Electrochemical characterisation of the redox behaviour of quinoide components in membrane models The leading idea of this thesis is to study the effects of (i) membrane composition and (ii) membrane environment (aqueous phases) on the redox properties of membrane confined redox active compounds. For solutions it is known since long how strong solvents affect the redox properties of dissolved redox active species. However for membranes this question has not yet been addressed although it can be supposed that such effects may be important to understand the role of membrane confined redox active compounds in biological systems. To interrogate this problem a monolayer model was chosen. It consists of a lipid monolayer with embedded menaquinones on mercury electrodes. Since ion transfer across membranes is also a crucial question in the first part of this project 2 2 diphenyl 1 picrylhydrazyl (DPPH) was studied as a new redox probe for transferring anions and cation between an organic and an aqueous phase. The important findings of this thesis are: (i) accessing the ion pair equilibrium constant of anions and cations with DPPH redox probe as a model study using the three phase electrochemistry (ii) the redox potentials of menaquinone 4 7 and 9 in 1 2 dimyristoyl sn glycero 3 phosphocholine (DMPC) monolayers and the acidity constants of menaquinones (MK’s) in membranes monolayer model and (iii) the effects of membrane composition and the aqueous environment on the thermodynamics and kinetics of MK’s in membrane models. Elektrochemie biological membranes electrochemistry kinetics lipid monolayers menaquinones thermodynamics three phase electrochemistry vitamin K2