School of Chemistry - Research Publications
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ItemQuantifying the Relaxation Dynamics of Higher Electronic Excited States in Perylene.(American Chemical Society, 2023-08-31)Gating logical operations through high-lying electronic excited states presents opportunities for developing ultrafast, subnanometer computational devices. A lack of molecular systems with sufficiently long-lived higher excited states has hindered practical realization of such devices, but recent studies have reported intriguing photophysics from high-lying excited states of perylene. In this work, we use femtosecond spectroscopy supported by quantum chemical calculations to identify and quantify the relaxation dynamics of monomeric perylene's higher electronic excited states. The 21B2u state is accessed through single-photon absorption at 250 nm, while the optically dark 21Ag state is excited via the 11B3u state. Population of either state results in subpicosecond relaxation to the 11B3u state, and we quantify 21Ag and 21B2u state lifetimes of 340 and 530 fs, respectively. These lifetimes are significantly longer than the singlet fission time constant from the perylene 21B2u state, suggesting that the higher electronic states of perylene may be useful for gating logical operations.
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ItemA sandwich-like structural model revealed for quasi-2D perovskite films(Royal Society of Chemistry, 2021-04-28)The excellent performance and stability of perovskite solar cells (PSCs) based on quasi-2D Ruddlesden–Popper perovskites (RPPs) holds promise for their commercialization. Further improvement in the performance of 2D PSCs requires a detailed understanding of the microstructure of the quasi-2D perovskite films. Based on scanning transmission electron microscopy (STEM), time-resolved photoluminescence, and transient absorption measurements, a new sandwich-like structural model is proposed to describe the phase distribution of RPPs. In contrast to the conventional gradient distribution, it is found that small-n RPPs are sandwiched between large-n RPP phase layers at the front and back sides owing to crystallization initiated from both interfaces during film formation. This sandwich-like distribution profile facilitates excitons funneling from the film interior to both surfaces for dissociation while free carriers transport via large-n channels that permeate the film to ensure efficient charge collection by the corresponding electrodes, which is favorable for high-performance photovoltaics. This discovery provides a new fundamental understanding of the operating principles of 2D PSCs and has valuable implications for the design and optimization strategies of optoelectronic devices based on quasi-2D RPPs films.
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ItemA luminescent solar concentrator ray tracing simulator with a graphical user interface: features and applications(IOP PUBLISHING LTD, 2020-07-01)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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ItemDiscovery and Biosynthesis of the Cytotoxic Polyene Terpenomycin in Human Pathogenic Nocardia(AMER CHEMICAL SOC, 2023-07-27)Nocardia are opportunistic human pathogens that can cause a range of debilitating and difficult to treat infections of the lungs, brain, skin, and soft tissues. Despite their close relationship to the well-known secondary metabolite-producing genus, Streptomyces, comparatively few natural products are known from the Nocardia, and even less is known about their involvement in the pathogenesis. Here, we combine chemistry, genomics, and molecular microbiology to reveal the production of terpenomycin, a new cytotoxic and antifungal polyene from a human pathogenic Nocardia terpenica isolate. We unveil the polyketide synthase (PKS) responsible for terpenomycin biosynthesis and show that it combines several unusual features, including "split", skipped, and iteratively used modules, and the use of the unusual extender unit methoxymalonate as a starter unit. To link genes to molecules, we constructed a transposon mutant library in N. terpenica, identifying a terpenomycin-null mutant with an inactivated terpenomycin PKS. Our findings show that the neglected actinomycetes have an unappreciated capacity for the production of bioactive molecules with unique biosynthetic pathways waiting to be uncovered and highlights these organisms as producers of diverse natural products.
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ItemBrownian Tree‐Shaped Dendrites in Quasi‐2D Perovskite Films and Their Impact on Photovoltaic Performance(Wiley, 2022-05)Quasi-2D Ruddlesden–Popper perovskites (RPPs) are candidates for constructing perovskite solar cells (PSCs) with superior stability due to their tolerance to the external environment. Fully understanding the film growth mechanism and structure is crucial to further improve the performance of 2D-PSCs while maintaining device stability. In this work, the origin of Brownian tree-shaped dendrites formed in hot-cast methylammonium chloride (MACl)-doped BA2MAn−1PbnI3n+1 ( = 5) quasi-2D perovskite films are reported. Investigations based on optical, electronic, atomic force, and fluorescence microscopies reveal that the dendrites are assembled from large-n RPPs-dominated grains, while the nondendritic film area is composed of small-n RPPs grains and associated with film surface pits caused by the evaporation of MACl. It is proposed that these dendrites are grown by the diffusion-limited aggregation of the MA-rich intermediate phase domains that initially crystallize from the precursor. The formation of these dendrites in quasi-2D perovskite films upon MACl doping is accompanied by improved organization and crystallinity of the 2D RPPs, which benefits the photovoltaic performance. This work provides new insights into the formation mechanism of quasi-2D perovskite films that should assist device engineering strategies to further improve the performance of 2D PSCs.
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ItemNo Preview AvailableIncorporating whey protein aggregates produced with heat and ultrasound treatment into rennet gels and model non-fat cheese systems(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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ItemFamilial ALS-associated SFPQ variants promote the formation of SFPQ cytoplasmic aggregates in primary neurons(ROYAL SOC, 2022-09-28)Splicing factor proline- and glutamine-rich (SFPQ) is a nuclear RNA-binding protein that is involved in a wide range of physiological processes including neuronal development and homeostasis. However, the mislocalization and cytoplasmic aggregation of SFPQ are associated with the pathophysiology of amyotrophic lateral sclerosis (ALS). We have previously reported that zinc mediates SFPQ polymerization and promotes the formation of cytoplasmic aggregates in neurons. Here we characterize two familial ALS (fALS)-associated SFPQ variants, which cause amino acid substitutions in the proximity of the SFPQ zinc-coordinating centre (N533H and L534I). Both mutants display increased zinc-binding affinities, which can be explained by the presence of a second zinc-binding site revealed by the 1.83 Å crystal structure of the human SFPQ L534I mutant. Overexpression of these fALS-associated mutants significantly increases the number of SFPQ cytoplasmic aggregates in primary neurons. Although they do not affect the density of dendritic spines, the presence of SFPQ cytoplasmic aggregates causes a marked reduction in the levels of the GluA1, but not the GluA2 subunit of AMPA-type glutamate receptors on the neuronal surface. Taken together, our data demonstrate that fALS-associated mutations enhance the propensity of SFPQ to bind zinc and form aggregates, leading to the dysregulation of AMPA receptor subunit composition, which may contribute to neuronal dysfunction in ALS.
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ItemParaspeckle subnuclear bodies depend on dynamic heterodimerisation of DBHS RNA-binding proteins via their structured domains(ELSEVIER, 2022-11-04)RNA-binding proteins of the DBHS (Drosophila Behavior Human Splicing) family, NONO, SFPQ, and PSPC1 have numerous roles in genome stability and transcriptional and posttranscriptional regulation. Critical to DBHS activity is their recruitment to distinct subnuclear locations, for example, paraspeckle condensates, where DBHS proteins bind to the long noncoding RNA NEAT1 in the first essential step in paraspeckle formation. To carry out their diverse roles, DBHS proteins form homodimers and heterodimers, but how this dimerization influences DBHS localization and function is unknown. Here, we present an inducible GFP-NONO stable cell line and use it for live-cell 3D-structured illumination microscopy, revealing paraspeckles with dynamic, twisted elongated structures. Using siRNA knockdowns, we show these labeled paraspeckles consist of GFP-NONO/endogenous SFPQ dimers and that GFP-NONO localization to paraspeckles depends on endogenous SFPQ. Using purified proteins, we confirm that partner swapping between NONO and SFPQ occurs readily in vitro. Crystallographic analysis of the NONO-SFPQ heterodimer reveals conformational differences to the other DBHS dimer structures, which may contribute to partner preference, RNA specificity, and subnuclear localization. Thus overall, our study suggests heterodimer partner availability is crucial for NONO subnuclear distribution and helps explain the complexity of both DBHS protein and paraspeckle dynamics through imaging and structural approaches.
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ItemGenetic and chemical validation of Plasmodium falciparum aminopeptidase PfA-M17 as a drug target in the hemoglobin digestion pathway(eLIFE SCIENCES PUBL LTD, 2022-09-13)Plasmodium falciparum, the causative agent of malaria, remains a global health threat as parasites continue to develop resistance to antimalarial drugs used throughout the world. Accordingly, drugs with novel modes of action are desperately required to combat malaria. P. falciparum parasites infect human red blood cells where they digest the host's main protein constituent, hemoglobin. Leucine aminopeptidase PfA-M17 is one of several aminopeptidases that have been implicated in the last step of this digestive pathway. Here, we use both reverse genetics and a compound specifically designed to inhibit the activity of PfA-M17 to show that PfA-M17 is essential for P. falciparum survival as it provides parasites with free amino acids for growth, many of which are highly likely to originate from hemoglobin. We further show that loss of PfA-M17 results in parasites exhibiting multiple digestive vacuoles at the trophozoite stage. In contrast to other hemoglobin-degrading proteases that have overlapping redundant functions, we validate PfA-M17 as a potential novel drug target.