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Light addressable machinery translation to lipid membrane structures is highly desirable for a variety of uses such as liposome drug or imaging agent delivery, membrane-bound photosynthesis analogues, etc., but little is known in this area. This thesis focuses on two objectives: the translation of triplet-triplet annihilation upconversion (TTA-UC) to liposomal systems and the use of MSLBs as tools to interrogate the behaviour of photosensitizers in these systems using surface sensitive methods. TTA-UC produces high-energy photon from low- energy excitation via Dexter energy transfer mechanism between photosensitizer and annihilator. TTA-UC uses low-power non-coherent light sources to produce anti-Stokes emission. It thus holds significant potential for photoactivated drug delivery and biological imaging since it can be stimulated using low-frequency light that penetrates biological tissue. Incorporating molecular elements into liposomes and TTA-UC in cell membranes can help biological applications and treatment without harming other organs. However, TTA-UC in a liposome or cell membrane is difficult and requires appropriate photosensitizer and annihilator that can be co-confined to the membrane and where their collisional energy transfer is supported. This thesis explores TTA-UC in solution and lipid bilayer membrane using BODIPY- and Ru(II) complex-based photosensitizers. Using new BODIPY-perylene-based photosensitizers, heavy atom effects that increase intersystem crossing via spin-orbit coupling and other heavy atom-free photosensitizers that support triplet state formatting for efficient TTA-UC are investigated. TTA-UC efficacy in cell membrane models is assessed by incorporating the molecules into liposomes, which emit intense oxygen sensitive blue/violet emission upon green excitation. The liposome-based TTA-UC further expanded into various membrane compositions with varying membrane’s physicochemical properties to simulate the effects of viscosity/fluidity on

Light addressable machinery translation to lipid membrane structures is highly desirable for a variety of uses such as liposome drug or imaging agent delivery, membrane-bound photosynthesis analogues, etc., but little is known in this area. This thesis focuses on two objectives: the translation of triplet-triplet annihilation upconversion (TTA-UC) to liposomal systems and the use of MSLBs as tools to interrogate the behaviour of photosensitizers in these systems using surface sensitive methods. TTA-UC produces high-energy photon from low- energy excitation via Dexter energy transfer mechanism between photosensitizer and annihilator. TTA-UC uses low-power non-coherent light sources to produce anti-Stokes emission. It thus holds significant potential for photoactivated drug delivery and biological imaging since it can be stimulated using low-frequency light that penetrates biological tissue. Incorporating molecular elements into liposomes and TTA-UC in cell membranes can help biological applications and treatment without harming other organs. However, TTA-UC in a liposome or cell membrane is difficult and requires appropriate photosensitizer and annihilator that can be co-confined to the membrane and where their collisional energy transfer is supported. This thesis explores TTA-UC in solution and lipid bilayer membrane using BODIPY- and Ru(II) complex-based photosensitizers. Using new BODIPY-perylene-based photosensitizers, heavy atom effects that increase intersystem crossing via spin-orbit coupling and other heavy atom-free photosensitizers that support triplet state formatting for efficient TTA-UC are investigated. TTA-UC efficacy in cell membrane models is assessed by incorporating the molecules into liposomes, which emit intense oxygen sensitive blue/violet emission upon green excitation. The liposome-based TTA-UC further expanded into various membrane compositions with varying membrane’s physicochemical properties to simulate the effects of viscosity/fluidity on

Miltefosine an alkylphosphocholine analogue, is the only drug taken orally for the treatment of leishmaniasis-a parasitic disease caused by sandflies. Although it is believed that Miltefosine exerts its activity by acting at the lipid membrane, detailed understanding of the interaction of this drug with eukaryotic membranes is still lacking. Herein, we exploit microcavity pore suspended lipid bilayers (MSLBs) as a biomimetic platform in combination with a highly sensitive label-free electrochemical impedance spectroscopy (EIS) technique to gain biophysical insight into the interaction of Miltefosine with host cell membrane as a function of lipid membranes composition. Four membrane compositions with increasing complexity were evaluated; DOPC, DOPC:Chol (75:25), domain forming DOPC:SM:Chol (40:40:20) and mammalian plasma membrane (MPM) mimetic DOPC:DOPE:Chol:SM:DOPS (32:25:20:15:8) and used to study the interaction of Miltefosine in a concentration-dependent manner using EIS. The membrane resistance changes in response to Miltefosine were modelled by an empirical Langmuir isotherm binding model to provide estimates of binding saturation and equilibrium association constant. Miltefosine was found to have greatest impact on electrochemical properties of the simpler membrane systems; DOPC and DOPC:Chol, where these membranes were found to be more susceptible to membrane thinning, attributed to strong permeation/penetration of the drug whilst, compositions that included both Chol and SM, expected to contain large liquid-ordered domains exhibited weaker changes to membrane resistance but strongest drug association. In contrast, at the MPM membrane, Miltefosine exerts weakest association, which is tentatively attributed to electrostatic effects from the anionic DOPS but some membrane thinning is observed reflected in change in resistance and capacitance values attributed to some weak permeation.

Miltefosine an alkylphosphocholine analogue, is the only drug taken orally for the treatment of leishmaniasis-a parasitic disease caused by sandflies. Although it is believed that Miltefosine exerts its activity by acting at the lipid membrane, detailed understanding of the interaction of this drug with eukaryotic membranes is still lacking. Herein, we exploit microcavity pore suspended lipid bilayers (MSLBs) as a biomimetic platform in combination with a highly sensitive label-free electrochemical impedance spectroscopy (EIS) technique to gain biophysical insight into the interaction of Miltefosine with host cell membrane as a function of lipid membranes composition. Four membrane compositions with increasing complexity were evaluated; DOPC, DOPC:Chol (75:25), domain forming DOPC:SM:Chol (40:40:20) and mammalian plasma membrane (MPM) mimetic DOPC:DOPE:Chol:SM:DOPS (32:25:20:15:8) and used to study the interaction of Miltefosine in a concentration-dependent manner using EIS. The membrane resistance changes in response to Miltefosine were modelled by an empirical Langmuir isotherm binding model to provide estimates of binding saturation and equilibrium association constant. Miltefosine was found to have greatest impact on electrochemical properties of the simpler membrane systems; DOPC and DOPC:Chol, where these membranes were found to be more susceptible to membrane thinning, attributed to strong permeation/penetration of the drug whilst, compositions that included both Chol and SM, expected to contain large liquid-ordered domains exhibited weaker changes to membrane resistance but strongest drug association. In contrast, at the MPM membrane, Miltefosine exerts weakest association, which is tentatively attributed to electrostatic effects from the anionic DOPS but some membrane thinning is observed reflected in change in resistance and capacitance values attributed to some weak permeation.