title: Photoisomerization of arylstilbazolium ligands in the presence of DNA.
abstract: The ability of the DNA duplex to behave as an efficient organized medium for trans-cis photoisomerization has been explored. The presence of DNA affected isomerization in a variety of ways depending on the aryl moiety properties of the ligand and its DNA-binding mode. Contrary to intercalating ligands, 9-[2-(N-methylpyridinium-4-yl)vinyl]phenanthrene (2) and 9-[2-(N-methylpyridinium-4-yl)vinyl]anthracene (3), which gave only cis and trans isomers, the additional products--cyclobutane photodimers--were detected for 2-[2-(N-methylpyridinium-4-yl)vinyl]naphthalene (1), which binds cooperatively to the minor groove of DNA. Photostationary states (pss) for all ligands were seriously affected by the presence of DNA. A trans isomer-rich pss and restriction of trans --> cis process, observed for ligands 1 and 2, were explained in terms of a different binding affinity of DNA toward particular isomers. On the contrary, 9-anthryl derivative 3 isomerized against the isomer-binding preferences, showing cis isomer-rich pss and enhanced quantum yield of isomerization. The unique behavior of ligand 3-DNA complex was attributed to different isomerization mechanism that consists in quantum chain isomerization from an excited singlet state possessing a charge transfer character. This is the first example of ligand, which undergoes DNA-mediated cis-trans isomerization in the opposite direction than expected from DNA-binding preferences. The analysis of pss data based on two alternative pathways of photoisomerization showed that investigated ligands follow the model that allows isomerization of both free and DNA-bound ligands.
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland. juskowia@main.amu.edu.pl
authors.forename: Bernard
authors.initials: B
authors.lastname: Juskowiak
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Chudak
mesh_terms: D000818:Animals; D001555:Benzene Derivatives / Q000737:chemistry* / Q000528:radiation effects; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D004735:Energy Transfer; D007364:Intercalating Agents / Q000737:chemistry; D007536:Isomerism; D008024:Ligands; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000737:chemistry*; D011084:Polycyclic Aromatic Hydrocarbons / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000737:chemistry*; D011740:Pyrimidine Dimers / Q000737:chemistry; D013997:Time Factors
chemical_list: D001555:Benzene Derivatives; D004268:DNA-Binding Proteins; D007364:Intercalating Agents; D008024:Ligands; D017319:Photosensitizing Agents; D011084:Polycyclic Aromatic Hydrocarbons; D011726:Pyridinium Compounds; D011740:Pyrimidine Dimers; D004247:DNA