School of Chemistry - Research Publications

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    Bond dissociation energy of FeCr+ determined through threshold photodissociation in a cryogenic ion trap
    Marlton, SJP ; Liu, C ; Bieske, EJ (American Institute of Physics, 2024-01-21)
    The bond dissociation energy of FeCr+ is measured using resonance enhanced photodissociation spectroscopy in a cryogenic ion trap. The onset for FeCr+ → Fe + Cr+ photodissociation occurs well above the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit. In contrast, the higher energy FeCr+ → Fe+ + Cr photodissociation process exhibits an abrupt onset at the energy of the Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) limit, enabling accurate dissociation energies to be extracted: D(Fe-Cr+) = 1.655 ± 0.006 eV and D(Fe+-Cr) = 2.791 ± 0.006 eV. The measured D(Fe-Cr+) bond energy is 10%-20% larger than predictions from accompanying CAM (Coulomb Attenuated Method)-B3LYP and NEVPT2 and coupled cluster singles, doubles, and perturbative triples electronic structure calculations, which give D(Fe-Cr+) = 1.48, 1.40, and 1.35 eV, respectively. The study emphasizes that an abrupt increase in the photodissociation yield at threshold requires that the molecule possesses a dense manifold of optically accessible, coupled electronic states adjacent to the dissociation asymptote. This condition is not met for the lowest Cr+(6S, 3d5) + Fe(5D, 3d64s2) dissociation limit of FeCr+ but is satisfied for the higher energy Cr(7S, 3d54s1) + Fe+(6D, 3d64s1) dissociation limit.
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    A self-healing waterborne acrylic latex coating based on intrinsic hydrogen bonding
    Beach, MA ; Davey, TW ; Subramanian, P ; Such, GK (Elsevier, 2024-03)
    Acrylic coatings suffer damage in the form of cracking, which degrades both their protective and aesthetic performance over time. Self-healing technology offers the ability to solve this problem by allowing cracks to spontaneously heal without external diagnosis or intervention, offsetting the enormous costs associated with coating damage and repair. However, there is currently no efficient self-healing acrylic coating design, and research in the area remains noticeably sparse. In this research we sought to imbue a mechanically tough methyl methacrylate (MMA)/butyl acrylate (BA)/acrylic acid (AA) acrylic coating with self-healing functionality by incorporating self-healing monomers within the formulation. We synthesized a library of four acrylic monomers containing both a long amphiphilic spacer of variable length, and the 2-ureido-4[1H]-pyrimidinone (UPy) unit, which forms strong self-complementary quadruple hydrogen bonds. These UPy-monomers were able to participate in the emulsion polymerization of MMA, BA and AA, forming intrinsic hydrogen bonding networks within the subsequent acrylic coatings. These UPy functionalized coatings displayed optical self-healing and strain recovery over 24 h both at room temperature (∼28 %), and at elevated temperatures up to 50 °C (∼80 %). The coatings also displayed repeatable self-healing after four healing cycles, relative to an MMA/BA/AA coating.
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    Organic Photovoltaic Stability: Understanding the Role of Engineering Exciton and Charge Carrier Dynamics from Recent Progress
    Zhang, K-N ; Du, X-Y ; Yan, L ; Pu, Y-J ; Tajima, K ; Wang, X ; Hao, X-T (Wiley, 2024-02-20)
    Benefiting from the synergistic development of material design, device engineering, and the mechanistic understanding of device physics, the certified power conversion efficiencies (PCEs) of single-junction non-fullerene organic solar cells (OSCs) have already reached a very high value of exceeding 19%. However, in addition to PCEs, the poor stability is now a challenging obstacle for commercial applications of organic photovoltaics (OPVs). Herein, recent progress made in exploring operational mechanisms, anomalous photoelectric behaviors, and improving long-term stability in non-fullerene OSCs are highlighted from a novel and previously largely undiscussed perspective of engineering exciton and charge carrier pathways. Considering the intrinsic connection among multiple temporal-scale photocarrier dynamics, multi-length scale morphologies, and photovoltaic performance in OPVs, this review delineates and establishes a comprehensive and in-depth property-function relationship for evaluating the actual device stability. Moreover, this review has also provided some valuable photophysical insights into employing the advanced characterization techniques such as transient absorption spectroscopy and time-resolved fluorescence imagings. Finally, some of the remaining major challenges related to this topic are proposed toward the further advances of enhancing long-term operational stability in non-fullerene OSCs.
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    Overcoming Disordered Preaggregation in Liquid State for Highly Efficient Organic Solar Cells Printed from Nonhalogenated Solvents
    Sun, M ; Zhang, K-N ; Qiao, J-W ; Wang, L-H ; Li, M ; Lu, P ; Qin, W ; Xiao, Z ; Zhang, L ; Hao, X-T ; Ding, L ; Du, X-Y (Wiley, 2023-03)
    The current power conversion efficiencies of laboratory-sized organic solar cells (OSCs), based on the spin-coating process with halogenated solvents, have exceeded 19%. Environmentally friendly printing is needed to bridge the gap between laboratory and industrialization by being compatible with roll-to-roll large-area production. Here, the molecular design rules are revealed for enhancing the green printing potential of the state-of-the-art photovoltaic martial systems by investigating the detailed structure formation dynamic and the key determining factors. By comparing two model systems based on D18:Y6 and D18:BTP-eC9, it is found that disordered preaggregation in liquid state can result in over-sized domains with reduced crystallinity and disordered molecular orientation, which significantly limits device performance. By systematically tuning the length of the inner alkyl side chains with multiple Y-series materials, the authors demonstrate that molecular side-chain engineering can effectively supress the detrimental disordered preaggregation in liquid state during environmentally friendly printing process, leading to enhanced crystallization with preferential faceon molecular orientation, more efficient exciton dissociation and charge carrier transport, and finally high upscaling potential. The work provides deeper insights into molecular engineering and structure formation dynamics toward environmentally friendly production of OSCs.
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    Reducing Limitations of Aggregation-Induced Photocarrier Trapping for Photovoltaic Stability via Tailoring Intermolecular Electron-Phonon Coupling in Highly Efficient Quaternary Polymer Solar Cells
    Zhang, K-N ; Du, X-Y ; Chen, Z-H ; Wang, T ; Yang, Z-Q ; Yin, H ; Yang, Y ; Qin, W ; Hao, X-T (Wiley, 2022-02-10)
    The kinetic aggregation of nonfullerene acceptors under nonequilibrium conditions can induce electron–phonon interaction roll-off and electronic band structure transition, which represents an important limitation for long-term operational stability of organic solar cells (OSCs). However, the fundamental underlying mechanisms have received limited attention. Herein, a photophysical correlation picture between intermolecular electron–phonon coupling and trapping of electronic excitation is proposed based on the different aggregation behaviors of BTP-eC9 in bulk-heterojunction and layer-by-layer processed multicomponent OSCs. Two separate factors rationalize their correlation mechanisms: 1) the local lattice and/or molecular deformation can be regarded as the results of BTP-eC9 aggregates in binary system under continuous heating, which brings about attenuated intermolecular electron–phonon coupling with intensified photocarrier trapping. 2) The higher density of trap states with more extended tails into the bandgap give rise to the formation of highly localized trapped polarons with a longer lifetime. The stabilized intermolecular electron–phonon coupling through synergistic regulation of donor and acceptor materials effectively suppresses unfavorable photocarrier trapping, delivering the improved device efficiency of 18.10% and enhanced thermal stability in quaternary OSCs. These results provide valuable property–function insights for further boosting photovoltaic stability in view of modulating intermolecular electron–phonon coupling.
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    Global double hybrids do not work for charge transfer: A comment on "Double hybrids and time-dependent density functional theory: An implementation and benchmark on charge transfer excited states"
    Casanova-Paez, M ; Goerigk, L (Wiley, 2021-03-30)
    We comment on the results published by Ottochian et al. in J. Comput Chem. 2020, 41, 1242. Therein, the authors claim that the second-order, perturbative correlation correction applied to the time-dependent version of the PBE-QIDH global double-hybrid functional approximation (DHDFA) enables the description of charge-transfer (CT) excitations. Herein, we point out some inadvertent oversights related to what had already been previously known and achieved in the field of time-dependent DHDFAs. Exemplified for the same four systems that Ottochian et al. have used to analyze intermolecular CT excitations, we show how a systematic and unacceptably large redshift in global DHDFAs is rectified when using the latest long-range corrected DHDFAs published earlier in J. Chem. Theory Comput. 2019, 15, 4735.
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    Hepatic concentrations of per- and polyfluoroalkyl substances (PFAS) in dolphins from south-east Australia: Highest reported globally
    Foord, CS ; Szabo, D ; Robb, K ; Clarke, BO ; Nugegoda, D (ELSEVIER, 2024-01-15)
    Per- and polyfluoroalkyl substances (PFAS) concentrations were investigated in hepatic tissue of four dolphin species stranded along the south-east coast of Australia between 2006 and 2021; Burrunan dolphin (Tursiops australis), common bottlenose dolphin (Tursiops truncatus), Indo-Pacific bottlenose dolphin (Tursiops aduncus), and short-beaked common dolphin (Delphinus delphis). Two Burrunan dolphin populations represented in the dataset have the highest reported global population concentrations of ∑25PFAS (Port Phillip Bay median 9750 ng/g ww, n = 3, and Gippsland Lakes median 3560 ng/g ww, n = 8), which were 50-100 times higher than the other species reported here; common bottlenose dolphin (50 ng/g ww, n = 9), Indo-Pacific bottlenose dolphin (80 ng/g ww, n = 1), and short-beaked common dolphin (61 ng/g ww, n = 12). Also included in the results is the highest reported individual ∑25PFAS (19,500 ng/g ww) and PFOS (18,700 ng/g ww) concentrations, at almost 30 % higher than any other Cetacea reported globally. Perfluorooctane sulfonate (PFOS) was above method reporting limits for all samples (range; 5.3-18,700 ng/g ww), and constituted the highest contribution to overall ∑PFAS burdens with between 47 % and 99 % of the profile across the dataset. The concentrations of PFOS exceed published tentative critical concentrations (677-775 ng/g) in 42 % of all dolphins and 90 % of the critically endangered Burrunan dolphin. This research reports for the first time novel and emerging PFASs such as 6:2 Cl-PFESA, PFMPA, PFEECH and FBSA in marine mammals of the southern hemisphere, with high detection rates across the dataset. It is the first study to show the occurrence of PFAS in the tissues of multiple species of Cetacea from the Australasian region, demonstrating high global concentrations for inshore dolphins. Finally, it provides key baseline knowledge to the potential exposure and bioaccumulation of PFAS compounds within the coastal environment of south-east Australia.
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    Widespread Family of NAD+-Dependent Sulfoquinovosidases at the Gateway to Sulfoquinovose Catabolism
    Kaur, A ; Pickles, IB ; Sharma, M ; Soler, NM ; Scott, NE ; Pidot, SJ ; Goddard-Borger, ED ; Davies, GJ ; Williams, SJ (AMER CHEMICAL SOC, 2023-12-15)
    The sulfosugar sulfoquinovose (SQ) is produced by photosynthetic plants, algae, and cyanobacteria on a scale of 10 billion tons per annum. Its degradation, which is essential to allow cycling of its constituent carbon and sulfur, involves specialized glycosidases termed sulfoquinovosidases (SQases), which release SQ from sulfolipid glycoconjugates, so SQ can enter catabolism pathways. However, many SQ catabolic gene clusters lack a gene encoding a classical SQase. Here, we report the discovery of a new family of SQases that use an atypical oxidoreductive mechanism involving NAD+ as a catalytic cofactor. Three-dimensional X-ray structures of complexes with SQ and NAD+ provide insight into the catalytic mechanism, which involves transient oxidation at C3. Bioinformatic survey reveals this new family of NAD+-dependent SQases occurs within sulfoglycolytic and sulfolytic gene clusters that lack classical SQases and is distributed widely including within Roseobacter clade bacteria, suggesting an important contribution to marine sulfur cycling.
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    The structure and activity of the glutathione reductase from Streptococcus pneumoniae
    Sikanyika, M ; Aragao, D ; McDevitt, CA ; Maher, MJ (INT UNION CRYSTALLOGRAPHY, 2019-01)
    The glutathione reductase (GR) from Streptococcus pneumoniae is a flavoenzyme that catalyzes the reduction of oxidized glutathione (GSSG) to its reduced form (GSH) in the cytoplasm of this bacterium. The maintenance of an intracellular pool of GSH is critical for the detoxification of reactive oxygen and nitrogen species and for intracellular metal tolerance to ions such as zinc. Here, S. pneumoniae GR (SpGR) was overexpressed and purified and its crystal structure determined at 2.56 Å resolution. SpGR shows overall structural similarity to other characterized GRs, with a dimeric structure that includes an antiparallel β-sheet at the dimer interface. This observation, in conjunction with comparisons with the interface structures of other GR enzymes, allows the classification of these enzymes into three classes. Analyses of the kinetic properties of SpGR revealed a significantly higher value for Km(GSSG) (231.2 ± 24.7 µM) in comparison to other characterized GR enzymes.
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    Semisynthesis and Cytotoxic Evaluation of an Ether Analogue Library Based on a Polyhalogenated Diphenyl Ether Scaffold Isolated from a Lamellodysidea Sponge
    Ramage, KS ; Lock, A ; White, JM ; Ekins, MG ; Kiefel, MJ ; Avery, VM ; Davis, RA (MDPI AG, 2024)
    The known oxygenated polyhalogenated diphenyl ether, 2-(2′,4′-dibromophenoxy)-3,5-dibromophenol (1), with previously reported activity in multiple cytotoxicity assays was isolated from the sponge Lamellodysidea sp. and proved to be an amenable scaffold for semisynthetic library generation. The phenol group of 1 was targeted to generate 12 ether analogues in low-to-excellent yields, and the new library was fully characterized by NMR, UV, and MS analyses. The chemical structures for 2, 8, and 9 were additionally determined via single-crystal X-ray diffraction analysis. All natural and semisynthetic compounds were evaluated for their ability to inhibit the growth of DU145, LNCaP, MCF-7, and MDA-MB-231 cancer cell lines. Compound 3 was shown to have near-equivalent activity compared to scaffold 1 in two in vitro assays, and the activity of the compounds with an additional benzyl ring appeared to be reliant on the presence and position of additional halogens.