Os Complexes Research Articles

Synthesis and photophysical characterization of a bis-pincer osmium complex

The neutral bis-pincer transition metal complex Os(PCP)2 (PCP=2,6-(CH2PPh2)2C6H3, Ph=C6H5) was prepared via two synthetic routes with up to 42% yield. The lemon-yellow complex is air stable as a neat solid and in solution, and is thermally stable as can be purified by high vacuum zone sublimation at 280-240-200°C under 1×10−6torr. The pincer ligands coordinate in a pseudo-octahedral arrangement around the metal center. X-ray crystallography reveals that the complex is in pseudo-D2 geometry symmetry due to the twist caused by the methylenes. NMR studies at varied temperatures between 223 and 343K along with low temperature inversion recovery studies show the fluxional behavior and exchanging process between the two enantiomers (Ea=8.6kcal/mol). The Os(PCP)2 shows no emission in solution at room temperature, but emits at 77K in 2-MeTHF glass (Φ=60%). At room temperature, the neat solid of Os(PCP)2 shows yellow emission of 3% quantum yield. TDDFT predicted S0→S1 transition shows that the lowest singlet state (S1) is metal-ligand (the Os-Xylyl fragments) to ligand’ (the PPh2 fragments) charge transfer (ML-L’CT) in character with a small contribution from the higher lying metal centered (1MC) states. The large spin–orbit coupling constant of osmium leads to effective intersystem crossing to a triplet state with increased MC character. The DFT predicted triplet spin surface of Os(PCP)2 indicates that the emission is dominated by 3MC state. Significant Os–P bonds elongation at the lowest triplet excited state also strongly supports the conclusion.

Rigid Medium Effects on Photophysical Properties of MLCT Excited States of Polypyridyl Os(II) Complexes in Polymerized Poly(ethylene glycol)dimethacrylate Monoliths

Higher-energy emissions from the metal-to-ligand charge-transfer (MLCT) excited states of a series of polypyridyl Os(II) complexes were observed at the fluid-to-film transition in PEG-DMA550. The higher-energy excited states, caused by a "rigid medium effect" in the film, led to enhanced emission quantum yields and longer excited-state lifetimes. Detailed analyses of spectra and excited-state dynamics by Franck-Condon emission spectral analysis and application of the energy gap law for nonradiative excited-state decay reveal that the rigid medium effect arises from the inability of part of the local medium dielectric environment to respond to the change in charge distribution in the excited state during its lifetime. Enhanced excited-state lifetimes are consistent with qualitative and quantitative predictions of the energy gap law.

In vitro multiwavelength PDT with 3IL states: teaching old molecules new tricks.

The purpose of the present investigation was to ascertain whether (3)IL excited states with microsecond lifetimes are universally potent for photodynamic applications, and if these long-lived states are superior to their (3)MLCT counterparts as in vitro PDT agents. A family of blue-green absorbing, Ru(II)-based transition metal complexes derived from the π-expansive dppn ligand was prepared and characterized according to its photodynamic activity against HL-60 cells, and toward DNA in cell-free media. Complexes in this series that are characterized by low-energy and long-lived (3)IL excited states photocleaved DNA with blue, green, red, and near-IR light. This panchromatic photodynamic effect translated to in vitro multiwavelength photodynamic therapy (PDT) with red-light cytotoxicities as low as 1.5 μM (EC50) for the parent complex and 400 nM for its more lipophilic counterpart. This potency is similar to that achieved with Ru(II)-based dyads containing long-lived (3)IL excitons located on appended pyrenyl units, and appears to be a general property of sufficiently long-lived excited states. Moreover, the red PDT observed for certain members of this family was almost 5 times more potent than Photofrin with therapeutic indices 30 times greater. Related Ru(II) complexes having lowest-lying (3)MLCT states of much shorter duration (≤1 μs) did not yield DNA photodamage or in vitro PDT with red or near-IR light, nor did the corresponding Os(II) complex with a submicrosecond (3)IL excited state lifetime. Therefore, metal complexes that utilize highly photosensitizing (3)IL excited states, with suitably long lifetimes (≫ 1 μs), are well-poised to elicit PDT at wavelengths even where their molar extinction coefficients are very low (<100 M(-1) cm(-1)). Herein we demonstrate that such unexpected reactivity gives rise to very effective PDT in the typical therapeutic window (600-850 nm).

Determination of rhenium and osmium complexes by surface-assisted laser desorption/ionization coupled to Orbitrap mass analyzer

A surface-assisted laser desorption/ionization (SALDI) source is coupled to the Orbitrap mass analyzer; the instrumental approach is tested for the analysis of rhenium (Re) and osmium (Os) complexes with 8-mercaptoquinoline. Silicon (Si) material obtained by laser treatment of monocrystalline Si is used as SALDI substrate. All studied complexes are detected as radical cations, with no protonated molecules. The comparison of SALDI, matrix-assisted laser desorption/ionization (MALDI), and direct laser desorption/ionization (LDI) on metal plates in the same instrumental setup demonstrated that the detection of the studied complexes using SALDI provides the highest sensitivity. The ability to analyze samples rapidly, high purity of spectra, and good analytical parameters make SALDI coupled to the Orbitrap mass analyzer a potentially powerful tool for the detection of Re and Os complexes and related organic, UV-absorbing compounds.

Wired Pyrroloquinoline Quinone Soluble Glucose Dehydrogenase Enzyme Electrodes Operating at Unprecedented Low Redox Potential

We report unprecedented high current densities for the enzymatic oxidation of glucose already at 0 V versus Ag/AgCl. The modified electrodes were made by assembling pyrroloquinoline quinone (PQQ)-soluble glucose dehydrogenase (PQQ-sGDH) from Acinetobacter calcoaceticus with osmium-based redox polymers and a cross-linker. Both redox mediators are made of a poly(4-vinylpyridine) (PVP) polymer with Os complexes tethered to the polymer backbone via long C chains, giving the Os complexes flexibility and mobility inside the redox hydrogels. Current densities larger than 1 mA cm(-2) were measured already below 0 V with a plateau value of 4.4 mA cm(-2). Similar hydrogel electrodes comprising the same redox polymers and glucose oxidase (GOx) showed less than half the current densities of the PQQ-sGDH electrodes. The current versus potential curve dependence showed a sigmoidal shape characteristic of mediated enzyme catalysis but with a current increase versus potential less sharp than expected. Surprisingly, the midwave redox potential was positively shifted with respect to the potential of the redox mediator.

Solvent-Dependent Formation of Os(0) Complexes by Electrochemical Reduction of [Os(CO)(2,2′-bipyridine)(L)Cl2]; L = Cl–, PrCN

Cyclic voltammetry and ultraviolet-visible/infrared (UV-vis/IR) spectroelectrochemistry were used to study the cathodic electrochemical behavior of the osmium complexes mer-[Os(III)(CO) (bpy)Cl3] (bpy = 2,2'-bipyridine) and trans(Cl)-[Os(II)(CO) (PrCN)(bpy)Cl2] at variable temperature in different solvents (tetrahydrofuran (THF), butyronitrile (PrCN), acetonitrile (MeCN)) and electrolytes (Bu4NPF6, Bu4NCl). The precursors can be reduced to mer-[Os(II)(CO) (bpy(•-))Cl3](2-) and trans(Cl)-[Os(II)(CO)(PrCN) (bpy(•-))Cl2](-), respectively, which react rapidly at room temperature, losing the chloride ligands and forming Os(0) species. mer-[Os(III)(CO) (bpy)Cl3] is reduced in THF to give ultimately an Os-Os-bonded polymer, probably [Os(0)(CO) (THF)(bpy)]n, whereas in PrCN the well-soluble, probably mononuclear [Os(0)(CO) (PrCN)(bpy)], species is formed. The same products were observed for the 2 electron reduction of trans(Cl)-[Os(II)(CO)(PrCN) (bpy)Cl2] in both solvents. In MeCN, similar to THF, the [Os(0)(CO) (MeCN)(bpy)]n polymer is produced. It is noteworthy that the bpy ligand in mononuclear [Os(0)(CO) (PrCN)(bpy)] is reduced to the corresponding radical anion at a significantly less negative potential than it is in polymeric [Os(0)(CO) (THF)(bpy)]n: ΔE1/2 = 0.67 V. Major differences also exist in the IR spectra of the Os(0) species: the polymer shows a broad ν(CO) band at much smaller wavenumbers compared to the soluble Os(0) monomer that exhibits a characteristic ν(Pr-CN) band below 2200 cm(-1) in addition to the intense and narrow ν(CO) absorption band. For the first time, in this work the M(0)-bpy (M = Ru, Os) mono- and dicarbonyl species soluble in PrCN have been formulated as a mononuclear complex. Density functional theory (DFT) and time-dependent-DFT calculations confirm the Os(0) oxidation state and suggest that [Os(0)(CO) (PrCN)(bpy)] is a square planar moiety. The reversible bpy-based reduction of [Os(0)(CO) (PrCN)(bpy)] triggers catalytic reduction of CO2 to CO and HCOO(-).

Preparation and reactivity towards hydrazines of bis(cyanamide) and bis(cyanoguanidine) complexes of the iron triad

Bis(diethylcyanamide) [Fe(N≡CNEt2)2L4](BPh4)2 1a and bis(cyanoguanidine) [Fe{N≡CN(H)C(NH2)=NH}2L4](BPh4)2 1b [L = P(OEt)3] complexes were prepared by allowing iron(II) chloride to react first with an excess of P(OEt)3 and then of the appropriate cyanamide, followed by addition of an excess of NaBPh4. Instead, bis(complexes) of ruthenium and osmium [M(N≡CNEt2)2L4](BPh4)2 2a, 3a and [M{N≡CN(H)C(NH2)=NH}2L4](BPh4)2 2b, 3b (M = Ru 2, Os 3) were prepared by reacting hydrides MH2L4 first with either triflic acid HOTf or methyltriflate MeOTf and then with an excess of the appropriate cyanamide. Hydride-diethylcyanamide [MH(N≡CNEt2)L4]BPh4 4a, 5a and hydride-cyanoguanidine complexes [MH{N≡CN(H)C(NH2)=NH}L4](BPh4)2 4b, 5b (M = Ru 4, Os 5) were also obtained by reacting MH2L4 first with one equivalent of HOTf or MeOTf and then with the appropriate cyanamide. Treatment of bis(cyanamide) and bis(cyanoguanidine) complexes 1-3 with hydrazines RNHNH2 afforded hydrazinecarboximidamide derivatives [M{η(2)-N(H)=C(NEt2)N(R)NH2}L4](BPh4)2 6a-12a and [M{η(2)-N(H)=C[N=C(NH2)2]N(R)NH2}L4](BPh4)2 6b-12b (M = Fe 6-8, Ru 9, 10, Os 11, 12; R = H 6, 9, 11, Me 7, 10, 12, Ph 8). A reaction path involving nucleophilic attack by hydrazine on the cyanamide carbon atom is proposed. All the complexes were characterised by spectroscopy and X-ray crystal structure determination of [Os{η(2)-NH=C[N=C(NH2)2]N(CH3)NH2}{P(OEt)3}4](BPh4)2 12b.

Ruthenium(ii) and osmium(ii) 1,2,3-triazolylidene organometallics: a preliminary investigation into the biological activity of ‘click’ carbene complexes

Taking advantage of the facile and versatile synthetic properties of 'click' 1,2,3-triazolylidene N-heterocyclic carbenes (tzNHC's), a range of new organometallic Ru(II) and Os(II) arene complexes containing functionalised tzNHC ligands, [M(η(6)-p-cymene)(tzNHC)Cl2] [M = Ru(II), Os(II)], have been synthesised and fully characterised, including the X-ray crystal structure of one of the Os(II) complexes. The tzNHC ligands remain coordinated to the metal centres under relevant physiological conditions, and following binding to the model protein, ubiquitin. The in vitro cytotoxicity of the compounds towards human ovarian cancer cells is dependent on the substituent on the tzNHC ligand but is generally <50 μM and in some cases <1 μM, whilst still retaining a high degree of selectivity towards cancer cells over healthy cells (1.85 μM in A2780 ovarian cancer cells versus 435 μM in human embryonic kidney cells in one case).

Synthesis, Characterization, and Reactivity of the First Osmium β-Diketiminato Complexes and Application in Catalysis

The strongly chelating anionic beta-diketiminate ligand has been employed to formulate complexes involving almost every metal of the periodic table; however, the heavier metals of the d block remain relatively unexplored. This paper describes the synthesis and characterization of the first two osmium, beta-diketiminato compounds, including a coordinatively unsaturated cationic complex. In parallel to the analogous Ru(II) complexes, the cationic (eta(6)-arene)osmium(II) complex demonstrates bifunctional behavior through [4 + 2] cycloaddition with ethylene, cleavage of dihydrogen under mild conditions, and protonation/chloride addition with [Et2OH]Cl. Metal-centered activity in both the Ru(II) and Os(II) beta-diketiminates has until now remained elusive, as the cationic Os complex is shown to readily coordinate an aryl isonitrile. The applicability of Os(II) beta-diketiminato complexes in catalytic olefin hydrogenation demonstrates significantly greater activity in terms of conversion and TOF for a range of substrates, including styrene, cyclohex-1-ene, and 1-methylcyclohex-1-ene. Moreover, selective hydrogenation of the exocyclic alkenyl group in limonene was observed, whereas the corresponding isostructural Ru(II) complexes are inactive. In contrast, the cationic (eta(6)-arene)ruthenium(II) beta-diketiminato complex proved more active for the catalytic dehydrogenation of N,N-dimethylamine borane (Me2NBH3) than the equivalent Os(II) species. A detailed DFT study of the Ru(II) and Os(II) beta-diketiminato species using charge decomposition analysis (CDA) demonstrates differences in metal ligand interactions, which in turn considerably influences the extent of bifunctional reactivity.

Ru(II) and Os(II) Complexes Based on Terpyridyl-Imidazole Ligand Rigidly Linked to Pyrene: Synthesis, Structure, Photophysics, Electrochemistry, and Anion-Sensing Studies

We report in this work a new family of bis-tridentate ruthenium(II) and osmium(II) complexes bearing a terpyridyl ligand rigidly link to pyrenyl-benzimidazole moiety (tpy-HImzPy = 10-(4-[2,2':6',2''-terpyridine]terpyridin-4'-yl-phenyl)-9H-9,11-diaza-cyclopenta[e]pyrene) along with other tridentate ligands such as 4'-(2-naphthyl)-2,2':6',2″-terpyridine (tpy-NaPh) and 2,6-bis(benzimidazole-2-yl)pyridine (H2pbbzim). All the complexes are thoroughly characterized by their elemental analysis, ESI mass spectrometry, and (1)H NMR spectroscopy. The molecular structures of two complexes [Ru(tpy-HImzPy)2](ClO4)2 (3) and [(pbbzim)Ru(tpy-HImzPy)] (2a) in the solid state were determined by X-ray crystallography. The absorption, steady-state, and time-resolved luminescence and electrochemical properties of all the four compounds have been studied. On excitation at their MLCT bands, all four compounds exhibit moderately strong room-temperature luminescence with lifetimes ranging between 3.8 and 161.1 ns in aerated condition, whereas in the deaerated (N2 purged) condition, the lifetimes vary between 8.2 and 199.1 ns, depending upon the nature of the solvents. The presence of imidazole N-H protons in all the complexes motivates us to study anion sensing properties of the complexes in solution through different channels. Spectrophotometeric, fluorometric, (1)H NMR spectroscopic, and cyclic voltammetric studies of the complexes in presence of anions reveal that the complexes sense principally F(-), CN(-), and to a lesser extent for AcO(-). Multichannel anion sensing studies also indicate that anion-induced deprotonation of the imidazole N-H protons occur in all four compounds. The equilibrium constant of this deprotonation steps have been estimated from UV-vis absorption and emission titration data. Anion-induced modulation of lifetimes makes all the four complexes suitable for lifetime-based sensors for selective anions.

Cellobiose dehydrogenase entrapped within specifically designed Os-complex modified electrodeposition polymers as potential anodes for biofuel cells

Electron-transfer pathways between cellobiose dehydrogenase from Myriococcum thermophilum (MtCDH) and the related flavodehydrogenase domain (FAD-MtCDH) and electrodes were evaluated using specifically designed Os-complex modified electrodeposition paints (EDPs). The properties of the Os-complex modified EDPs were varied by variation of the monomer composition, the coordination sphere of the polymer-bound Os-complexes, and the length and flexibility of the spacer chain between Os complex and polymer backbone. The MtCDH-to-EDP weight ratio, the pH value, as well as the operational temperature have been optimized.

Unsaturated Triosmium Carbonyl Cluster Complexes with Bridging Aryl Ligands: Structures, Bonding, and Transformations

Reactions of Os3(CO)10(NCMe)2, 1, with the series of aryl-gold complexes ArylAu(PPh3) [Aryl = phenyl = Ph, 2-naphthyl = 2-Np (2-C10H7) and 1-pyryl (1-C16H10)] have provided the series of electronically unsaturated triosmium complexes Os3(CO)10(μ-η1-Ar)(μ-AuPPh3) [2, Ar = phenyl = Ph; 3, Ar = 2-naphthyl = 2-Np (2-C10H7); and Ar = 4 and 5, 2-pyryl and 4-pyryl], containing bridging η1-Ar ligands and a bridging Au(PPh3) group that bridges the same unsaturated Os–Os bond in the 46-electron cluster complex. All new compounds were characterized by single-crystal X-ray diffraction analyses. A DFT computational analysis of 2 has revealed that bonding of the bridging phenyl ligand to the metal atoms consists of a combination of delocalized σ-bonding between the ipso-carbon atom and the two proximate metal atoms and π-donation from the π-orbitals of the ring to those same metal atoms. There is no significant metal to ring π-back-bonding. Compound 3 exists as two isomers, 3a and 3b. Compound 3a contains a μ-η1-2-Np l...

ChemInform Abstract: Near‐Infrared Phosphorescence: Materials and Applications

AbstractReview: 482 refs.

On the Accuracy of Calculated Reduction Potentials of Selected Group 8 (Fe, Ru, and Os) Octahedral Complexes

The theoretical calculations of reduction potentials for the [M(H2O)6]2+/3+, [M(NH3)6]2+/3+, [M(en)3]2+/3+, [M(bipy)3]2+/3+, [M(CN)6]4–/3–, and [MCl6]4–/3– systems (M = Fe, Os, Ru) were carried out. The DFT(PBE)/def2-TZVP//DFT(PBE)/def2-SVP quantum chemical method was employed to obtain presumably accurate ionization energies, whereas the conductor-like screening model for real solvents (COSMO-RS) was selected as the most suitable method for calculations of solvation energies of the oxidized and reduced forms of the studied species. It has been shown that COSMO-RS may overcome problems related to directionality of hydrogen bonds in the second solvation sphere that previously led to errors of ∼1 V for the [Ru(H2O)6]2+ complex employing PCM-like models. Thus, most of the values for (2+) → (3+) oxidations are now within 0.1–0.2 V from the experimental data, once the anticipated spin–orbit coupling effects in Os complexes (downshifting the calculated reduction potentials by ∼0.3 V) are taken into account. The...

Modification of Poly‐ and Oligosaccharides with Os(VI)pyridine. Voltammetry of the Os(VI) Adducts Obtained by Ligand Exchange

AbstractPolysaccharides and oligosaccharides were modified with Os(VI)pyridine complex followed by ligand exchange with different ligands such as 2,2′‐bipyridine or N,N,N′,N′‐tetramethylethylenediamine. The time of the modification was much shorter (taking about 15 min) then direct modification with the given Os(VI) complex. The resulting saccharide adducts were analyzed by voltammetric methods at carbon and mercury electrodes. The results showed that the proposed technique gives promise for a new approach to analysis of glycoproteins.

A Pyrene-Substituted Tris(bipyridine)osmium(II) Complex as a Versatile Redox Probe for Characterizing and Functionalizing Carbon Nanotube- and Graphene-Based Electrodes

We report the functionalization of nanostructured graphene-based electrode with an original (bis(2,2'-bipyridine)(4,4'-bis(4-pyrenyl-1-ylbutyloxy)-2,2'-bipyridine]osmium(II) hexafluorophosphate complex bearing pyrene groups. Graphene oxide (GO) and chemically reduced graphene oxide (c-RGO) paper electrodes were prepared by the flow-directed filtration method. After film transfer via the soluble membrane technique, the homogeneous and stable GO electrode was electrochemically reduced in water to achieve electrochemically reduced graphene oxide (e-RGO) film on the electrode. The electrochemical properties of GO, c-RGO, and e-RGO electrodes were characterized by scanning electron microscopy and electrochemistry. Cyclic voltammetry of the Ru(NH3)6(2+/3+) redox probe underlines the important influence of the RGO preparation method on electrochemical properties. We finally achieved the flexible functionalization of graphene-based electrodes using either supramolecular binding of the Os(II) complex bearing pyrene groups or its electropolymerization via the irreversible oxidation of pyrene. The properties of these functionalized graphene paper electrodes were compared to glassy carbon (GC) and multiwalled carbon nanotube (MWCNT) electrodes. Thanks to its divalent binding sites, the Os(II) complex constitutes a useful tool to probe the π-extended graphitic surface of RGO and MWCNT films. The Os(II) complex interacts strongly via noncovalent π-π interactions, with π-extended graphene planes, thus acting as a marker to quantify the electroactive surface of both MWCNT and RGO electrodes and to illustrate their ease of functionalization.

A Combined Experimental and DFT/TD-DFT Investigation of Structural, Electronic, and Cation-Induced Switching of Photophysical Properties of Bimetallic Ru(II) and Os(II) Complexes Derived from Imidazole-4,5-Dicarboxylic Acid and 2,2′-Bipyridine

Experimental results coupled with computational studies were utilized to investigate the structural and electronic properties of mixed-ligand bimetallic ruthenium(II) and osmium(II) complexes of composition [(bpy)2M(Imdc)M(bpy)2](+) [M = Ru(II) (1) and M = Os(II) (2)], where H3Imdc = imidazole-4,5-dicarboxylic acid and bpy = 2,2'-bipyridine. The X-ray crystal structures of both the bimetallic complexes were determined which showed that compound 1 crystallizes in monoclinic form with space group P2(1)/c, while 2 is obtained in orthorhombic form with the space group Pca2(1). The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the single-crystal X-ray data. The absorption spectra, redox behaviors, and luminescence properties of the complexes were thoroughly investigated. The complexes display very intense, ligand-centered absorption bands in the UV and moderately intense MLCT bands in the visible regions. While the Ru(II) complex displays moderately strong luminescence, the corresponding Os(II) complex does not luminesce at room temperature. Both the bimetallic complexes show two successive one-electron reversible metal-centered oxidations. The effect of alkali, alkaline earth, and transition metal cations on the absorption and emission spectral behavior of the complexes has also been studied in detail. As compared to the luminescence intensities and the quantum yields of the free complexes, those of the complexes were enhanced substantially in the presence of selective cations showing cation-induced molecular switching behaviors. Density functional theory (DFT) and time-dependent DFT (TD-DFT) studies provide insight into the nature of the ground and excited states with resulting detailed assignments of the orbitals involved in absorption and emission transitions. In particular, the blue-shifts of the absorption and emission bands in the presence of cations are also reproduced by our calculations.

Syntheses, Characterisation and Electrochemical Properties of C70-metal Cluster Complexes

The complexes [Os3(CO)9( μ3- η2: η2: η2-C70)] and [Re3( μ-H)3(CO)9( μ3- η2: η2: η2-C70)] have been prepared by reaction of C70 with [Os3(CO)10(NCMe)2] or [Re3( μ-H)3(CO)11(NCMe)] and their electrochemical properties studied by cyclic voltammetry in chlorobenzene solutions. The complex [Re3( μ-H)3(CO)8(CNCH2Ph)( μ3- η2: η2: η2-C70)] has also been synthesised by reaction between [Re3( μ-H)3(CO)9( μ3- η2: η2: η2-C70)] and PhCH2N=PPh3.

Reactivity study of a hydroxyl coordinated osmium vinyl complex OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)

We studied the reactivity of an osmium vinyl complex containing a coordinated hydroxyl group OsCl2(PPh3)2[CH=C(PPh3)-CHPh(OH)] (1) toward bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB), π acid ligand (CO), base (Cs2CO3) and heat. Two osmium vinyl complexes OsCl2(dppb)[CH=C(PPh3)CHPh(OH)] (2) and OsCl2(CO)2(PPh3)[CH=C(PPh3)CHPh(OH)] (3), as well as two relatively rare phosphonium-containing osmafuran complexes Os(η2-OCOO)(PPh3)2[CHC(PPh3)CPhO] (4) and OsCl2(PPh3)2[CHC(PPh3)CPhO] (5), were obtained in high yields from these reactions. All products were characterized by NMR spectroscopy, elemental analysis, and their structures were further confirmed by single crystal X-ray diffraction.

Optimization of a Membraneless Glucose/Oxygen Enzymatic Fuel Cell Based on a Bioanode with High Coulombic Efficiency and Current Density

After initial testing and optimization of anode biocatalysts, a membraneless glucose/oxygen enzymatic biofuel cell possessing high coulombic efficiency and power output was fabricated and characterized. Two sugar oxidizing enzymes, namely, pyranose dehydrogenase from Agaricus meleagris (AmPDH) and flavodehydrogenase domains of various cellobiose dehydrogenases (DH(CDH)) were tested during the pre-screening. The enzymes were mixed, "wired" and entrapped in a low-potential Os-complex-modified redox-polymer hydrogel immobilized on graphite. This anode was used in combination with a cathode based on bilirubin oxidase from Myrothecium verrucaria adsorbed on graphite. Optimization showed that the current density for the mixed enzyme electrode could be further improved by using a genetically engineered variant of the non-glycosylated flavodehydrogenase domain of cellobiose dehydrogenase from Corynascus thermophilus expressed in E. coli (ngDH(CtCDHC310Y)) with a high glucose-turnover rate in combination with an Os-complex-modified redox polymer with a high concentration of Os complexes as well as a low-density graphite electrode. The optimized biofuel cell with the AmPDH/ngDH(CtCDHC310Y) anode showed not only a similar maximum voltage as with the biofuel cell based only on the ngDH(CtCDHC310Y) anode (0.55 V) but also a substantially improved maximum power output (20 μW cm(-2)) at 300 mV cell voltage in air-saturated physiological buffer. Most importantly, the estimated half-life of the mixed biofuel cell can reach up to 12 h, which is apparently longer than that of a biofuel cell in which the bioanode is based on only one single enzyme.