Cyclometalated Osmium Compounds and beyond: Synthesis, Properties, Applications.

The synthesis of cyclometalated osmium complexes is usually more complicated than of other transition metals such as Ni, Pd, Pt, Rh, where cyclometalation reactions readily occur via direct activation of C-H bonds. It differs also from their ruthenium analogs. Cyclometalation for osmium usually occurs under more severe conditions, in polar solvents, using specific precursors, stronger acids, or bases. Such requirements expand reaction mechanisms to electrophilic activation, transmetalation, and oxidative addition, often involving C-H bond activations. Osmacycles exhibit specific applications in homogeneous catalysis, photophysics, bioelectrocatalysis and are studied as anticancer agents. This review describes major synthetic pathways to osmacycles and related compounds and discusses their practical applications.

TAML activator-based amperometric analytical devices as alternatives to peroxidase biosensors.

The ferric TAML catalysts [Fe{C(6)H(2)-1,2-( NCOCMe(2)NCO)(2)CMe(2)}(OH(2))](-) (1) with counterions Na(+) (a) and PPh(4)(+) (b) function similar to horseradish peroxidase in the mediated electron transfer relays, which constitute a basis for amperometric biosensors. The mediators are mono- and bis-cyclometalated Ru and Os compounds of the type of [M(C∼N)(x)(N∼N)(3-x)](m+) with x = 1 and 2 (N∼N = 2,2'-bipyridine, (-)C∼N = 2-phenylpyridinato). Cyclic voltammograms of the Ru and Os compounds are not affected by 1a though cathodic currents increase drastically in the presence of hydrogen peroxide. The reduction potentials of [M(C∼N)(x)(N∼N)(3-x)](m+) complexes vary with both the nature of metal (Ru or Os) and the number of cyclometalated ligands x (1 or 2) and therefore the potential of working electrode can be set in the range of from -0.1 to +0.6 V versus the normal hydrogen electrode (NHE). A prototype of a biosensor for H(2)O(2) is described, in which the 1b catalyst and [Os(C∼N)(2)(N∼N)](+) mediator were coimmobilized on the surface of the glassy carbon electrode using a polymeric coating.

Density Functional Theory and UPLC/MS/ESI+ studies of the zwitterionic surfactant-Na+ pair formation.

The formation in solution of supramolecular complexes type zwitterion-cation have been shown. The industrial grade zwitterion surfactants cocamidopropyl hydroxysultaine and cocamidopropyl betaine with sodium ion were studied. A combined experimental and theoretical point of view was performed, through the use of Ultra-Performance Liquid Chromatography/Mass Spectrometry/ElectroSpray Ionization with positive mode (UPLC/MS/ESI+) analytic technique and Density Functional Theory (DFT) theoretical approach. Then, the supramolecular complex zwitterion-cation-anion triplets are shown to be viable. Mass/Charge (m/z) relationships have been determined through MS/ESI using positive mode as an ionization source, obtaining five and four molecular species for industrial grade sultaine and betaine chemical products, respectively. Also, molecular zwitterion-NaCl complexes were theoretically studied in three different dielectric constants corresponding to water, methanol, and acetone solvents. It was found that acetone, the lower dielectric constant solvent studied, shows the higher interaction energy. In both vacuum neutral, zwitterion-NaCl, and vacuum positive, zwitterion-Na+, molecular complexes the interaction of the cocamidopropyl hydroxysultaine pairs is less strong than cocamidopropyl betaine ones.

Quantum molecular design and experimental testing of a high-performance zwitterionic corrosion inhibitor for oxidized iron surfaces.

A zwitterionic-based chemical, the 3,3'-(octadecylamino)dipropionic acid, was quantum-theoretically designed to be applied as a corrosion inhibitor for protecting oxidized iron surfaces against the attack of very corrosive gasolines. Its performance, as well as those of worldwide-employed nitrogen-free carboxylic-diacid-based corrosion inhibitors, were experimentally evaluated and compared. Through Density-Functional-Theory calculations of the molecular interactions of the corrosion inhibitors with an iron-oxide cluster model, along with the experimental corrosion-inhibiting evaluations, it is revealed that the zwitterionic-based chemical substantially overcomes the performance of nitrogen-free chemicals. It is shown by the theoretical results that the two carboxylic heads of either, the zwitterionic-based or the nitrogen-free corrosion inhibitors, reinforce the octahedral coordination around the exposed Fe3+ atom of the iron oxide. Furthermore, when the zwitterionic-based chemical is bonded to the Fe3+ atom, a two-rings chelate is formed, in contrast to the one-ring chelate formed by the nitrogen-free corrosion inhibitors. Finally, it is theoretically predicted that oleic solvents improve the performance of the zwitterionic-based corrosion inhibitor because preclude the steric hindrance of nitrogen.

A redox ruthenium compound directly targets PHD2 and inhibits the HIF1 pathway to reduce tumor angiogenesis independently of p53.

Targeting specific tumor metabolic needs represents an actively investigated therapeutic strategy to bypass tumor resistance mechanisms. In this study, we describe an original approach to impact the cancer metabolism by exploiting the redox properties of a ruthenium organometallic compound. This organometallic complex induced p53-independent cytotoxicity and reduced size and vascularization of patients-derived tumor explants that are resistant to platinum drugs. At the molecular level, the ruthenium complex altered redox enzyme activities and the intracellular redox state by increasing the NAD+/NADH ratio and ROS levels. Pathway analysis pointed to HIF-1 as a top deregulated metabolite pathway. Unlike cisplatin, treatment with the ruthenium complex decreased HIF1A protein levels and expression of HIF1A target genes. The rapid downregulation of HIF1A protein levels involved a direct interaction of the ruthenium compound with the redox enzyme PHD2, a HIF1A master regulator. HIF1A inhibition led to decreased angiogenesis in patient-derived xenografted using fragments of primary human colon tumors. Altogether, our results show that a ruthenium compound impacts metabolic pathways acting as anticancer agents in colon cancer via an original mechanism of action that affects redox enzymes differently than platinum-based drugs.

A Study of the Effect of Surfactants on the Aggregation Behavior of Crude Oil Aqueous Dispersions through Steady-State Fluorescence Spectrometry.

Unconventional crude oil as heavy, extra heavy, bitumen, tight, and shale oils will meet 10% of worldwide needs for 2035, perhaps earlier. Petroleum companies will face problems concerning crude oil extraction, production, transport, and refining, and some of these are addressed by the use of surfactants and other chemicals. For example, water-in-crude oil emulsions are frequently found during the production of mature wells where enhanced recovery techniques have been deployed. Nevertheless, the selection of adequate surfactant, dosage, type of water (sea, tap or oilfield), kind of crude oil (light, heavy, extra heavy, tight, shale, bitumen) affect the effectivity of treatment and usual bottle tests give limited information. We developed a fluorescence technique to study the effect of surfactants on medium, heavy, and extra heavy crude oil employing the natural fluorophore molecules from petroleum. We first carried out the characterization of commercial and synthetic surfactants, then dispersions of petroleum in water were studied by steady-state fluorometry and the size of petroleum aggregates were measured. The aggregation of petroleum incremented from medium to extra heavy crude oil and we discussed the effect of different surfactants on such aggregation.

Demulsification of crude oil-in-water emulsions by means of fungal spores.

The present feature describes for the first time the application of spores from Aspergillus sp. IMPMS7 to break out crude oil-in-water emulsions (O/W). The fungal spores were isolated from marine sediments polluted with petroleum hydrocarbons. The spores exhibited the ability to destabilize different O/W emulsions prepared with medium, heavy or extra-heavy Mexican crude oils with specific gravities between 10.1 and 21.2°API. The isolated fungal spores showed a high hydrophobic power of 89.3 ± 1.9% and with 2 g of spores per liter of emulsion, the half-life for emulsion destabilization was roughly 3.5 and 0.7 h for extra-heavy and medium crude oil, respectively. Then, the kinetics of water separation and the breaking of the O/W emulsion prepared with heavy oil through a spectrofluorometric technique were studied. A decrease in the fluorescence ratio at 339 and 326 nm (I339/I326) was observed in emulsions treated with spores, which is similar to previously reported results using chemical demulsifiers.

A glance at the reactivity of osma(II)cycles [Os(C-N)x(bpy)3-x](m+) (x=0-3) Covering a 1.8 V potential range toward peroxidase through Monte Carlo Simulations ((-)C-N=o-2-phenylpyridinato, bpy=2,2'-bipyridine).

Three cyclometalated and one coordination compounds [Os(C-N)x(bpy)3-x](m) (x/m=0/2+ (4); 1/1+ (3); 2/1+ (2); 3/0 (1); (-)C-N=2-phenylpyridinato, bpy=2,2'-bipyridine) with drastically different reduction potentials have been used for analyzing the second-order rate constants for one-electron, metal-based osmium(II) to osmium(III) oxidation of the complexes by compound I (k2) and compound II (k3) of horseradish peroxidase. Previously unknown k2 and k3 have been determined by digital simulation of cyclic voltammograms measured in phosphate buffer of pH7.6 and 21 ± 1°C. Osmium(II) species derived from osmium(III) complexes 1 and 2 were generated electrochemically in situ. Under the conditions used the reduction potentials for the Os(III/II) feature equal -0.90, -0.095, 0.23 and 0.85V versus NHE (normal hydrogen electrode) for 1-4, respectively. The rate constants k2 equal ~5 × 10(7), 6 × 10(8), 2 × 10(6) and 1 × 10(5)M(-1)s(-1) and the rate constants k3 equal ~9 × 10(6), 4× 10(7), 1 ×10(6) and 1 × 10(5)M(-1)s(-1) for complexes 1-4, respectively. Both rate constants k2 and k3 first increase with increasing the reaction driving force on going from 4 to 2 but then both decrease on going to complex 1 though the reaction driving force is the highest in this case. The system described has been explored theoretically using docking Monte Carlo simulations.

Cyclometalated [Os(C-N)x(N-N)(3-x)]m+ mimetics of tris(2,2'-bipyridine)osmium(II): covering a 2 V potential range by known (x = 0, 1) and new (x = 2, 3) species (C-N = o-2-phenylpyridinato).

Electrochemical studies of [Os(C-N)(x)(N-N)(3-x)](m+) (1) consisting of known Os(II) species with x = 0 (a) and 1 (b) and crystallographically characterized new Os(III) bis- and tris-metalacycles with x = 2 (c) and 3 (d) (N-N = 2,2'-bipyridine, (-)C-N = 2-phenylpyridinato) revealed a Nernstian behavior in MeCN. A stepwise replacement of neutral N-N ligands by three anionic C-N donors covers a 2 V potential range from -1 to +1 V vs. Ag/AgCl for the Os(III)/Os(II) feature.

Easy access to bio-inspired osmium(II) complexes through electrophilic intramolecular C(sp2)-H bond cyclometalation.

Mild electrophilic C(sp2)-H cyclometalation of 2-phenylpyridine and N,N-dimethylbenzylamine by the chloro-bridged osmium(II) dimer [OsCl(micro-Cl)(eta6-C6H6)]2 in acetonitrile affords cyclometalated pseudotetrahedral OsII complexes [Os(C approximately N)(eta6-C6H6)(NCMe)]PF6 (C approximately N=o-C6H4py-kappa C,N (2) and o-C6H4CH2NMe2-kappa C,N (5), respectively) in good to excellent yields. The cyclometalation reactions are super sensitive to the nature of an external base. Sodium hydroxide is essential for cyclometalation of 2-phenylpyridine, but NaOH retards metalation of N,N-dimethylbenzylamine, the tertiary amine being self-sufficient as a base. Further reactions of compounds 2 and 5 with 1,10-phenanthroline or 2,2'-bipyridine (N approximately N) lead to the substitution of the eta6-bound benzene to produce octahedral species [Os(C approximately N)(N approximately N)(NCMe)2]PF6 or [Os(C approximately N)(N approximately N)2]PF6 in MeCN or MeOH as solvent, respectively. The cis configuration of the MeCN ligands in [Os(C approximately N)(phen)(NCMe)2]PF6 has been confirmed by an X-ray crystallographic study. Electrochemical investigation of the octahedral osma(II)cycles by cyclic voltammetry showed a pseudoreversible MIII/II redox feature at (-50)-(+109) and 190-300 mV versus Ag/AgCl in water and MeCN, respectively. As a possible application of the compounds, a rapid electron exchange between the reduced active site of glucose oxidase enzyme from Aspergillus niger and the electrochemically generated OsIII species has been demonstrated. The corresponding second-order rate constants cover the range (0.7-4.8)x10(6) M(-1) s(-1) at 25 degrees C and pH 7.