School of Chemistry - Theses

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Subject: nanoparticles × Author: Karoui, Hedi ×

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    Tailor-made covalent organic-inorganic polyoxometalate hybrids: versatile platforms for the elaboration of novel molecular architectures
    Karoui, Hedi ( 2018)
    Covalent organic-inorganic polyoxometalate (POM or POMs) hybrids constitute versatile platforms for the elaboration of functional molecular architectures. This Ph.D. research project aimed to synthesize novel organic-inorganic POM hybrids using pre- and post-functionalization methods. The synthesis of organic-inorganic hybrids starting from POMs, known as direct functionalization, is a well-established synthetic procedure. However, as the complexity of the targeted functional system increases, a multi-step strategy relying on the post-functionalization of preformed hybrid POMs is necessary. Herein, both approaches are explored. Following hybridization of POM surfaces using organic units, ranging from small groups to large polymeric chains, this work provides a significant step forward in the rational design and synthesis of POMs, which permits the elaboration of POM based nanomaterials. At first, boronic acids and esters ligands were selected for POMs’ post-functionalization. Three organoboron functionalized Anderson-Evans and one organoboron functionalized Lindqvist POM were synthesized using Schiff base chemistry; with the general formulas of the Anderson-Evans POM hybrids being [MnIIIMo6VIO18((OCH2)3)CN=CHC6H4(B(OR)2)2]3− (where R = H, Me), [MnIIIMo6VIO18((OCH2)3)CN=CHC6H4(BO2(CH2)3)2]3-, with the formula of the Lindqvist POM hybrid being [VV6O13{(OCH2)3CN=CHC6H4B(OH)2}2]2-. These compounds have been characterized in the solid state by single-crystal X-ray diffraction (XRD), FT-IR spectroscopy and elemental analysis and in solution using Nuclear Magnetic Resonance (NMR) spectroscopy. This work has further been extended to organosilane functionalized mono and di lacunary Keggin POMs. Two organoboron functionalized Keggin POMs were synthesized using N, N'-dicyclohexylcarbodiimide (DCC) coupling; with the general formulas being [β2-SiW11O39{O(Si(CH2)3NHC=O-C12H17BO2)2}]4- and [γ-SiW10O36{O(Si(CH2)3NHC=OC12H17BO2)2}]4-. These compounds have been characterized in the solid state by FT-IR spectroscopy and elemental analysis and in solution using NMR spectroscopy. Later, the employment of microwave-assisted synthesis permitted the generation of novel mixed metal tris(alkoxo)molybdovanadates. The reaction of [β-Mo8O24]4- and [H3V10O28]3- with pentaerythritol or tris(hydroxymethyl)aminomethane yielded compounds with the general formula [V3Mo3O16(O3-R)]2- where R = C5H8OH or C4H6NH2. Post-synthetic esterification of the alcohol derivative yielded the acylated derivative [V3Mo3O16(O3-R)]2- where R = C7H11O2. Single-crystal X-ray Diffraction (XRD), NMR spectroscopy, High-Resolution Mass Spectrometry (HR-MS) and FT-IR spectroscopy have been used in combination to rationalize the structural isomerization observed within these systems. The rational design and synthesis of two novel covalent organic-inorganic hybrid polymers via Atom Transfer Radical Polymerization (ATRP), composed of either a Lindqvist POM macro initiator of formula [V3Mo3O19{(OCH2)3CNHC=OC(CH3)2Br}]2- or an Anderson-Evans POM macro initiator of formula [MnIIIMo6O18{(OCH2)3CNHC=OC(CH3)2Br}2]3- and pH-responsive poly(2 (diethylamino)ethyl methacrylate) (PDEAEMA) polymer, was investigated. POM macro initiators were characterized using single-crystal X-ray diffraction (XRD), 1H NMR spectroscopy, FT-IR spectroscopy, UV-Vis and elemental analysis; while POM-polymer hybrids were characterized using 1H NMR spectroscopy, FT-IR spectroscopy, thermogravimetric analysis (TGA) and UV-Vis spectroscopy to assess the integrity of the POM units. These POM-polymer hybrids self-assemble into nanoparticles via copolymerization with poly(2-(diethylamino)ethyl methacrylate)-b-poly(ethylene glycol) (PDEAEMA-b-PEG), when the pH is increased above the pKa of PDEAEMA. Dynamic Light Scattering (DLS) studies were conducted to investigate the size distribution of the nanoparticles, while disassembly studies proved that they respond to biologically relevant pH variations. These observations were supported by Cryo-TEM imaging which provided valuable direct visualization of the nanoparticles. Importantly, growing polymer chains from POM macro initiators offers an excellent control over the loading of the POM clusters inside the nanoparticles.