening, bio-analytical sensing, and biomedical imaging. Among many lanthanide-based nanomaterials, europium (III) ions are of particular interest in biological assays due to their long luminescent lifetimes, limited photobleaching, monochromatic emission at 614 nm, and large Stokes shifts. Compared to well-known lanthanide-doped matrices such as yttrium fluoride and lanthanum fluoride, calcium fluoride matrix has shown to have promise as an imaging agent due to their greater luminescent efficiency and high biocompatibility. This work focuses on synthesizing novel europium-based nanomaterials and functionalization of the surface of the nanoparticles with a melanocortin stimulating hormone (MSH-4) peptide targeting human cells expressing human melanocortin receptors (hMCRs). A microwave-based synthetic method was optimized to prepare europium-doped calcium fluoride nanoparticles with a controlled size distribution in the 100-120 nm range. The optimized parameters include a pH of 6, reaction time of 30 minutes at a microwave power of 100W. Control over size distribution of the nanoparticles was achieved by adjusting the initial reactant ratios. The nanoparticles were characterized by using powder X-ray diffraction (XRD), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), luminescent spectroscopy (UV-Vis), and transmission electron microscopy (TEM). The melanocortin stimulating hormone (MSH-4) peptide was synthesized using the standard solid phase peptide synthesis method and characterized using LCMS and was determined to be 67% pure. The europium-based nanoparticles were functionalized with the MSH-4 peptide which is an agonist for hMCRs. Further research will be carried out to investigate the potential of using peptide functionalized nanoparticles for biomedical imaging.
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    Luminescent studies of europium (III) fluorobenzoic acid derivatives: Correlating the calculated electronic energies and the experimental luminescent efficiencies through computational studies
    (Faculty of Science, University of Kelaniya, Sri Lanka, 2021) Silva, C. R. De; Fratarcangeli, M.
    Europium (III)-based luminescent complexes promise extensive potential applications in immunoassay technology, high throughput drug screening, organic light emitting diodes (OLEDs), and biomedical imaging. Europium-ligand complexes present unique properties such as monochromatic emission at 614 nm, long luminescent lifetimes enabling time-resolved measurements, minimal photobleaching, and large Stokes shifts. Ligand design for enhancing the quantum efficiency of europium complexes is currently active. For this reason, it is important to understand the electronic mechanisms that allow europium-metal complexes to fluoresce. Here, we report the structural and spectroscopic properties of a series of europium (III) complexes containing fluorobenzoic acid derivatives using density functional theory calculations. Calculations were carried out using the B3LYP method and 6-31G* and 6-311+G** basis sets. Upon increasing the ligand fluorination, the absorption maximum wavelength shows a blue shift. Excited state energy gaps of the complexes were found to be sensitive to the identity and the position of the ligand substituents. A nitro substitution results in a decrement of the vertical excited states, significantly reducing the luminescent quantum yield. The inter-system crossing energy gap is strongly regulated by the position of the ligand substituent. It is significantly reduced by having substituents closer to the metal coordination site. The optimum energy gaps resulting in enhanced luminescent quantum yields were identified. The correlation among the calculated experimental luminescent quantum yields and the calculated electronic energy levels will be discussed to provide insight into designing highly luminescent europium complexes.