Detection of three rotational correlation times for a rigid asymmetric molecule using frequency-domain fluorometry

We measured the frequency response of the polarized emission of Y_t-base in propylene glycol at 10 ° C. Data were obtained for excitation wavelengths of 290, 312 and 346 nm, for which the fundamental anisotropies are 0.05, 0.19 and 0.32, respectively. Additionally, data were obtained using CCl₄, to decrease the mean decay time from 9.1 to 4.2 ns. These nine sets of data were analyzed globally to recover the anisotropy decay law. Three correlation times were needed to fit the data, 0.8, 3.0 and 5.6 ns, a range of only 7-fold. We believe this is the first reported detection of three correlation times for a rigid molecule.     

Syntheses, spectra and crystal structures of ruthenium(II) complexes with polypyridyl: [Ru(bipy)2(phen)](ClO4)2 · H2O and [Ru(bipy)2(Me-phen)](ClO4)2

Two ruthenium(II) complexes with polypyridyl, Ru(bipy)₂(phen)](ClO₄)₂·H₂O (1) and [Ru(bipy)₂(Me-phen)](ClO₄)₂ (2), (phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, Me-phen = 5-methyl-1,10-phenanthroline), were synthesized and characterized by IR, MS and NMR spectra. Their structures were determined by single crystal X-ray diffraction techniques. The strong steric interaction between the polypyridyl ligands was relieved neither by the elongation of the Ru---N bonds nor increase of the N---Ru---N bite angles. The coordination sphere was distorted to relieve the ligand interaction by forming specific angles (δ) between the polypyridyl ligand planes and coordination planes (N---Ru---N), and forming larger twisted angles between the two pyridine rings for each bipy. The bond distances of Ru---N(bipy) and Ru---N(phen) were virtually identical with experimental error, as expected of π back-bonding interactions which statistically involve each of the ligands present in the coordination sphere.     

Time-resolved spectral observations of cadmium-enriched cadmium sulfide nanoparticles and the effects of DNA oligomer binding

We measured the steady-state and time-resolved fluorescence spectral properties of cadmium-enriched nanoparticles (CdS-Cd2+). These particles displayed two emission maxima, at 460 and 580 nm. The emission spectra were independent of excitation wavelength. Surprisingly, the intensity decays were strongly dependent on the observation wavelength, with longer decay times being observed at longer wavelengths. The mean lifetime increased from 150 to 370 ns as the emission wavelength was increased from 460 to 650 nm. The wavelength-dependent lifetimes were used to construct the time-resolved emission spectra, which showed a growth of the long-wavelength emission at longer times, and decay-associated spectra, which showed the longer wavelength emission associated with the longer decay time. These nanoparticles displayed anisotropy values as high as 0.35, depending on the excitation and emission wavelengths. Such high anisotropies are unexpected for presumably spherical nanoparticles. The anisotropy decayed with two correlation times near 5 and 370 ns, with the larger value probably due to overall rotational diffusion of the nanoparticles. Addition of a 32-base pair oligomer selectively quenched the 460-nm emission, with less quenching being observed at longer wavelengths. The time-resolved intensity decays were minimally affected by the DNA, suggesting a static quenching mechanism. The wavelength-selected quenching shown by the nanoparticles may make them useful for DNA analysis.     

Variation of DNA photocleavage efficiency for [(TL)2Ru(dpp)]Cl2 complexes where TL=2,2'-bipyridine, 1,10-phenanthroline, or 4,7-diphenyl-1,10-phenanthroline

The complexes [(bpy)₂Ru(dpp)]Cl₂, [(phen)₂Ru(dpp)]Cl₂, and [(Ph₂phen)₂Ru(dpp)]Cl₂ (where dpp = 2,3-bis(2-pyridyl)pyrazine, bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, Ph₂phen = 4,7-diphenyl-1,10-phenanthroline) have been investigated and found to photocleave DNA via an oxygen-mediated pathway. These light absorbing complexes possess intense metal-to-ligand charge transfer (MLCT) transitions in the visible region of the spectrum. The [(TL)₂Ru(dpp)]²⁺ systems populate ³MLCT states after visible light excitation, giving rise to emissions in aqueous solution centered at 692, 690, and 698 nm for TL = bpy, phen, and Ph₂phen respectively. The ³MLCT states and emissions are quenched by O₂, producing a reactive oxygen species. These complexes photocleave DNA with varying efficiencies, [(Ph₂phen)₂Ru(dpp)]²⁺ > [(phen)₂Ru(dpp)]²⁺ > [(bpy)₂Ru(dpp)]²⁺. The presence of the polyazine bridging ligand will allow these chromophores to be incorporated into larger supramolecular assemblies.     

Nitrogen atom transfer and redox chemistry of terpyridyl phosphoraniminato complexes of osmium (IV)

Rapid reactions occur between [Os^VI(tpy)(Cl)₂(N)]X (X = PF₆⁻, Cl⁻, tpy = 2,2′:6′,2″-terpyridine) and aryl or alkyl phosphi nes (PPh₃, PPh₂Me, PPhMe₂, PMe₃ and PEt₃) in CH₂Cl₂ or CH₃CN to give [Os^IV(tpy)(Cl)₂(NPPh₃)]⁺ and its analogs. The reaction between trans-[Os^VI(tpy)(Cl)₂(N)]⁺ and PPh₃ in CH₃CN occurs with a 1:1 stoichiometry and a rate law first order in both PPh₃ and Os^VI with k(CH₃CN, 25°C) = 1.36 ± 0.08 × 10⁴ M⁻ s⁻¹. The products are best formulated as paramagnetic d⁴ phosphoraniminato complexes of Os^IV based on a room temperature magnetic moment of 1.8 μ_B for trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆), contact shifted ¹H NMR spectra and UV-Vis and near-IR spectra. In the crystal structures of trans-[Os^IV(tpy)(Cl)₂( NPPh₃)](PF₆)·CH₃CN (monoclinic, P2₁/n with a = 13.384(5) Å, b = 15.222(7) Å, c = 17.717(6) Å, β = 103.10(3)°, V = 3516(2) ų, Z = 4, R_w = 3.40, R_w = 3.50) and cis-[Os^IV(tpy)(Cl)₂(NPPh₂Me)]-(PF₆)·CH₃CN (monoclinic, P2₁/c, with a = 10.6348(2) Å, b = 15.146(9) ÅA, c = 20.876(6) Å, β = 97.47(1)°, V = 3334(2) ų, Z = 4, R = 4.00, R_w = 4.90), the long Os-N(P) bond lengths (2.093(5) and 2.061(6) Å), acute Os-N-P angles (132.4(3) and 132.2(4)°), and absence of a significant structural trans effect rule out significant Os-N multiple bonding. From cyclic voltammetric measurements, chemically reversible Os^V/IV and Os^IV/III couples occur for trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆) in CH₃CN at +0.92 V (Os^V/IV) and −0.27 V (Os^IV/III) versus SSCE. Chemical or electrochemical reduction of trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆) gives isolable trans-Os^III(tpy)(Cl)₂(NPPh₃). One-electron oxidation to Os^V followed by intermolecular disproportionation and PPh₃ group transfer gives [Os^VI(tpy)Cl₂(N)]⁺, [OS^III(tpy)(Cl)₂(CH₃CN)]⁺ and [Ph₃=N=PPh₃]⁺ (PPN⁺). trans-[Os^IV(tpy)(Cl)₂(NPPh₃)](PF₆) undergoes reaction with a second phosphine under reflux to give PPN⁺ derivatives and Os^II(tpy)(Cl)₂(CH₃CN) in CH₃CN or Os^II(tpy)(Cl)₂(PR₃) in CH₂Cl₂. This demonstrates that the Os^VI nitrido complex can undergo a net four-electron change by a combination of atom and group transfers.     

Syntheses and molecular structures of ruthenium(II) complexes of the atropisomeric ligands 1,1′-biphenyl-2,2′-diamine and 3,3′-diamino-2,2′-bipyridine

The unique ligands of [Ru(bipy)₂(bpda)](PF₆)₂ (1, BPDA=1,1′-biphenyl-2,2′-diamine) and [Ru(bipy)₂(dabipy)](PF₆)₂ (2, DABIPY=3,3′-diamino-2,2′-bipyridine) are atropisomeric (exhibit hindered rotation about the sigma bonds that connect the two aromatic groups), so the complexes are diasteromeric with conformation isomers possible for the atropisomeric ligands and configurational isomers possible at the metal centers. Only one diastereomer is observed in the solid-state in both cases. The seven- (1) and five-membered (2) chelate ring of dabipy and bpda (the ligand is bound through its pyridyl groups) ligands are δ when the configuration at the metal is Δ. No evidence for atropisomerization is found in solution. For 1, we conclude bpda binds stereospecifically; however, the atropisomerization barrier of dabipy may be sufficiently low for 2 to preclude the observation of diastereomers by low-temperature NMR spectroscopy.     

High resolution spectroscopy of the lowest excited state in Re tetra-carbonyl complexes

The luminescence and absorption properties of [Re(bpy)(CO)₄](PF₆) and [Re(phen)(CO)₄](PF₆) are consistent with representation of the lowest excited states as nominally ³LC with an admixture of ¹CT character. Using high resolution spectroscopic techniques at cryogenic temperatures, such as luminescence line narrowing spectroscopy or spectroscopy in single crystals, the vibrational sideband information which is normally lost in the ‘natural’ solution environment can be observed in the luminescence and absorption spectra. Mixing between the ³LC and ¹CT excitation (3%) has previously been reported in [Re(bpy)(CO)₄](PF₆), resulting in metal-ligand sidebands at 184 and 198 cm⁻¹ in the absorption spectrum and a short luminescence lifetime (33.0 μs). In the luminescence spectra (line narrowed) the metal-ligand sidebands are observed at 194 cm⁻¹. Weak mixing ( 1%) of the ¹CT excitation (32 100 cm⁻¹) with the ³LC excitation (22 100 cm⁻¹) in [Re(phen)(CO)₄](PF₆) gives rise to the observation of metal-ligand vibrational sidebands in the luminescence spectrum (204 cm⁻¹) and a luminescence lifetime of τ= 295±5 μs at 20 K. A spin-orbit mixing matrix element of ³LC|H_so|¹CT for [Re(phen)(CO)₄](PF₆) of 65 cm⁻¹ is calculated, compared to 261 cm⁻¹ in [Re(bpy)(CO)₄](PF₆).     

Nitrogen, sulfur and oxygen donor adducts with copper(II) complexes of antitumor 2-formylpyridinethiosemicarbazone analogs: Physicochemical and cytotoxic studies

The preparation of N-, S- and O-donor ligand adducts with CuX⁺(HX=6-methyl-2-formylpyridinethiosemicarbazone (6HL); 2-formylpyridine-2^′-methylthiosemicarbazone (2′L); 2-formylpyridine-4′-methylthiosemicarbazone (4′HL)) is described. The N-donors, 2,2′-bipyridyl (bipy), 4-dimethylaminopyridine (dmap) give the complexes [Cu(6L)(bipy)]PF₆, [Cu(6L)(bipy)]Cl·5H₂O, [Cu(4′L)(bipy)]PF₆, [Cu(6L)(dmap)₂]PF₆·2.5 H₂O and [Cu(4′L)(dmap)₂]PF₆·H₂O which have been characterized by physical and spectroscopic techniques. Pentafluorothiophenolate (pftp) gives S-donor complexes [CuX(pftp)] (X=6L and 4′L) and thiolato co-ordination is proposed on the basis of spectroscopic evidence. Paratritylphenolate (ptp) and HPO²⁻₄ give O-donor complexes [Cu(6L)(ptp)], [Cu(4′L)(ptp)], [{Cu(6L)}₂HPO₄]·4H₂O, and [{Cu(4^′L)}₂HPO₄]·5H₂O which have been characterized by physical and spectroscopic techniques, as have the precursor complexes [Cu(6L)(CH₃COO)]·H₂O, [Cu(4′L)(CH₃COO)], Cu(6HL)(CF₃COO)](CF₃COO)·0.5H₂O, [Cu(4′HL)(CF₃COO)](CF₃COO), [Cu(2′L)Cl₂] and [Cu(2′L)(NO₃)₂]. Protonation constants for the ligands and some of their complexes have been determined. 2-Formylpyridinethiosemicarbazone (HL) complexes of silver, gold, zinc, mercury, cadmium and lead are also discussed. Cytotoxicity against the human tumor cell line HCT-8 and antiviral data for selected compounds are presented.     

First- and second-order mechanisms for oxidative addition for bound methyl disulfide in the complex W(CO)3(phen)(MeSSMe)

The rate of oxidative addition of methyl disulfide in the complex W(CO)₃(1,10-phenanthroline) (MeSSMe) in methylene chloride has been studied. The dominant reaction pathway is second order in metal complex and inhibited by excess methyl disulfide. Formation of a dinuclear complex [W(CO)₃(phen)]₂(MeSSMe) is proposed to lead to the transition state for cleavage of the sulfur-sulfur bond in the second-order mechanism. In neat methyl disulfide, or in concentratred solutions of methyl disulfide at low metal complex concentrations, the reaction occurs at reduced rate and follows a first-order mechanism. Addition of Mo(CO)₃(1,10-phenanthroline) (MeSSMe) to the corresponding tungsten complex results in a ten-fold increase in the rate of oxidative addition of the tungsten complex and production of Mo(CO)₄(1,10-phenanthroline) as the sole molybdenum-containing product. The faster rate of reaction in the presence of the molybdenum complex is attributed to the faster formation of the heteronuclear dinuclear intermediate by initial loss of MeSSMe from the molybdenum versus tungsten center. Additional kinetic/mechanistic studies are described using a new flow-through FT-IR/microscope reaction system designed to allow convenient monitoring of small quantities of sensitive/hazardous reactants.     

Synthesis and near IR photoluminescence of Os(II) bis(2,2′-bipyridine) (3,8-diarylethynyl-1,10-phenanthroline) complexes: anomalous behavior in the 3,8-dinitrophenylethynyl-substituted homologue

A large bathochromic shift (?50 nm) and emission in the near infrared is observed by attaching arylethynyl groups at the 3,8-positions of the 1,10-phenanthroline ligand (phen) of [Os(bipy)₂(phen)]²⁺ (where bipy = 2,2′-bipyridine). Thus [Os(bipy)₂(3,8-di-4-methoxyphenylethynyl-1,10-phenathroline)]²⁺ emits at 795 nm, while [Os(bipy)₂(3,8-diphenylethynyl-1,10-phenanthroline)]²⁺ emits at 815 nm. According to this trend it would have been expected that [Os(bipy)₂(3,8-di-4-nitrophenylethynyl-1,10-phenathroline)]²⁺ emits farther in the near infrared. Nevertheless, this complex is not photoluminescent because of intramolecular electron transfer quenching of the MLCT excited state by the nitroaromatic group. These results set structural and redox potential standards in the design of near infrared emitters based on [Os(bipy)₂(phen)]²⁺ type complexes.     

Structure, physical, chemical and photophysical properties of Pt(bph) (CO)2, where bph is the biphenyl dianion

The complex Pt(bph) (CO)₂ crystallizes in the space group Cmcm with a = 18.647(6), B = 9.566(2) and C = 6.4060(5) Å. The geometry of the molecule is slightly distorted from square planar with a Pt---C(CO) bond distance of 1.98(2) Å and a Pt---C(bph) bond distance of 2.04(2) Å. The Pt(bph)(CO)₂ complex serves as a precursor for the preparation of a wide variety of Pt(bph)X₂ complexes, where X = monodentate ligands such as acetonitrile, pyridine, etc., and X₂ = bidentate ligands such as bypyridine, 1,10-phenanthroline, etc. In the solid state, the complex exhibits a green color, but when ground with an alkali metal salt turns deep blue to purple. In CH₂Cl₂, the color disappears but optical transitions are observed at 271 nm (2.7 × 10⁴ M⁻¹ cm⁻¹), 303 nm (1.1 × 10⁴ M⁻¹ cm⁻¹) and 330 nm (5.5 × 10³ M⁻¹ cm⁻¹). The complex is a weak emitter exhibiting a structured spectrum in CH₂Cl₂ at r.t. with maxima located at 562 and 594 nm and an emission lifetime of 3.1 μs when excited at 337 nm.     

Synthesis and characterization of polypyridineruthenium(II) complexes containing a linear ambidentate ligand, NCO or NCS, and reaction of isocyanato complexes under acidic conditions

Isocyanato and isothiocyanatopolypyridineruthenium complexes, [Ru(NCX)Y(bpy)(py)₂]ⁿ⁺ (bpy=2,2′-bipyridine, PY=pyridine; X=O, Y=NO₂ for n=0, and Y=py for n=1; X=S, Y=NO₂ for n=0, Y=NO for n=2, and Y=py for n=1), were synthesized by the reaction of polypyridineruthenium complexes with potassium cyanate or sodium thiocyanate salt. Isocyanatoruthenium(II) complexes, [Ru(NCO)(NO₂)(bpy)(py)₂] and [Ru(NCO)(bpy)(py)₃]⁺, react under acidic conditions to form the corresponding ammineruthenium complexes, [Ru(NO)(NH₃)(bpy)(py)₂]³⁺. The molecular structures of [Ru(NCO)(bpy)(py)₃]ClO₄, [Ru(NCS)(NO)(bpy)(py)₂](PF₆)₂ and [Ru(NO)(NH₃)(bpy)(py)₂](PF₆)₃ were determined by X-ray crystallography.     

Three-photon induced fluorescence of the calcium probe Indo-1.

We report the calcium-dependent emission spectral properties of the calcium probe Indo-1 for three-photon excitation. We found that Indo-1 could be readily excited with the femtosecond pulses from a mode-locked Ti:sapphire laser at 885 nm. This wavelength is too long for two-photon excitation, which is expected to occur for wavelengths no longer than twice the longest single-photon absorption wavelength of 400 nm. For excitation at 885 nm the emission intensity was found to depend on the cube of the laser power, as expected for simultaneous interaction with three photons. At wavelengths below 840 nm the emission intensity depends on the square of the laser power, indicating two-photon excitation at shorter wavelengths. The intensity decays of Indo-1 were found to be dependent on Ca2+ and essentially identical for one- and three-photon excitation. The emission anisotropy of Indo-1 was found to be considerably higher for three-photon excitation than for one-photon excitation, consistent with cos6 theta photoselection, as compared with cos2 theta photoselection for one-photon excitation. The high values of the anisotropy are in agreement with those expected for a three-photon process. Calcium-dependent emission spectra were observed for Indo-1 with three-photon excitation, demonstrating that three-photon excitation of Indo-1 can be used for calcium imaging by emission intensity ratio measurements. The calcium-dependent emission spectra indicate a higher three-photon cross-section for the calcium-free form of Indo-1 than for the calcium-bound form. The possible advantages of three-photon excitation include the availability of the appropriate wavelengths with solid-state lasers, enhanced spatial resolution due to a reduced size of the excited volume, absence of light quenching, and possibly high selectivity of the three-photon excitation process.     

Ammonia ruthenium complexes for the access to new hydrido, carbonyl and isocyanide ruthenium-alkynyl derivatives

The potential in preparative chemistry of the precursors trans-[Ru(NH₃)(CC---R¹)(Ph₂PCH₂CH₂PPh₂)₂]PF₆ (3) has been studied. They offer a convenient access, by NH₃ displacement, to new functional alkynyl-ruthenium derivatives. Complexes 3 react with alkynes HCC---R² to give unsymmetrical trans-Ru(---CC---R¹)(---CC---R²)(dppe)₂ compounds 4a-c, and with sodium methoxide in methanol they open the route to a variety of mixed hydride complexes 5a-c, trans-Ru(H)(---CC---R¹)(dppe)₂. In contrast, with carbon monoxide or isocyanides CN---R³ (R³:CH₂Ph, C₆H₁₁, Me₃C) they allow the preparation of cationic derivatives trans-(Ru(CO)(---CC---R¹)(dppe)₂]PF₆ (6a-c) or trans-[Ru(CNR³)(---CC---R¹)(dppe)₂]PF₆ (7a-d).     

Charge transfer photochemistry of quadruply bonded ditungsten halophosphine complexes

The quadruple metal-metal bonded complexes, W₂Cl₄(PR₃)₄ (PR₃ = PMe₃, PMe₂Ph, PBu₃), photoreact in dichloromethane with near-UV excitation (λ>375 nm) to yield a mixed valence W₂(II,III) photoproduct. Electronic absorption and EPR spectra of photolyzed solutions are identical to those obtained from the thermal oxidation of W₂Cl₄(PR₃)₄ by PhICI₂, which is known to yield W₂Cl₅(PR₃)₃. Subsequent reaction of the photolyzed solution yields the oxidized, confacial biotahedral W₂(III,III) halophosphine. Analysis of the organic photoproduct reveals that the halocarbon solvent is reduced by one electron to yield the chloromethyl radical. When the radical is produced in low yields, hydrogen abstraction from solvent appears to be sufficiently efficient to compete with dimerization and only chloromethane is observed; however, at higher concentrations, the chloromethyl radicals couple to produce dichloroethane. Photoreaction is observed only with near-UV excitation of the LMCT absorption manifold of W₂Cl₄(PR₃)₄. At lower energy wavelengths, transient absorption spectroscopy shows the production of the ¹δδ^* excited state, which decays to ground state over times commensurate with the decay of ¹δδ^* luminescence. In hydrocarbon solutions, no transient intermediate or photochemistry is observed, indicating that the LMCT excited state, although capable of reducing a C---X bond, cannot activate the stronger C---H bonds of hydrocarbons. The photochemistry and transient absorption spectroscopy results of the W₂Cl₄(PR₃)₄ complexes are compared to our previous studies of the homologs.     

Enantioselectivity of resolved Δ and Λ orthoruthenated 2-phenylpyridine complexes [Ru(o-C6H4-2-py)(LL)2]PF6 (LL = bpy and phen) toward glucose oxidase

Cyclometalated 2-phenylpyridine complexes [Ru^II(o-C₆H₄-2-py)(LL)₂]PF₆, LL = 2,2′-bipyridine (1) and 1,10-phenanthroline (2) were resolved into Δ and Λ enantiomers using column chromatography on SP Sephadex C-25 in the presence of (+)-2,3-dibenzoyl-D-tartrate. The absolute configuration of enantiomers was established using circular dichroism spectroscopy. The rate constants k_et for the electron transfer from reduced glucose oxidase (GO from Aspergillus niger) and PQQ-dependent glucose dehydrogenase (GDH) at the generated Ru^III species were measured by cyclic voltammetry and UV–vis spectroscopy. The electron transfer shows enantioselectivity. In the case of GO, the bell-shaped pH profile for the ratio k_Λ/k_Δ has a maximum at pH 7 (k_Λ/k_Δ equals 3.4 and 3.9 for 1 and 2, respectively), but its inversion is observed at pH around 5 and 9. The k_Λ/k_Δ ratio equals 2.0 for 2 and GDH at pH 7. The results of theoretical modeling of biological electron transfer for GO using functional docking Monte-Carlo simulations are presented and analyzed together with the experimental observations.     

Monomeric and dimeric mixed-ligand copper(II) complexes of 2,2′-bipyridine/1,10-phenanthroline and 1-methylimidazole with imidazoles as catalysts for superoxide dismutation

Monomeric complexes [Cu(LL)(L′)(NO₃)₂] (where LL is 2,2′-bipyridine or 1,10-phenanthroline and L′ is 1-methylimidazole) and dimeric complexes [Cu₂(LL)₂(L″)]NO₃ (where L″ is an anion of imidazole or 2-methylimidazole) have been synthesized. These complexes show a d-d transition in the range of 600 to 710 nm. The infrared spectra of monomeric complexes show that the NO₃⁻ is coordinated to copper as a monodentate ligand through an oxygen atom. The ESR spectra of monomeric complexes indicate that the ligands are bonded in axial environment around copper (square pyramidal geometry) with three nitrogen donors occupying an equatorial plane. The ESR spectra of dimeric complexes show a broad signal at about G = 2 with an additional weak signal at about G = 4. This suggests that two copper atoms are in close proximity of < 7 Å. The ESR studies reveal that the formation of imidazolate-bridged binuclear copper(II) complexes from [Cu(LL)(L′)(NO₃)₂] and imidazole is pH dependent with apparent pK_a values of 8.25 to 8.30. The superoxide dismutase activity of ICu(phen)(L′)(NO₃)₂], [Cu(bipy)(L′)(NO₃)₂], and [Cu₂(bipy)₂(L′)₂(L″)]NO₃ has been measured and the latter two complexes show better activity than the former complex.     

The synthesis and reactivity of electrophilic iridium (III) complexes containing bis (diphenylphosphino) ethane

The complex Ir(CH₃) (CO) (CF₃SO₃)₂ (dppe) (1) has been synthesized from the reaction of Ir(CH₃)I₂(CO) (dppe) and silver triflate. Methane and IrH(CO) (CF₃SO₃)₂ (dppe) (2) are formed when a methylene chloride solution of 1 is placed under 760 torr dihydrogen. Conductivity studies indicate that methylene chloride solutions of complexes 1 and 2 are weak electrolytes and only partially ionized at concentrations above 1 mM. Complex 2 is an effective hydrogenation catalyst for ethylene and 1-hexene while acetone hydrogenation is inhibited by the formation of [IrH₂(HOCH(CH₃)₂) (CO) (dppe)] (OTf) (3). Linear dimerization and polymerization of styrene occurs via a carbocationic mechanism initiated by triflic acid elimination from 2. Treatment of an acetonitrile solution of Ir(CH₃)I₂(CO) (dppe) with silver hexafluorophosphate produces the solvent promoted carbonyl insertion product [Ir(C(O)CH₃) (NCCH₃)₃ (dppe)] [PF₆]₂ (7) which readily undergoes deinsertion in methylene chloride to form [Ir(CH₃) (CO) (NCCH₃)₂ (dppe)] [PF₆]₂ (8) and acetonitrile.     

Dynamics of supercoiled and relaxed pTZ18U plasmids probed with a long-lifetime metal-ligand complex

[Ru(bpy)2(dppz)](2+) (bpy = 2,2'-bipyridine, dppz = dipyrido- [3,2-a:2',3'-c]phenazine) (RuBD), a long-lifetime metalligand complex, displays favorable photophysical properties. These include long lifetime, polarized emission, but no significant fluorescence from the complex that is not bound to DNA. To show the usefulness of this luminophore (RuBD) for probing the bending and torsional dynamics of nucleic acids, its intensity and anisotropy decays when intercalated into supercoiled and relaxed pTZ18U plasmids were examined using frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source. The mean lifetimes for the supercoiled plasmids (< tau > = 148 ns) were somewhat shorter than those for the relaxed plasmids (< tau > = 160 ns). This suggests that the relaxed plasmids were shielded more efficiently from water. The anisotropy decay data also showed somewhat shorter slow rotational correlation times for supercoiled plasmids (288 ns) than for the relaxed plasmids (355 ns). The presence of two rotational correlation times suggests that RuBD reveals both the bending and torsional motions of the plasmids. These results indicate that RuBD can be useful for studying both the bending and torsional dynamics of nucleic acids.