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Abstract
Multiple G‐tracts within the promoter region of the c‐myc oncogene may fold into various G‐quadruplexes with the recruitment of different tracts and guanosine residues for the G‐core assembly. Thermodynamic profiles for the folding of wild‐type and representative truncated as well as mutated sequences were extracted by comprehensive DSC experiments. The unique G‐quadruplex involving consecutive G‐tracts II–V with formation of two one‐nucleotide and one central two‐nucleotide propeller loop, previously proposed to be the biologically most relevant species, was found to be the most stable fold in terms of its Gibbs free energy of formation at ambient temperatures. Its stability derives from its short propeller loops but also from the favorable type of loop residues. Whereas quadruplex folds with long propeller loops are significantly disfavored, a snap‐back loop structure formed by incorporating a 3’‐terminal guanosine into the empty position of a tetrad seems highly competitive based on its thermodynamic stability. However, its destabilization by extending the 3’‐terminus questions the significance of such a species under in vivo conditions.
Electrochemical characterisation of the redox behaviour of quinoide components in membrane models
(2020)
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.