Fakultät für Chemie und Pharmazie - Digitale Hochschulschriften der LMU - Teil 04/06 Archiv

The thesis involves three different aspects of quantum dynamics in cold and isolated molecular systems that are investigated theoretically with methods ranging from wavepacket dynamics to density matrix propagation. In the first part the efficiency of cavity sideband cooling of trapped molecules is theoretically investigated for the case in which the infrared transition between two ro-vibrational states is used as a cycling transition. The molecules are assumed to be trapped either by a radio frequency or optical trapping potential, depending on whether they are charged or neutral, and confined inside a high-finesse optical resonator that enhances radiative emission into the cavity mode. Using realistic experimental parameters and Carbonyl sulfide as a molecular representative, we show that in this setup, cooling to the trap ground state is feasible. The second part investigates femtosecond pump-probe spectroscopy of single MgH+ ions confined in an ion trap. The molecular ions are embedded in a coulomb crystal of atomic magnesium ions which are laser cooled to a few millikelvin. Single molecules are addressed by femtosecond ultraviolet laserpulses and the induced molecular processes are investigated. The simulations of the wave packet motion and dissociation behavior were used to predict the experimental parameter regime and are compared directly to the laboratory results. For this purpose a multiscale model is developed which involves the wave packet motion as well as the problem of vibrational heating occurring on a millisecond time scale under laboratory conditions. The third part investigates the gas phase SN2 collision reaction of chloride and methyl iodine. Motivated by the experimental results of Roland Wester and co-workers [Mikosch et al., Science 319, 183 (2008)], remaining questions were addressed. The collision reaction is simulated by solving the time dependent Schrödinger equation on ab initio potential energy surfaces. With the chosen reactive coordinates it is possible to reproduce the basic features of the immediate collision reaction. The internal molecular coordinates are transformed into reaction path based model which allows for an efficient numerical description of the nuclear dynamics. The energy transfer in the system is investigated and compared to the experimental results. From the new insight into the process, an intuitive concept of a dynamical barrier can be derived. Moreover the role of the spectator mode can be clarified.

In this work, we were able to take advantage of a deregulated wnt signaling pathway – a condition which is found in most gastrointestinal cancers, in particular in colorectal carcinomas. In order to restrict reporter gene expression to the desired cell type, we utilized the β-catenin dependent CTP4-promoter to restrict the expression of Firefly Luciferase and enhanced green fluorescent fusion protein (EGFPLuc) to cell lines with deregulated wnt signaling including SW480, LS174T, HepG2, Coga2 and Coga12. Stable cell lines containing this CTP4-driven EGFPLuc construct were established with the help of a lentiviral vector to monitor wnt activity by transgene expression. With these stably transduced cell lines, we performed a therapeutic target screen via siRNA-mediated knock-down of a number of potentially therapeutic targets within the wnt pathway – osteoprotegerin (OPG), Traf2 and Nck-interacting kinase (TNIK), SRY-related HMG-box (Sox2), protease-activated receptor 1 (PAR-1), β-catenin and transcription factor 4 (TCF4). The in vitro screening system was utilized as a prevalidation tool for therapeutically relevant targets. The degree of interference of our novel targets was determined and the search for a suitable siRNA target in colorectal cancer cells was narrowed down to β-catenin, PAR-1 and TNIK. As proof of principle the siRNA-mediated knock down of β-catenin was verified on mRNA and protein level in LS174T cells. After the initial read-out of various cell lines with different siRNAs has been established via the reduction of Luciferase expression levels, the biological effect of these targets were validated. For this purpose colony formation and cell motility/invasion assays were conducted for all relevant target cell lines. Furthermore in the in vitro experiments, the tumor-selectivtiy of the CTP4-promoter was employed in the delivery of the cytotoxic protein diphteria toxin A (DTA) in colorectal cancer target cells. Data evaluation of all in vitro assays pointed at reduced levels of proliferation, invasive behavior and aggressiveness, which yielded three candidates (PAR-1, TNIK and β-catenin) considered as viable for a treatment attempt in vivo. In the in vivo experiments, systemic delivery of siRNA against β-catenin, sticky siRNA targeting PAR-1 and plasmid DNA encoding for CTP4 controlled DTA were evaluated in a disseminated liver metastasis model of LS174T colorectal cancer. Specific knock-downs of β-catenin and PAR-1 were achieved which was confirmed via mRNA analysis. As for CTP4-DTA pDNA delivery the overall tumor load of the liver was reduced without any significant systemic toxicity, indicating specific DTA expression in tumor tissue. Also knock down of PAR1 using sticky siRNA significantly reduced tumor growth. All in all, the therapeutic effect of PAR-1 and β-catenin knock-down could be verified in various in vitro assays analyzing invasive behavior and anchorage independent growth and ultimately also in vivo. The tumor-specific expression of DTA pDNA could also be confirmed in vitro and was further investigated in an orthotopic liver dissemination model in NMRI nude mice.