B21-High Throughput SAXS
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Diamond Proposal Number(s):
[21470, 22925]
Abstract: The self-assembly of the amphiphilic lipopeptide PAEPKI-C16 (P = proline, A = alanine, E = glutamic acid, K = lysine, I = isoleucine, and C16 = hexadecyl) was investigated using a combination of microscopy, spectroscopy, and scattering methods and compared to that of C16-IKPEAP with the same (reversed) peptide sequence and the alkyl chain positioned at the N-terminus and lacking a free N-terminal proline residue. The catalytic activity of these peptides was then compared using a model aldol reaction system. For PAEPKI-C16, the cryo-TEM images showed the formation of micrometer-length fibers, which by small-angle X-ray scattering (SAXS) were found to have radii of 2.5–2.6 nm. Spectroscopic analysis shows that these fibers are built from β-sheets. This behavior is in complete contrast to that of C16-IKPEAP, which forms spherical micelles with peptides in a disordered conformation [Hutchinson J. Phys. Chem. B 2019, 123, 613]. In PAEPKI-C16, spontaneous alignment of fibers was observed upon increasing pH, which was accompanied by observed birefringence and anisotropy of SAXS patterns. This shows the ability to form a nematic phase, and unprecedented nematic hydrogel formation was also observed for these lipopeptides at sufficiently high concentrations. SAXS shows retention of an ultrafine (1.7 nm core radius) fibrillar network within the hydrogel. PAEPKI-C16 with free N-terminal proline shows enhanced anti:syn diastereoselectivity and better conversion compared to C16-IKPEAP. The cytotoxicity of PAEPKI-C16 was also lower than that of C16-IKPEAP for both fibroblast and cancer cell lines. These results highlight the sensitivity of lipopeptide properties to the presence of a free proline residue. The spontaneous nematic phase formation by PAEPKI-C16 points to the high anisotropy of its ultrafine fibrillar structure, and the formation of such a phase at low concentrations in aqueous solution may be valuable for future applications.
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Mar 2020
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Abdullah M
Alotaibi
,
Benjamin A. D.
Williamson
,
Sanjay
Sathasivam
,
Andreas
Kafizas
,
Mahdi
Alqahtani
,
Carlos
Sotelo-vazquez
,
John
Buckeridge
,
Jiang
Wu
,
Sean P.
Nair
,
David O.
Scanlon
,
Ivan P.
Parkin
Abstract: Multifunctional thin films which can display both photocatalytic and antibacterial activity are of great interest industrially. Here, for the first time, we have used aerosol assisted chemical vapour deposition (AACVD) to deposit highly photoactive thin films of Cu-doped anatase TiO2 on glass substrates. The films displayed much enhanced photocatalytic activity relative to pure anatase, and showed excellent antibacterial (vs S.Aureus and E.Coli) ability. Using a combination of transient absorption spectroscopy (TAS), photoluminescence (PL) measurements and hybrid density functional theory calculations, we have gained nanoscopic insights into the improved properties of the Cu-doped TiO2 films. Our analysis has highlighted that the interactions between substitutional and interstitial Cu in the anatase lattice can explain the extended exciton lifetimes observed in the doped samples, and the enhanced UV/visible light photoactivities observed.
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Feb 2020
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[19033]
Abstract: Heteromolecular bilayers of π-conjugated organic molecules (COM) on metals, considered as model systems for more complex thin film heterostructures, are investigated with respect to their structural and electronic properties. By exploring the influence of the organic-metal interaction strength in bilayer systems, we determine the molecular arrangement in the physisorptive regime for copper-hexadecafluorophthalocyanine (F16CuPc) on Au(111) with intermediate layers of 5,7,12,14-pentacenetetrone (P4O) and perylene-3,4,9,10-tetracarboxylic diimide (PTCDI). Using the X-ray standing wave (XSW) technique to distinguish the different molecular layers, we show that these two bilayers are ordered following their deposition sequence. Surprisingly, F16CuPc as the second layer within the heterostructures exhibits an inverted intramolecular distortion compared to its monolayer structure.
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Feb 2020
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[19093]
Abstract: With the potential of delivering reversible capacities of up to 300 mAh/g, Li-rich transition metal oxides hold great promise as cathode materials for future Li-ion batteries. However, a cohesive synthesis-structure-electrochemistry relationship is still lacking for these materials, which impedes progress in the field. This work investigates how and why different synthesis routes, specifically solid-state and modified Pechini sol-gel methods, affect the properties of Li2MnO3, a compositionally simple member of this material system. Through a comprehensive investigation of the syn-thesis mechanism along with crystallographic, morphological and electrochemical characterization, the effects of different synthesis routes were found to predominantly influence the degree of stacking faults and particle morphology. That is, the modified Pechini method produced isotropic spherical particles with approx. 57% faulting and the solid state samples possessed heterogeneous morphology with approx. 43% faulting probability. Inevitably, these differences lead to variations in electrochemical performance. This study accentuates the importance of understanding how syn-thesis affects the electrochemistry of these materials, which is critical considering the crystallographic and electrochemical complexities of the class of materials more generally. The methodology employed here is extendable to studying synthesis-property relationships of other compositionally complex Li-rich layered oxide systems.
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Jan 2020
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B22-Multimode InfraRed imaging And Microspectroscopy
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Barbara E.
Souza
,
Lorenzo
Donà
,
Kirill
Titov
,
Paolo
Bruzzese
,
Zhixin
Zeng
,
Yang
Zhang
,
Arun S.
Babal
,
Annika F.
Moeslein
,
Mark D.
Frogley
,
Magda
Wolna
,
Gianfelice
Cinque
,
Bartolomeo
Civalleri
,
Jin-chong
Tan
Diamond Proposal Number(s):
[14902, 20281]
Abstract: Nanocomposites comprising metal organic frameworks (MOFs) embedded in a polymeric matrix are promising carriers for drug delivery applications. While understanding the chemical and physical transformations of MOFs during the re-lease of confined drug molecules is challenging, this is central to devising better ways for controlled release of therapeutic agents. Herein we demonstrate the efficacy of synchrotron microspectroscopy to track the in situ release of 5-fluorouracil (5-FU) anticancer drug molecules from a drug@MOF/polymer composite (5-FU@HKUST-1/polyurethane). Using experimental time-resolved infrared spectra jointly with newly developed density functional theory calculations, we reveal the detailed dynamics of vibrational motions underpinning the dissociation of 5-FU bound to the framework of HKUST-1 upon water exposure. We discover that HKUST-1 creates hydrophilic channels within the hydrophobic polyurethane matrix hence helping to tune drug release rate. The synergy between a hydrophilic MOF with a hydrophobic polymer can be harnessed to engineer a tunable nanocomposite that alleviates the unwanted burst effect commonly encountered in drug delivery.
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Jan 2020
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I09-Surface and Interface Structural Analysis
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Diamond Proposal Number(s):
[18974]
Abstract: Potassium-ion (K-ion) batteries potentially offer numerous advantages over conventional lithium-ion batteries as a result of the high natural abundance of potassium and its lower positive charge density, compared with lithium. This introduces the possibility of using K-ion in fast charging applications, in which cost effectiveness is also a major factor. Unlike for sodium-ion batteries, graphite can be used as an anode in K-ion cells, for which an extensive supply chain, electrode manufacturing infrastructure, and knowledge already exists. However, the performance of graphite anodes in K-ion cells does not meet expectations, with rapid capacity fading and poor first cycle irreversible capacities often reported. Here we investigate the formation and composition of the solid electrolyte interphase (SEI) as well as K+ insertion in graphite anodes in K-ion batteries. Through the use of energy-tuned synchrotron-based X-ray photoelectron spectroscopy, we make a detailed analysis at three probing depths up to ~50 nm of graphite anodes cycled to various potentials on the first discharge-charge cycle. Extensive SEI formation from a KPF6/DEC:EC electrolyte system is found to occur at low potentials during the insertion of potassium into graphite. During the subsequent removal of potassium from the structure, the thick SEI is partially stripped from the electrode, demonstrating that the SEI layer is unstable and contributes to a significant proportion of the capacity on both discharge and charge. With this in mind, further work is required to develop an electrolyte system with stable SEI layer formation on graphite in order to advance K-ion battery technology.
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Nov 2019
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[18523]
Abstract: A novel lipopeptide C16KTTβAH was designed that incorporates the KTT tripeptide sequence from “Matrixyl” lipopeptides along with the bioactive βAH (β-alanine-histidine) carnosine dipeptide motif, attached to a C16 hexadecyl lipid chain. We show that this peptide amphiphile self-assembles above a critical aggregation concentration into β-sheet nanotape structures in water, PBS and cell culture media. Nanotape bundle structures were imaged in PBS, the bundling resulting from nanotape associations due to charge screening in the buffer. In addition, hydrogelation was observed and the gel modulus was measured in different aqueous media conditions, revealing tunable hydrogel modulus depending on concentration and nature of the aqueous phase. Stiff hydrogels were observed by direct dissolution in PBS and it was also possible to prepare hydrogels with unprecedented high modulus from low concentration solutions by injection of dilute aqueous solutions into PBS. These hydrogels have exceptional stiffness compared to previously reported β-sheet peptide-based materials. In addition, macroscopic soft threads can be drawn from concentrated aqueous solutions of the lipopeptides which contain aligned nematic structures. The anti-cancer activity of the lipopeptide was assessed using two model breast cancer cell lines, compared to two fibroblast cell line controls. These studies revealed selective concentration-dependent cytotoxicity against MCF-7 cancer cells in a mM concentration range. It was shown that this occurs below the onset of lipopeptide aggregation (i.e. below the critical aggregation concentration), indicating that the cytotoxicity is not related to self-assembly but is an intrinsic property of C16KTTβAH. Finally, hydrogels of this lipopeptide demonstrated slow uptake and release of the dye Congo red, a model diagnostic compound.
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Aug 2019
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Thomas J.
Whittles
,
Tim D.
Veal
,
Christopher N.
Savory
,
Peter J.
Yates
,
Philip A. E.
Murgatroyd
,
James T.
Gibbon
,
Max
Birkett
,
Richard J.
Potter
,
Jonathan D.
Major
,
Ken
Durose
,
David O.
Scanlon
,
Vinod R.
Dhanak
Abstract: The earth-abundant semiconductor Cu3BiS3 (CBS) exhibits promising photovoltaic properties and is often considered analogous to the solar absorbers copper indium gallium diselenide (CIGS) and copper zinc tin sulfide (CZTS) despite few device reports. The extent to which this is justifiable is explored via a thorough X-ray photoemission spectroscopy (XPS) analysis: spanning core levels, ionization potential, work function, surface contamination, cleaning, band alignment, and valence-band density of states. The XPS analysis overcomes and addresses the shortcomings of prior XPS studies of this material. Temperature-dependent absorption spectra determine a 1.2 eV direct band gap at room temperature; the widely reported 1.4–1.5 eV band gap is attributed to weak transitions from the low density of states of the topmost valence band previously being undetected. Density functional theory HSE06 + SOC calculations determine the band structure, optical transitions, and well-fitted absorption and Raman spectra. Valence band XPS spectra and model calculations find the CBS bonding to be superficially similar to CIGS and CZTS, but the Bi3+ cations (and formally occupied Bi 6s orbital) have fundamental impacts: giving a low ionization potential (4.98 eV), suggesting that the CdS window layer favored for CIGS and CZTS gives detrimental band alignment and should be rejected in favor of a better aligned material in order for CBS devices to progress.
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Jul 2019
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I07-Surface & interface diffraction
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Mengxue
Chen
,
Dan
Liu
,
Wei
Liu
,
Robert S.
Gurney
,
Donghui
Li
,
Jinlong
Cai
,
Emma L. K.
Spooner
,
Rachel C.
Kilbride
,
James D.
Mcgettrick
,
Trystan M.
Watson
,
Zhe
Li
,
Richard A. L.
Jones
,
David G.
Lidzey
,
Tao
Wang
Diamond Proposal Number(s):
[20419]
Abstract: Fluorination of conjugated molecules has been established as an effective structural modification strategy to influence properties, and has attracted extensive attention in organic solar cells (OSCs). Here, we have investigated optoelectronic and photovoltaic property changes of OSCs made of polymer donors with the non-fullerene acceptors (NFAs) ITIC and IEICO and their fluorinated counterparts IT-4F and IEICO-4F. Device studies show that fluorinated NFAs lead to reduced Voc but increased Jsc and FF, and therefore the ultimate influence to efficiency depends on the compensation of Voc loss and gains of Jsc and FF. Fluorination lowers energy levels of NFAs, reduces their electronic bandgaps and red-shifts the absorption spectra. The impact of fluorination on the molecular order depends on the specific NFA, with the conversion of ITIC to IT-4F reduces structural order, which can be reversed after blending with the donor PBDB-T. Contrastingly, IEICO-4F presents stronger π−π stacking after fluorination from IEICO, and this is further strengthened after blending with the donor PTB7-Th. The photovoltaic blends universally present a donor-rich surface region which can promote charge transport and collection towards anode in inverted OSCs. The fluorination of NFAs, however, reduces the fraction of donors in this donor-rich region, consequently encourage the intermixing of donor/acceptor for efficient charge generation.
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Jun 2019
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Abstract: Metal-organic frameworks (MOFs) have shown great promise for sensing of dangerous chemicals, including environmental toxins, nerve agents and explosives. However, challenges remain, such as the sensing of larger analytes and the discrimination between similar analytes at different concentrations. Herein we present the synthesis and development of a new, large-pore MOF for explosives sensing, and demonstrate its excellent sensitivity against a range of relevant explosive compounds including trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN). We have developed an improved, thorough methodology to eliminate common sources of error in our sensing protocol. We then combine this new MOF with two others as part of a three-MOF array for fluorescent sensing and discrimination of five explosives. This sensor works at part-per-million concentrations and importantly, can discriminate explosives with high accuracy without reference to their concentration.
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Mar 2019
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