John H. Nelson

Electrochemistry of flavonoids: Relationships between redox potentials, inhibition of mitochondrial respiration, and production of oxygen radicals by flavonoids

We have investigated the redox behavior of a series of structurally related flavonoids employing cyclic voltammetry under physiological conditions. The flavonoids that auto-oxidized and produced oxygen radicals had oxidation potentials (E 1/2) significantly lower [-30 to +60 mV vs (SCE)] than those that did not undergo auto-oxidation (+130 to +340 mV vs SCE). The range of E 1/2 values for the auto-oxidizable flavonoids was comparable to the E 1/2 range reported for the optimum quinone induced production of superoxide (O2 pi) in mitochondrial NADH-CoQ reductase (complex I). The most potent flavonoid inhibitors of mitochondrial succinate-CoQ reductase (complex II) possessed hydroxyl configurations capable of supporting redox reactions. For a series of 3,5,7-trihydroxyflavones that differed by b-ring hydroxylation it was found that decreasing E 1/2 of the flavonoids was associated with decreasing I50 values towards succinoxidase. These findings suggest that the electrochemical properties of the flavonoids may contribute to their biological activity.

Affinity of activated carbon towards some gold(I) complexes

Abstract The adsorption of dicyanoaurate(I), dithioureaaurum(I), dithiocyanatoaurate(I), and dithiosulfatoaurate(I) complexes onto activated carbon has been investigated. A flow-through miniature column connected on-line to a flow injection analysis system with a flame atomic absorption spectrometry detector provided information on the relative rates and extent of adsorption of gold(I) complexes. The corresponding adsorption isotherms have also been determined. Scanning electron micrographs of the barren and loaded carbon surfaces (from K[Au(SCN)2]) are presented. These show that Au(SCN)2−1 is reduced to metallic gold on the carbon surface. It is established that the effectiveness of activated carbon in removing complexed gold from aqueous solutions decreases in the following ligand order: SCN− > SC(NH2)2 > CN− ⪢ S2O32−.

A 13C-NMR study of the biosynthesis of 3-methylpentacosane in the American cockroach

13C-NMR spectrometry was used to examine the in vivo incorporation of 13C-labeled precursors into 3-methylpentacosane in the cockroach Periplaneta americana. Natural abundance 13C-NMR of 3-methylpentacosane showed that carbons 1 through 6, 23 through 25 and the branching methyl carbon (C26) each gave distinct signals, with carbons 7 through 22 indistinguishable from each other. The label from dipotassium 2-[methyl-13C]methylmalonate was incorporated primarily into the methyl branch of 3-methylpentacosane, demonstrating the 2-methylmalonate is the precursor to the methyl branch unit. The carboxyl carbon from sodium [1-13C]propionate was incorporated exclusively into the 4-position. This indicates that propionate, as a 2-methylmalonyl derivative, is incorporated as the second unit during chain synthesis rather than toward the end of the elongation process. The labeled carbon from sodium [1-13C]acetate was incorporated into carbons 2, 6 and 24 and the labeled carbon from [2-13C]acetate was incorporated into carbons 1, 5, 23 and 25 of 3-methylpentacosane, respectively. These data are consistent with an elongation-decarboxylation pathway for 3-methylpentacosane biosynthesis.

Comparative catalytic activity of selected metal oxides and sulfides for the photo-oxidation of cyanide

Abstract The photocatalytic oxidation of cyanide by TiO 2 (anatase and rutile), ZnS, ZnO, CdS, V 2 O 5 , SiO 2 and Fe 2 O 3 was investigated and compared with the photo-oxidation in the absence of catalyst. Only TiO 2 and ZnO are satisfactory catalysts. Cyanide is first oxidized to cyanate and then via nitrite to nitrate. In most systems cyanide is also volatilized as HCN. The amount of HCN volatilized is a function of the pH of the solution and the surface area of the catalyst and generally increases with decreasing pH and increasing surface area.

Improved Syntheses of Tetraphenylphosphonium Bromide and 1-Phenyldibenzophosphole

Abstract Improved syntheses of tetraphenylphosphonium bromide and 1-phenyldibenzophosphole are described. Also described are syntheses of tetrakis(p-chlorophenyl)phosphonium bromide, tetrak is (p-tolyl)phosphonium bromide, 1-phenyldi-benzophosphole oxide, 1-phenyldibenzophosphole sulfide, 1-phenyldibenzophosphole selenide and 5-p-tolyl-2,8-dimethyldibenzophosphole oxide. These compounds were all characterized by elemental analyses and 31P {1H} NMR spectroscopy. An investigation of the relative catalytic efficiencies of NiBr2, [Ph2PH]4Ni and (Ph3P)2Ni(CO)2 in the synthesis of 1-phenyldibenzophosphole is also reported.

Photocatalytic oxidation of cyanide to nitrate at TiO2 particles

Abstract The photocatalytic oxidation of cyanide at titanium(IV) oxide powder induced by UV irradiation was investigated. It is verified that cyanide is first oxidized to cyanate. However, contrary to earlier studies, it is established that cyanate is subsequently further photocatalytically oxidized via nitrite all the way to nitrate. Experimental conditions were varied and the effects of various sparging gases and pH, as well as the concentrations of both cyanide and photocatalyst, were investigated. As nitrate is a significantly less hazardous contaminant than cyanide, complete photocatalytic oxidation of cyanide to nitrate may be a viable method for decontamination of cyanide wastes.

Metabolism of propionate to acetate in the cockroach Periplaneta americana

Carbon-13 NMR and radiotracer studies were used to determine the precursor to methylmalonate and to study the metabolism of propionate in the cockroach Periplaneta americana. [3,4,5-13C3]Valine labeled carbons 3, 4, and 26 of 3-methylpentacosane, indicating that valine was metabolized via propionyl-CoA to methylmalonyl-CoA and served as the methyl branch unit precursor. Potassium [2-13C]propionate labeled the odd-numbered carbons of hydrocarbons and potassium [3-13C]propionate labeled the even-numbered carbons of hydrocarbons in this insect. This labeling pattern indicates that propionate is metabolized to acetate, with carbon-2 of propionate becoming the methyl carbon of acetate and carbon-3 of propionate becoming the carboxyl carbon of acetate. In vivo studies in which products were separated by HPLC showed that [2-14C]propionate was readily metabolized to acetate. The radioactivity from sodium [1-14C]propionate was not incorporated into succinate nor into any other tricarboxylic acid cycle intermediate, indicating that propionate was not metabolized via methylmalonate to succinate. Similarly, [1-14C]propionate did not label acetate. An experiment designed to determine the subcellular localization of the enzymes involved in converting propionate to acetate showed that they were located in the mitochondrial fraction. Data from both in vivo and in vitro studies as a function of time indicated that propionate was converted directly to acetate and did not first go through tricarboxylic acid cycle intermediates. These data demonstrate a novel pathway of propionate metabolism in insects.

Conformationally rigid diphosphine arene–ruthenium(II) complexes as catalysts for transfer hydrogenation of ketones

Abstract Conformationally rigid [(η6-arene)Ru(PP)Cl]CF3SO3 (arene=C6H6 (1), p-MeC6H5CHMe2 (2), 1,3,5-Me3C6H3 (3), and Me6C6 (4); PP is 2-diphenylphosphino-5,6-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-5-ene) compounds have been synthesized from [(η6-arene)RuCl2(DMPP)] (DMPP=3,4-dimethyl-1-phenylphosphole) and diphenylvinylphosphine (DPVP) in the presence of AgCF3SO3. The structures of 2, 3 and 4 were determined by X-ray crystallography. These complexes have been found to be quite effective catalysts for the transfer hydrogenation of ketones in 2-propanol in the presence of KOH.

Photocatalytic oxidation of aqueous ammonia (ammonium ion) to nitrite or nitrate at TiO2 particles

SummaryThe photocatalytic oxidation of ammonia (ammonium ion) in the presence of air or pure oxygen at titanium(IV) oxide powder surfaces and induced by UV light was investigated. Experimental conditions were varied and the effect ofpH, sparging gas, as well as the concentration of both ammonia (ammonium ion) and photocatalyst were investigated. It has been established that the principal product of photocatalytic oxidation depends onpH, and is either nitrite or nitrate. A gas-diffusion flow injection analysis system with conductivity detection was used for on-line monitoring of ammonia concentration. In addition, ion-chromatography with UV detection was utilized for offline monitoring of nitrite and nitrate concentrations. The use of a photocatalyst such as TiO2 may prove to be a viable method for conversion of ammonia (ammonium ion) to either nitrite or nitrate.ZusammenfassungEs wurde die photokatalytische Oxidation von Ammoniak (Ammoniumion) mittels Luft oder reinem Sauerstoff an Titan(IV)oxid-Pulveroberflächen unter Induktion von UV-Licht untersucht. Die experimentellen Bedingungen wurden variiert, wobei der Effekt despH-Wertes, des Spülgases und sowohl die Ammoniak- als auch die Photokatalysator-Konzentration berücksichtigt wurde. Dabei ergab sich, daß das Hauptprodukt der photokatalytischen Oxidation vompH abhängt und entweder Nitrit oder Nitrat ist. Ein Gasdiffusions-Fließinjektions-Analysensystem wurde zur on-line-Kontrolle der Ammoniak-Konzentration verwendet. Off-line-Ionenchromatographie mit UV-Detektion wurde zur Konzentrationsbestimmung für Nitrit und Nitrat herangezogen. Die Verwendung von Photokatalysatoren wie Titanoxid könnte sich als gangbarer Weg erweisen, um Ammoniak (Ammoniumion) entweder zu Nitrit oder zu Nitrat umzusetzen.

The nature of PtSnCl3− salts in solution by multinuclear NMR. Unusually large spin-spin coupling, cluster size, fluxionality, and a caveat

It was recently shown that even when tin envirnoments are averaged by intramolecular rearrangement, the number of tin atoms in the molecule can be deduced from the ll9sn NMR because of the fortuitous presence of ll9sn-ll7sn coupling (i). We recently have extended these principles to an investigation of the platinum trichlorostannates which are effective homogeneous catalysts for a variety of reactions (2,3). A few examples are noteworthy at this time.