naphthoquinones and malic-acid

The toxic oxyanion tellurite (TeO3(2-)) is acquired by cells of Rhodobacter capsulatus grown anaerobically in the light, via acetate permease ActP2 and then reduced to Te(0) in the cytoplasm as needle-like black precipitates. Interestingly, photosynthetic cultures of R. capsulatus can also generate Te(0) nanoprecipitates (TeNPs) outside the cells upon addition of the redox mediator lawsone (2-hydroxy-1,4-naphtoquinone). TeNPs generation kinetics were monitored to define the optimal conditions to produce TeNPs as a function of various carbon sources and lawsone concentration. We report that growing cultures over a 10 days period with daily additions of 1mM tellurite led to the accumulation in the growth medium of TeNPs with dimensions from 200 up to 600-700 nm in length as determined by atomic force microscopy (AFM). This result suggests that nucleation of TeNPs takes place over the entire cell growth period although the addition of new tellurium Te(0) to pre-formed TeNPs is the main strategy used by R. capsulatus to generate TeNPs outside the cells. Finally, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) analysis of TeNPs indicate they are coated with an organic material which keeps the particles in solution in aqueous solvents.

Topics: Fructose; Lactic Acid; Malates; Nanoparticles; Naphthoquinones; Photosynthesis; Pyruvic Acid; Rhodobacter capsulatus; Tellurium

A manganese(III)-mediated reaction between 2-benzoyl-1,4-naphthoquinones and 1,3-dicarbonyl compounds is described. This reaction provides an effective method for the synthesis of naphtho[2,3-c]furan-4,9-diones and naphthacene-5,12-diones, and it shows fair to high chemoselectivity depending on the electronic effect of the benzoyl group substituent on the reactants. With ethyl benzoylacetate and 1,3-diketones, the novel naphtho[2,3-c]furan-4,9-diones were produced effectively with high selectivity.

Topics: Esters; Ketones; Kinetics; Malates; Manganese; Models, Molecular; Molecular Structure; Naphthoquinones

The mitochondrial permeability pore is subject to regulation by a thiol-dependent voltage sensor (Petronilli, V., Costantini, P., Scorrano, L., Colonna, R., Passamonti, S., and Bernardi, P., J. Biol. Chem. 269, 16638-16642, 1994); thiol oxidation increases the gating potential, which increases the probability of pore opening. Monofunctional sulfhydryl-alkylating agents, by preventing formation of the disulfide, inhibit oxidant-induced changes in the gating potential. According to this paradigm, redox-cycling and arylating quinones should have distinct and opposing effects on the voltage-dependent permeabilization of mitochondrial membranes. Freshly isolated rat liver mitochondria were susceptible to a calcium-dependent permeability transition characterized by osmotic swelling and membrane depolarization, both of which were inhibited by Cyclosporine A. 1,4-Naphthoquinone, 2-methyl-1,4-naphthoquinone (menadione), and 2,3-dimethoxy-1,4-naphthoquinone elicited an increase in gating potential of the permeability pore that was prevented by Cyclosporine A or N-ethylmaleimide and reversed by dithiothreitol. Benzoquinone, on the other hand, inhibited NADH-ubiquinone oxidoreductase. Accordingly, in mitochondria energized with glutamate plus malate benzoquinone caused a direct, calcium-independent depolarization of membrane potential and mitochondrial swelling that were not inhibited by Cyclosporine A. In contrast, benzoquinone did not interfere with succinate-supported mitochondrial bioenergetics. In fact, adding benzoquinone to succinate-energized mitochondria prevented induction of the mitochondrial permeability transition by all three redox-cycling naphthoquinones. We attribute this to the electrophilic, sulfhydryl-arylating reactivity of benzoquinone. The results suggest that differences in the mechanisms by which quinones of varying chemical reactivity interfere with mitochondrial bioenergetics can be explained in terms of the distinct manner in which they react with the thiol-dependent voltage sensor of the mitochondrial permeability pore.

Topics: Animals; Benzoquinones; Energy Metabolism; Glutamic Acid; In Vitro Techniques; Indicators and Reagents; Intracellular Membranes; Ion Channels; Malates; Membrane Potentials; Membrane Proteins; Mitochondria, Liver; Mitochondrial Swelling; Naphthoquinones; Oxidation-Reduction; Permeability; Porins; Rats; Voltage-Dependent Anion Channels