C-nucleosides of 4-methylbenzophenone, 4-methoxybenzophenone, and 2'-methoxyacetophenone were synthetically incorporated as internal photosensitizers into DNA double strands. This structurally new approach makes it possible to study the distance dependence of thymidine dimer formation because the site of photoinduced triplet energy transfer injection is clearly defined. The counterstrands to these modified strands lacked the phosphodiester bond between the two adjacent thymidines that are supposed to react with each other. Their dimerization could be evidenced by gel electrophoresis because the covalent connection by cyclobutane formation between the two thymidines changes the mobility. A shallow exponential distance dependence for the formation of thymidine dimers over up to 10 A-T base pairs was observed that agrees with a Dexter-type triplet-triplet energy transfer mechanism. Concomitantly, a significant amount of photoinduced DNA crosslinking was observed.
A new type of a bifunctional DNA architecture based on a three way junction is developed that combines the structural motif of sticky perylene bisimide caps with a tris-bipyridyl metal ion lock in the center part. A clear stabilizing effect was observed in the presence of Fe(3+), Ni(2+) and Zn(2+) by the formation of corresponding bipyridyl complexes in the branching part of the DNA three way junctions. The dimerization of the 5'-terminally attached perylene diimides (PDI) chromophores by hydrophobic interactions can be followed by significant changes in the UV/Vis absorption and steady-state fluorescence. The PDI-mediated DNA assembly occurs at temperatures below the melting temperature and is not influenced by the metal-ion bipyridyl locks in the central part. The corresponding AFM images revealed the formation of higher-ordered structures as the result of DNA assemblies mediated by the PDI interactions.
Die C-Nucleoside von 4-Methylbenzophenon, 4-Methoxybenzophenon und 2'-Methoxyacetophenon wurden als interne Photosensibilisatoren synthetischi nD NA-Doppelstränge eingebaut. Dieser strukturell neuartige Ansatz erlaubt es,die Distanzabhängigkeit der Thymidin-Dimerbildung zu untersuchen, weil der Ort der photoinduzierten Injektion der Triplettenergie eindeutig definiert ist. Den Gegensträngen dieser modifizierten Oligonucleotide fehlte die Phosphodiesterbindung zwischen zwei benachbarten Thymidinen, die miteinander reagieren sollten. Deren Dimerisierung konnte durch Gelelektrophorese nachgewiesen werden, weil die kovalente Verbindung durch die Cyclobutanbildung zwischen den zwei Thymidinen die Mobilitätv erändert. Eine schwache exponentielle Distanzabhängigkeit der Thymidin-Dimerbildung wurde über bis zu 10 AT -Basenpaare beobachtet, was im Einklang mit einem Dexter-Triplett-Triplett-Energietransfermechanismus steht. Gleichzeitig wurde eine deutliche Menge an photoinduzierten DNA-Crosslinks beobachtet.
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