1,675 research outputs found
Targeted ligand design using a combined computational and experimental approach to unlock new metal separations
No full textAs societal demand for metals grows, sustainable routes to their efficient recovery from primary ores and secondary waste streams have become increasingly important. In this regard, understanding the chemical detail of metal separations is implicit to designing more efficient and environmentally benign processes. Herein, we report a combined computational and experimental approach to targeted ligand design by modification of a simple diamide (L), previously reported as a selective precipitant for Au. This afforded three new reagents through the addition of electron-donating (LOMe) and withdrawing (LCl) groups, and the inversion of the amide linkage (Linv). Computational studies confirmed the expected trends in protonation of the amide and subsequent metal uptake experiments showed all ligands act as selective precipitants for Au at low acid concentrations in the presence of an excess of ligand. Significantly however, the use of stoichiometric amounts of LOMe and LCl resulted in a switch in selectivity from square-planar (AuCl4-) to tetrahedral metalates (GaCl4- and FeCl4-), with precipitation suppressed for Linv. Computational modelling rationalised this reversal in metalate selectivity with LOMe and LCl on thermodynamic grounds, while Hirshfeld surfaces, NCI plots and QTAIM analyses highlighted halogen bonding as the most important structure directing interaction. Importantly, preliminary studies with LOMe suggested a viable pathway to the separation of Ga and Fe from industrially generated waste streams, which could be exploited in the recycling of zinc residues and end-of-life GaN light-emitting diodes
Why I Can’t Love the Homemade Semantic Web
Full text linkCitation: Bengtson, Jason. "Why I Can't Love the Homemade Semantic Web." B Sides Jan (2010) : n. pag. Web.Almost all information professionals agree that the web needs to move to a semantic structure. While work is proceeding in this area, movements to get individual web authors to use semantic markup tools have also been on the rise. This author argues that such efforts are ill conceived and he proposes an automated alternative
Controlled photocatalytic hydrocarbon oxidation by uranyl complexes
Full text linkControlled, photocatalytic C−H bond activations are key reactions in the toolkits of the modern synthetic chemist. While it is known that the uranyl(VI) ion, [UVIO2]2+, the environmentally dominant form of uranium, is photoactive, most literature examines its luminescent properties, neglecting its potential synthetic utility for photocatalytic C−H bond cleavage. Here, we synthesise and fully characterise an air‐stable and hydrocarbon‐soluble uranyl phenanthroline complex, [UVIO2(NO3)2(Ph2phen)], UPh2phen, and demonstrate that it can catalytically abstract hydrogen atoms from a variety of organic substrates under visible light irradiation. We show that the commercially available parent complex, uranyl nitrate ([UVIO2(NO3)2(OH2)2]⋅4H2O; UNO3), is also competent, but from electronic spectroscopy we attribute the higher rates and selectivity of UPh2phen to ligand‐mediated electronic effects. Ketones are selectively formed over other oxygenated products (alcohols, etc.), and the catalytic oxidation of substrates containing a benzylic C−H position is particularly improved for UPh2phen. We also show uranyl‐mediated photocatalytic C−C bond cleavage in a model lignin compound for the first time
Gold precipitation by diamides - ICP-OES and NMR data
No full textThe efficient separation of gold and other metals from their ores and composite secondary sources such as electronic waste is necessary to realising circularity in metal supply chains. Processes based on precipitation are becoming increasingly popular and their development is reliant on designing and understanding chemical recognition to achieve selectivity. Here we show that the simple tertiary diamide PhC(O)NMe(CH2CH2)NMeC(O)Ph (L) precipitates gold selectively and directly from aqueous acidic solutions as the ion pair [HL][AuCl4], including from aqua regia solutions of electronic waste. The X-ray crystal structure of the precipitate displays an infinite chain of diamide cations, formed through an intermolecular proton chelate, interleaved with tetrachloridoaurate. Gold is released quantitatively from the isolated precipitate as HAuCl4 on contact with water, enabling ligand recycling. The diamide is highly selective, with its addition to a mixture of 29 metals in 2 M HCl resulting in 70% gold uptake and minimal removal of all other metals. Increasing the HCl concentration to 6 M allows complete collection of gold, iron, tin, and platinum, demonstrating that L is an adaptable selective metal precipitant controlled by just one variable. Thus, this discovery could be exploited in metal refining and recycling processes due to its tuneable selectivity under different metal leaching conditions, the avoidance of organic solvents inherent to biphasic extraction, and the straightforward recycling of the precipitant
Copper precipitation and carbon analysis
No full textQuantitative ICP-OES and ICP-MS data for all precipitation and solvent extraction experiments, infrared spectroscopic data, powder X-ray diffraction data, X-ray fluorescence data, life cycle inventory, nuclear magnetic resonance (NMR) spectroscopic data and matrix assisted laser desorption/ionisation mass spectrometry (MALDI-MS) data.Excel workbook: Raw_Data_Vance_Chatzisymeon_Morrison_Love comprising ICP, FTIR, PXRD and XRF raw data
Excel workbook: Life_Cycle_Inventory_Vance_Chatzisymeon_Morrison_Love comprising inventory data used for life-cycle analysi
Triggering redox activity in a thiophene compound: radical stabilization and coordination chemistry
Full text linkThe synthesis, metalation, and redox properties of an acyclic bis(iminothienyl)methene L− are presented. This π-conjugated anion displays pronounced redox activity, undergoing facile one-electron oxidation to the acyclic, metal-free, neutral radical L* on reaction with FeBr2. In contrast, reaction of L− with CuI forms the unique, neutral Cu2I2(L*) complex of a ligand-centered radical, whereas reaction with the stronger oxidant AgBF4 forms the metal-free radical dication L*2+
Correspondence, Jason Brown to Frank B. Sanborn, September 10, 1885
No full textA letter to Franklin B. Sanborn from Jason Brown, refusing a one hundred dollar check sent to him by William Lloyd Garrison. 1 page
Euripides’ Medea and Jason: A Study in the Social Power of Love
No full textEuripides’ Medea resonates with modern issues in intimate relationships. However, little has been written on this, especially from the social-psychological perspective. This paper explores the breakdown of the Jason-Medea marriage in terms of the social-psychological theory of love as an exchange in a power game in which a certain degree of imbalance in the exchange could account for such a breakdown. I analyse the Medea text in terms of Olson and Cromwell’s (1975) tripartite theoretical framework, namely: (a) the bases on which social power is built; (b) the processes by which social power is wielded; and (c) the outcomes produced by the use of social power. I find that Medea carried a greater burden of love towards Jason than Jason did towards her, fuelled and sustained by her enduring and greater need for security and happiness. And in intimate relationships, the principle of least interest (Waller and Hill 1951) works: the beloved tends to dominate the lover. Jason, however, overreached himself when he violated the minimum conditions of his own desirability – fidelity to and respect for Medea. I conclude that Medea’s violent reaction to Jason’s conduct indicates the fragility of love as a basis of social power in intimate relationships
Earth-Abundant Mixed-Metal Catalysts for Hydrocarbon Oxygenation
Full text linkThe
oxygenation of aliphatic and aromatic hydrocarbons using earth-abundant
Fe and Cu catalysts and “green” oxidants such as hydrogen
peroxide is becoming increasingly important to atom-economical chemical
processing. In light of this, we describe that dinuclear CuII complexes of pyrrolic Schiff-base macrocycles, in combination with
ferric chloride (FeCl3), catalyze the oxygenation of π-activated
benzylic substrates with hydroperoxide oxidants at room temperature
and low loadings, representing a novel design in oxidation catalysis.
Mass spectrometry and extended X-ray absorption fine structure analysis
indicate that a cooperative action between CuII and FeIII occurs, most likely because of the interaction of FeCl3 or FeCl4– with the dinuclear
CuII macrocycle. Voltammetric measurements highlight a
modulation of both CuII and FeIII redox potentials
in this adduct, but electron paramagnetic resonance spectroscopy indicates
that any Cu–Fe intermetallic interaction is weak. High ketone/alcohol
product ratios, a small reaction constant (Hammett analysis), and
small kinetic isotope effect for H-atom abstraction point toward a
free-radical reaction. However, the lack of reactivity with cyclohexane,
oxidation of 9,10-dihydroanthracene, oxygenation by the hydroperoxide
MPPH (radical mechanistic probe), and oxygenation in dinitrogen-purge
experiments indicate a metal-based reaction. Through detailed reaction
monitoring and associated kinetic modeling, a network of oxidation
pathways is proposed that includes “well-disguised”
radical chemistry via the formation of metal-associated radical intermediates
Radical relatives: facile oxidation of hetero-diarylmethene anions to neutral radicals
Full text linkDifuryl- and dithienymethene anions are potential chelating ligands for metals and are shown to exhibit marked redox activity, undergoing facile one-electron oxidation to form stable, neutral radicals. The stability of the anions and the ease of formation of the neutral radicals are related to the extent of conjugation, the substituent pattern, and the nature of the heteroatom
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