Redox-active Complexes Research Articles

Reactivity of Bulged Bases in Duplex DNA with Redox-active Nickel and Cobalt Complexes

The square-planar, macrocyclic complex NiCR (CR=(2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaenato)) as well as CoCl 2 have been investigated as catalysts for the site-specific oxidation of bulged T, C, and A nucleotides in duplex DNA oligomers. Previous studies of NiCR using KHSO 5 as oxidant indicated that this combination of reagents successfully probes the accessibility of N7 of guanine residues in non-canonical DNA and folded RNA structures. In the present study, the order of reactivity of bulged bases in synthetic oligodeoxynucleotides with NiCR/KHSO 5 is shown to be G>C>T∼A. Although the nickel complex generates a less-reactive oxidant than does cobalt, its selectivity for bulged bases is much greater, rendering it a useful probe of exposed Cs and Ts in addition to Gs in DNA and RNA structure.

A diruthenum(III) complex possessing a diazine and two chloride bridges: synthesis, structure, and properties.

A dinuclear Ru(III) complex, [Ru2Cl2(PPh3)2(μ-Cl)2(μ-salhn)], has been synthesized and characterized by analytical, spectroscopic, magnetic, and X-ray diffractometry. The redox active complex displ...

Redox-Activity in Complexes with Mo(NO) and Mo(O) Cores: Facts and Consequences

A series of mono, di-, tri- and tetranuclear nitrosyl and oxo molybdenum complexes containing the tris(3,5-dimethylpyrazolyl)borato ligand exhibit a range of redox processes which are controlled mainly by the ligands and by the extent of oligonucleation. Homo-and hetero-dinuclear complexes have a range of properties dependent on this redox behaviour, and linear (electrochromism in the near infrared) and non-linear (second harmonic generation) properties are described.

Electrochemical Properties of Dinuclear Ru Complex Langmuir-Blodgett Films towards Molecular Electronics

A novel amphiphilic Ru dinuclear complex, [(L 18)Ru(tppz)Ru(L18)]4+, was synthesized and was introduced as a redox-active complex in Langmuir-Blodgett (LB) films, where L18= 2,6-bis(2′-(1′-octadecylbenzimidazolyl))pyridine and 2,3,5,6-tetrakis(2′-pyridyl)pyrazine (tppz). This Ru complex leads to a stable LB film formation and monolayers of this complex were transferred on glass and indium-tin oxide (ITO) substrates. The π-A isotherm indicates an orientation of the complex with Ru-Ru axis nearly parallel to the substrate surface. Two succesive one-electron oxidation processes were observed for the LB monolayer on ITO electrode.

Hydrogen-Bonding Cavities about Metal Ions: A Redox Pair of Coordinatively Unsaturated Paramagnetic Co-OH Complexes.

Nature uses hydrogen bonds to regulate a variety of metal-based reactions. These effects are emulated in the stabilization of trigonal-bipyramidal, paramagnetic Co-OH complexes such as the mono- or dianionic redox-active complex 1 by use of a new hydrogen-bonding ligand.

Diamine preparation for synthesis of a water soluble Ni(II) salen complex

A reliable and efficient synthesis of NiNi(II) salen complex useful in probing nucleic acid structure is described and illustrates a general approach for constructing cis diamines suitable for assembly into N 2O 2 Schiff base complexes. Two equivalents of an aryllithium reacted with 1,4-dimethylpiperazine-2,3-dione to form the symmetric α-dione. This material was then converted to its dioxime and reduced by TiCl 4/NaBH 4 to yield the meso-diamine. Condensation of the diamine and salicyladehyde, coordination of nickel and final methylation generated the desired water soluble and redox active complex.

Spectral and Electrochemical Behavior of Copper(II)-Phenanthrolines Bound to Calf Thymus DNA. [(5,6-dimethyl-OP)(2)Cu](2+) (5,6-dimethyl-OP = 5,6-Dimethyl-1,10-phenanthroline) Induces a Conformational Transition from B to Z DNA.

The interaction of 1:2 copper(II) complexes of 1,10-phenanthroline (OP) and variously methyl-substituted phenanthrolines with calf thymus DNA has been investigated by viscometry and spectral and electrochemical techniques. Viscometry and competitive ethidium bromide (EthBr) emission studies reveal that substitutions at 4- and 4,7-positions confer the complex a reduced affinity for DNA via partial intercalative interaction of the middle ring of OP between the base pairs of DNA, while substitutions at 5- and 5,6-positions confer a weak affinity toward DNA. The tetramethyl substitution at 3,4,7,8-positions lead to an intermediate behavior for the complex. Circular dichroism spectral studies of the interaction disclose for the first time that, of all the complexes, the 5,6-dimethyl-OP complex is a unique and remarkable reagent in that it reversibly binds to DNA and effects the important conversion of right-handed B DNA to left-handed Z DNA even in the presence of EthBr, an allosteric effector of the B conformation of DNA. This novel conformational transition is unexpected of the low GC content of natural DNA. The ratios of the binding constants (K(+)/K(2+)) for DNA binding of the Cu(I) and Cu(II) forms of the redox active OP complexes rather than the Cu(II)/Cu(I) redox potentials (0.023 to -0.098 V vs SCE) are good measures of the substituent dependent DNA cleavage efficiency and rate. They also reveal that the Cu(I) form of OP and 4-methyl- and 5,6-dimethyl-substituted OP complexes displays enhanced affinity to bind but noncovalently to the minor groove of DNA. Attempts have been made to illustrate the cleavage rate and efficiency of nucleolytic reactions in the light of the relative binding constants of Cu(I) and Cu(II) forms of the OP complexes.

Characterization of a redox active cross-linked complex between cyanobacterial photosystem I and soluble ferredoxin.

A covalent stoichiometric complex between photosystem I (PSI) and ferredoxin from the cyanobacterium Synechocystis sp. PCC 6803 was generated by chemical cross-linking. The photoreduction of ferredoxin, studied by laser flash absorption spectroscopy between 460 and 600 nm, is a fast process in 60% of the covalent complexes, which exhibit spectral and kinetic properties very similar to those observed with the free partners. Two major phases with t(1/2) <1 micros and approximately 10-14 micros are observed at two different pH values (5.8 and 8.0). The remaining complexes do not undergo fast ferredoxin reduction and 20-25% of the complexes are still able to reduce free ferredoxin or flavodoxin efficiently, thus indicating that ferredoxin is not bound properly in this proportion of covalent complexes. The docking site of ferredoxin on PSI was determined by electron microscopy in combination with image analysis. Ferredoxin binds to the cytoplasmic side of PSI, with its mass center 77 angstroms distant from the center of the trimer and in close contact with a ridge formed by the subunits PsaC, PsaD and PsaE. This docking site corresponds to a close proximity between the [2Fe- 2S] center of ferredoxin and the terminal [4Fe-4S] acceptor FII of PSI and is very similar in position to the docking site of flavodoxin, an alternative electron acceptor of PSI.

The specificity of mitochondrial complex I for ubiquinones.

We report the first detailed study on the ubiquinone (coenzyme Q; abbreviated to Q) analogue specificity of mitochondrial complex I, NADH:Q reductase, in intact submitochondrial particles. The enzymic function of complex I has been investigated using a series of analogues of Q as electron acceptor substrates for both electron transport activity and the associated generation of membrane potential. Q analogues with a saturated substituent of one to three carbons at position 6 of the 2,3-dimethoxy-5-methyl-1,4-benzoquinone ring have the fastest rates of electron transport activity, and analogues with a substituent of seven to nine carbon atoms have the highest values of association constant derived from NADH:Q reductase activity. The rate of NADH:Q reductase activity is potently but incompletely inhibited by rotenone, and the residual rotenone-insensitive rate is stimulated by Q analogues in different ways depending on the hydrophobicity of their substituent. Membrane potential measurements have been undertaken to evaluate the energetic efficiency of complex I with various Q analogues. Only hydrophobic analogues such as nonyl-Q or undecyl-Q show an efficiency of membrane potential generation equivalent to that of endogenous Q. The less hydrophobic analogues as well as the isoprenoid analogue Q-2 are more efficient as substrates for the redox activity of complex I than for membrane potential generation. Thus the hydrophilic Q analogues act also as electron sinks and interact incompletely with the physiological Q site in complex I that pumps protons and generates membrane potential.

Synthesis, Structure, and Properties of Dinuclear and Trinuclear Rack‐Type RuII Complexes

Linear arrangements of metal centers fixed by polydentate bridging ligands are found in new RuII complexes. In the redox-active complex 1 (X = H, 9-anthryl), which resmbles a rack, the metal centers can communicate through the bridging ligand.

Synthesis, spectral properties and redox behaviour of cis-dioxo-molybdenum(VI) complexes with tridentate arylazo ligands

Molybdenum complexes of type [MoO 2L] ( 2) [where HL = 1-(2-hydroxyphenylazo)-2-hyydroxynaphthalene or its substituted derivative] have been isolated. They are deep red coloured, non-electrolytic and diamagnetic in nature and have been characterized by elemental analyses and spectroscopic techniques (electronic, IR, and 1H NMR). They react with different Lewis bases (B) to yeild [MoO 2L(B)] ( 3) complexes. The redox activity of complexes 2 were systematically examined by cyclic voltammetry at a glassy carbon electrode in non-aqueous medium. All the complexes show a one-electron reduction of quasi-reversible nature near −0.6 V vs SCE.

Redox-active organometallic Ir complexes containing biphenyl-2,2′-diyl

The redox-active complexes [Ir(PPh3)2(biph)Cl]3 and [Ir(PMe3)3(biph)Cl]6 contain biphenyl-2,2-diyl (biph), the organometallic analogue of bipy; 3 shows an unexpected five-coordinate structure lying between T and Y geometry and oxidation of 6 by NOBF4 gives [Ir(PMe3)3(biphBF)Cl]+(8)+, an unprecedented IrIV boryl complex.

Molecular Mechanisms of the Reduction of NO to NH2OH at MoS Centers

The coordinatively flexible and redox-active complex fragment [Mo(NO)(′S4′)] in 1 makes the stepwise, and in principle catalytic, reduction of NO to NH2OH possible. The two single steps can be clearly distinguished as 2e/2H+ and 1e/1H+ reductions. This reaction may be considered a model for the molecular processes in the reduction of NO to NH2OH within the conversion of NO to NH3 in the nitrogen cycle in nature.

Hydrogen Peroxide Dependent Oxidative Degradation of DNA by Copper Epinephrine

The hydrogen peroxide dependent oxidation of the epinephrine-copper complex to adrenochrome is mediated by free copper ions. The oxidation is enhanced by chloride ions and by the presence of serum albumin. The reaction is not inhibited by SOD or by hydroxyl radical scavengers. The 2:1 epinephrine or dopamine:Cu(II) complexes are able to bind to DNA and to catalyze its oxidative destruction in the presence of hydrogen peroxide. The DNA-epinephrine-Cu(II) terenary complex has characteristic spectral properties. It has the capacity to catalyze the reduction of oxygen or H2O2 and it preserves the capacity over a wide range of complex:DNA ratios. The rate of DNA clevage is proportional to the rate of epinephrine oxidation and the rate determining step of the reaction seems to be the reduction of free Cu(II) ions. The ability to form redox active stable DNA ternary complexes, suggests that under specific physiological conditions, when "free" copper ions are available, catecholamines may induce oxidative degradation of DNA and other biological macromolecules.

Redox-active daunomycin-spin-labeled nucleic acid complexes

Interaction studies between daunomycin (DM) and enzymatically spin-labeled nucleic acid duplexes reveal two modes of binding by electron spin resonance (ESR) spectroscopy. At a low drug/nucleotide (D/N) ratio, the drug binds in the intercalative mode with only a slight reduction in base mobility. Saturation in the intercalative mode is achieved at a lower D/N ratio for B' DNA than for B DNA. After full intercalation, further addition of DM seems to destabilize the helix and to allow the formation of redox-active DM stacks complexed to the nucleic acid lattice. These stacks will irreversibly oxidize all the nitroxides covalently bound to the 4- or 5-position of the pyrimidine base. Interactions between DM and spin-labeled single-stranded nucleic acids lead directly to the formation of redox-active complexes, while mixing of the drug with spin-labeled nucleic acid building blocks not incorporated in a nucleic acid lattice causes no ESR signal change. Complete disappearance of the ESR signal of spin-labeled nucleic acids extrapolates to a D/N value which is a constant for a particular lattice system and is independent of spin-labeling content.

Binuclear halide-bridged ruthenium(II) complexes containing terminal alkene, alkyne, and dinitrogen ligands

Convenient, high-yield routes to the new redox-active complexes [(PEt2Ph)3Ru(µ-Cl)3RuL(PEt2Ph)2]BF4(L = C2H4, PhCCH, N2 etc.) and [(PEt2Ph)3ClRu(µ-Cl)2RuL′2Cl(PEt2Ph)](L′= C2H4 or PhCCH) are described.

Redox-active planar complexes. Electrochemical investigations of palladium and platinum bis(dithioacetylacetonate) complexes and their structural analogues

Direct- and alternating-current voltammetric investigations in CH2Cl2 of 17 variously substituted planar bis(dithio-β-diketonate) complexes [M(S2C3RHR′)2](M = Ni, Pd, or Pt and R,R′= But,CF3, Me, or Ph), including many new palladium and platinum complexes, confirm two reversible reductions in each case. The rapid rearrangement reported for [M(S2C3MeHMe)2]– is largely suppressed in the other derivatives, apparently for steric rather than electronic reasons. The successive one-electron transfers are found to be ligand-centred in [M(S2C3RHR)2], as in the metal ‘dithienes’[M(S2C2R2)2], despite their difference in topology. An orderly and comparable dependence of reduction potentials on substituent influence (σ*R) is displayed by all such systems. The isostructural diketonates, [M(O2C3RHR′)2](M = Pd or Pt), show a parallel trend in first reduction potential and are systematically ca. 0.4 V more difficult to reduce than their dithio-analogues.

Existence of specific binding sites in 1:1 oxidations of reduced parsley 2-Fe ferredoxin with inorganic complexes

Competition studies using redox active and inactive inorganic complexes have indicated that single unique binding sites are effective in individual reactions, and for the series of reactions investigated selection and utilization of different sites varies with the charge and/or ligand type on the complex.