Molecular Design of Viologens to Exhibit Low-Order Liquid-Crystalline Phases

Viologens that are useful as stimulus-responsive compounds and exhibit a low-order liquid-crystalline (LC) phase at relatively low temperatures (approximately 20 °C), can be developed into materials that combine the redox...

Organised Functional Liquids for Photon Upconversion

<p>Photon upconversion is a process by which lower energy photons are converted to higher energy photons, which can be achieved by the interaction of two triplet excited states. This process holds potential for wavelength shifting solid films in photovoltaic cells. Not all wavelengths emitted by the sun have sufficient energy to be utilized by such devices. Typical solar cells have a band gap of around 1 µm, however there is a significant amount of energy output by the sun that falls below this threshold. Upconversion could lead to more efficient use of energy by converting these lower energy wavelengths to wavelengths that could be directly absorbed by the solar panel. Upconversion has thus far been harnessed in solution, where diffusion is the limiting factor for the efficiency of the process. However, for technological applications it would be better to create thin solid films. In these films, molecules would have to be brought within the distance on which upconversion occurs, as the process would no longer be defined by diffusion. One way to achieve this would be to create liquid crystalline derivatives of upconversion emitter molecules. This would provide ordering in the system, which would enhance electronic coupling and bring molecules within the scale on which upconversion occurs. The work of this thesis has focused on the synthesis of these organised functional liquids: liquid crystals of common upconversion emitter molecules. 9,10-diphenylanthracene (DPA) and 9,10-bis(phenylethynyl)anthracene (BPEA) are popular emitter molecules, and derivatives of these molecules were synthesized. A variety of alkyl chains were attached with or without phenyl linkers. The alkyl chains would provide entropy to the system in order to induce the formation of liquid crystalline phases. The resulting phase behaviour of these derivatives was studied using differential scanning calorimetry (DSC) and polarised optical microscopy (POM). Eight novel derivatives of DPA and BPEA were synthesized. New information was gained as to the requirements of inducing liquid crystallinity in these dye molecules. Direct addition of chains symmetrically to the central dye molecules did not result in the formation of liquid crystalline phases. Through extension of the central core by an extra phenyl ring a liquid crystalline behaviour was observed. A synthesized derivative of DPA exhibited extreme supercooling, which is one of a few derivatives of 9,10-diphenylanthracene to exhibit a liquid state at room temperature. A derivative of BPEA was synthesized that exhibited formation of a mesophase (liquid crystal phase). These two derivatives were investigated for potential use as a material for upconversion.</p>

Organised Functional Liquids for Photon Upconversion

<p>Photon upconversion is a process by which lower energy photons are converted to higher energy photons, which can be achieved by the interaction of two triplet excited states. This process holds potential for wavelength shifting solid films in photovoltaic cells. Not all wavelengths emitted by the sun have sufficient energy to be utilized by such devices. Typical solar cells have a band gap of around 1 µm, however there is a significant amount of energy output by the sun that falls below this threshold. Upconversion could lead to more efficient use of energy by converting these lower energy wavelengths to wavelengths that could be directly absorbed by the solar panel. Upconversion has thus far been harnessed in solution, where diffusion is the limiting factor for the efficiency of the process. However, for technological applications it would be better to create thin solid films. In these films, molecules would have to be brought within the distance on which upconversion occurs, as the process would no longer be defined by diffusion. One way to achieve this would be to create liquid crystalline derivatives of upconversion emitter molecules. This would provide ordering in the system, which would enhance electronic coupling and bring molecules within the scale on which upconversion occurs. The work of this thesis has focused on the synthesis of these organised functional liquids: liquid crystals of common upconversion emitter molecules. 9,10-diphenylanthracene (DPA) and 9,10-bis(phenylethynyl)anthracene (BPEA) are popular emitter molecules, and derivatives of these molecules were synthesized. A variety of alkyl chains were attached with or without phenyl linkers. The alkyl chains would provide entropy to the system in order to induce the formation of liquid crystalline phases. The resulting phase behaviour of these derivatives was studied using differential scanning calorimetry (DSC) and polarised optical microscopy (POM). Eight novel derivatives of DPA and BPEA were synthesized. New information was gained as to the requirements of inducing liquid crystallinity in these dye molecules. Direct addition of chains symmetrically to the central dye molecules did not result in the formation of liquid crystalline phases. Through extension of the central core by an extra phenyl ring a liquid crystalline behaviour was observed. A synthesized derivative of DPA exhibited extreme supercooling, which is one of a few derivatives of 9,10-diphenylanthracene to exhibit a liquid state at room temperature. A derivative of BPEA was synthesized that exhibited formation of a mesophase (liquid crystal phase). These two derivatives were investigated for potential use as a material for upconversion.</p>

Experimental Advances in Nanoparticle-Driven Stabilization of Liquid-Crystalline Blue Phases and Twist-Grain Boundary Phases

Recent advances in experimental studies of nanoparticle-driven stabilization of chiral liquid-crystalline phases are highlighted. The stabilization is achieved via the nanoparticles’ assembly in the defect lattices of the soft liquid-crystalline hosts. This is of significant importance for understanding the interactions of nanoparticles with topological defects and for envisioned technological applications. We demonstrate that blue phases are stabilized and twist-grain boundary phases are induced by dispersing surface-functionalized CdSSe quantum dots, spherical Au nanoparticles, as well as MoS2 nanoplatelets and reduced-graphene oxide nanosheets in chiral liquid crystals. Phase diagrams are shown based on calorimetric and optical measurements. Our findings related to the role of the nanoparticle core composition, size, shape, and surface coating on the stabilization effect are presented, followed by an overview of and comparison with other related studies in the literature. Moreover, the key points of the underlying mechanisms are summarized and prospects in the field are briefly discussed.

Highly regioselective surface acetylation of cellulose and shaped cellulose constructs in the gas-phase

Gas-phase acylation of cellulose is an attractive method for modifying the surface properties of cellulosics. However, little is known concerning the regioselectivity of the chemistry, in terms of which cellulose positions are preferentially acylated and if acylation can be restricted to the surface, preserving crystallinities/morphologies. Consequently, we reexplore simple gas-phase acetylation of modern-day cellulosic building blocks – cellulose nanocrystals, pulps, regenerated fibre and aerogels. The gas-phase acetylation is shown to be highly regioselective for the C6-OH, is further supported with computational modelling. This contrasts with liquid-state acetylation, highlighting that the gas-phase chemistry is much more controllable, yet with similar kinetics to the uncatalyzed liquid-phase reactions. Furthermore, this method preserves both the native crystalline structure of cellulose and the supramolecular morphologies of even delicate cellulosic constructs (aerogel exhibiting retention of chiral cholesteric liquid crystalline phases). Therefore, we are convinced that this methodology will lead to more rapid adoption of precisely tailored and cellulosic materials

Liquid-crystalline lipid phase transitions in lipid droplets selectively remodel the LD proteome

Lipid droplets (LDs) are reservoirs for triglycerides (TGs) and sterol-esters (SEs). How lipids are organized within LDs and influence the LD proteome remains unclear. Using in situ cryo-electron tomography, we show that glucose restriction triggers lipid phase transitions within LDs generating liquid-crystalline lattices inside them. Mechanistically, this requires TG lipolysis, which alters LD neutral lipid composition and promotes SE transition to a liquid-crystalline phase. Fluorescence imaging and proteomics further reveal that LD liquid-crystalline lattices selectively remodel the LD proteome. Some canonical LD proteins including Erg6 re-localize to the ER network, whereas others remain on LDs. Model peptide LiveDrop also redistributes from LDs to the ER, suggesting liquid-crystalline-phases influence ER-LD inter-organelle transport. Proteomics also indicates glucose restriction elevates peroxisome lipid oxidation, suggesting TG mobilization provides fatty acids for cellular energetics. This suggests glucose restriction drives TG mobilization, which alters the phase properties of LD lipids and selectively remodels the LD proteome.

Cationic Liposomes as Vectors for Nucleic Acid and Hydrophobic Drug Therapeutics

Cationic liposomes (CLs) are effective carriers of a variety of therapeutics. Their applications as vectors of nucleic acids (NAs), from long DNA and mRNA to short interfering RNA (siRNA), have been pursued for decades to realize the promise of gene therapy, with approvals of the siRNA therapeutic patisiran and two mRNA vaccines against COVID-19 as recent milestones. The long-term goal of developing optimized CL-based NA carriers for a broad range of medical applications requires a comprehensive understanding of the structure of these vectors and their interactions with cell membranes and components that lead to the release and activity of the NAs within the cell. Structure–activity relationships of lipids for CL-based NA and drug delivery must take into account that these lipids act not individually but as components of an assembly of many molecules. This review summarizes our current understanding of how the choice of the constituting lipids governs the structure of their CL–NA self-assemblies, which constitute distinct liquid crystalline phases, and the relation of these structures to their efficacy for delivery. In addition, we review progress toward CL–NA nanoparticles for targeted NA delivery in vivo and close with an outlook on CL-based carriers of hydrophobic drugs, which may eventually lead to combination therapies with NAs and drugs for cancer and other diseases.