Cooperative effects on functionalised vesicles

were examined and successfully applied to enhance the aqueous hydrolysis of active esters and the upconversion of light. In addition, a fast screening technique for visible light photocatalysis reactions was developed. Chapter 1 briefly introduces into the topic of functionalised vesicles and explains the design of the projects in this thesis spanning from cooperative effects on functionalised vesicles to the development of a screening technique. Chapter 2 presents the concept of cooperative hydrolysis on the surface of membranes. Hydrolytic activity is provided by vesicles functionalised with an amphiphilic zinc complex, which acts as a Lewis acid and is able to hydrolyse aryl esters. We showed that co-embedding of different membrane additives into the surface of the vesicles increases the hydrolytic rate up to 16-fold. We examined different lipids and observed the highest cooperative enhancement of hydrolysis in fluid DOPC membranes. Mechanistic studies suggested that in such fluid membranes the reactions follow a Michaelis-Menten saturation kinetic, while in rigid DSPC vesicles second order kinetics are observed. Chapter 3 shows that, not only catalytic activity of functionalised vesicles can be enhanced using membrane additives, but also the selectivity. By co-embedding of an amphiphilic nonchiral hydrolysis catalyst with amphiphilic chiral additives into the membrane of a phospholipid vesicle we were able to introduce enantioselectivity to a non-chiral catalyst. This was shown for enantiomerically pure amino acid esters, which in the presence of an appropriate chiral additive show a twofold enhancement of the hydrolysis rate of one enantiomer. In Chapter 4 we tried to simplify the concept of functionalised vesicles for hydrolysis and instead of using custom made amphiphilic metal complexes we examined the direct adsorption of lanthanide ions onto the surface of the vesicles. We show that their interaction with vesicles prepared from zwitterionic phosphatidylcholine lipids provides soft particles with surface functionalised with lanthanide ions. This was confirmed via sensitisation of europium ions by pyrene that was co-embedded inside the phospholipid bilayer. Such assembly provides a high density of Lewis-acidic metal centres, which hydrolyse phosphodiesters 17 times faster compared to homogeneous aqueous lanthanide solutions. Chapter 5 is a study on triplet-triplet annihilation upconversion process in vesicles. We show that such light upconverting soft particles can be made on the basis of fluid DOPC vesicles in aqueous media. This process consists of the interaction between two sets of dyes (sensitizer and annihilator). We studied the effect of their position in the membrane on the upconversion efficiency: High local concentration of the dyes in the membrane increases the intensity of the detected delayed fluorescence. This was observed whether the dyes were on the surface of the bilayer or inside. Crucial for the upconversion to take place in vesicles is the fluidity of the membrane. In rigid membranes no upconversion is observed. In Chapter 6 we developed a high throughput screening technique for photocatalytic transformations using known indicators and microtiter plate instrumentation. Photocatalytic reactions often produce beside the desired products a stoichiometric by-product, such as reactive oxygen species or acids. These can be easily detected by an indicator allowing to perform 96 reactions at once and evaluate the reaction conversion by addition of the indicator measuring its absorbance. The concept is able to reproduce reported reaction results and correlates well with GC analysis. We used this system for identifying two new catalysts for the hydroxylation of boronic acids. We successfully employed the technique for photochemical reductions, monitoring the formation of aryl radicals from aryl halides. To confirm the robustness of the method for different substrates we screened various drugs bearing an aryl halide moiety and identified two new dehalogenation reactions