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The activities of critical metabolic and regulatory proteins can be altered by exposure to natural or synthetic redox-cycling compounds. Many bacteria, therefore, possess mechanisms to transport or transform these small molecules. The opportunistic pathogen Pseudomonas aeruginosa PA14 synthesizes phenazines, redox-active antibiotics that are toxic to other organisms but have beneficial effects for their producer. Phenazines activate the redox-sensing transcription factor SoxR and thereby induce the transcription of a small regulon, including the operon mexGHI-opmD, which encodes an efflux pump that transports phenazines, and PA14_35160 (pumA), which encodes a putative monooxygenase. Here, we provide evidence that PumA contributes to phenazine resistance and normal biofilm development, particularly during exposure to or production of strongly oxidizing N-methylated phenazines. We show that phenazine resistance depends on the presence of residues that are conserved in the active sites of other putative and characterized monooxygenases found in the antibiotic producer Streptomyces coelicolor. We also show that during biofilm growth, PumA is required for the conversion of phenazine methosulfate to unique phenazine metabolites. Finally, we compare ∆mexGHI-opmD and ∆pumA strains in assays for colony biofilm morphogenesis and SoxR activation, and find that these deletions have opposing phenotypic effects. Our results suggest that, while MexGHI-OpmD-mediated efflux has the effect of making the cellular phenazine pool more reducing, PumA acts on cellular phenazines to make the pool more oxidizing. We present a model in which these two SoxR targets function simultaneously to control the biological activity of the P. aeruginosa phenazine pool.

A synthesis of two series of homoleptic phenolate complexes with fluorinated aryloxide ligands A2[M(OAr)4] with M = Co(super 2+) or Cu(super 2+), OAr(super -) = (OC6F5)(super -) (OAr(super F)) or {3,5-OC6H3(CF3)2}(super -) (OAr'), A(super +) = K (18-crown-6)(super +), Tl(super +), Ph4P(super +), Et3HN(super +), or Me4N(super +) was conducted.

The attainable steady-state limiting currents and time responses of membrane-covered and membrane-independent gas sensors incorporating different electrode and electrolyte materials have been compared. A new design comprising a membrane-free microelectrode modified with a thin layer of a room temperature ionic liquid is considered. While the use of ionic liquid as electrolyte eliminates the need for a membrane and added supporting electrolyte, the slower diffusion of analyte within the more viscous medium results in slower time responses. Such sensors do, however, have potential application in more extreme operating conditions, such as high temperature and pressure, where traditional solvents would volatise.

The one-electron reduction of oxygen was investigated by cyclic voltammetry at a gold microdise electrode in the RTILs, 1-ethyl-3-methylimidazotium bis ((trifluoromethyl) sulfonyl) imide ([EMIM][(Tf)(sub 2)]) and hexyltriethylammonium bis ((trifluoromethyl) sulfonyl) imide ([N (sub 6222][N (Tf)(sub 20]). The study results of the higher viscosity of [N (sub 6222][N (Tf)(sub 2)] in comparison to [EMIM][N (Tf)(sub 2)] due to the structural differences in cationic component.

The reactivity of electrogenerated bromine with cyclohexane is studied on a platinum microelectrode. The reaction mechanism for bromination in acetonitrile is modeled using digital simulation.

An investigation was conducted on the reduction of oxygen in the presence of carbon dioxide by cyclic voltammetry at a gold microdisk electrode in two room-temperature ionic liquids. With increasing levels of CO2, cyclic voltammetry showed an increase in the reductive wave and diminishing of the oxidative wave, which indicated that the generated superoxide readily reacts with carbon dioxide.

Two series of homoleptic phenolate complexes with fluorinated aryloxide ligands A2[M(OAr)4] with M = Co2+ or Cu2+ OAr- = (OC6F5)- (OArF) or {3,5-OC6H3(CF3)2}- (OAr′), A+ = K (18-crown-6)+, Tl+, Ph4P+, Et3HN+, or Me4N+ have been synthesized. Two related complexes with nonfluorinated phenoxide ligands have been synthesized and studied in comparison to the fluorinated aryloxides demonstrating the dramatic structural changes effected by modification of OPh to OArF. The compounds {K(18-crown-6)}2[Cu(OArF)4], 1a; {K(18-crown-6)}2[Cu(OAr′)4], 1b; [Tl2Cu(OArF)4], 2a; [Tl2Cu(OAr′)4], 2b; (Ph4P)2[Cu(OArF)4], 3; (nBu4N)2[Cu(OArF)4], 4; (HEt3N)2[Cu(OArF)4], 5; {K(18-crown-6) }2[Cu2(μ2-OC6H5)2(OC6H5)4], 6; {K(18-crown-6) }2[Co(OArF)4], 7a; {K(18-crown-6) }2[Co(OAr′)4], 7b; [Tl2Co(OArF)4], 8a; [Tl2Co(OAr′)4], 8b; (Me4N)2[Co(OArF)4], 9; [Cp2Co]2[Co(OAr′)4], 10; and {K(18-crown-6) }2[Co2(μ2-OC6H5)2(OC6H5)4], 11, have been characterized with UV-vis and multinuclear NMR spectroscopy and solution magnetic moment studies. Cyclic voltammetry was used to study 1a, 1b, 7a, and 7b. X-ray crystallography was used to characterize 1b, 3, 4, 5, 6, 7a, 7b, 10, and 11. The related [MX4]2 compound (Ph4P)2[Co(OArF)2Cl2], 12, has also been synthesized and characterized spectroscopically, as well as with conductivity and single-crystal X-ray diffraction. Use of fluorinated aryloxides permits synthesis and isolation of the mononuclear, homoleptic phenolate anions in good yield without oligomerized side products. The reaction conditions that result in homoleptic la and 7a with OArF upon changing the ligand to OPh result in μ2-OPh bridging phenoxides and the dimeric complexes 6 and 11. The [M(OArF)4]2 and [M(OAr′)4]2- anions in 1a, 1b, 3, 4, 5, 7a, 7b, 9, and 10 demonstrate that stable, isolable homoleptic phenolate anions do not need to be coordinatively or sterically saturated and can be achieved by increasing the electronegativity of the ligand. [ABSTRACT FROM AUTHOR]