School of Chemistry - Research Publications

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    Electronic Structure Engineering in ZnSe/CdS Type-II Nanoparticles by Interface Alloying
    Boldt, K ; Schwarz, KN ; Kirkwood, N ; Smith, TA ; Mulvaney, P (American Chemical Society, 2014-06-19)
    We report the synthesis and characterization of type-II ZnSe/CdS semiconductor nanocrystals that exhibit strong charge separation, high photoluminescence quantum yields, low optical gain thresholds, and alloyed core–shell interfaces. Shell growth rates and the degree of alloying both depend strongly on the shelling temperature. The core–shell NCs exhibit band edge PL with emission wavelengths spanning the blue to orange region of the electromagnetic spectrum (380–562 nm). Fluorescence quantum yields up to 75% can be obtained by deposition of an additional ZnS layer. Transient absorption spectroscopy reveals that the population of the first two exciton states (1Se–1Sh, 1Se–2Sh) in the type-II structures can be controlled by alloying. Increased alloying leads to a greater population of the 2S hole state exciton.
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    A monophasic extraction strategy for the simultaneous lipidome analysis of polar and nonpolar retina lipids
    Lydic, TA ; Busik, JV ; Reid, GE (ELSEVIER, 2014-08)
    Lipid extraction using a monophasic chloroform/methanol/water mixture, coupled with functional group selective derivatization and direct infusion nano-ESI-high-resolution/accurate MS, is shown to facilitate the simultaneous analysis of both highly polar and nonpolar lipids from a single retina lipid extract, including low abundance highly polar ganglioside lipids, nonpolar sphingolipids, and abundant glycerophospholipids. Quantitative comparison showed that the monophasic lipid extraction method yielded similar lipid distributions to those obtained from established "gold standard" biphasic lipid extraction methods known to enrich for either highly polar gangliosides or nonpolar lipids, respectively, with only modest relative ion suppression effects. This improved lipid extraction and analysis strategy therefore enables detailed lipidome analyses of lipid species across a broad range of polarities and abundances, from minimal amounts of biological samples and without need for multiple lipid class-specific extractions or chromatographic separation prior to analysis.
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    A Comparison of the Effectiveness of Sonication, High Shear Mixing and Homogenisation on Improving the Heat Stability of Whey Protein Solutions
    Koh, LLA ; Chandrapala, J ; Zisu, B ; Martin, GJO ; Kentish, SE ; Ashokkumar, M (SPRINGER, 2014-02)
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    A novel low-cost detection method for screening of arsenic in groundwater
    Fontas, C ; Vera, R ; Batalla, A ; Kolev, SD ; Antico, E (SPRINGER HEIDELBERG, 2014-10-01)
    In the present work, a novel and simple detection system for As inorganic species contained in groundwater is presented. To reach the required detection limit, the proposed methodology is based on two steps: first is the transport and preconcentration of the inorganic arsenic species using a polymer inclusion membrane (PIM) system and second is the formation of a coloured complex, the absorbance of which is measured. Different parameters related to the membrane composition and the transport kinetics have been studied, and it was found that membranes made of polyvinyl chloride (PVC) as a polymer, and Aliquat 336 as a carrier, ensured efficient arsenic transport when the carrier content was at least 31 % (w/w). The implementation of the designed PIM in a special device that contained only 5 mL of the stripping solution (0.1 M NaCl) allowed As preconcentration from a 100-mL water sample, thus facilitating its detection with the colorimetric method. The new method developed here was validated, and its analytical figures of merit were determined, i.e. limit of detection of 4.5 μg L(-1) at 820 nm and a relative standard deviation within the range 8-10 %. Finally, the method was successfully applied to the analysis of different water samples from Catalonia region with naturally occurring As.
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    A routine method for cloning, expressing and purifying Aβ(1-42) for structural NMR studies
    Weber, DK ; Sani, M-A ; Gehman, JD (SPRINGER WIEN, 2014-10)
    Nuclear magnetic resonance (NMR) is a key technology in the biophysicist's toolbox for gaining atomic-level insight into structure and dynamics of biomolecules. Investigation of the amyloid-β peptide (Aβ) of Alzheimer's disease is one area where NMR has proven useful, and holds even more potential. A barrier to realizing this potential, however, is the expense of the isotopically enriched peptide required for most NMR work. Whereas most biomolecular NMR studies employ biosynthetic methods as a very cost-effective means to obtain isotopically enriched biomolecules, this approach has proven less than straightforward for Aβ. Furthermore, the notorious propensity of Aβ to aggregate during purification and handling reduces yields and increases the already relatively high costs of solid phase synthesis methods. Here we report our biosynthetic and purification developments that yield pure, uniformly enriched ¹⁵N and ¹³C¹⁵N Aβ(1-42), in excess of 10 mg/L of culture media. The final HPLC-purified product was stable for long periods, which we characterize by solution-state NMR, thioflavin T assays, circular dichroism, electrospray mass spectrometry, and dynamic light scattering. These developments should facilitate further investigations into Alzheimer's disease, and perhaps misfolding diseases in general.
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    Novel molecularly imprinted polymeric microspheres for preconcentration and preservation of polycyclic aromatic hydrocarbons from environmental samples
    Krupadam, RJ ; Korde, BA ; Ashokkumar, M ; Kolev, SD (SPRINGER HEIDELBERG, 2014-09)
    Molecularly imprinted polymer (MIP) microspheres with diameters in the range 60-500 μm were synthesized in a continuous segmented flow microfluidic reactor and used as packing material for microtraps for the selective separation of benzo[a]pyrene (BAP) from environmental aqueous samples. The synthesis involved the pumping of monodisperse droplets of acetonitrile containing methacrylic acid as the functional monomer, BAP as a template, and ethylene glycol dimethacrylate as the cross-linking monomer into the microchannels of the microfluidic reactor. The microspheres showed high adsorption capacity and selectivity for BAP in aqueous solutions; both are important for the environmental monitoring and analysis of BAP. The adsorption capacity for BAP of the smallest MIP microspheres (size range 60-80 μm), prepared as part of this study, was 75 mg g(-1) in aqueous solutions; furthermore, this adsorption capacity was close to 300 % higher than that of commercially used activated carbon. Microtraps packed with MIP retained BAP intact for at least 30 days, whereas microtraps packed with activated carbon for BAP showed 40 % reduction in BAP concentration for the same period. This study has demonstrated that MIP microtraps have significant potential for the selective enrichment and preservation of targeted polycyclic aromatic hydrocarbons from complex environmental samples.
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    The McClure and Weiss models of Fe-O2 bonding for oxyhemes, and the HbO2 + NO reaction
    Harcourt, RD (SPRINGER, 2014-01)
    For the Fe-O2(S = 0) linkages of oxyhemes, valence bond (VB) structures are re-presented for the McClure [Fe(II)(S = 1) + O2(S = 1)], Pauling-Coryell [Fe(II)(S = 0) + O2*(S = 0)], and Weiss [Fe(III)(S = ½) + O2 (-)(S = ½)] models of bonding. The VB structures for the McClure and Weiss models are of the increased-valence type, with more electrons participating in bonding than occur in their component Lewis structures. The Fe-O bond number and O-O bond order for the McClure structure are correlated with measured Fe-O and O-O bond lengths for oxymyoglobin. Back-bonding from O2(-) to Fe(III) of the Weiss structure gives a restricted form of the McClure structure. The McClure and Weiss increased-valence structures are used to provide VB formulations of mechanisms for the oxyhemoglobin + NO reaction. The products of these two formulations are Hb(+) and NO3(-) (where Hb is hemoglobin) and Hb(+) and OONO(-), respectively. Because Hb(+) and NO3(-) are the observed products, they provide an experimental procedure for distinguishing the McClure and Weiss models. It is also shown that the same type of agreement between McClure-type theory and experiment occurs for oxycoboglobin + NO, cytochrome P450 monooxygenases, and related hydrogen atom transfer reactions. In the appendices, the results of density functional theory and multireference molecular orbital calculations for oxyhemes are related to one formulation of the increased-valence wavefunction for the McClure model, and theory is presented for the calculation of approximate weights for the Lewis structures that are components of the McClure increased-valence structure.
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    Oxygenase-Catalyzed Desymmetrization of N,N-Dialkyl-piperidine-4-carboxylic Acids
    Rydzik, AM ; Leung, IKH ; Kochan, GT ; McDonough, MA ; Claridge, TDW ; Schofield, CJ (WILEY-V C H VERLAG GMBH, 2014-10-06)
    γ-Butyrobetaine hydroxylase (BBOX) is a 2-oxoglutarate dependent oxygenase that catalyzes the final hydroxylation step in the biosynthesis of carnitine. BBOX was shown to catalyze the oxidative desymmetrization of achiral N,N-dialkyl piperidine-4-carboxylates to give products with two or three stereogenic centers.
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    Reactions in nitroimidazole triggered by low-energy (0-2 eV) electrons: methylation at N1-H completely blocks reactivity.
    Tanzer, K ; Feketeová, L ; Puschnigg, B ; Scheier, P ; Illenberger, E ; Denifl, S (Wiley, 2014-11-03)
    Low-energy electrons (LEEs) at energies of less than 2 eV effectively decompose 4-nitroimidazole (4NI) by dissociative electron attachment (DEA). The reactions include simple bond cleavages but also complex reactions involving multiple bond cleavages and formation of new molecules. Both simple and complex reactions are associated with pronounced sharp features in the anionic yields, which are interpreted as vibrational Feshbach resonances acting as effective doorways for DEA. The remarkably rich chemistry of 4NI is completely blocked in 1-methyl-4-nitroimidazole (Me4NI), that is, upon methylation of 4NI at the N1 site. These remarkable results have also implications for the development of nitroimidazole based radiosensitizers in tumor radiation therapy.
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    Non-enzymatic chemistry enables 2-hydroxyglutarate-mediated activation of 2-oxoglutarate oxygenases
    Tarhonskaya, H ; Rydzik, AM ; Leung, IKH ; Loik, ND ; Chan, MC ; Kawamura, A ; McCullagh, JSO ; Claridge, TDW ; Flashman, E ; Schofield, CJ (NATURE PUBLISHING GROUP, 2014-03)
    Accumulation of (R)-2-hydroxyglutarate in cells results from mutations to isocitrate dehydrogenase that correlate with cancer. A recent study reports that (R)-, but not (S)-2-hydroxyglutarate, acts as a co-substrate for the hypoxia-inducible factor prolyl hydroxylases via enzyme-catalysed oxidation to 2-oxoglutarate. Here we investigate the mechanism of 2-hydroxyglutarate-enabled activation of 2-oxoglutarate oxygenases, including prolyl hydroxylase domain 2, the most important human prolyl hydroxylase isoform. We observe that 2-hydroxyglutarate-enabled catalysis by prolyl hydroxylase domain 2 is not enantiomer-specific and is stimulated by ferrous/ferric ion and reducing agents including L-ascorbate. The results reveal that 2-hydroxyglutarate is oxidized to 2-oxoglutarate non-enzymatically, likely via iron-mediated Fenton-chemistry, at levels supporting in vitro catalysis by 2-oxoglutarate oxygenases. Succinic semialdehyde and succinate are also identified as products of 2-hydroxyglutarate oxidation. Overall, the results rationalize the reported effects of 2-hydroxyglutarate on catalysis by prolyl hydroxylases in vitro and suggest that non-enzymatic 2-hydroxyglutarate oxidation may be of biological interest.