School of Chemistry - Research Publications

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    Evidence for decreased copper associated with demyelination in the corpus callosum of cuprizone-treated mice
    Hilton, JBW ; Kysenius, K ; Liddell, JR ; Mercer, SW ; Hare, DJ ; Buncic, G ; Paul, B ; Wang, Y ; Murray, SS ; Kilpatrick, TJ ; White, AR ; Donnelly, PS ; Crouch, PJ (OXFORD UNIV PRESS, 2024-01-05)
    Demyelination within the central nervous system (CNS) is a significant feature of debilitating neurological diseases such as multiple sclerosis and administering the copper-selective chelatorcuprizone to mice is widely used to model demyelination in vivo. Conspicuous demyelination within the corpus callosum is generally attributed to cuprizone's ability to restrict copper availability in this vulnerable brain region. However, the small number of studies that have assessed copper in brain tissue from cuprizone-treated mice have produced seemingly conflicting outcomes, leaving the role of CNS copper availability in demyelination unresolved. Herein we describe our assessment of copper concentrations in brain samples from mice treated with cuprizone for 40 d. Importantly, we applied an inductively coupled plasma mass spectrometry methodology that enabled assessment of copper partitioned into soluble and insoluble fractions within distinct brain regions, including the corpus callosum. Our results show that cuprizone-induced demyelination in the corpus callosum was associated with decreased soluble copper in this brain region. Insoluble copper in the corpus callosum was unaffected, as were pools of soluble and insoluble copper in other brain regions. Treatment with the blood-brain barrier permeant copper compound CuII(atsm) increased brain copper levels and this was most pronounced in the soluble fraction of the corpus callosum. This effect was associated with significant mitigation of cuprizone-induced demyelination. These results provide support for the involvement of decreased CNS copper availability in demyelination in the cuprizone model. Relevance to human demyelinating disease is discussed.
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    Energy dissipation during homogeneous wetting of surfaces with randomly and periodically distributed cylindrical pillars
    Kumar, P ; Mulvaney, P ; Harvie, DJE (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2024-04)
    HYPOTHESIS: Understanding contact angle hysteresis on rough surfaces is important as most industrially relevant and naturally occurring surfaces possess some form of random or structured roughness. We hypothesise that hysteresis can be described by the dilute defect model of Joanny & de Gennes [1] and that the energy dissipation occurring during the stick-slip motion of the contact line is key to developing a predictive equation for hysteresis. EXPERIMENTS: We measured hysteresis on surfaces with randomly distributed and periodically arranged microscopic cylindrical pillars for a variety of different liquids in air. The inherent (flat surface) contact angles tested range from lyophilic (θe=33.8°) to lyophobic (θe=112.0°). FINDINGS: A methodology for averaging the measured advancing and receding contact angles on random surfaces is presented. Based on these results correlations for roughness-induced energy dissipation are derived, and an equation for predicting the advancing and receding contact angles during homogeneous (Wenzel) wetting on random surfaces is presented. Equations that predict the onset of the alternate wetting conditions of hemiwicking, split-advancing, split-receding and heterogeneous (Cassie) wetting are also derived, thus defining the range of validity for the homogeneous wetting equation. A 'cluster' concept is proposed to explain the measurably higher hysteresis exhibited by structured surfaces compared to random surfaces.
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    A framework for multiexcitonic logic
    Hudson, RJ ; Macdonald, TSC ; Cole, JH ; Schmidt, TW ; Smith, TA ; McCamey, DR (NATURE PORTFOLIO, 2024-02)
    Exciton science sits at the intersection of chemical, optical and spin-based implementations of information processing, but using excitons to conduct logical operations remains relatively unexplored. Excitons encoding information could be read optically (photoexcitation-photoemission) or electrically (charge recombination-separation), travel through materials via exciton energy transfer, and interact with one another in stimuli-responsive molecular excitonic devices. Excitonic logic offers the potential to mediate electrical, optical and chemical information. Additionally, high-spin triplet and quintet (multi)excitons offer access to well defined spin states of relevance to magnetic field effects, classical spintronics and spin-based quantum information science. In this Roadmap, we propose a framework for developing excitonic computing based on singlet fission (SF) and triplet-triplet annihilation (TTA). Various molecular components capable of modulating SF/TTA for logical operations are suggested, including molecular photo-switching and multi-colour photoexcitation. We then outline a pathway for constructing excitonic logic devices, considering aspects of circuit assembly, logical operation synchronization, and exciton transport and amplification. Promising future directions and challenges are identified, and the potential for realizing excitonic computing in the near future is discussed.
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    Synergistic effects of hole blocking and Forster resonance energy transfer process in high-performance photomultiplication organic photodetectors
    Shi, X ; Qiao, J-W ; Jeong, SY ; Lu, P ; Du, X-Y ; Yin, H ; Qin, W ; Woo, HY ; Hao, X-T (AIP Publishing, 2023-12-04)
    Organic photodetectors (OPDs) are a potential next-generation photodetection technology because they are lightweight, flexible, and have customizable spectral responses. However, high dark currents with low detectability remain major challenges, limiting the widespread application of photomultiplication OPDs (PM-OPDs). This work describes a straightforward interface modification strategy based on the PBDB-T:N2200 bulk heterojunction (BHJ) structure to improve the PM-OPD performance. Introducing a thin rubrene layer achieves the synergistic effects of hole blocking and the Förster resonance energy transfer (FRET) process, resulting in a two-order-of-magnitude reduction in dark current density and an increased responsivity of 19.77 A W−1 at 660 nm. Moreover, the external quantum efficiency improves significantly through FRET, and a specific detectivity of 4.39 × 1013 Jones is demonstrated at 660 nm, which is the highest value among existing PM-OPDs, using BHJ structures. An impressive increase in the linear dynamic range from 91 to 144 dB was obtained due to the improved photocurrent density and balanced charge transport. The broad applicability of the strategy was verified through a PM6:Y6-based OPD system. Our approach offers more general application prospects by improving the detection capability of photodetectors for low-light environments.
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    Total Synthesis of Icumazole A Using a Modified Cadiot-Chodkiewicz Coupling
    Buntine, J ; Dasgupta, S ; Dorney, K ; Rubinstein, O ; Salimimarand, M ; White, JM ; Rizzacasa, MA (AMER CHEMICAL SOC, 2024-01-29)
    The first total synthesis of myxobacteria metabolite icumazole A (1) is reported. Key steps in the route include an organocatalyzed asymmetric self-aldol reaction followed by an acetate aldol reaction to form the stereotriad present in the oxazole moiety, an intramolecular Diels-Alder reaction to form the isochromanone, and an acetylide addition and selective methylation. The final steps involved a high-yielding modified Cadiot-Chodkiewicz coupling and stereoselective reduction to secure the Z,Z-diene and afford 1.
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    Tuning valence tautomerism in a family of dinuclear cobalt complexes incorporating a conjugated bridging bis(dioxolene) ligand with weak communication
    Fischer, TE ; Janetzki, JT ; Zahir, FZM ; Gable, RW ; Starikova, AA ; Boskovic, C (ROYAL SOC CHEMISTRY, 2024-02-13)
    Valence tautomerism (VT) involves the stimulated reversible intramolecular electron transfer between a redox-active metal and ligand. Dinuclear cobalt complexes bridged by bis(dioxolene) ligands can undergo thermally-induced VT with access to {CoIII-cat-cat-CoIII}, {CoIII-cat-SQ-CoII} and {CoII-SQ-SQ-CoII} states (cat2- = catecholate, SQ˙- = semiquinonate, CoIII refers to low spin CoIII, CoII refers to high spin CoII). The resulting potential for two-step VT interconversions offers increased functionality over mononuclear examples. In this study, the bis(dioxolene) ligand 3,3',4,4'-tetrahydroxy-5,5'-dimethoxy-benzaldazine (thMH4) was paired with Mentpa (tpa = tris(2-pyridylmethyl)amine, n = 0-3 corresponds to methylation at 6-position of the pyridine rings) to afford [{Co(Mentpa)}2(thM)](PF6)2 (1a, n = 0; 2a, n = 2; 3a, n = 3). Structural, magnetic susceptibility and spectroscopic data show that 1a and 3a remain in the temperature invariant {CoIII-cat-cat-CoIII} and {CoII-SQ-SQ-CoII} forms in the solid state, respectively. In contrast, 2a exhibits incomplete thermally-induced VT between these two tautomeric forms via the mixed {CoIII-cat-SQ-CoII} tautomer. In solution, room temperature electronic absorption spectra are consistent with the assignments from the solid-state, with VT observed only for 2a. From electrochemistry, the proximity of the two 1e--processes for the thMn- ligand indicates weak electronic communication between the two dioxolene units, supporting the potential for a two-step VT interconversion in thMn- containing complexes. Comparison of the redox potentials of the Co and thMn- processes suggests that only 2a has these processes in sufficient proximity to afford the thermally-induced VT observed experimentally. Density functional theory calculations are consistent with the prerequisite energy ordering for a two-step transition for 2a, and temperature invariant {CoIII-cat-cat-CoIII} and {CoII-SQ-SQ-CoII} states for 1a and 3a, respectively. This work presents the third example, and the first formally conjugated example, of a bridging bis(dioxolene) ligand that can afford two-step VT in a Co complex, suggesting new possibilities towards applications based on multistep switching.
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    Direct measurement of the structural change associated with amorphous solidification using static scattering of coherent radiation
    Petersen, CF ; Harrowell, P (AIP Publishing, 2023-12-28)
    In this paper, we demonstrate that the weak temperature dependence of the structure factor of supercooled liquids, a defining feature of the glass transition, is a consequence of the averaging of the scattering intensity due to angular averaging. We show that the speckle at individual wavevectors, calculated from a simulated glass former, exhibits a Debye-Waller factor with a sufficiently large temperature dependence to represent a structural order parameter capable of distinguishing liquid from glass. We also extract from the speckle intensities a quantity proportional to the variance of the local restraint, i.e., a direct experimental measure of the amplitude of structural heterogeneity.
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    Electrophoretic Deposition of Single Nanoparticles
    Zhang, H ; Liu, Y ; Dong, Y ; Ashokan, A ; Widmer-Cooper, A ; Ko''hler, J ; Mulvaney, P (AMER CHEMICAL SOC, 2024-02-01)
    The controlled assembly of colloid particles on a solid substrate has always been a major challenge in colloid and surface science. Here we provide an overview of electrophoretic deposition (EPD) of single charge-stabilized nanoparticles. We demonstrate that surface templated EPD (STEPD) assembly, which combines EPD with top-down nanofabrication, allows a wide range of nanoparticles to be built up into arbitrary structures with high speed, scalability, and excellent fidelity. We will also discuss some of the current colloid chemical limitations and challenges in STEPD assembly for sub-10 nm nanoparticles and for the fabrication of densely packed single particle arrays.
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    Cooperative assemblies featuring hydrogen bonding and C-H...π interactions in 2-(methanesulfonamido)benzohydrazide derivatives: Experimental, computational and biochemical assessment
    Munir, R ; Zaib, S ; Khan, I ; Yousaf, A ; McAdam, CJ ; White, JM ; Hokelek, T ; Awwad, NS ; Ibrahium, HA ; Frontera, A (ELSEVIER, 2024-01-05)
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    Spectroelectrochemistry of CdSe/CdS Core-Shell Quantum Dots
    Ashokan, A ; Hutchison, JA ; Mulvaney, P (AMER CHEMICAL SOC, 2024-02-16)