No abstract

We developed a (1)O(2)-sensitive linker based on a 9,10-dialkoxyanthracene structure. Its cleavage in the presence of (1)O(2) is quick and high-yielding. A phosphoramidite containing this fragment was prepared and coupled to a variety of molecular fragments, including nucleosides, fluorescent dyes, and a cholesteryl derivative. On the basis of this building block we prepared a fluorogenic probe for monitoring (1)O(2) in live mammalian cells and visible-light-activated "caged" oligodeoxyribonucleotides. In particular, the fluorogenic (1)O(2) probe is a conjugate of 4,7,4',7'-tetrachlorofluorescein and N,N,N',N'-tetramethylrhodamine coupled to each other via the (1)O(2)-sensitive linker. Fluorescence of the dyes in this probe is quenched. In the presence of (1)O(2), the linker is cleaved with formation of 9,10-anthraquinone and two strongly fluorescent dyes: 4,7,4',7'-tetrachlorofluorescein and N,N,N',N'-tetramethylrhodamine derivatives. We observed that the fluorescence of the probe correlates with the amount of (1)O(2) present in solution. The red-light-activated "caged" oligodeoxyribonucleotides are stable duplexes, which consist of an unmodified strand and a blocker strand. The (1)O(2)-sensitive linker is introduced in the interior of the blocker strand. Upon exposure of the duplex to red light in the presence of In(3+)(pyropheophorbide-a) chloride, the linker is cleaved with formation of the unstable duplex structure. This product decomposes spontaneously, releasing the unmodified strand, which can bind to the complementary target nucleic acid. This uncaging reaction is high-yielding. In contrast, previously reported visible-light-activated reagents are uncaged inefficiently due to competing reactions of sulfoxide and disulfide formation.

DNA origami, the folding of a long single-stranded DNA sequence (scaffold strand) by hundreds of short synthetic oligonucleotides (staple strands) into parallel aligned helices, is a highly efficient method to form advanced self-assembled DNA-architectures. Since molecules and various materials can be conjugated to each of the short staple strands, the origami method offers a unique possibility of arranging molecules and materials in well-defined positions on a structured surface. Here we combine the action of light with AFM and DNA nanostructures to study the production of singlet oxygen from a single photosensitizer molecule conjugated to a selected DNA origami staple strand on an origami structure. We demonstrate a distance-dependent oxidation of organic moieties incorporated in specific positions on DNA origami by singlet oxygen produced from a single photosensitizer located at the center of each origami.

The nature of the allosteric metal ion M (Pd2+ or Pt2+) in complexes ML of a polytopic ligand controls uptake of additional Cu2+ ions; while [Cu2Pd(L-4H)]2+ is a highly active catalyst for phosphodiester cleavage, [CuPt(L-4H)] is inactive.

The novel polydentate ligand N, -4H-pyrazole-3-carbonyl)-1,2-diaminoethane (L) was prepared in one-pot synthesis, employing Claisen condensation of 2-acetylpyridine and diethyl ethylene-1,2-bis(oxamate) followed by treatment with hydrazine hydrate. L possesses four bidentate chelating units and is expected to be able to bind metal ions in bis(binucleating) or tetradentate modes. Reaction of L with 1 equiv. of copper() or nickel() hydroxides in the presence of 2 equiv. KOH in DMSO affords mononuclear anionic complexes K 2) containing metal ions in square-planar environment of two pairs of deprotonated amide and pyrazolato nitrogens. Reaction of 1 with 2 equiv. of Cu(NO 3 ) 2 leads to complete rearrangement of the coordination sphere, yielding a tetranuclear product which was crystallised in the presence of picric acid in the form) was obtained as a result of spontaneous self-assembly from L and copper() nitrate in aqueous acetic acid. Reaction of 2 with 2 equiv. of Ni(NO 3 ) 2 yields a tetranuclear cationic complex 4) which contains four octahederal Ni ions coordinated in bis(binucleating) mode to two ligand threads disposed in side-by-side fashion and cis with respect to the Ni(1)-Ni(2) axis. In both 3a and 3b the ligand is coordinated in the same bis(binucleating) mode as in Ni complex 4, however, the Cu ions are squarepyramidal and the two ligand threads are disposed trans with respect to the Cu(1)-Cu(2) axis, thus giving rise to the double helical structures. 3a and 3b are the first examples of helicates comprising of bimetallic units. Formation of different topologies in 3a,b and 4 is elucidated in terms of different stereochemical preferences of these ions in mixed N,O-donor environments. All compounds were characterised by elemental analysis, ESI and MALDI mass spectrometry and UV-VIS spectroscopy, and complexes 3a, 3b and 4 by single crystal X-ray analysis. Magnetic susceptibility measurements (1.7-300 K) of powdered samples of tetranuclear complexes revealed strong (3b) or moderate (4) antiferromagnetic coupling within the dimeric units incorporating double pyrazolato bridges between paramagnetic centres. ExperimentalAll chemicals were commercial products of reagent grade and used without further purification. 1 H NMR spectra were recorded on Bruker AC-400 (400.13 MHz) and Bruker AC-500 DALTON