Construction of multiporphyrin arrays using ruthenium and rhodium coordination to phosphines

The synthesis of linear multiporphyrin arrays with mono- and bisphosphine-substituted porphyrins as ligand donors and ruthenium(II) or rhodium(III) porphyrins as ligand acceptors is described. With appropriate amounts of the building blocks mixed, linear dimeric and trimeric arrays have been synthesized and analyzed by (1)H NMR and (31)P NMR spectroscopy. The Ru/Rh acceptor porphyrins can be located either at the periphery or in the center of the array. Likewise, the monophosphine porphyrins can be positioned at the periphery, thus allowing a high degree of freedom in the overall composition of the arrays. This way, both donor and acceptor porphyrins can act as chain extenders or terminators. One of the trimeric complexes with two nickel and one ruthenium porphyrin has also been analyzed by X-ray crystallography. Attempts have also been made to synthesize higher order arrays by mixing appropriate amounts of the porphyrins; however, from the NMR data it cannot be concluded if monodisperse five, seven, or nine porphyrin arrays are present or if the solutions are composed of a statistical mixture of smaller and larger arrays.     

The determination of uranium in biological materials by neutron activation analysis using the fission product134I

A method for the determination of uranium based on²³⁵U thermal neutron fission, has been developed and employed on samples of ashed fish tissue and seaweed. The method involves a post-irradiation ion exchange separation of iodine isotopes. The 884 keV photopeak of¹³⁴I is used for measurement. Uranium detection limits in the samples concerned have been estimated to be 1·10⁻⁸g in terms of natural uranium. The precision achieved in analysing several series of 3–5 samples was 4–10 per cent. The accuracy of the method was tested by employing an independent neutron activation procedure based on²³⁹U measurement. The accuracy of both methods was checked by analysing NBS SRM 1571 ‘Orchard Leaves’.     

Treatment of zinc-contaminated water using a multistage ferrihydrite sorption system

Previous studies demonstrated the environmental and economic benefits of treating lead(II)-contaminated water streams with ferrihydrite in multiple equilibrium sorption stages. In this work, multistage ferrihydrite sorption systems were evaluated for their effectiveness in reducing single-solute zinc(II) (Zn(II)) concentrations in contaminated water streams to very low levels. As for lead(II) (Pb(II)), experimental data and modeling results indicate that a multistage sorption system can significantly reduce Zn(II) effluent concentrations for the same total amount of sorbent or, alternatively, dramatically lower total sorbent consumption for the same effluent Zn(II) concentration. Compared to Pb(II), however, Zn(II) removal requires on the order of 10 times more sorbent to achieve the same target effluent concentration for the same pH and number of stages. Model predictions were made using a steady-state, multistage, equilibrium adsorber model that was previously developed for and integrated into OLI Systems' Environmental Simulation Program (ESP). The modified triple-layer model was used to simulate Zn(II) surface-liquid equilibria within the adsorber model. Engineering screening evaluations again indicate that a 2- to 3-stage sorption process can provide significant economic savings when compared to a 1-stage process operating with the same target effluent Zn(II) concentration. Additional equilibrium stages beyond 2 or 3 provide diminishing economic returns. The major economic driver for multiple contacting stages is reduced capital investment and operating costs for sludge handling, dewatering, and disposal.     

Enantioselective aziridination using copper complexes of biaryl Schiff bases

Racemic 2,2'-diamino-6,6'-dimethylbiphenyl is resolved using simulated moving bed chromatography, and the absolute configuration of the enantiomers is confirmed via the X-ray crystal structure of a derivative. The diamine is condensed with a range of aldehydes to give bidentate aldimine proligands L. Molecular structures of the complexes formed between L and Cu(I) fall into two classes; bimetallic double helices ([Cu(2)L(2)](2+)) and monometallic ([CuL](+)). The latter are strikingly more efficient in the aziridination of alkenes than are the former in terms of rate, turnover, and enantioselection. In particular, the imine ligand formed from the diamine and 2,6-dichlorobenzaldehyde gives, in combination with Cu(I) or Cu(II), up to 99% ee in the aziridination of 6-acyl-2,2-dimethylchromene and 88-98% ee for a range of cinnamate esters. Styrenic and other alkenes are converted with lower selectivities (5-54%). The catalytic system shows a linear response in product ee to catalyst ee, and the product ee does not vary significantly during the reaction. UV spectrophotometric investigations indicate that conversion of Cu(I) to Cu(II) is not essential for catalysis but that Cu(II) is probably also a competent system.