Ru-TAP complexes with btz and pytz ligands: novel candidates as photooxidizing agents

Two ligands containing 1,2,3-triazole moieties 1 and 3 were easily prepared by a Cu(I)-catalysed "click reaction" between commercially available (trimethylsilyl)alkynes and benzyl azide. These ligands were used in the synthesis of Ru(II) complexes with TAP ligands, i.e. [Ru(TAP)(2)btz](2+)2 and [Ru(TAP)(2)pytz](2+)4. The electrochemical and photophysical properties of these complexes were investigated. The data show that both complexes should behave as highly oxidizing agents under illumination. However, complex 4 displays more attractive photophysical properties than complex 2 and constitutes thus a Ru-TAP compound that can be easily derivatized for photodamaging biomolecules.     

Synthesis of cyclobuteniminium salts derived from aldo-keteniminium salts and study of their reactivity in Diels–Alder reaction

The synthesis of broad scope of novel monosubstituted cyclobuteniminium salts derived from aldo-keteniminium salts and acetylene or 1-propyne is described. The reactivity of cyclobuteniminium salts in Diels–Alder reactions has been studied in detail by DFT calculations and by performing competition reaction with cyclobutenone derivatives.     

Non-resonant microwave absorption studies of superconducting MgB2 and MgB2 + MgO

Non-resonant microwave absorption (NRMA) studies of superconducting MgB₂ and a sample containing ∼10% by weight of MgO in MgB₂ are reported. The NRMA results indicate near absence of intergranular weak links in the pure MgB₂ sample. A linear temperature dependence of the lower critical field H _c1 is observed indicating a non-s wave superconductivity. However, the phase reversal of the NRMA signal which could suggest d wave symmetry is also not observed. In the MgB₂ + MgO sample, much larger low field dependent absorption is observed indicating the presence of intergranular weak links. The hysteretic behavior of NRMA is compared and contrasted in the two samples. In the pure MgB₂ sample, a large hysteresis is observed between the forward and the reverse scans of the magnetic field indicating strong pinning of flux lines. This hysteresis saturates a few degrees below T _c while in the MgB₂ + MgO sample, a much slower increase of hysteresis with decreasing temperature is observed, a signature of weaker pinning.     

Dendritic tetranuclear Ru(II) complexes based on the nonsymmetrical PHEHAT bridging ligand and their building blocks: synthesis, characterization, and electrochemical and photophysical properties

Dinuclear and tetranuclear Ru(II) compounds 1, 2, 3, and 4 based on the PHEHAT ligand (PHEHAT = 1,10-phenanthrolino[5,6-b]-1,4,5,8,9,12-hexaazatriphenylene) are prepared and characterized on the basis of the data for other related mononuclear species. Their electrochemical and spectroscopic behaviors are discussed. The nonspectroelectrochemical correlation obtained for 1, 2, 3, and 4 is explained on the basis of these data. From the behavior in emission, it is concluded that the internal energy transfer takes place from the core to the peripheral metallic units in 3 and 4.     

Detection of secondary structures in 17-mer Ru(II)-labeled single-stranded oligonucleotides from luminescence lifetime studies

The emission properties of a non intercalating complex, [Ru(TAP)2(dip)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene; dip = 4,7-diphenyl-1,10-phenanthroline), tethered to 17-mer single-stranded oligodeoxyribonucleotides (ODNs) either in the middle or at the 5'-end of the sequence, are determined. The results highlight the fact that the luminescence of this metallic compound is sufficiently sensitive to its microenvironment to probe self-structuration of these short single-stranded ODNs. It is shown that the weighted averaged emission lifetimes (tau(M)) along with the quenching rate constants of luminescence by oxygen reflect particularly well different structures adopted by the different ODNs sequences. The determination of these parameters thus offers an elegant way to examine possible structurations of synthetic single-stranded ODNs that play important roles in biological applications.     

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.     

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.     

The Performance of an Electrorheological Fluid in Dynamic Squeeze Flow: The Influence of Solid Phase Size

This paper is concerned with an experimental investigation of a comparison of the rheological performance of an ER fluid, consisting of a carrier with a range of solid phase sizes, in oscillatory squeeze-flow under DC conditions. The fluid is sandwiched between two parallel plane electrodes, the upper one stationary and the lower one oscillating normal to its plane. It is seen that the dynamic performance of the fluid, in terms of the capacity for the transmission of imposed forces across the fluid, is highly dependent on the size of the dispersed solid phase and has an optimum value which is dependent on the mean value of the interelectrode gap. In addition the paper includes some measurements of the current through the fluid which may help to shed some further light on the mechanism of the ER effect. Finally the implications of the results to vibration control are discussed. Copyright 1999 Academic Press.     

Ru(phen)2(PHEHAT)]2+ and [Ru(phen)2(HATPHE)]2+: two ruthenium(II) complexes with the same ligands but different photophysics and spectroelectrochemistry

The properties of two mononuclear Ru(II) complexes formed with the extended planar ligand PHEHAT depend drastically on the chelation site by the metallic ion. When the chelation takes place on the HAT site of the ligand (case of the novel complex [Ru(phen)2(HATPHE)]2+), the emission behavior is quite similar to that of [Ru(phen)2(HAT)]2+. In contrast, when the chelation is on the phen motif of the ligand (case of [Ru(phen)2(PHEHAT)]2+), the spectroscopic (absorption and emission) and electrochemical data for the complex do not obey the linear spectroelectrochemical correlation and the emission behavior is comparable to that of the extensively studied dppz complex ([Ru(phen/bpy)2(dppz)]2+). Thus, for [Ru(phen)2(PHEHAT)]2+, the emission lifetimes and intensities as a function of temperature exhibit a maximum for nitrile solvents. However, in contrast to the dppz case, at least three different states (two emitting and one dark) participate in the deactivation with different contributions depending on the temperature. These different contributions explain the observed maximum. Moreover, the fact that the solvent is liquid or frozen also influences the nature of the luminescent species.     

Photophysical properties of ruthenium(II) polyazaaromatic compounds: a theoretical insight

Quantum-chemical methods are applied to study the nature of the excited states relevant in the photophysical processes (absorption and emission) of a series of polyazaaromatic-ligand-based ruthenium(II) complexes. The electronic and optical properties of the free polyazaaromatic ligands and their corresponding ruthenium(II) complexes are determined on the basis of correlated Hartree-Fock semiempirical approaches. While the emission of complexes containing small-size ligands, such as 1,10-phenanthroline or 2,2'-bipyridine, arises from a manifold of metal-to-ligand charge-transfer triplet states ((3)MLCTs), an additional ligand-centered triplet state ((3)L) is identified in the triplet manifold of complexes containing a pi-extended ligand such as dipyrido[3,2-a:2',3'-c]phenazine, tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazine, and 1,10-phenanthrolino[5,6-b]-1,4,5,8,9,12-hexaazatriphenylene. Recent experimental data are interpreted in light of these theoretical results; namely, the origin for the abnormal solvent- and temperature-dependent emission measured in pi-extended Ru complexes is revisited.