School of Chemistry - Research Publications

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    A luminescent solar concentrator ray tracing simulator with a graphical user interface: features and applications
    Zhang, B ; Yang, H ; Warner, T ; Mulvaney, P ; Rosengarten, G ; Wong, WWH ; Ghiggino, KP (IOP PUBLISHING LTD, 2020-07)
    A Monte-Carlo ray tracing simulator with a graphical user interface (MCRTS-GUI) has been developed to provide a quantitative description, performance evaluation and photon loss analysis of luminescent solar concentrators (LSCs). The algorithm is applied to several practical LSC device structures including multiple dyes in the same waveguiding layer, and structures where a dye layer is sandwiched between clear substrates. The effect of the host matrix absorption and the influence of the neighboring layers are investigated. Validations demonstrate that the MCRTS-GUI developed provides a reliable and accurate description of LSC performance. Code for the mixed-dye single layer configuration is converted into a ray-tracing package with a user-friendly interface and is made available as open source software.
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    Incorporating whey protein aggregates produced with heat and ultrasound treatment into rennet gels and model non-fat cheese systems
    Gamlath, CJ ; Leong, TSH ; Ashokkumar, M ; Martin, GJO (Elsevier, 2020-12-01)
    Native whey proteins (WP) are expulsed from cheese coagulation during syneresis. Although incorporating denatured WP aggregates into cheese gels has been previously proposed to improve the overall cheese yield, the effects of WP aggregate properties on gelation kinetics and protein retention are not yet fully understood. In this study, heat and power ultrasound were used to produce denatured whey protein aggregates with a wide range of sizes. The effects of size and hydrophobicity differences in WP aggregates produced by heat and heat coupled with ultrasound were investigated in relation to the kinetics of rennet gelation and protein retention in model non-fat cheddar cheeses. Rheological measurements showed that sufficiently large, denatured WP aggregates could avoid impairment of rennet gelation caused by native WP, irrespective of changes in the soluble calcium concentration or the surface hydrophobicity of the aggregates. WP aggregates formed by the combined heat and ultrasound treatment were more hydrophobic than the larger heat-treated aggregates and were better retained in the cheese. However, inclusion of sufficiently large aggregates in cheese milk conferred an openness to the cheese microstructure and showed promise in improving the otherwise rigid non-fat cheese.
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    Incorporation of Vanadium and Molybdenum into Yttrium-Arsenotungstates Supported by Amino Acid Ligands
    Bagherjeri, FA ; Ritchie, C ; Gable, RW ; Bryant, G ; Boskovic, C (CSIRO PUBLISHING, 2020)
    The preference for incorporation of molybdenum over tungsten into specific sites of a family of yttrium-arsenotungstates with amino acid ligands prompted exploration of the incorporation of other metals, affording three new vanadium-containing (V/W and V/Mo/W) analogues: K2(GlyH)10[As4(V2W2)W44Y4O160(Gly)8(H2O)12]·11Gly (1), (MBAH)9(L-NleH)3[As4(V2W2)W44Y4O160(L-Nle)8(H2O)12] (2), and (MBAH)9(L-NleH)3[As4(V2W2)Mo2W42Y4O160(L-Nle)8(H2O)12] (3) (Gly=glycine and L-Nle=l-norleucine, MBAH=4-methylbenzylammonium). These hybrid polyoxometalates all possess a tetrametallic oxo-bridged {VIV2WVI2} central core surrounded by an amino acid-ligated cyclic metal-oxo framework. X-Ray photoelectron, UV-visible reflectance, and electron paramagnetic resonance spectroscopy, together with metal analysis, confirm the incorporation of vanadium into the polyoxometalates, while single crystal X-ray diffraction analysis supports the location of the vanadium atoms in the central core.
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    Tetrahalocatecholate Rare Earth Complexes: Dinuclear Motifs with Intramolecular RE•••XC(Ar) Interactions
    Rousset, E ; Gable, RW ; Starikova, A ; Boskovic, C (AMER CHEMICAL SOC, 2020-05-06)
    The reaction of yttrium or cerium nitrate and tetrachloro- or tetrabromocatecholate (X4Cat2- with X = Cl or Br) has afforded the compounds (Et3NH)2[{Y(Cl4Cat)(H2O)2}2(μ-Cl4Cat)2]·2MeOH·2H2O (1-Cl), (Et3NH)2[{Y(Br4Cat)(H2O)2}2(μ-Br4Cat)2]·1.5MeCN (1-Br), (Et3NH)4[(Cl4Cat)(H2O)2Y(μ-Cl4Cat)2Y(Cl4Cat)2]·2.5MeOH·3.5H2O (2-Cl), (Et3NH)4[{Y(Cl4Cat)(Cl4CatH)(H2O)}2(μ-Cl4Cat)2]·4H2O (3-Cl), (Et3NH)7[{CeIV(Cl4CatH)(NO3)(μ2-Cl4Cat)3}2CeIII](NO3)2 (4-Cl), and (Et3NH)4[CeIV(X4Cat)4] (5-X with X = Cl, Br). Small variations of the reaction stoichiometry and crystallization methods allow the isolation of dinuclear yttrium complexes with four, five, and six tetrachlorocatecholate ligands in 1-Cl, 2-Cl, and 3-Cl, respectively. Single crystal X-ray diffraction studies of these compounds reveal a conserved tetrachlorocatecholate-bridged dinuclear yttrium core in each case, but with different peripheral ligation. A key feature of the core unit is Y···ClC(Ar) intramolecular interactions with a catecholate chloro substituent ortho to one of the coordinating oxygen atoms. The tetrabromocatecholate analogue 1-Br has also been obtained. Applying similar methods to redox-active cerium, rather than yttrium, instead affords an unusual mixed-valence trinuclear {CeIIICeIV2} complex in 4-Cl, as well as two mononuclear cerium(IV) complexes in 5-Cl and 5-Br. Density functional theory calculations confirm the [CeIV(Cl4Cat)4]4- charge distribution for 5-Cl.
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    Understanding the Origin of One- or Two-Step Valence Tautomeric Transitions in Bis(dioxolene)-Bridged Dinuclear Cobalt Complexes
    Gransbury, GK ; Livesay, BN ; Janetzki, JT ; Hay, MA ; Gable, RW ; Shores, MP ; Starikova, A ; Boskovic, C (AMER CHEMICAL SOC, 2020-06-17)
    Valence tautomerism (VT) involves a reversible stimulated intramolecular electron transfer between a redox-active ligand and redox-active metal. Bis(dioxolene)-bridged dinuclear cobalt compounds provide an avenue toward controlled two-step VT interconversions of the form {CoIII-cat-cat-CoIII} ⇌ {CoIII-cat-SQ-CoII}⇌{CoII-SQ-SQ-CoII} (cat2- = catecholate, SQ•- = semiquinonate). Design flexibility for dinuclear VT complexes confers an advantage over two-step spin crossover complexes for future applications in devices or materials. The four dinuclear cobalt complexes in this study are bridged by deprotonated 3,3,3',3'-tetramethyl-1,1'-spirobi(indan)-5,5',6,6'-tetraol (spiroH4) or 3,3,3',3'-tetramethyl-1,1'-spirobi(indan)-4,4',7,7'-tetrabromo-5,5',6,6'-tetraol (Br4spiroH4) with Mentpa ancillary ligands (tpa = tris(2-pyridylmethyl)amine, n = 0-3 corresponds to methylation of the 6-position of the pyridine rings). Complementary structural, magnetic, spectroscopic, and density functional theory (DFT) computational studies reveal different electronic structures and VT behavior for the four cobalt complexes; one-step one-electron partial VT, two-step VT, incomplete VT, and temperature-invariant {CoIII-cat-cat-CoIII} states are observed. Electrochemistry, DFT calculations, and the study of a mixed-valence {ZnII-cat-SQ-ZnII} analog have allowed elucidation of thermodynamic parameters governing the one- and two-step VT behavior. The VT transition profile is rationalized by (1) the degree of electronic communication within the bis(dioxolene) ligand and (2) the matching of cobalt and dioxolene redox potentials. This work establishes a clear path to the next generation of two-step VT complexes through incorporation of mixed-valence class II and class II-III bis(dioxolene) bridging ligands with sufficiently weak intramolecular coupling.
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    Widespread remodeling of proteome solubility in response to different protein homeostasis stresses
    Sui, X ; Pires, DEV ; Ormsby, AR ; Cox, D ; Nie, S ; Vecchi, G ; Vendruscolo, M ; Ascher, DB ; Reid, GE ; Hatters, DM (National Academy of Sciences, 2020-02-04)
    The accumulation of protein deposits in neurodegenerative diseases has been hypothesized to depend on a metastable subproteome vulnerable to aggregation. To investigate this phenomenon and the mechanisms that regulate it, we measured the solubility of the proteome in the mouse Neuro2a cell line under six different protein homeostasis stresses: 1) Huntington’s disease proteotoxicity, 2) Hsp70, 3) Hsp90, 4) proteasome, 5) endoplasmic reticulum (ER)-mediated folding inhibition, and 6) oxidative stress. Overall, we found that about one-fifth of the proteome changed solubility with almost all of the increases in insolubility were counteracted by increases in solubility of other proteins. Each stress directed a highly specific pattern of change, which reflected the remodeling of protein complexes involved in adaptation to perturbation, most notably, stress granule (SG) proteins, which responded differently to different stresses. These results indicate that the protein homeostasis system is organized in a modular manner and aggregation patterns were not correlated with protein folding stability (ΔG). Instead, distinct cellular mechanisms regulate assembly patterns of multiple classes of protein complexes under different stress conditions.
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    A new fluorone-based bridging ligand for discrete and polymeric assemblies including Mo and W based [4+4] metallocycles
    Sutton, AL ; Abrahams, BF ; Hudson, TA ; Robson, R (Royal Society of Chemistry, 2020-07-21)
    Redox-active ligands are of interest for their ability to link metal centres and generate electroactive materials. We report the synthesis of 9-hydrogen-2,3,7-trihydroxyfluorone, which is able to serve as a bridging ligand and has the potential to exist in multiple oxidation states. Anionic [4+4] metallocycles in which Mo or W centres are linked by the trianion of this ligand are also described.
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    Semi-conducting mixed-valent X(4)TCNQ(I-/II-)(X = H, F) charge-transfer complexes with C6H2(NH2)(4)
    Sutton, AL ; Abrahams, BF ; D'Alessandro, DM ; Goerigk, L ; Hudson, TA ; Robson, R ; Usov, PM (Royal Society of Chemistry, 2020-07-21)
    We report further characterisation on the previously described [C6H2(NH2)4][TCNQ] charge-transfer (CT) complex. An in-depth analysis of the crystallographic data aided by spectroscopic methods indicates the compound is mixed-valent with TCNQI−/II− species. The analogous F4TCNQ CT complex has been synthesised and spectroscopic methods suggest that [C6H2(NH2)4][F4TCNQ] is also mixed-valent. Electrical conductivity measurements on both complexes indicate semi-conductor behaviour, with [C6H2(NH2)4][TCNQ] exhibiting a σ300K = 9.8 × 10−4 S cm−1 and an Ea = 0.10(1) eV. Density functional theory studies on both CT complexes reveal band structures suggestive of ambipolar transport, with a super-exchange mechanism.
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    Oxidative damage of proline residues by nitrate radicals (NO3): a kinetic and product study
    Nathanael, JG ; White, JM ; Richter, A ; Nuske, MR ; Wille, U (ROYAL SOC CHEMISTRY, 2020-09-21)
    Tertiary amides, such as in N-acylated proline or N-methyl glycine residues, react rapidly with nitrate radicals (NO3˙) with absolute rate coefficients in the range of 4-7 × 108 M-1 s-1 in acetonitrile. The major pathway proceeds through oxidative electron transfer (ET) at nitrogen, whereas hydrogen abstraction is only a minor contributor under these conditions. However, steric hindrance at the amide, for example by alkyl side chains at the α-carbon, lowers the rate coefficient by up to 75%, indicating that NO3˙-induced oxidation of amide bonds proceeds through initial formation of a charge transfer complex. Furthermore, the rate of oxidative damage of proline and N-methyl glycine is significantly influenced by its position in a peptide. Thus, neighbouring peptide bonds, particularly in the N-direction, reduce the electron density at the tertiary amide, which slows down the rate of ET by up to one order of magnitude. The results from these model studies suggest that the susceptibility of proline residues in peptides to radical-induced oxidative damage should be considerably reduced, compared with the single amino acid.
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    Exchange-Biasing in a Dinuclear Dysprosium(III) Single-Molecule Magnet with a Large Energy Barrier for Magnetisation Reversal
    Han, T ; Giansiracusa, MJ ; Li, Z-H ; Ding, Y-S ; Chilton, NF ; Winpenny, REP ; Zheng, Y-Z (WILEY-V C H VERLAG GMBH, 2020-05-26)
    A dichlorido-bridged dinuclear dysprosium(III) single-molecule magnet [Dy2 L2 (μ-Cl)2 (thf)2 ] has been made by using a diamine-bis(phenolate) ligand, H2 L. Magnetic studies show an energy barrier for magnetisation reversal (Ueff ) around 1000 K. An exchange-biasing effect is clearly seen in magnetic hysteresis with steps up to 3 K. Ab initio calculations exclude the possibility of a pure dipolar origin of this effect leading to the conclusion that super-exchange through the chloride bridging ligands is important.