Jameson cell fundamentals - A revised perspective

The Jameson Cell concept was developed by Graeme Jameson of the University of Newcastle and the technology was developed for commercial application by Mount Isa Mines Limited (MIM). Laboratory investigations highlighted significant differences between Jameson Cells and other flotation technologies. The installation of Jameson Cells in MIM's copper concentrator in 2002 has allowed a detailed investigation of Jameson Cell fundamentals to be conducted within a mineral flotation system. On line measurements, together with non-invasive measurement techniques for detailing operation within the primary contacting zone (the downcomer) and the secondary contacting zone (the tank) has allowed a detailed review of Jameson Cell operation to be conducted. This paper shows that assumptions based on mechanical flotation cells, conventional and non-conventional flotation columns and even pneumatic flotation devices do not necessarily transfer to the Jameson Cell. The effects of feed flow rate, feed percent solids, froth depth and aeration rate are discussed in relation to the Jameson Cell downcomer residence time. Aeration effects within the Jameson Cell tank are also discussed

CW and pulse EPR of cytochrome P450 to determine structure and function

Cytochromes P450 (P450s) are a diverse class of biological monooxy-genases found in a wide variety of organisms, known for their chemical versatility and reaction specificity. While an array of chemical techniques are available to study P450s, continuous wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopies provide unique insight into the structure and function of the protein by probing various paramagnetic states. In this review we will demonstrate how EPR techniques are used to reveal information about the arrangement and conformation of P450 electron-transport protein complexes, characterise the active site oxidation state and the interactions with substrates and inhibitors. In addition, when combined with sample preparation using cryoreduction and freeze-quench techniques, EPR can be used to characterise short-lived intermediates formed during the catalytic cycle

Elucidating the mechanism of the Ley-Griffith (TPAP) alcohol oxidation

The Ley-Griffith reaction is utilized extensively in the selective oxidation of alcohols to aldehydes or ketones. The central catalyst is commercially available tetra-n-propylammonium perruthenate (TPAP, nPr(4)N[ RuO4]) which is used in combination with the co-oxidant N-methylmorpholine N-oxide (NMO). Although this reaction has been employed for more than 30 years, the mechanism remains unknown. Herein we report a comprehensive study of the oxidation of diphenylmethanol using the Ley-Griffith reagents to show that the rate determining step involves a single alcohol molecule, which is oxidised by a single perruthenate anion; NMO does not appear in rate law. A key finding of this study is that when pure n-Pr4N[RuO4] is employed in anhydrous solvent, alcohol oxidation initially proceeds very slowly. After this induction period, water produced by alcohol oxidation leads to partial formation of insoluble RuO2, which dramatically accelerates catalysis via a heterogeneous process. This is particularly relevant in a synthetic context where catalyst degradation is usually problematic. In this case a small amount of n-Pr4N[RuO4] must decompose to RuO2 to facilitate catalysis

Root-Secreted Coumarins and the Microbiota Interact to Improve Iron Nutrition in Arabidopsis

Plants benefit from associations with a diverse community of root-colonizing microbes. Deciphering the mechanisms underpinning these beneficial services are of interest for improving plant productivity. We report a plant-beneficial interaction between Arabidopsis thaliana and the root microbiota under iron deprivation that is dependent on the secretion of plant-derived coumarins. Disrupting this pathway alters the microbiota and impairs plant growth in iron-limiting soil. Furthermore, the microbiota improves ironlimiting plant performance via a mechanism dependent on plant iron import and secretion of the coumarin fraxetin. This beneficial trait is strain specific yet functionally redundant across phylogenetic lineages of the microbiota. Transcriptomic and elemental analyses revealed that this interaction between commensals and coumarins promotes growth by relieving iron starvation. These results show that coumarins improve plant performance by eliciting microbe-assisted iron nutrition. We propose that the bacterial root microbiota, stimulated by secreted coumarins, is an integral mediator of plant adaptation to ironlimiting soils