Preparation and properties of osmoglobins. Oxidation-reduction catalytic activity of ruthenated osmoglobin

Reconstitution of native and ruthenium-modified sperm whale myoglobins (Mb and Ru₃Mb) with [Os^II(MIX)(CO)(EtOH)] (MIX = mesoporphyrin IX-dicarboxylic acid) and [Os^II(MIX)(DMF)₂] yields carbonyl osmoglobin ([Os^II(CO)][Mb]) and oxidized osmoglobins ([Os^III][Mb], [Os^III][Ru₃Mb]). The visible spectrum of [Os^II(CO)][Mb] exhibits and bands at 538 and 510 nm, respectively. The ascorbate reduction of dioxygen to water is catalyzed by [Os^III][Ru₃Mb].Contribution No. 7720 from the Arthur Amos Noyes Laboratory, California Institute of Technology, Pasadena, California 911255, U.S.A., and the Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong.     

Voltammetric study of electrocatalysis for dioxygen reduction by trinuclear rutheniumammine complex confined in a polymer membrane

Electrocatalytic O₂ reduction was studied using a modified electrode coated with a Nafion membrane (Nf) dispersing a trinuclear ruthenium ammine complex ([(NH₃)₅Ru^IIIORu^IV(NH₃)₄ORu^III(NH₃)₅]Cl₆, Ru-red). When measuring cyclic voltammogram under O₂ atmosphere (at 0.5 mV s⁻¹), catalytic currents due to O₂ reduction were found to develop below −0.2 V (vs. Ag/AgCl). Since Ru-red undergoes irreversible decomposition into the mononuclear complexes via the reduced state (Ru^III-Ru^III-Ru^III) (∼−0.1 V), it is suggested that the electrocatalysis originates from the decomposed species (initial active species: Ru^II(NH₃)₅(OH₂) and Ru^II(NH₃)₄(OH₂)₂) rather than from the Ru-red. Although the present electrocatalyst was also applied to H₂O₂ reduction system, the catalytic activity was found to be poor from the voltammetric behavior. It appeared that the kinetics of the electrocatalysis is much faster in the O₂ reduction than in the H₂O₂ one. A selective and direct catalysis for O₂ reduction into H₂O was suggested from a ring-disk voltammogram to take place by an aggregate of the mononuclear ruthenium complexes in the polymer matrix. In addition, it was found that electrocatalytic O₂ reduction involves a slow kinetic process, so that factors affecting the overall kinetics were discussed in terms of the catalysis mechanism.     

New Organometallic Tetraphenylethylene⋅Iridium(III) Complexes with Antineoplastic Activity

Iridium(III) complexes have attracted more and more attention in the past few years because of their potential antineoplastic activity. In this study, four Ir^III complexes of the types [(η⁵-Cp^x)Ir(N^N)Cl]PF₆ (complexes 1 and 2 ) and [Ir(Phpy)₂(N^N)]PF₆ (complexes 3 and 4 ) have been synthesized and characterized. They exhibit potential antineoplastic activity towards A549 cells, especially in the case of complex 1 [IC₅₀=(3.56±0.5) μm ], which was nearly six times as effective as cisplatin [(21.31±1.7) μm ]. Additionally, these complexes show some selectivity towards cancer cells over normal cells. They could be transported by serum albumin (binding constants were changed from 0.37×10⁵ to 81.71×10⁵ m ⁻¹). Ir^III complexes 1 and 2 could catalyze the transformation of nicotinamide adenine dinucleotide reduced form (NADH) into NAD⁺ (turnover numbers 43.2, 11.9] and induce the accumulation of reactive oxygen species, thus confirming their antineoplastic mechanism of oxidation, whereas the cyclometalated complexes 3 and 4 were able to target the lysosome [Pearson co-localization coefficient (PCC)=0.73], cause lysosomal damage, and induce apoptosis. Understanding the mechanism of action would help further structure–activity optimization on these Ir^III complexes as emerging cancer therapeutics.     

Separation and preconcentration followed by ICP-OES and ICP-MS determination of precious metals using silica gel chemically modified with dithiocarbamate groups

ABSTRACT

Silica gel chemically modified with dithiocarbamate groups (DTCS) was used for separation and preconcentration of precious metals and their subsequent determination in geological samples and their processing products by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry. DTCS was characterized by TGA/DSC, FT-IR, and CHNS-analysis. DTCS quantitatively extracted Au³⁺, Pd²⁺, Pt²⁺, Pt⁴⁺ at 20°C from 0.5 to 4.0 M HCl media and Rh³⁺, Ir⁴⁺, Ru⁴⁺, and Os⁴⁺ at 95°C in the presence of 0.025 M SnCl₂. Two-column procedure was proposed to separate precious metals from matrix components and to separate kinetically inert precious metals from kinetically labile ones.     

Structure and electrochemistry of a tetrakis(ferrocenecarboxylato)diruthenium(II,III) diadduct: evidence for ferrocenyl–ferrocenyl communication

1-Propanol and ethanol adducts of tetrakis(ferrocenecarboxylato)diruthenium(II,III) hexafluorophosphate have been synthesized and the 1-propanol diadduct has been characterized by X-ray crystallography. The cyclopentadienyl rings of all four ferrocenyl groups showed on average a 13° deviation from the eclipsed conformation. Cyclic voltammetry measurements in 1,2-dichloroethane show an irreversible Ru^IIIRu^II/Ru^IIRu^II reduction and four partially superimposed one-electron ferrocenyl-centred electron transfer processes. The existence of ferrocenyl-based mixed-valent intermediate states posessing Fe^III and Fe^II sites are implied by the splitting of the ferrocenyl wave into two observable cathodic and anodic peaks. The first cathodic wave shows typical desorption behaviour. Osteryoung Square Wave Voltammetry (OSWV) supports the above findings.     

A Hydroxyquinoline-Based Unnatural Amino Acid for the Design of Novel Artificial Metalloenzymes

We have examined the potential of the noncanonical amino acid (8-hydroxyquinolin-3-yl)alanine (HQAla) for the design of artificial metalloenzymes. HQAla, a versatile chelator of late transition metals, was introduced into the lactococcal multidrug-resistance regulator (LmrR) by stop codon suppression methodology. LmrR_HQAla was shown to complex efficiently with three different metal ions, Cu^II, Zn^II and Rh^III to form unique artificial metalloenzymes. The catalytic potential of the Cu^II-bound LmrR_HQAla enzyme was shown through its ability to catalyse asymmetric Friedel-Craft alkylation and water addition, whereas the Zn^II-coupled enzyme was shown to mimic natural Zn hydrolase activity.     

Synthetic and Spectroscopic Studies of Polymeric Metal Complexes Involving 1,4-[5-Disulphonyl-8-Hydroxyquinoline]piperazine

The polymeric metal complexes of Co^II, Ni^II, Cu^II, Zn^II, Cd^II , Ce^III, La^III and UO₂ ^II with 1,4-[5-disulphonyl-8-hydroxyquinoline]piperazine have been synthesized. It has been found that the ligand coordinates to the metal ion as a bibasic tetradentate chelating agent and can form polymeric metal complexes. The structure of the isolated metal complexes is supported by chemical analysis, thermoanalytical data, and conductivity measurements, as well as uv-visible, ¹H-NMR, and IR spectroscopy. The stoichiometry of these metal complexes is M:L=2:3. A tetrahedral stereochemical configuration is suggested for the polymeric metal complexes with the exception of the Ce^III and La^III complexes, which form six-coordinate polymeric metal complexes.     

Electrocatalysis Characteristics of a Polynuclear Cyanide Complex, Ruthenium Purple, for Dihydrogen Oxidation

An electrocatalytic dihydrogen oxidation was found to take place on an electrode coated with iron(III) ruthenocyanide (i.e., repeating unit cell structure: Fe^III ₄[Ru^II(CN)₆]₃ or MFe^III[Ru^II(CN)₆] and M = alkali metal counter ion) called ruthenium purple (RP). It was shown by voltammetric study that an electrocatalytic dihydrogen oxidation is induced on oxidizing the Fe^II ion in the cyanometallate. When the electrocatalysis characteristics of RP were investigated by voltammetry, especially in terms of the kinds of electrolyte used (K⁺ or Na⁺), RP exhibited a more efficient electrocatalysis in the K⁺ than in the Na⁺ electrolyte system. While a one-electron electro-oxidation of Fe^II to Fe^III occurs, there is also a release of hydrated alkali metal cation(s) from the anionic RP (i.e., reduced RP) to compensate for charge. Moreover, cation transport through the cyanometallate network is more facile for the K⁺ electrolyte system (cf., size of hydrated cation: Na⁺ at 0.36 nm lattice channel of RP at 0.35 nm > K⁺ at 0.24 nm). Therefore, it was most probable that the present electrocatalysis is kinetically dominated by the electro-oxidation.     

Efficient Electron Transfer Processes and Enhanced Electrocatalytic Activity of Cobalt(II) Porphyrin Anchored on Graphene Oxide

We investigated the electronic perturbation between graphene oxide and cobalt porphyrin to reveal the origin of the enhanced electrocatalytic activity of a hybrid complex using time-resolved spectroscopic measurements and theoretical calculations. The impulsively generated charge-separated state, GO⁻-(Co^IIAPFP)⁺, undergoes fast charge recombination (<10 ps) between GO⁻ and (Co^IIAPFP)⁺ moieties. This fast charge recombination is directly related to the quick neutralization of (Co^IIAPFP)⁺, which shortens the dead time of inactive Co^IIIAPFP after the electrocatalytic reduction reaction. The fast transformation of inactive Co^IIIAPFP to active Co^IIAPFP is an important factor in the enhanced electrocatalytic activity of the hybrid complex.     

Triazolyl-Functionalized N-Heterocyclic Carbene Half-Sandwich Compounds: Coordination Mode,Reactivity and in vitro Anticancer Activity

We report investigations on the anticancer activity of organometallic [M^II/III(η⁶-p-cymene/η⁵-pentamethylcyclopentadienyl)] (M=Ru, Os, Rh, and Ir) complexes of N-heterocyclic carbenes (NHCs) substituted with a triazolyl moiety. Depending on the precursors, the NHC ligands displayed either mono- or bidentate coordination via the NHC carbon atom or as N,C-donors. The metal complexes were investigated for their stability in aqueous solution, with the interpretation supported by density functional theory calculations, and reactivity to biomolecules. In vitro cytotoxicity studies suggested that the nature of both the metal center and the lipophilicity of the ligand determine the biological properties of this class of compounds. The Ir^III complex 5 d bearing a benzimidazole-derived ligand was the most cytotoxic with an IC₅₀ value of 10 μM against NCI-H460 non-small cell lung carcinoma cells. Cell uptake and distribution studies using X-ray fluorescence microscopy revealed localization of 5 d in the cytoplasm of cancer cells.     

Electrochemical disproportionation in new ruthenium (II) nitro complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine detected by IR spectroelectrochemistry with an OTTLE cell

The syntheses and characterization of new nitro complexes of Ru(II) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and different substituted bipyridines are reported. A disproportionation reaction can occur after applying an oxidation potential corresponding to the couple Ru^II/Ru^III forming the nitrate and the nitrosyl complexes, which were detected by cyclic voltammetry. This reaction was confirmed by IR-spectroelectrochemistry with an OTTLE cell, for the first time. Additionally, for 2,2′-bipyridine we have obtained as ClO₄⁻ salt a new nitrosyl-complex which presents an elevated IR stretching frequency.     

Ruthenium(II)–Arene Thiocarboxylates: Identification of a Stable Dimer Selectively Cytotoxic to Invasive Breast Cancer Cells

Ru^II-arene complexes provide a versatile scaffold for novel anticancer drugs. Seven new Ru^II-arene-thiocarboxylato dimers were synthesized and characterized. Three of the complexes ( 2 a , b and 5 ) showed promising antiproliferative activities in MDA-MB-231 (human invasive breast cancer) cells, and were further tested in a panel of fifteen cancerous and noncancerous cell lines. Complex 5 showed moderate but remarkably selective activity in MDA-MB-231 cells (IC₅₀=39±4 μm Ru). Real-time proliferation studies showed that 5 induced apoptosis in MDA-MB-231 cells but had no effect in A549 (human lung cancer, epithelial) cells. By contrast, 2 a and b showed moderate antiproliferative activity, but no apoptosis, in either cell line. Selective cytotoxicity of 5 in aggressive, mesenchymal-like MDA-MB-231 cells over many common epithelial cancer cell lines (including noninvasive breast cancer MCF-7) makes it an attractive lead compound for the development of specifically antimetastatic Ru complexes with low systemic toxicity.     

Theranostics Through the Synergistic Cooperation of Heterometallic Complexes

Heterometallic drugs are emerging as a great alternative to conventional metallodrugs. Careful selection of different metallic fragments makes possible to enhance not only the therapeutic potential by a synergistic effect, but also to incorpore key features like traceability. Drugs that integrate traceability and therapy in one system are known as theranostic agents. In cancer research, theranostic agents are becoming increasingly important. They deliver crucial information regarding their biological interplay that can ultimately be used for optimization. The well-established therapeutic potential of Pt^II-, Ru^II- and Au^I-based drugs combined with the outstanding optical properties of d⁶ transition metal complexes grant the delivery of traceable metallodrugs. These species can be easily fine-tuned through modification of their respective ligands to provide a new generation of drugs.     

Magnetic behavior of polycarbosilazane ?FeII, ?FeIII and mixed‐valence ?FeII–III chloride metallopolymers

Fe^II, Fe^III and mixed‐valence Fe^II–III chlorides were reacted with poly[N,N′‐bis(dimethylsilyl)ethylenedi‐ amine], [? Si(CH₃)₂NHCH₂CH₂NH? ]_n, to form the corresponding Fe‐polycarbosilazane macromolecular complexes. The average chain–chain spacing in these materials was estimated from X‐ray diffraction data and found to be 6.94, 7.29, 7.30 and 7.45 Å in metal‐free and Fe^II? , Fe^III? and Fe^II–III‐containing polycarbosilazanes, respectively. This demonstrates that Fe^II, Fe^III and Fe^II–III chlorides are encapsulated between the polycarbosilazane chains. The chain–chain expansions in the divalent Fe^II and trivalent Fe^III chloride macromolecular complexes are comparable, but less than that in the Fe^II–III chloride analog, which suggests that different chain–chain packings exist in the mixed‐valence macromolecular complex. The magnetic properties of the resulting complexes were investigated by measuring the magnetization in magnetic fields up to 8 kOe and in the temperature range from liquid nitrogen temperature to room temperature. Copyright © 2007 Society of Chemical Industry     

Mechanistic comparison between oxidative and reductive charge transport by [(bpy)2(H2O)RuORu(H2O)(bpy)2] confined in a Nafion membrane as studied by potential-step chronocoulospectrometry

Charge transport (CT) in a Nafion membrane containing μ-oxobis[aquabis(2,2′-bipyridine)ruthenium(III)] complex, [(bpy)₂(H₂O)RuORu(H₂O)(bpy)₂]⁴⁺ (bpy=2,2′-bipyridine, abbreviated to Ru^IIIORu^III) was investigated by potential-step chronocoulospectrometry (PSCCS). Electrochemical reduction of Ru^IIIORu^III in the membrane occurred irreversibly to form [Ru(bpy)₂(OH₂)₂]²⁺ monomer. The CT by reduction of Ru^IIIORu^III in the membrane was suggested to take place by physical displacement of the complex, which is quite different from the mechanism in the CT by oxidation of Ru^IIIORu^III in the same membrane in which charge is transported by charge hopping based on reversible redox reaction between Ru^IIIORu^III and Ru^IIIORu^IV. The fractions of the electrochemically reacted complex in the membrane for the oxidative CT was dependent on the complex concentration, and the yield was low (maximum fraction=0.42 at 0.87 M) relative to the reductive CT. By contrast, the fraction for the reductive CT was independent of the concentration over 0.12 M and close to unity. The different concentration dependence of the fraction was discussed related to the difference in the CT mechanism.     

Reductively Induced Catalytic DNA Cleavage of Water Soluble Rh<Superscript>III</Superscript>-Br<Subscript>8</Subscript>TMPyP

Abstract  

The Rh^III(Br₈TMPyP)⁵⁺ showed a catalytic DNA cleavage in the presence of ascorbic acid. The UV–visible, Cyclic Votlammetric (CV) and Electron Spin Resonance (ESR) data confirmed involvement of the reduced form of the Rh^III-Br₈TMPyP, Rh^III(Br₈TMPyP)^4+· radical, in the catalytic cycle. Gel-electrophoresis, results revealed that, Rh^III(Br₈TMPyP)⁵⁺ could cleave DNA at 0.01–0.1 μM levels which is significantly higher than that of other metalloporphyrins.     

Feasible attachment of dinuclear ruthenium complex to gold electrode surface via new ligand substitution reaction

A general method has been developed for accumulation of a dinuclear ruthenium complex [Ru₂(dhpta)(μ-O₂CCH₃)₂]⁻ (H₅dhpta = 1,3-diamino-2-hydroxypropane-N,N,N′,N′-tetraacetic acid) on a gold surface. The accumulation using a ligand substitution reaction of bridging acetate in the complex by terminal benzoic acid in a self-assembled monolayer (SAM) with ω-mercaptoalkoxy benzoic acid (HOOC-C₆H₄-O-(CH₂)_n-SH) (n = 4, 6, 12) is undergone. The methyl benzoate-containing alkyl disulfides capable to form SAMs on gold electrode have been synthesized utilizing reductive dimerization of the corresponding alkyl thiocyanates with tetraphenylphosphonium tetrathiomolybdate. The methyl benzoate group in the SAM was converted into benzoic acid group by base hydrolysis, which was confirmed by surface-enhanced Raman scattering measurements for silver electrode. After the ligand substitution reactions to accumulate the complex on the gold electrode surface, in the case of n = 6 and n = 12, voltammetric waves for surface confined redox process, which corresponds to Ru^IIIRu^III/Ru^IIIRu^II redox couple are observed, respectively, and these surfaces of gold electrodes are covered with the complex completely. The present ligand substitution reaction should be widely applicable for the accumulation of other complexes and useful for designing of functional electrodes.     

Aqueous radical polymerization of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylacrylamide redox-initiated by aerobically catalytic oxidation of water-soluble tertiary amines

Catalytic oxidation of water-soluble tertiary amines by complexes of Cu^II, Fe^III and Co^II was utilized to initiate radical polymerization of N,N-dimethylacrylamide (DMAAm) in aqueous solution at 70–80 °C. The oxidation of tertiary amines by Cu^II was studied by proton nuclear magnetic resonance spectroscopy and online ultraviolet–visible spectrophotometry. The polymerization kinetics was monitored by gas chromatography, and molecular weight of the PDMAAm was measured by gel-permeation chromatography coupled with multi-angle laser light scattering. Oxidation of tertiary amines occurs predominantly via formation of C_alpha·radicals to initiate polymerization of electron-deficient monomers and N-dealkylation, and redox equilibrium between Cu^I/L and Cu^II/L is established at a faster rate in aqueous media. Fe^III and Cu^II complexes are efficient catalysts as each catalyst molecule could generate above 10 propagating radicals in 5 h, while Co^II complex might involve in oxidation of tertiary amines in non-radical pathway, leading to a low catalytic efficiency. Water-soluble tertiary amines such as N,N-dialkylethanolamine (alkyl = methyl, ethyl etc.) are reducing agents of a higher activity in aqueous media than those primary or secondary analogues. Our strategy renders it possible to prepare polymer of alpha-amino functionality via one-pot process from commercially available commodity reagents under practical conditions with negligible catalyst residue.     

Aggregation-induced Phosphorescence Enhancement in IrIII Complexes

Transition metal complexes that efficiently emit from an excited state with formally triplet character are an appealing class of compounds. However, they typically suffer from severe quenching, e. g. triplet-triplet annihilation, in aggregated phase that often hampers their use in the solid-state. Nonetheless, an intriguing effect, namely aggregation-induced phosphorescence enhancement, has been sometimes observed, but clear elucidation of the mechanisms underlying this phenomenon is far from trivial. Nowadays, cyclometalated Ir^III emitters play a leading role due to their outstanding features. Aiming at a rationalization of the AIPE effect, an overview of the different classes of Ir^III emitters displaying enhancement of the emission upon aggregation will be herein provided along with their potential applications. Their photophysical properties will be discussed jointly with their X-ray structural analysis. Ir^III complexes represent the largest family of AIPE-active compounds to date.     

Synthesis,characterization and catalytic activities of ruthenium complexes containing triphenylphosphine/triphenylarsine and tetradentate Schiff bases

Ruthenium(II) complexes of the type [Ru(CO)(B)(L)] (B=AsPh₃, pyridine, piperidine or morpholine; L=dianion of tetradentate Schiff bases) have been synthesized and characterized by physico-chemical methods. These complexes are found to be effective catalysts in the oxidation of primary and secondary alcohols using N-methylmorpholine-N-oxide as oxidant. The catalytic activity of these triphenylarsine complexes have been compared with that of triphenylphosphine complexes and with similar ruthenium(III) complexes. The formation of high valent Ruⁿ⁺²O species as catalytic intermediate is proposed for the catalytic processes.