Mechanistic investigation of cyclohexane oxidation by a non-heme iron complex: evidence of product inhibition by UV/vis stopped-flow studies

We report herein studies examining a binuclear non-heme iron model complex that is capable of catalytically oxidizing cyclohexane to cyclohexanol in excess of 200 turnovers, relative to the iron complex, and cyclohexanone (5 turnovers) via heterolytic cleavage of the mechanistic probe peroxide MPPH. Low-temperature stopped-flow electronic spectroscopy was utilized to investigate the mechanism of the reaction of this diiron(II) compound, Fe(2)(H(2)Hbamb)(2)(N-MeIm)(2), (H(2)Hbamb = 2,3-bis(2-hydroxybenzamido)dimethylbutane) (1) with MPPH. In the absence of substrates, the reaction proceeds in three consecutive steps starting with oxygen atom transfer to the diferrous complex to generate a putative [Fe(IV)=O species], thought to be the oxidant in the catalytic cycle. Over time, the rate of catalysis is observed to decrease without consumption of all available peroxide. By utilizing low-temperature stopped-flow UV/vis kinetic studies, the diferrous complex, 1, is shown to undergo product inhibition arising from the interaction of either cyclohexanol or MPP-OL product species to the diiron center, therefore precluding further reaction with MPPH.     

Double Salts Iodide Scintillators: Cesium Barium Iodide,Cesium Calcium Iodide,and Barium Bromine Iodide

In this study we review the state‐of‐the‐art for double salt iodide scintillators, in particular cesium barium iodide (CBI), cesium calcium iodide (CCI) and barium bromine iodide (BBI), as well as report on their scintillation and optical properties. Double salt iodides inherently have high density and atomic number which translates to good stopping power for energetic particles, in particular gamma rays. Light yields of 54,000 ph/MeV for CBI, 51,000 ph/MeV for CCI, and 46,000 ph/MeV for BBI were measured. A FWHM energy resolution for the 662 keV full absorption peak was observed at 5.7% for CBI, 16.3% for CCI and 3.56% for BBI. The principal scintillation decay timing for CBI was 840 ns, 462 ns for BBI, and two distinct time components of 9 ns and 1900 ns were observed for CCI.     

Synthesis of some halogenated and disubstituted amino benzylacyclouridine derivatives

1′-Halogenomethyl, 1′-azidomethyl and 1′-disubstituted aminomethyl derivatives of BAU (5-benzylacyclouridine) and BBAU (5-benzyloxybenzylacyclouridine) were synthesized in the course of our studies of benzylacyclouridines. Two new and more convenient preparations of the previously known aminomethyl-and hydroxymethyl-parent compounds of these two series, AM-BAU, AM-BBAU and HM-BBAU are also reported. These compounds were synthesized during a search for potential antiviral agents and pyrimidine phosphorylase inhibitors.     

Correlations between electron and positron workfunctions on copper surfaces

We have performed contact potential difference measurements on low-index faces of copper in ultrahigh vacuum using positrons as positive test particles in a retarding field analyzer. For negative positron affinity surfaces bombarded with keV positrons we also measured energy distributions of reemitted slow positrons and found them to sharply peaked in energy about a value which we label ?φ⁺. Both adsorbing sulfur on a Cu(111) sample and raising its temperature cause changes in φ⁺ which are equal and opposite to the contact potential change of the sample, i.e. the electron workfunction change. This result is in complete accordance with φ⁺ being a measure of the negative positron workfunction of the sample and high temperature or adsorbates inducing a change only in the electrostatic surface dipole layer.     

Determination of platinum and palladium in geological materials by neutron-activation analysis after fire-assay preconcentration

Fire-asay preconcentration followed by neutron-activation analysis permits the determination of as little as 0.5 ppM of platinum and 0.5 ppM of palladium on a 20-g sample. Platinum and palladium are separated with carriers and beta-counted. Results for the platinum and palladium content of seven U.S.G.S. standard rocks are presented.