LIGAND-DEPENDENT INTERACTION OF RUTHENIUM(II) POLYPYRIDYL COMPLEXES WITH DNA PROBED BY EMISSION SPECTROSCOPY

The nature of the interaction in buffered aqueous solution of several homo and heteroleptic ruthenium(II) polypyridyl complexes containing 2,2'-bipyridine (bpy), 2,2'-bipyrazine (bpz), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (dip), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmp), 1,4,5,8-tetraazaphenanthrene (tap), and 1,4,5,8,9,12-hexaazatriphenylene (hat) with calf thymus DNA and poly(dA-dT).poly(dA-dT) (pdAT) has been investigated by steady-state spectroscopy and emission lifetime measurements. Those complexes containing two or more tap/hat ligands photo-oxidize the guanine base upon binding to DNA with efficiencies that parallel their excited state redox potentials, but display "normal" behavior (increase of both the emission intensity and lifetime) when bound to pdAT. However Ru(tap)(hat)2+2 and Ru(hat)2+3 even photooxidize the adenine base of pdAT, so that their excited states are also quenched in the presence of either polynucleotide. The electron transfer quenching mechanism has been confirmed previously by detection of the monoreduced complex in laser flash photolysis experiments in the presence of mononucleotides. Most of the complexes investigated appear to bind to DNA, at least in part via intercalation, with affinities being dependent on the nature of the largest ligand (hat shows the highest ability in heteroleptic complexes). From lifetime quenching experiments, in the presence of moderate amounts of NaCl, surface binding does not appear to be a general mode for the complexes investigated, and it has been demonstrated unequivocally only for Ru(phen)2+3. In addition, the intercalation of complexes into DNA increases as the ionic strength of the medium decreases, the DNA/Ru ratio increases, or when water is partially replaced by glycerol.     

Adduct formation by photo-induced electron transfer between photo-oxidising Ru(II) complexes and tryptophan

The (3)MLCT excited state of Ru(II) complexes with 1,4,5,8-tetraazaphenanthrene (TAP) ligands in the presence of tryptophan gives rise to an electron transfer process from the amino acid with subsequent formation of an adduct between the two partners, strongly influenced by oxygen.     

Interrelations and Dissimilarities Between Distinct Approaches to Ontic Vagueness

This paper outlines the often striking parallels of various approaches to ontic vagueness, as well as their even more striking differences. Though circling around the same idea, some of these approaches were developed to solve quite diverse theoretical problems and encounter different challenges. In addition to these difficulties, the frequently disregarded epistemological problems of all theories of ontic vagueness turn out to be even more serious under critical scrutiny. The same holds for the difficulties of deciding, for every case of vagueness, whether the vagueness involved is semantic or ontic.     

PHOTOINDUCED ELECTRON TRANSFER QUENCHING OF EXCITED Ru(II) POLYPYRIDYLS BOUND TO DNA: THE ROLE OF THE NUCLEIC ACID DOUBLE HELIX

In the presence of double helical polynucleotides (sodium poly(dA-dT).poly(dA-dT) or calf thymus DNA), the efficiency of oxidative or reductive electron transfer between photoexcited ruthenium(II) chelates Ru(tap)2(hat)2+ or Ru(phen)2+(3) (where tap = 1,4,5,8-tetraazaphenanthrene, hat = 1,4,5,8,9,12-hexaazatriphenylene, and phen = 1,10-phenanthroline) and appropriate cationic quenchers (ethidium, Ru(NH3)3+(6), methyl viologen, or M(phen)3+(3), where M = Co, Rh, Cr) increases 1-2 orders of magnitude compared to the efficiency of the same quenching in microhomogeneous aqueous medium (kq = 0.3-1.8 x 10(9) M-1 s-1). The enhancement is more pronounced when the binding constant of the quencher (10(3) less than Kb less than 10(6) M-1) is large. Similar trends are found when the biopolymers are replaced by sodium poly(styrenesulfonate) (PSS). The accelerated electron transfer process is proposed to be due mainly to the effect of accumulation of the reagents in the electrostatic field of the polymer; if corrections for this effect are introduced (e.g. ratioing [quencher]/[polynucleotide]), the reaction rate becomes essentially independent of the polymer concentration. Based upon a model for electron transfer reaction of the complexes within a small cylindrical interface around the DNA helix, calculations of the bimolecular electron transfer rate constants are computed to be 10(3) times smaller when the reactants are bound to the double-stranded polynucleotides and decreased mobility of the cationic species is apparent. The effect is less pronounced if a simpler polyelectrolyte (PSS) is employed. Emission lifetimes of the Ru(II) polypyridyls bound to the DNA (0.32-2 microseconds, double exponential decays) are discussed as well.     

Beitrag zur potentiometrischen Untersuchung von Resorufin und einigen seiner Derivate

Zusammenfassung Durch potentiometrische Untersuchung des Verhaltens von Resorufin, o-Acetylresorufin und Äthoxyresorufin wurde festgelegt, unter welchen Bedingungen es zur Bildung von Semichinon kommt. Ferner wurden die Bedingungen für die titanometrische und stannometrische Bestimmung der angeführten Substanzen ermittelt.

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Summary Potentiometric investigation of the behavior of resorufin,o-acetylresorufin and ethoxyresorufin revealed the conditions that lead to the formation of semiquinone. The conditions for the titanometric and the stannometric determination of these materials were also established.

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Résumé On a établi les conditions de formation d'une hémiquinone, par l'étude potentiométrique du comportement de la résorufine, de l'o-acétylrésomfine et de l'éthoxyrésorufine. On en a déduit les conditions du titrage titanométrique et stannométrique de ces substances.

     

Synthesis of aramides in solutions of poly(vinylpyrrolidone)

Results on polycondensation of poly(1.4 benzamide) (PBA) and 2.5.DCIPDAcoTPA in solutions of poly(vinylpyrrolidone) (PVP) will be presented. For polycondensation, the method of OGATA, using triphenylphosphine and hexachloroethane, and the low-temperature solution polycondensation of dicarboxylic acid dichlorides and diamines, were applied. It is shown that the molar mass of PBA depends strongly on the PVP:PBA ratio. To explain this dependence, one has to take into account the phase behavior of the ternary rigid rod polymer/flexible coil polymer/solvent system and the influence of the matrix polymer. An enhancement of the molar mass of the PBA produced can be observed when the PVP:PBA is high enough to prevent an association of the PBA, i.e. when one stays in the isotropic one-phase area of the phase diagram. Under these circumstances, it is possible to obtain one-phase systems in nonsolvents for the aramides.     

Single-Atom Catalysts on Covalent Triazine Frameworks: at the Crossroad between Homogeneous and Heterogeneous Catalysis

Heterogeneous single-site and single-atom catalysts potentially enable combining the high catalytic activity and selectivity of molecular catalysts with the easy continuous operation and recycling of solid catalysts. In recent years, covalent triazine frameworks (CTFs) found increasing attention as support materials for particulate and isolated metal species. Bearing a high fraction of nitrogen sites, they allow coordinating molecular metal species and stabilizing particulate metal species, respectively. Dependent on synthesis method and pretreatment of CTFs, materials resembling well-defined highly crosslinked polymers or materials comparable to structurally ill-defined nitrogen-containing carbons result. Accordingly, CTFs serve as model systems elucidating the interaction of single-site, single-atom and particulate metal species with such supports. Factors influencing the transition between molecular and particulate systems are discussed to allow deriving tailored catalyst systems.